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The era of modern smartphones, running on Android version 7.0 and higher, facilitates nowadays acquisition of raw dual-frequency multi-constellation GNSS observations. This paves the way for GNSS community data to be potentially exploited for precise positioning, GNSS reflectometry or geoscience applications at large. The continuously expanding global GNSS infrastructure along with the enormous volume of prospective GNSS community data bring, however, major challenges related to data acquisition, its storage, and subsequent processing for deriving various parameters of interest. In addition, such large datasets cannot be managed manually anymore, leading thus to the need for fully automated and sophisticated data processing pipelines. Application of Machine Learning Technology for GNSS IoT data fusion (CAMALIOT) was an ESA NAVISP Element 1 project (NAVISP-EL1-038.2) with activities aiming to address the aforementioned points related to GNSS community data and their exploitation for scientific applications with the use of Machine Learning (ML). This contribution provides an overview of the CAMALIOT project with information on the designed and implemented cloud-native software for GNSS processing and ML at scale, developed Android application for retrieving GNSS observations from the modern generation of smartphones through dedicated crowdsourcing campaigns, related data ingestion and processing, and GNSS analysis concerning both conventional and smartphone GNSS observations. With the use of the developed GNSS engine employing an Extended Kalman Filter, example processing results related to the Zenith Total Delay (ZTD) and Slant Total Electron Content (STEC) are provided based on the analysis of observations collected with geodetic-grade GNSS receivers and from local measurement sessions involving Xiaomi Mi 8 that collected GNSS observations using the developed Android application. For smartphone observations, ZTD is derived in a differential manner based on a single-frequency double-difference approach employing GPS and Galileo observations, whereas satellite-specific STEC time series are obtained through carrier-to-code leveling based on the geometry-free linear combination of observations from both GPS and Galileo constellations. Although the ZTD and STEC time series from smartphones were derived on a demonstration basis, a rather good level of consistency of such estimates with respect to the reference time series was found. For the considered periods, the RMS of differences between the derived smartphone-based time series of differential zenith wet delay and reference values were below 3.1 mm. In terms of satellite-specific STEC time series expressed with respect to the reference STEC time series, RMS of the offset-reduced differences below 1.2 TECU was found. Smartphone-based observations require special attention including additional processing steps and a dedicated parameterization in order to be able to acquire reliable atmospheric estimates. Although with lower measurement quality compared to traditional sources of GNSS data, an augmentation of ground-based networks of fixed high-end GNSS receivers with GNSS-capable smartphones would however, form an interesting source of complementary information for various studies relying on GNSS observations. [ABSTRACT FROM AUTHOR]

In this study, the Atmospheric Infrared Sounder (AIRS) Observations for Model Intercomparison Projects (Obs4MIPs) V2.1 tropospheric air temperature, specific humidity, and relative humidity data are utilized to evaluate the global tropospheric temperature and humidity simulations in the fully coupled global climate models from the Coupled Model Intercomparison Project phases 3, 5, and 6 (CMIP3, CMIP5, and CMIP6), and possible simulation improvement in CMIP6 models in comparison to CMIP3 and CMIP5 models. Our analyses indicate that all three phases of CMIP models share similar tropospheric air temperature, specific humidity, and relative humidity biases in their multi‐model ensemble means relative to AIRS. Cold biases up to 4 K and positive relative humidity biases up to 20% are found in the free troposphere almost globally with maxima over the mid‐latitude storm tracks. Warm biases up to 2 K are seen over the Southern Ocean in the lower troposphere. Positive specific and relative humidity biases exist over the off‐equatorial oceans while negative specific and relative humidity biases are seen near the equator in the tropical free troposphere, which are related to the double‐intertropical convergence zone bias in the models. Both the air temperature and specific humidity biases are important to the relative humidity biases except in the tropical free troposphere where the specific humidity biases dominate. The tropospheric air temperature, specific humidity, and relative humidity biases are reduced from CMIP3 to CMIP5 and to CMIP6 at almost all pressure levels except at 300 hPa for specific humidity and in the boundary layer for relative humidity. Plain Language Summary: In this study, we use the Atmospheric Infrared Sounder (AIRS) data to assess how well the fully coupled global climate models simulate temperature and humidity in the troposphere. We focus on the climate models from the recent three phases of Coupled Model Intercomparison Project (CMIP3, CMIP5, and CMIP6) and investigate if there is any bias reduction in the recent CMIP6 models compared to the earlier CMIP3 and CMIP5 models. To conduct our evaluation, we compare the CMIP model ensemble averages with the AIRS data and find that all three phases of CMIP models exhibit similar biases in tropospheric temperature and humidity. For example, cold biases up to 4 K and positive relative humidity biases up to 20% are seen in the free troposphere over most regions, with the maximum biases over the midlatitudes. Positive specific and relative humidity biases are found over the off‐equatorial oceans while negative specific and relative humidity biases are seen near the equator in the tropical free troposphere. We also note a possible temperature and humidity bias reduction from the CMIP3 models to the CMIP5 models and then to the CMIP6 models at most pressure levels. Key Points: CMIP Phase 3, 5 and 6 climate models share similar tropospheric air temperature, specific and relative humidity biases relative to Atmospheric Infrared SounderCold biases and positive relative humidity biases are prevalent in free troposphere almost globally with maxima over the mid‐latitude oceansDouble‐intertropical convergence zone bias‐related specific and relative humidity biases are evident in tropical free troposphere: positive (negative) off (near) the equator [ABSTRACT FROM AUTHOR]

Synoptic forcings have traditionally played a pivotal role in extreme rainfall over North China. However, there are still large unexplained gaps in understanding the formation of extreme rainfalls over this region. The heavy rainfall event, lasting from 29 July to 2 August 2023 (referred to as "23·7" event), is characterized by long duration, widespread coverage, and high accumulated rainfall over North China. Overall, the persistent extreme rainfall is closely associated with the remnant vortex originating from typhoon Doksuri(2305), tropical storm Khanun(2306), and the unusual westward extended western Pacific subtropical high (WPSH), as well as quasi-stationary cold dry air masses surrounding North China on the west and north sides. Based on wind profiles and rainfall characteristics, the life history of the "23·7" event is divided into two stages. In the first stage, the western boundary of the western Pacific subtropical high (WPSH) was destroyed by the tropical storm Doksuri, appearing that the WPSH retreated eastward with decreasing height. As a result, an inclined vertical distribution on the western boundary was established below 500 hPa. Therefore, convections were limited by the tilted WPSH with warm-dry cover embedded in the low-to-middle troposphere. Meanwhile, the orography in the west of North China was controlled by cold air masses above nearly 3.0 km. Combining the orographic and cold air blockings, only a shallow southeasterly layer (between 1.3 and 3.0 km) can overpass mountains. Although the warm and moist southeasterly flows were lifted by orography, no convections were triggered because of the local capped cold and dry air masses overhead. Under this framework, equivalent potential temperature (θe) gradients were established between warm humid and dry cold air masses, similar to a warm front, causing warm air to lift and generate widespread rainfall but low intensity. However, the lifting was too weak to allow convection to be highly organized. In the second stage, the WPSH was further destroyed by enhanced Khanun, and thus the embedded warm-dry cover associated with the tilted WPSH was significantly thinned. Consequently, convections triggered by orographic blocking can move upward and consequently further develop, forming deep convections. Comparatively speaking, the convections in the second stage are much deeper than those in the first stage. The results gained herein may shed new light on better understanding and forecasting of long-lasting extreme rainfall. [ABSTRACT FROM AUTHOR]

This study evaluates the representation of the composite-mean surface response to sudden stratospheric warmings (SSWs) in 28 CMIP6 models. Most models can reproduce the magnitude of the SLP response over the Arctic, although the simulated Arctic SLP response varies from model to model. Regarding the structure of the SLP response, most models exhibit a basin-symmetric negative Northern Annular Mode (NAM)-like response with a cyclonic Pacific SLP response, whereas the reanalysis shows a highly basin-asymmetric negative NAO-like response without a robust Pacific center. We then explore the drivers of these model biases and spread by applying a multiple linear regression (MLR). The results show that the polar cap temperature anomalies at 100 hPa (ΔT100) modulate the magnitude of both the Arctic SLP response and the cyclonic Pacific SLP response. Apart from ΔT100, the intensity and latitudinal location of the climatological eddy-driven jet in the troposphere also affect the magnitude of the Arctic SLP response. The compensation of model biases in these two tropospheric metrics and the good model representation of ΔT100 explain the good agreement between the ensemble mean and the reanalysis on the magnitude of the Arctic SLP response, as indicated by the fact that the ensemble mean lies well within the reanalysis uncertainty range and that the reanalysis mean sits well within the model distribution. The Niño-3.4 SST anomalies and North Pacific SST dipole anomalies together with ΔT100 modulate the cyclonic Pacific SLP response. In this case, biases in both oceanic drivers work in the same direction and lead to the cyclonic Pacific SLP response in models that are not present in the reanalysis. Significance Statement: Sudden stratospheric warmings (SSWs) represent an important source of skill for forecasting winter weather on subseasonal-to-seasonal time scales. To what extent SSWs could be used to improve the prediction of surface weather depends on how well stratosphere–troposphere coupling associated with SSWs is represented in climate models. Therefore, we evaluate the representation of stratosphere–troposphere coupling associated with SSWs in 28 state-of-the-art climate models. The representation is found to diverge widely among climate models, and some are biased noticeably from the reanalysis. The models' spread and bias are largely driven by five major factors and can be reduced substantially by making bias corrections to these factors. [ABSTRACT FROM AUTHOR]

Upward propagating waves of lower atmospheric origin play an important role in coupling terrestrial weather with space weather on daily to inter‐annual timescales. Quantifying their short‐term (<30 days) variability is a difficult challenge because simultaneous observations at multiple local times are needed to sample diurnal cycles. This study demonstrates and validates a short‐term estimation method of the DE3 non‐migrating tide at the equator and then applies the technique to three independent data sets: MIGHTI, SABER, and TIDI. We find that daily DE3 estimates from SABER, MIGHTI, and TIDI at equator agree well with correlation coefficients ranging between 0.76 and 0.85. The daily DE3 amplitude variability is typically ∼7 m/s in zonal winds and ∼3 K in temperature. We also find that daily MLT variations and F‐region ionospheric DE3 from COSMIC‐2 Global Ionospheric Specification (GIS) show a correlation of 0.55–0.65, suggesting that not all ionospheric variability can be attributed to the E‐region dynamo; however, increasing correlation with increasing time‐scale suggests that lower atmospheric variability has pronounced impact on the ionosphere on intra‐seasonal scales. We find that the MLT and the F‐region ionosphere exhibit strong coherent intra‐seasonal oscillations (residual amplitudes upto 50%–60%); their coherency with the MJO in 2020 suggests a possible modulation of the upward propagating DE3 tide related to this major tropical tropospheric weather pattern. In addition, we find stratospheric QBO signatures in the MLT DE3 on inter‐annual scales. This study offers fresh observational insights into the pivotal role of tropospheric weather in shaping variability in the coupled thermosphere‐ionosphere system. Plain Language Summary: A growing body of research unequivocally demonstrates the important role upward propagating waves from the lower atmosphere play in shaping the meteorology of the mesosphere, thermosphere and ionosphere from daily to inter‐annual time scales. Understanding these variations is crucial for space weather studies and applications, including radio wave propagation, satellite communication, and space orbital debris. Among these oscillations, the diurnal eastward propagating tide with zonal wave number 3 (DE3) holds particular importance. This oscillation, driven by expansive tropospheric weather systems, can attain substantial amplitudes in the upper atmosphere. The primary objective of this study is to demonstrate and validate a methodology facilitating the short‐term estimation of DE3 to understand the tidal weather of the upper atmosphere. Our approach starts by using a physics‐based model of the upper atmosphere to test and validate this new daily DE3 retrieval method. Next, we apply our tidal estimation method to extensive satellite‐based measurements of winds, temperatures, and ionospheric electron density. Lastly, we analyze the results to provide fresh observational insights into the pivotal role of tropospheric weather on Earth's near space environment from daily to inter‐annual time scales. Key Points: Demonstrated and validated a short‐term DE3 tidal estimation technique at the equatorDaily DE3 tidal amplitude variability at the equator is typically ∼7 m/s in zonal winds and ∼3 K in temperatureStrong intra‐seasonal variations in MLT region DE3 and F‐region ionosphere electron densities possibly due to the MJO are observed [ABSTRACT FROM AUTHOR]

The tropospheric production of O3 is complex, depending on nitrogen oxides (NOx = NO + NO2), volatile organic compounds (VOCs), and solar radiation. We present a case study showing that the O3 concentration is higher in a rural area, 14 km downwind from a coastal town in Central Italy, compared with the urban environment. The hypothesis is that the O3 measured inland results from the photochemical processes occuring in air masses originating at the urban site, which is richer in NOx emissions, during their transport inland.To demonstrate this hypothesis, a feed forward neural network (FFNN) is used to model the O3 measured at the rural site, comparing the modeled O3 and the measured O3 in different scenarios, which include both input parameters related to local O3 production by photochemistry and input parameters associated with regional transport of O3 precursors. The simulation results show that the local NOx concentration is not a good input to model the observed O3 (R = 0.17); on the contrary including the wind speed and direction as input of the FFNN model, the modelled O3 is well correlated with that measured O3 (R = 0.82). [ABSTRACT FROM AUTHOR]

Tropospheric ozone (O3) is an important greenhouse gas that is also hazardous to human health. The formation of O3 is sensitive to the levels of its precursors NOx (≡NO + NO2) and peroxy radicals, for example, generated by the oxidation of volatile organic compounds (VOCs). A better understanding of this sensitivity will show how changes in the levels of these trace gases could affect O3 levels today and in the future, and thus air quality and climate. In this study, we investigate O3 sensitivity in the tropical troposphere based on in situ observations of NO, HO2 and O3 from four research aircraft campaigns between 2015 and 2023. These are OMO (Oxidation Mechanism Observations), ATom (Atmospheric Tomography Mission), CAFE Africa (Chemistry of the Atmosphere Field Experiment in Africa) and CAFE Brazil, in combination with simulations using the EMAC atmospheric chemistry—climate model. We use the metric α(CH3O2) together with NO to investigate the O3 formation sensitivity. We show that O3 formation is generally NOx‐sensitive in the lower and middle tropical troposphere and is in a transition regime in the upper troposphere. By distinguishing observations impacted by lightning or not we show that NO from lightning is the most important driver of O3 sensitivity in the tropics. NOx‐sensitive chemistry predominates in regions without lightning impact, with α(CH3O2) ranging between 0.56 and 0.82 and observed average O3 levels between 35 and 55 ppbv. Areas affected by lightning exhibit strongly VOC‐sensitive O3 chemistry with α(CH3O2) of about 1 and average O3 levels between 55 and 80 ppbv. Plain Language Summary: Ozone (O3) in the troposphere is both an air pollutant and a greenhouse gas. It is formed from nitrogen oxides (NOx) and volatile organic compounds (VOCs). The formation can be sensitive to either of these precursors depending on their abundance. Considering the high relevance of O3 in regard to human health and global warming, it is important to understand this sensitivity of O3 formation, which allows to predict future changes in O3. Here, we investigate O3 formation sensitivity toward NOx and VOCs in the tropical troposphere based on aircraft measurements during four research campaigns between 2015 and 2023, and a global model. We include observations of NO, HO2 (hydroperoxyl radicals) and O3 over South America, the Middle East and the Pacific, Atlantic and Indian Ocean. We find that O3 formation is sensitive to NOx in the lower tropical troposphere. In the upper tropical troposphere, lightning events control O3 chemistry and promote strong VOC‐sensitive O3 formation. Key Points: α(CH3O2) correlated with NO is a powerful metric for indicating O3 sensitivity and is valid throughout the troposphereO3 chemistry in the remote tropical lower troposphere is found to be NOx‐sensitiveNO emissions from lightning drive O3 sensitivity in the tropical upper troposphere and induce highly VOC‐sensitive chemistry [ABSTRACT FROM AUTHOR]

A historic rainstorm occurred over Henan, China, in July 2021 ("7.20" extreme precipitation event), resulting in significant human casualties and socioeconomic losses. A global variable-resolution model (MPAS-Atmosphere v7.3) was employed to simulate this extreme precipitation event. A series of simulations have been done at both quasi-uniform (60 and 15 km) and variable-resolution (60–15 and 60–3 km) meshes from hydrostatic to nonhydrostatic scale with two parameterization scheme suites. For the 48 h peak precipitation duration (20–22 July), the 60–3 km variable-resolution simulation coupled with the scale-aware convection-permitting parameterization scheme suite stands out predominantly among other simulation experiments as it reproduces this extreme precipitation event most accurately. At 15 km resolution, the 60–15 km variable-resolution simulation achieves comparable forecasting skills to the 15 km quasi-uniform simulation but at a much reduced computing cost. In addition, we found that the default mesoscale suite generally outperforms the convection-permitting suite at 15 km resolution as simulations coupled with the convection-permitting suite missed the third peak of this extreme precipitation event, while the mesoscale suite did not. Furthermore, it is found that the large-scale circulation plays a critical role in the peak precipitation simulations at 15 km resolution, via influencing the simulated low-level wind. During the second peak precipitation period, simulations with the convection-permitting parameterization scheme suite at 15 km resolution generate a prominent low-level easterly wind component bias, which is largely attributed to the excessively evaporative cooling in the lower troposphere. This study further reveals that at 15 km resolution the diabatic heating from the grid-scale precipitation accounts more for the low-level wind bias than the convective-scale precipitation. Given that two different cloud microphysics schemes, namely Thompson and WSM6 schemes, are used in the convection-permitting and default mesoscale parameterization scheme suites, respectively, these microphysics schemes are found to be the primary contributor to the low-level wind simulation bias. [ABSTRACT FROM AUTHOR]

New particle formation in the free troposphere is a major source of cloud condensation nuclei globally. The prevailing view is that in the free troposphere, new particles are formed predominantly in convective cloud outflows. We present another mechanism using global observations. We find that during stratospheric air intrusion events, the mixing of descending ozone-rich stratospheric air with more moist free tropospheric background results in elevated hydroxyl radical (OH) concentrations. Such mixing is most prevalent near the tropopause where the sulfur dioxide (SO2) mixing ratios are high. The combination of elevated SO2 and OH levels leads to enhanced sulfuric acid concentrations, promoting particle formation. Such new particle formation occurs frequently and over large geographic regions, representing an important particle source in the midlatitude free troposphere. [ABSTRACT FROM AUTHOR]

The equatorial mixed Rossby–gravity wave (MRGW) is an important contributor to tropical variability. Its excitation mechanism capable of explaining the observed MRGW variance peak at synoptic scales in the troposphere remains elusive. This study investigates wave–mean flow interactions as a generation process for the MRGWs using the TIGAR model, which employs Hough harmonics as the basis of spectral expansion on the sphere, thereby representing MRGWs as prognostic variables. Idealized numerical simulations reveal the interactions between waves emanating from a symmetric tropical heat source and an asymmetric subtropical zonal jet as an excitation mechanism for the MRGWs. The excited MRGWs have variance spectra resembling the observed MRGWs in the tropical troposphere. The mixed Rossby–gravity energy spectrum has a maximum at zonal wavenumbers k=4$$ k=4 $$–5 also in the case of an asymmetric forcing that generates MRGWs across large scales. Effects of wave–wave interactions appear of little importance for the MRGW growth compared with wave–mean flow interactions. Application of the zonal‐mean zonal wind profiles from ERA5 reaffirms the importance of the asymmetry of the zonal mean flow. [ABSTRACT FROM AUTHOR]

Mesoscale convective systems (MCSs) that occur in the Baiu frontal zone (BFZ) can cause devastating flash floods during early summer in Japan; however, the environmental conditions necessary for their development require further investigation. High‐frequency atmospheric soundings, conducted using multiple marine vessels in the East China Sea on 19 June 2022, captured the detailed environmental conditions pertaining to the development of an MCS within the BFZ. The MCS, which developed rapidly without any remarkable preceding synoptic or mesoscale disturbance in the mid‐ or upper troposphere, caused intense precipitation exceeding 80 mm/hr. The MCS persisted for approximately 6 hr, and it intensified when the influx of nearly saturated air near the sea surface toward a weak surface front overlapped with the influx of free‐tropospheric moist air. The influx of nearly saturated air near the sea surface ensured conditional instability within the lower troposphere. The influx of moist air in the free troposphere contributed to the near‐saturation conditions above the boundary layer, a feature inherent to the BFZ, and played an important role in minimizing the reduction in the buoyancy of air parcels. The results of this study indicate that a better forecast of the horizontal distribution of free tropospheric moist air is beneficial for limiting the potential area of genesis of MCS in the BFZ, and a more comprehensive understanding of the vertical variations in moisture transport contributes to an improved forecast skill for MCS in the BFZ. Plain Language Summary: A very long, stagnant atmospheric front that forms over East Asia in early summer is often associated with a mesoscale convective system (a cloud system that occurs in connection with an ensemble of thunderstorms and produces a contiguous precipitation area) that can cause flash floods. The recent increase in the number of heavy rainfall disasters has led to increased interest in the conditions under which such systems develop around the front. In this study, the conditions favorable for the development of such a system with no remarkable upper‐tropospheric low pressure system were investigated using an unprecedented high‐frequency and dense observation network. The system developed when the influxes of two very moist air masses, one near the sea surface and the other well above the sea surface, overlapped vertically. The moist air near the sea surface ensured that the atmosphere was unstable, and the moist air above contributed to the development of the system by suppressing convection weakening. The findings of this study indicate that a more comprehensive understanding of moist air transport may facilitate more accurate forecasting of convective systems. Key Points: Unprecedented high‐frequency atmospheric soundings of a mesoscale convective system were conducted within the Baiu frontal zoneThe system began to rapidly develop when the influxes of nearly saturated near‐surface and free‐tropospheric air overlappedThe areas where systems potentially develop are sensitive to small variations in the humidity distribution in the free troposphere [ABSTRACT FROM AUTHOR]

Using a reanalysis dataset, this work investigates the possible connection of winter East Asia (EA) flow patterns to stratospheric polar vortex (SPV) anomalies. Cluster analysis is performed on the principal components of daily 500 hPa geopotential height fields to identify five distinct flow patterns. SPV anomalies are considered in terms of the occurrence of major sudden stratospheric warmings (MSSWs). The results reveal that for the 15 days before the MSSWs, one of the five patterns occurs more frequently than usual, whereas another occurs less frequently. The former constructively interferes with the climatological EA trough in the troposphere and strengthens the planetary wave activity (heat flux) in the extratropical troposphere and stratosphere. It has a similar pattern in the 500 hPa height to the composite leading to the MSSWs, implying that such strengthening can contribute to the forcing of the MSSWs. The latter is in the opposite sense (destructive interference) and is disadvantageous before the MSSWs. Evidence of a stratospheric downward influence on the five flow patterns is relatively unclear. These results suggest a potential coupling between flow patterns or weather regimes in different regions through the SPV, as well as warrant further investigation of the downward influence on EA weather regimes. [ABSTRACT FROM AUTHOR]

The tropopause is part of the fundamental structure of the atmosphere, separating the dynamically and chemically distinct troposphere and stratosphere. Based on the concepts as, thermal, dynamical, and chemical or ozone, three different tropopauses are defined. The thermal tropopause is defined as the lowest level above 500hPa at which the lapse rate decreases to 2 K/km or less, provided that also the average lapse rate between this level and all higher levels within 2 km does not exceed 2 K/km. The dynamical tropopause is defined in terms of sharp changes in the potential vorticity which be a measures of the stratification and wind shears in air masses. The original concept of the dynamical tropopause is based on the isentropic gradient of potential vorticity which is typically determined in a thin layer with absolute potential vorticity values within 1 and 4 potential vorticity units. Chemical tropopause is another type of tropopause that is defined based on the vertical concentrations of the trace gases such as ozone mixing ratio and water vapor. In tropical latitudes, a useful reference for distinguishing the tropopause from the stratosphere is the cold point, where the temperature minimum occurs. The cold-point tropopause is the temperature minimum in the tropopause region. The cold point tropopause this acts as the thermal boundary between the troposphere and the stratosphere whose height varies from 18 km in the tropics to about 8 km in the poles. This boundary plays a crucial role in the troposphere-stratosphere exchange. In the present study, radiosonde data used are obtained from the Integrated Global Radiosonde Archive at the NOAA National Climatic Data Center. Daily temperature profiles in January and July 2000-2022 are taken from two radiosonde stations in the central and south of Iran including Tehran (51.31°E, 35.56°N), and Shiraz stations (52.60°E, 29.53°N), and are analyzed. Using radiosonde temperature profiles (green lines) at Tehran stations in a) January and b) July 2021, cold-point tropopause and monthly mean temperature (black lines) are here presented (see text). The blue plus signs are cold point tropopauses from individual profiles and the red plus sign is the average of all blue plus signs. The black thick line is the mean temperature profile and the purple plus sign is the coldest point of the mean temperature profile. ΔT is the difference between the red and purple plus signs. Although we only showed two months of data in January and July here to visualize the difference between the mean of cold point tropopause and the coldest point of the mean temperature profile, our calculation for ΔT is for the 2000-2022 period. The results showed that Shiraz station's lowest temperature of the tropical cold point tropopause is colder than the Mehrabad station of Tehran, and the lowest temperature of the tropical cold point tropopause is estimated in July. This difference is related to combining geographical-latitudinal characteristics of the two stations and the development of thermal low pressure in July over Iran, which has caused an increase in height and a decrease in the temperature of the tropical tropopause. Also, the results showed the average tropical cold point tropopause temperature in the stations is 2.5 degrees kelvin lower than the average cold point of the vertical temperature profile, and the thermal low pressure and cold high pressure are the cause of this difference. [ABSTRACT FROM AUTHOR]

The springtime atmosphere over the southeast Atlantic Ocean (SEA) is subjected to a consistent layer of biomass burning (BB) smoke from widespread fires on the African continent. An elevated humidity signal is coincident with this layer, consistently proportional to the amount of smoke present. The combined humidity and BB aerosol has potentially significant radiative and dynamic impacts. Here, we use aircraft-based observations from the NASA ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) deployments in conjunction with reanalyses to characterize covariations in humidity and BB smoke across the SEA. The observed plume–vapor relationship, and its agreement with the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis version 5 (ERA5) and Copernicus Atmosphere Monitoring Service (CAMS) reanalysis, persists across all observations, although the magnitude of the relationship varies as the season progresses. Water vapor is well represented by the reanalyses, while CAMS tends to underestimate carbon monoxide especially under high BB. While CAMS aerosol optical depth (AOD) is generally overestimated relative to ORACLES AOD, the observations show a consistent relationship between carbon monoxide (CO) and aerosol extinction, demonstrating the utility of the CO tracer to understanding vertical aerosol distribution. We next use k -means clustering of the reanalyses to examine multi-year seasonal patterns and distributions. We identify canonical profile types of humidity and of CO, allowing us to characterize changes in vapor and BB atmospheric structures, and their impacts as they covary. While the humidity profiles show a range in both total water vapor concentration and in vertical structure, the CO profiles primarily vary in terms of maximum concentration, with similar vertical structures in each. The distribution of profile types varies spatiotemporally across the SEA region and through the season, ranging from largely one type in the northeast and southwest to more evenly distributed between multiple types where air masses meet in the middle of the SEA. These distributions follow patterns of transport from the humid, smoky source region (greatest influence in the northeast of the SEA) and the seasonal changes in both humidity and smoke (increasing and decreasing through the season, respectively). With this work, we establish a framework for a more complete analysis of the broader radiative and dynamical effects of humid aerosols over the SEA. [ABSTRACT FROM AUTHOR]

Ozone trends in the upper troposphere and lower stratosphere (UTLS) remain highly uncertain because of sharp spatial gradients and high variability caused by competing transport, chemical, and mixing processes near the upper-tropospheric jets and extratropical tropopause as well as inhomogeneous spatially and temporally limited observations of the region. Subtropical jets and the tropopause act as transport barriers, delineating boundaries between atmospheric regimes controlled by different processes; they can thus be used to separate data taken in those different regimes for numerous purposes, including trend assessment. As part of the Observed Composition Trends And Variability in the UTLS (OCTAV-UTLS) Stratosphere-troposphere Processes And their Role in Climate (SPARC) activity, we assess the effectiveness of several coordinate systems in segregating air into different atmospheric regimes. To achieve this, a comprehensive dynamical dataset is used to reference every measurement from various observing systems to the locations of jets and tropopauses in different coordinates (e.g., altitude, pressure, potential temperature, latitude, and equivalent latitude). We assess which coordinate combinations are most useful for dividing the measurements into bins such that the data in each bin are affected by the same processes, thus minimizing the variability induced when combining measurements from different dynamical regimes, each characterized by different physical processes. Such bins will be particularly suitable for combining measurements with different sampling characteristics and for assessing trends and attributing them to changing atmospheric dynamics. Overall, the use of equivalent latitude and potential temperature leads to the most substantial reduction in binned variability across the UTLS. This coordinate pairing uses potential vorticity (PV) on isentropic surfaces, thus aligning with the adiabatic transport of tracers. [ABSTRACT FROM AUTHOR]

Tropopause-overshooting convection in the midlatitudes provides a rapid transport pathway for air from the lower troposphere to reach the upper troposphere and lower stratosphere (UTLS) and can result in the formation of above-anvil cirrus plumes (AACPs) that significantly hydrate the stratosphere. Such UTLS composition changes alter the radiation budget and impact climate. Novel in situ observations from the NASA Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) field campaign are used in this study to examine UTLS impacts from AACP-generating overshooting convection. Namely, a research flight on 31 May 2022 sampled active convection over the state of Oklahoma for more than 3 h with the NASA ER-2 high-altitude research aircraft. An AACP was bisected during this flight, providing the first such extensive in situ sampling of this phenomenon. The convective observations reveal pronounced changes in air mass composition and stratospheric hydration up to altitudes of 2.3 km above the tropopause and concentrations more than double background levels. Unique dynamic and trace gas signatures were found within the AACP, including enhanced vertical mixing near the AACP edge and a positive correlation between water vapor and ozone. Moreover, the water vapor enhancement within the AACP was found to be limited to the saturation mixing ratio of the low temperature overshoot and AACP air. Comparison with all remaining DCOTSS flights demonstrates that the 31 May 2022 flight had some of the largest tropospheric tracer and water vapor perturbations in the stratosphere and within the AACP. [ABSTRACT FROM AUTHOR]

Global Navigation Satellite System (GNSS) meteorology, in which the zenith total delay (ZTD) and precipitable water vapor (PWV) are retrievable from GNSS signals, is a well-established tool for weather and climate monitoring. The real-time provision of ZTD/PWV products has always been challenging in GNSS meteorology, which is basically limited by the timely accessibility to precise satellite ephemerides. GNSS open service is based on the broadcast ephemerides. The accuracy of Galileo broadcast ephemerides has been improved to a high level, enabling real-time retrieval of ZTD/PWV using Galileo open service and being independent of network communication environments and devices. Moreover, building additional data processing systems and dense ground tracking networks is no longer necessary (excluding issues necessitating extremely accurate real-time ZTD/PWV retrievals, such as the PWV along coastal boundaries). We propose the real-time precise point positioning (PPP) technology with Galileo broadcast ephemerides to retrieve the high-accuracy ZTD/PWV. The data sets from 22 globally distributed stations spanning a year are used for analysis. Results indicate that the accuracy of real-time ZTD estimates derived from ambiguity-float solutions can reach to 2 cm after an average initialization time of 52.9 min. Taking international GNSS service (IGS) and radiosonde results as the reference, the mean bias of ZTD and PWV errors is usually less than 6 and 2 mm, respectively, while the standard deviation (STD) is 15.7 and 2.5 mm. The performance of ZTD/PWV estimates is nearly comparable to that of IGS real-time data streams, while it is worse than that of IGS post-processed precise products. [ABSTRACT FROM AUTHOR]

Criegee intermediates, formed from the ozonolysis of alkenes, are known to have a role in atmospheric chemistry, including the modulation of the oxidizing capacity of the troposphere. Although studies have been conducted since their discovery, the synthesis of these species in the laboratory has ushered in a new wave of investigations of these structures, both theoretically and experimentally. In some of these theoretical studies, high-order corrections for correlation energy are included to account for the mid multi-reference character found in these systems. Many of these studies include a focus on kinetics; therefore, the calculated energies should be accurate (<1 kcal/mol in error). In this research, we compute the enthalpies of formation for a small set of Criegee intermediates, including higher-order coupled cluster corrections for correlation energy up to coupled cluster with perturbative quintuple excitations. The enthalpies of formation for formaldehyde oxide, anti-acetaldehyde oxide, syn-acetaldehyde oxide, and acetone oxide are presented at 0 K as 26.5, 15.6, 12.2, and 0.1 kcal mol−1, respectively. Additionally, we do not recommend the coupled cluster with perturbative quadruple excitations [CCSDT(Q)] energy correction, as it is approximately twice as large as that of the coupled cluster with full quadruple excitations (CCSDTQ). Half of the CCSDT(Q) energy correction may be included as a reliable, cost-effective estimation of CCSDTQ energies for Criegee intermediates. [ABSTRACT FROM AUTHOR]

This paper is intended to summarize the research conducted during the first 2 years of the Dragon 5 project 59,332 (geophysical and atmospheric retrieval from Synthetic Aperture Radar (SAR) data stacks over natural scenarios). Monitoring atmospheric phenomena, encompassing both tropospheric and ionospheric conditions, holds pivotal significance for various scientific and practical applications. In this paper, we present an exploration of advanced techniques for estimating tropospheric and ionospheric phase screens using stacks of Synthetic Aperture Radar (SAR) images. Our study delves into the current state-of-the-art in atmospheric monitoring with a focus on spaceborne SAR systems, shedding light on their evolving capabilities. For tropospheric phase screen estimation, we propose a novel approach that jointly estimates the tropospheric component from all the images. We discuss the methodology in detail, highlighting its ability to recover accurate tropospheric maps. Through a series of quantitative case studies using real Sentinel-1 satellite data, we demonstrate the effectiveness of our technique in capturing tropospheric variability over different geographical regions. Concurrently, we delve into the estimation of ionospheric phase screens utilizing SAR image stacks. The intricacies of ionospheric disturbances pose unique challenges, necessitating specialized techniques. We dissect our approach, showcasing its capacity to mitigate ionospheric noise and recover precise phase information. Real data from the Sentinel-1 satellite are employed to showcase the efficacy of our method, unraveling ionospheric perturbations with improved accuracy. The integration of our techniques, though presented separately for clarity, collectively contributes to a comprehensive framework for atmospheric monitoring. Our findings emphasize the potential of SAR-based approaches in advancing our knowledge of atmospheric processes, thus fostering advancements in weather prediction, geophysics, and environmental management.

For effective radiative forcing (ERF) to be an ideal metric for comparing the strength of different climate drivers (such as CO2 and aerosols), the ratio of radiative forcing to global-mean temperature change must be the same for each driver. Typically, this ratio is divided by the same ratio for CO2 and termed efficacy. Previously it has been shown that efficacy is close to unity in abrupt perturbation experiments for a range of climate drivers, but efficacy with respect to CO2 has not been investigated in transient realistic simulations. Here, we analyse transient simulations from CMIP6 experiments and show comparable results between transient and abrupt perturbation experiments. We demonstrate that aerosol efficacy is not significantly different from unity, however inter-model differences in aerosol experiments are notably large. [ABSTRACT FROM AUTHOR]

Stratosphere-to-troposphere transport results in the stratospheric intrusion (SI) of O 3 into the free troposphere through the folding of the tropopause. However, the mechanism of SI that influences the atmospheric environment through the cross-layer transport of O 3 from the stratosphere and free troposphere to the atmospheric boundary layer has not been elucidated thoroughly. In this study, an SI event over the North China Plain (NCP; 33–40° N, 114–121° E) during 19–20 May 2019 was chosen to investigate the mechanism of the cross-layer transport of stratospheric O 3 and its impact on the near-surface O 3 based on multi-source reanalysis, observation data, and air quality modeling. The results revealed a mechanism of stratospheric O 3 intrusion into the atmospheric environment induced by an extratropical cyclone system. The SI with downward transport of stratospheric O 3 to the near-surface layer was driven by the extratropical cyclone system, with vertical coupling of the upper westerly trough, the middle of the northeast cold vortex (NECV), and the lower extratropical cyclone, in the troposphere. The deep trough in the westerly jet aroused the tropopause folding, and the lower-stratospheric O 3 penetrated the folded tropopause into the upper and middle troposphere; the westerly trough was cut off to form a typical cold vortex in the upper and middle troposphere. The compensating downdrafts of the NECV further pushed the downward transport of stratospheric O 3 in the free troposphere; the NECV activated an extratropical cyclone in the lower troposphere; and the vertical cyclonic circulation governed the stratospheric O 3 from the free troposphere across the boundary layer top, invading the near-surface atmosphere. In this SI event, the average contribution of stratospheric O 3 to near-surface O 3 was accounted for at 26.77 %. The proposed meteorological mechanism of the vertical transport of stratospheric O 3 into the near-surface atmosphere, driven by an extratropical cyclone system, could improve the understanding of the influence of stratospheric O 3 on the atmospheric environment, with implications for the coordinated control of atmospheric pollution. [ABSTRACT FROM AUTHOR]

Trace gases and aerosols play a crucial role in shaping Arctic climate through their impacts on radiation and chemistry. The concentration of these substances over the Arctic is largely determined by long-range transport originating from midlatitude and tropical source regions. In this study, we explore how atmospheric circulation modulates the interannual variability of long-range transport into the Arctic by utilizing a chemistry–climate model. Idealized tracers, which have fixed lifetimes and spatially varying but temporally fixed surface emissions corresponding to the climatology of anthropogenic emissions of the year 2000, are employed to isolate the role of atmospheric transport from emission and chemistry in modulating interannual variability. Tracers emitted from different source regions are tagged to quantify their relative contributions. Model simulations reveal that tracers from Europe, East Asia, and North America contribute the most to Arctic tracer mass, followed by those from the Tibetan Plateau and South Asia, as well as the Middle East. These regional tracers are predominantly transported into the Arctic middle to upper troposphere, with the exception of tracers from Europe during winter, which are transported into the Arctic lower troposphere. Our analysis shows that the interannual variability of transport into the Arctic for each regional tracer is determined by the atmospheric circulation over the corresponding emission region; i.e., anomalous poleward and eastward winds over the source region promote transport into the Arctic. Considering tracers with global emissions, a southward shift of the midlatitude jet during winter favors increased transport into the Arctic, particularly for tracers emitted over Asia, aligning with previous studies. Comparisons of tracers with different lifetimes indicate that the interannual variability of shorter lifetime tracers is predominantly influenced by regional tracers with shorter transport pathways into the Arctic (e.g., Europe), while the interannual variability of longer lifetime tracers is more contributed by regional tracers with higher emissions (e.g., East Asia). [ABSTRACT FROM AUTHOR]

The relationship between precipitation and cloud properties in Southwest China are investigated by using the CLARA‐A2 cloud parameters data and TRMM‐3B43 precipitation data from 1998 to 2015. Ice water path (IWP) and cloud top height (CTH) are significantly and positively correlated with precipitation in all regions, indicating that ice‐phase processes and cloud development processes are the critical processes influencing precipitation. Precipitation is also directly associated with cloud fractional coverage (CFC) due to the significant positive correlation between CFC and precipitation in all regions except the Sichuan Basin (SCB). A positive correlation between liquid water path (LWP) and precipitation is found in the Eastern Tibetan Plateau (ETP) and Yunnan‐Kweichow Plateau (YKP), but not in the Western Tibetan Plateau (WTP) and SCB. Notably, the response of precipitation to LWP is not as good as that to IWP in SCB. Precipitation is significantly negatively correlated with ice effective radius (IREF) in WTP and ETP and positively correlated with liquid effective radius (LREF) in ETP, YKP and SCB. IREF and LREF are closely related to cloud microphysical processes. Specifically, small IREF could accelerate the Bergeron process and thus increase precipitation, while large LREF is closely related to the cloud droplets coalescence process. Results indicate that the difference in precipitation between the cold and warm seasons is related to convective available potential energy (CAPE) and low troposphere relative humidity (RH). High CAPE and RH favour the precipitation occurrence in Southwest China. The influence of CAPE and RH on precipitation is more significant in the ETP than that in the WTP, owing to the orographic lifting and moisture transport from the Indian Ocean. Thermodynamic and humidity conditions have a greater impact on precipitation by influencing LREF, LWP and IWP in YKP. In SCB, precipitation shows a strong dependence on CAPE, IWP and LREF, but not on RH. [ABSTRACT FROM AUTHOR]

Knowledge of wind field characteristics and variation principles in complex topographical regions is of great importance for the development of numerical prediction models, aviation safety support, and wind energy utilization. However, there has been limited research focused on the lower-tropospheric wind fields in the Qinghai-Tibet Plateau. This paper aims to study the wind characteristics, vertical distributions, and temporal variations in the northeast of the plateau by analyzing a four-year continuous dataset collected from a Doppler wind LiDAR deployed in Xining, Qinghai Province of China. The results indicate that the prevailing horizontal wind direction in the low levels is primarily influenced by the mountain-valley wind circulation. However, as the altitude increases, the prevailing winds are predominantly affected by the westerlies. From a diurnal perspective, noticeable transition processes between up-valley and down-valley winds can be observed. The west-northwest wind (down-valley wind) dominates from late night to morning, while the east-southeast wind (up-valley wind) prevails from afternoon to early evening. The vertical winds in the low levels exhibit a downward motion during the daytime and an upward motion during the nighttime. In this plateau valley, the wind shear exponent is found to be highest in spring and lowest in winter, and it is generally lower during the daytime compared to the nighttime. [ABSTRACT FROM AUTHOR]

FORMOSAT-7/COSMIC-2 radio occultation (RO) measurements show promise for observing the deep troposphere and for providing critical information on the Earth's planetary boundary layer (PBL). However, refractivity retrieved in the low troposphere can have severe biases under certain thermodynamic conditions. This research examines the characteristics of the deep tropospheric biases and presents methods for estimating the region-dependent refractivity bias using statistical regression models. The results show that the biases have characteristics that vary over land and oceans. With substantial correlation between local spectral width (LSW) and bias, the LSW-based bias estimation model can explain the general pattern of the refractivity bias but with deficiencies in measuring the bias in the ducting regions and in certain areas over land. The estimation model involving the relationship with temperature and specific humidity (TQ) can capture the large biases associated with ducting. Finally, a minimum variance estimation that combines the LSW and TQ provides the most accurate estimation of the refractivity bias. [ABSTRACT FROM AUTHOR]

This article examines the relationship between hydrogen and carbon monoxide in the atmosphere, particularly in the context of the increasing use of hydrogen energy. The study finds that the interactions between these two gases are complex and understanding them is crucial for assessing the environmental impacts of a shift to hydrogen energy. The research reveals that hydrogen can affect the levels of carbon monoxide, formaldehyde, hydroxyl, methane, ozone, and stratospheric water vapor in the atmosphere. The findings suggest that the warming effect of hydrogen leakage should be considered when expanding hydrogen energy. The article also discusses the interlinkage between hydrogen and carbon monoxide through incomplete combustion reactions and how carbon monoxide emissions can be used to estimate global hydrogen emissions. The study provides valuable insights into the relationship between hydrogen and carbon monoxide, contributing to our understanding of the potential environmental impacts of hydrogen energy. The research was funded by the HYDROGEN project and the Research Council of Norway. [Extracted from the article]

The results of a comparative analysis of various characteristics of the temperature conditions of the planetary atmospheres in the Solar System and their dependence on orbital parameters, in particular on the length and angular frequency of the annual cycle, are presented. A root dependence on the angular frequency of the dry adiabatic lapse rate is noted. The dependence of the planetary equilibrium temperature in the form of the cubic root of the angular frequency of the annual cycle is related to Kepler's third law. For Venus, Earth, Mars, Jupiter, and Saturn, the root dependence of the scale height and the troposphere height on the annual cycle length is manifested, and the atmospheric features of the most distant planets from the Sun—Uranus and Neptune—are noted. [ABSTRACT FROM AUTHOR]

The influence of atmospheric waves generated by a tropospheric convective source on the state of the upper atmosphere and ionosphere during the recovery phase of the geomagnetic storm on May 27–28, 2017 is studied. A new approach to accounting for atmospheric waves generated by tropospheric convective sources in large-scale atmospheric models without using wave parameterization is proposed and implemented. The developed approach makes it possible to comprehensively study the effects generated by atmospheric waves against the background of various geophysical events, including geomagnetic storms. The multimodel study shows that the proposed approach allows us to reproduce perturbations of the critical frequency of the ionosphere's ionospheric F2 layer caused by the propagation of atmospheric waves generated by a tropospheric meteorological source. It is shown that the inclusion of a heat inflow source simulating the propagation of atmospheric waves from the lower atmosphere in the global model enhances the effects of a geomagnetic storm, which manifests itself as an additional decrease in the critical frequency of the F2 layer, which can reach 7% of the absolute values. [ABSTRACT FROM AUTHOR]

This paper is intended to summarize the research conducted during the first 2 years of the Dragon 5 project 59,332 (geophysical and atmospheric retrieval from Synthetic Aperture Radar (SAR) data stacks over natural scenarios). Monitoring atmospheric phenomena, encompassing both tropospheric and ionospheric conditions, holds pivotal significance for various scientific and practical applications. In this paper, we present an exploration of advanced techniques for estimating tropospheric and ionospheric phase screens using stacks of Synthetic Aperture Radar (SAR) images. Our study delves into the current state-of-the-art in atmospheric monitoring with a focus on spaceborne SAR systems, shedding light on their evolving capabilities. For tropospheric phase screen estimation, we propose a novel approach that jointly estimates the tropospheric component from all the images. We discuss the methodology in detail, highlighting its ability to recover accurate tropospheric maps. Through a series of quantitative case studies using real Sentinel-1 satellite data, we demonstrate the effectiveness of our technique in capturing tropospheric variability over different geographical regions. Concurrently, we delve into the estimation of ionospheric phase screens utilizing SAR image stacks. The intricacies of ionospheric disturbances pose unique challenges, necessitating specialized techniques. We dissect our approach, showcasing its capacity to mitigate ionospheric noise and recover precise phase information. Real data from the Sentinel-1 satellite are employed to showcase the efficacy of our method, unraveling ionospheric perturbations with improved accuracy. The integration of our techniques, though presented separately for clarity, collectively contributes to a comprehensive framework for atmospheric monitoring. Our findings emphasize the potential of SAR-based approaches in advancing our knowledge of atmospheric processes, thus fostering advancements in weather prediction, geophysics, and environmental management. [ABSTRACT FROM AUTHOR]

Zenith tropospheric delay (ZTD) is an important atmospheric parameter in radio‐space‐geodetic techniques such as Global Navigation Satellite System (GNSS), which is pivotal for GNSS positioning, navigation and meteorology. The Vienna Mapping Function (VMF) data server is a widely utilized source for implementing ZTD, offering two types of models, that is, the empirical one and the discrete one with Grid‐wise and Site‐wise models. Therefore, to evaluate the accuracy of these models becomes the focus of this article. Specifically, this study investigates their performances in terms of calculation of ZTD, using the hourly values derived from the International GNSS Service data as references. The results show that the root mean square err (RMSE) of the Site‐wise, Grid‐wise and global pressure and temperature 3 model are 11.71/13.03/38.56 mm, respectively, indicating the discrete model performs generally better than the empirical model, and the Site‐wise model is the better of the two discrete models. From the perspective of spatial resolution, the performance of these three models in ZTD calculation shows obvious influences of latitude changes and elevation differences. From the temporal analysis, the accuracy of the discrete model shows differences over different UTC epochs, while the empirical model can only express the seasonal ZTD characteristics with the average RMSE at different epochs being similar, the specifically values are 39.67, 39.26, 39.38 and 39.18 mm at UTC 0:00, 6:00, 12:00 and 18:00, respectively. The histogram and boxplot well indicate the accuracy differences of the three models in different seasons. Additionally, the time series of three models at different latitudes were also explored in this research. These explorations are conducive to the selection of appropriate models for calculating ZTD based on specific requirements. Key Points: The discrete and empirical troposphere delay models of the VMF data server is comprehensibly evaluated using the global International GNSS Service (IGS) dataThe Site‐wise of discrete model exhibits the best accuracy and is recommended first, followed by the Grid‐wide and the empirical modelEach model shows different influences by the latitude, elevation, seasons and epochs [ABSTRACT FROM AUTHOR]

We present data and analysis of a set of balloon‐borne sounding profiles, which includes co‐located O3, CO, CH4, and particles, over the northern Tibetan Plateau during an Asian summer monsoon (ASM) season. These novel measurements shed light on the ASM transport behavior near the northern edge of the anticyclone. Joint analyses of these species with the temperature and wind profiles and supported by back trajectory modeling identify three distinct transport processes that dominate the vertical chemical structure in the middle troposphere, upper troposphere (UT), and the tropopause region. The correlated changes in profile structures in the middle troposphere highlight the influence of the strong westerly jet. Elevated constituent concentrations in the UT identify the main level of convective transport at the upstream source regions. Observed higher altitude maxima for CH4 characterize the airmasses' continued ascent following convection. These data complement constituent observations from other parts of the ASM anticyclone. Plain Language Summary: Asian summer monsoon deep convection transports surface pollutants to the stratosphere. Although satellite data have provided clear evidence of this transport, in situ measurements are critical for characterizing how monsoon is vertically re‐distributing the regional emissions. We report new balloon‐borne measurements over the Tibetan Plateau that provide a unique data set on the northern edge of the anticyclone, complementing other observations. Key Points: A novel set of in‐situ profile measurements of O3, CO, CH4 and particles from Tibetan Plateau during Asian summer monsoon are presentedJoint analyses of the profiles provide insights into transport processes controlling the northern edge of the Asian monsoon anticycloneObserved CO profile maxima at 13–14 km (∼360–370 K) identify the level of convective transport at the upstream source regions [ABSTRACT FROM AUTHOR]

The stratosphere has previously been shown to be a significant source of subseasonal tropospheric predictability. The ability of ensemble prediction systems to appropriately exploit this depends on their ability to reproduce the statistical properties of the real atmosphere. In this study, we investigate predictability properties of the coupled stratosphere‐troposphere system in the sub‐seasonal to seasonal prediction project hindcasts by fitting a simple, minimal model. We diagnose the signal and noise components of each system in the stratosphere and troposphere and their coupling. We find that while the correlation skill scores are similar in most systems, the signal to noise properties can be substantially different. In the stratosphere, some systems are significantly overconfident, with a quantifiable impact on the tropospheric confidence. We link the method and details of the design of a prediction system to these predictive properties. Plain Language Summary: Subseasonal weather prediction systems make use of ensemble forecasting approaches, in which each forecast is made up of a number of complimentary predictions (ensemble members), that produce more skillful predictions by averaging and allows forecasters to anticipate the uncertainty in any particular forecast. There is a "battle" between the useful signal, hidden in the initial conditions of a simulation run, against the noise that chaotically builds up over the run from inaccuracies in the representation of the initial conditions. We use a simple statistical model with a minimal number of parameters to investigate how well the prediction systems capture both the signal and noise properties of the real atmosphere. We find that while the skill in the troposphere and stratosphere are in line with expectations from the real‐world, the ratio between the signal and the noise is too large, particularly in the stratosphere. We find this has an impact on the troposphere below, increasing the signal‐to‐noise ratio there too—artificially inflating it—giving it an overconfidence which is not wholly statistically or physically justified. We link the method and details of the design of a prediction system to these predictive properties. Key Points: Fitting a detailed statistical model to subseasonal prediction systems reveals some have significant overconfidence in the stratosphereLarge diversity in stratospheric error growth properties between different systemsSystems that are overconfident in the stratosphere have an overconfidence bias in the troposphere [ABSTRACT FROM AUTHOR]

Peroxyacetyl nitrate (PAN) is a hazardous secondary pollutant and a nitrogen reservoir in the troposphere, while comprehensive studies on its spatiotemporal distribution, chemical sources, and control strategies are limited. This study addressed these issues based on 1-year multi-site observations in the Pearl River Delta region, showing a pattern of higher PAN levels in the cold season, particularly in coastal areas. Moreover, in situ modeling indicated a net photochemical PAN formation in the warm season, while PAN was dominated by regional transport in the cold season (i.e., rural and coastal areas), releasing NO2 and PA radicals and promoting ozone (O3) formation. In addition, the feasibility of joint control of PAN and O3 was confirmed by their isopleth diagrams. C7–C9 aromatics and C4–C5 alkenes, largely from vehicle exhaust and solvent usage, were identified as the predominant contributors to PAN formation in this region. Overall, this study deepens our understanding of PAN chemistry and provides valuable insights into its control measures. [ABSTRACT FROM AUTHOR]

Pseudolite positioning system can enhance GNSS (Global Navigation Satellite System) by improving satellite geometry and providing services independently in the GNSS unavailable environment. Many error items of pseudolite positioning system, e.g., tropospheric delay error, need to be corrected by an accurate model. While several tropospheric delay models suitable for pseudolite positioning systems have been proposed, the key parameters indicating the upper boundaries for tropospheric refraction are fixed to an experimental value in these models. In this paper, we studied the spatiotemporal characteristics of the upper boundary heights for hydrostatic and wet tropospheric delay based on the ERA5 global meteorological reanalysis data. With the refined height boundary term, we refine four existing tropospheric delay models for pseudolite positioning systems, including RTCA, MRTCA, Bouska and Hopfield models. To evaluate the performance of the refined models, we selected 12 airports distributed globally as experimental areas and analyzed the error characteristics of the four refined tropospheric models and the LTC model (independent of height). The experimental results show that when the slant distance between the pseudolite base station and the receiver is constant at 5 km, the MRTCA model has the best performance, with an RMSE (root mean square error) of about 0.15 m. When the elevation angle between the pseudolite base station and the receiver is constant, the RMSE of the LTC model is the smallest at the low elevation angle, and the RMSE of the MRTCA model is the smallest at the high elevation. The RMSE of pseudolite tropospheric delay models show seasonal variation. [ABSTRACT FROM AUTHOR]

Diabatic transport schemes with hybrid zeta coordinates, which follow isentropes in the stratosphere, are known to greatly improve Lagrangian transport calculations compared to the kinematic approach. However, some Lagrangian transport calculations with a diabatic approach, such as the Chemical Lagrangian Transport Model of the Stratosphere (CLaMS), are not well prepared to run on modern high-performance computing (HPC) architectures. Here, we implemented and evaluated a new diabatic transport scheme in the Massive-Parallel Trajectory Calculations (MPTRAC) model. While MPTRAC can be used either with shared-memory multiprocessing on CPUs or with GPUs to offload computationally intensive calculations, making it flexible for many HPC applications, it has been limited to kinematic trajectories in pressure coordinates. The extended modelling approach now enables the use of either kinematic or diabatic vertical velocities and the coupling of different MPTRAC modules based on pressure or hybrid zeta coordinates. This study focus on the accuracy of the implementation in comparison to the CLaMS model. The evaluation of the new transport scheme in MPTRAC shows that, after 90 d of forward calculations, distributions of air parcels in the upper troposphere and lower stratosphere (UTLS) are almost identical for MPTRAC and CLaMS. No significant bias between the two Lagrangian models was found. Furthermore, after 1 d, internal uncertainties (e.g. due to interpolation or the numerical integration method) in the Lagrangian transport calculations are at least 1 order of magnitude smaller than external uncertainties (e.g. from reanalysis selection or downsampling of ERA5). Differences between trajectories using either CLaMS or MPTRAC are on the order of the combined internal uncertainties within MPTRAC. Since the largest systematic differences are caused by the reanalysis and the vertical velocity (diabatic vs. kinematic), the results support the development efforts for trajectory codes that can access the full resolution of ERA5 in combination with diabatic vertical velocities. This work is part of a larger effort to adapt Lagrangian transport in state-of-the-art models such as CLaMS and MPTRAC to current and future HPC architectures and exascale applications. [ABSTRACT FROM AUTHOR]

For high-precision positioning applications, various GNSS errors need to be mitigated, including the tropospheric error, which remains a significant error source as it can reach up to a few meters. Although some commercial GNSS correction data providers, such as the Quasi-Zenith Satellite System (QZSS) Centimeter Level Augmentation Service (CLAS), have developed real-time precise regional troposphere products, the service is available only in limited regional areas. The International GNSS Service (IGS) has provided precise troposphere correction data in TRO format post-mission, but its long latency of 1 to 2 weeks makes it unable to support real-time applications. In this work, a real-time troposphere prediction method based on the IGS post-processing products was developed using machine learning techniques to eliminate the long latency problem. The test results from tropospheric predictions over a year using the proposed method indicate that the new method can achieve a prediction accuracy (RMSE) of 2 cm, making it suitable for real-time applications. [ABSTRACT FROM AUTHOR]

High-quality long-term observational records are essential to ensure appropriate and reliable trend detection of tropospheric ozone. However, the necessity of maintaining high sampling frequency, in addition to continuity, is often under-appreciated. A common assumption is that, so long as long-term records (e.g., a span of a few decades) are available, (1) the estimated trends are accurate and precise, and (2) the impact of small-scale variability (e.g., weather) can be eliminated. In this study, we show that the undercoverage bias (e.g., a type of sampling error resulting from statistical inference based on sparse or insufficient samples, such as once-per-week sampling frequency) can persistently reduce the trend accuracy of free tropospheric ozone, even if multi-decadal time series are considered. We use over 40 years of nighttime ozone observations measured at Mauna Loa, Hawaii (representative of the lower free troposphere), to make this demonstration and quantify the bias in monthly means and trends under different sampling strategies. We also show that short-term meteorological variability remains a cause of an inflated long-term trend uncertainty. To improve the trend precision and accuracy due to sampling bias, two remedies are proposed: (1) a data variability attribution of colocated meteorological influence can efficiently reduce estimation uncertainty and moderately reduce the impact of sparse sampling, and (2) an adaptive sampling strategy based on anomaly detection enables us to greatly reduce the sampling bias and produce more accurate trends using fewer samples compared to an intense regular sampling strategy. [ABSTRACT FROM AUTHOR]

Pressure, temperature and specific humidity profiles from COSMIC-2 are compared with those from ERA5 and radiosonde data from October 2019 to September 2020. The results demonstrate that COSMIC-2 pressure and specific humidity profiles show relatively poor accuracy and stability in the lower troposphere. The 1D-Var solution effectively improves the accuracy of temperature parameters in the troposphere. Three parameters show high accuracy over one climatological year, but show slight seasonal fluctuations, especially for the specific humidity profiles in summer. Furthermore, COSMIC-2 specific humidity data show low consistency with radiosonde and ERA5 in the equatorial region. [ABSTRACT FROM AUTHOR]

Convective Self‐Aggregation (CSA) is a common feature of idealized numerical simulations of the tropical atmosphere in Radiative‐Convective Equilibrium (RCE). However, at coarse grid resolution where deep convection is not fully resolved, the occurrence of this phenomenon is extremely sensitive to subgrid‐scale processes. This study examines the role of mixing and entrainment, provided by the turbulence model and the implicit numerical diffusion. The study compares the results of two models, WRF and SAM, by varying turbulence models, initial conditions, and horizontal spatial resolution. At a coarse grid resolution of 3 km, the removal of turbulent mixing prevents CSA in models with low numerical diffusivity but is preserved in models with high numerical diffusivity. When the horizontal grid resolution is refined to 1 km, CSA can only be achieved by increasing explicit turbulent mixing, even with a small amount of shallow clouds. Therefore, the sensitivity of CSA to horizontal grid resolution is not primarily caused by the decrease in shallow clouds. The analysis of the total water path spectrum suggests that the amplitude of initial humidity perturbations introduced by convection in the free troposphere is the key factor. This amplitude is regulated by turbulent mixing and diffusion at small scales. Prior to the onset of CSA, increased mixing makes updrafts more sensitive to the dryness of the free troposphere, which strengthens the moisture‐convection feedback. This leads to an increased distance between convective cores and a stronger humidity perturbation in the free troposphere, which can destabilize the RCE state. Plain Language Summary: Convection transports moisture from the surface to the troposphere and forms clouds. Clouds developing in dry environments can be diluted by turbulent mixing, while mixing in moist environments favors their deepening. Turbulent mixing thus favors convection over moist regions, making them moister, while the opposite is true for dry regions. This phenomenon is known as the moisture‐convection feedback. In atmospheric models with a horizontal grid resolution of about 1 km, the feedback is represented by the turbulence model and the numerical discretization errors. This study found that when simulating deep tropical convection, the use of coarse grid resolution strengthens the moisture‐convection feedback, initially creating larger clusters of clouds separated by larger areas free of convection. In these areas where convection is suppressed, the upper troposphere will dry out. The amplitude of this area and its associated dry perturbation of the upper troposphere are key factors in determining whether convection will continue to be suppressed or if it will be able to penetrate the free troposphere. The final clustering of clouds into a single moist patch, known as convective self‐aggregation, depends on these conditions. Therefore, it is necessary to accurately represent sub‐grid scale mixing processes to capture the convective self‐aggregation phenomenon in high‐resolution atmospheric models. Key Points: The initial amplitude of humidity perturbations introduced by convection in the free troposphere is the key factor for the onset of convective self‐aggregation.Prior to the onset of self‐aggregation, this amplitude is regulated by turbulent mixing and numerical diffusion, rather than the amount of shallow clouds.Coarse resolutions impose larger mixing which increases the distance between convective cores and the associated humidity perturbation in the free troposphere. [ABSTRACT FROM AUTHOR]

This paper presents the first quantitative relationship between the cold point tropopause (CPT) and tropical easterly jet (TEJ) using radiosonde observations over Gadanki (13.45° N, 79.2° E) during the Indian summer monsoon season 2006–2014. CPT and TEJ peak altitudes (HCPTandHTEJ) show amalgams of two categories of variability on the day‐to‐day scale. In category1 HTEJ occurs close to HCPT and they show in‐phase variation. While in Category2 HTEJ occurs far apart from HCPT and they do not show any relationship. For Category1 HCPT and HTEJ are strongly correlated (0.70), as well as HCPT and TCPT (CPT temperature) are moderately anticorrelated (−0.55) significant at a 95% confidence level, indicating the dominance of adiabatic processes. Whereas in Category2 HCPT and TCPT are not significantly anti‐correlated. Thus, when TEJ and CPT are close to each other, it may serve as an indicator for the prevalence of the synoptic‐scale effect. [ABSTRACT FROM AUTHOR]

We investigate the possibility for the South Atlantic Convergence Zone (SACZ) to act as a Rossby wave source for global scale teleconnections. A simple heating perturbation is applied to numerical simulations using a baroclinic model with differing basic states. Sixteen days after the perturbation is applied, wave propagation is diagnosed within the subtropical latitudes of the Northern Hemisphere for the basic states corresponding to El Niño and neutral years, which have normal and strong westerly flow in the upper troposphere over the Equatorial Atlantic Ocean. For La Niña basic states, there is very little propagation over the Equatorial Atlantic Ocean because the westerly flow is weak, confining Rossby waves to the Southern Hemisphere. We conclude that the SACZ may act as interhemispheric Rossby wave source, providing the tropical westerly flow is strong enough to permit wave propagation across the Equatorial Atlantic Ocean. [ABSTRACT FROM AUTHOR]

In the study of atmospheric wind fields from the upper troposphere to the stratosphere (10 km to 50 km), direct detection wind LiDAR is considered a promising method that offers high-precision atmospheric wind field data. In 2020, Xie et al. of the Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, developed an innovative rotating Rayleigh Doppler wind LiDAR (RRDWL). The system aims to achieve single-LiDAR detection of atmospheric wind fields by rotating the entire device cabin. In 2022, the feasibility of the system was successfully validated in laboratory conditions, and field deployment was completed. Due to the structural differences between this system and traditional direct-detection wind LiDAR, performance tests were conducted to evaluate its continuous detection capability in outdoor environments. Subsequently, based on the test results and error analysis, further analysis was carried out to identify the main factors affecting the system's detection performance. Finally, the error analysis and traceability of the detection results were conducted, and corresponding measures were discussed to provide a theoretical foundation for optimizing the performance of RRDWL. [ABSTRACT FROM AUTHOR]

The Tropospheric Ozone Lidar Network (TOLNet) was used to validate retrievals of ozone (O 3) profiles in the troposphere from the TROPOspheric Monitoring Instrument (TROPOMI) ultraviolet (UV), Cross-track Infrared Sounder (CrIS) infrared (IR), and a combined UV + IR wavelength retrieval from TROPOMI/CrIS. Observations from six separate ground-based lidar systems and various locations of ozonesondes distributed throughout North America and in the Netherlands were used to quantify systematic bias and random errors for each satellite retrieval. Furthermore, TOLNet data were used to intercompare idealized UV, IR, and UV + IR convolved lidar profiles of O 3 in the troposphere during case studies representative of high-O 3 events. This study shows that the improved sensitivity and vertical resolution in UV + IR retrievals in the middle- and upper-troposphere resulted in tropospheric degree of freedom (DOF) values ∼ 33 % higher compared to UV- and IR-only retrievals. The increased DOFs in the UV + IR retrievals allowed for improved reproduction of mid- and upper-tropospheric O 3 enhancements and, to a lesser degree, near-surface pollution enhancements compared to single-wavelength satellite products. The validation of O 3 profiles in the troposphere retrieved with the UV-only, IR-only, and UV + IR Tikhonov regularised Ozone Profile retrievAl with SCIATRAN (TOPAS) algorithm developed at the Institute for Environmental Physics, University of Bremen, demonstrated the utility of using TOLNet as a satellite evaluation data set. TOPAS UV-only, IR-only, and UV + IR wavelength retrievals had systematic biases, quantified with normalized mean bias, throughout the troposphere of 11.2 ppb (22.1 %), -1.7 ppb (-0.3 %), and 3.5 ppb (7.8 %), respectively, which meet the tropospheric systematic bias requirements defined by the science teams for the TROPOMI and CrIS sensors. The primary drivers of systematic bias were determined to be solar zenith angle, surface albedo, and cloud fraction. Random errors, representative of uncertainty in the retrievals and quantified by root mean squared errors (RMSEs), were large for all three retrievals, with UV-only, IR-only, and UV + IR wavelength retrievals having RMSEs throughout the troposphere of 17.4 ppb (19.8 % of mean tropospheric column values), 10.5 ppb (12.6 % of mean tropospheric column values), and 14.0 ppb (14.6 % of mean tropospheric column values), respectively. TOPAS UV-only profiles did not meet the uncertainty requirements defined for TROPOMI for the troposphere; however, CrIS IR-only retrievals did meet the uncertainty requirements defined by this mission. The larger random errors reflect the challenge of retrieving daily O 3 profiles due to the limited sensitivity and vertical resolution of these retrievals in the troposphere. Tropospheric systematic biases and random error were lower in IR-only and combined UV + IR retrievals compared to UV-only products due to the increased sensitivity in the troposphere allowing the retrievals to deviate further from the a priori profiles. Observations from TOLNet demonstrated that the performance of the three satellite products varied by season and altitude in the troposphere. TOLNet was shown to result in similar validation statistics compared to ozonesonde data, which are a commonly used satellite evaluation data source, demonstrating that TOLNet is a sufficient source of satellite O 3 profile validation data in the troposphere, which is critical as this data source is the primary product identified for the tropospheric O 3 validation of the recently launched Tropospheric Emissions: Monitoring of Pollution (TEMPO) mission. [ABSTRACT FROM AUTHOR]

Data assimilation of atmospheric observations traditionally relies on variational and Kalman filter methods. Here, an alternative neural network data assimilation (NNDA) with variational autoencoder (VAE) is proposed. The three‐dimensional variational (3D‐Var) data assimilation cost function is utilised to determine the analysis that optimally fuses simulated observations and the encoded short‐range persistence forecast (background), accounting for their errors. The minimisation is performed in the reduced‐order latent space discovered by the VAE. The variational problem is autodifferentiable, simplifying the computation of the cost‐function gradient necessary for efficient minimisation. We demonstrate that the background‐error covariance (B) matrix measured and represented in the latent space is quasidiagonal. The background‐error covariances in the grid‐point space are flow‐dependent, evolving seasonally and depending on the current state of the atmosphere. Data assimilation experiments with a single temperature observation in the lower troposphere indicate that the B matrix describes both tropical and extratropical background‐error covariances simultaneously. [ABSTRACT FROM AUTHOR]

Mercury (Hg) is a global atmospheric pollutant. In its oxidized form (HgII), atmospheric Hg can readily deposit to ecosystems, where it may bioaccumulate and cause severe health effects. High HgII concentrations are reported in the free troposphere, but spatiotemporal data coverage is limited. Underestimation of HgII by commercially available measurement systems hinders quantification of Hg cycling and fate. During spring-summer 2021 and 2022, we measured elemental (Hg0) and oxidized Hg using a calibrated dual-channel system alongside trace gases, aerosol properties, and meteorology at the high-elevation Storm Peak Laboratory (SPL) above Steamboat Springs, Colorado. Oxidized Hg concentrations displayed temporal behavior similar to previous work at SPL, but were approximately three times higher in magnitude due to improved measurement accuracy. We identified 18 multi-day events of elevated HgII (mean enhancement: 36 pg m-3) that occurred in dry air (mean ± s.d. RH = 32 ± 16 %). Lagrangian particle dispersion model (HYSPLIT-STILT) 10-day back-trajectories showed that the majority of transport prior to events occurred in the low to mid-free troposphere. Oxidized Hg was anticorrelated with Hg0 during events, with an average (± s.d.) slope of -0.39 ± 0.14, suggestive of upwind oxidation followed by deposition during transport. Concurrent sulfur dioxide measurements verified that three upwind coal-fired power plants did not measurably contribute ambient Hg at SPL. Principal Components Analysis revealed HgII consistently inversely related with Hg0 and was generally not associated with combustion tracers, confirming oxidation in the clean, dry free troposphere as its primary origin. [ABSTRACT FROM AUTHOR]

The rotational and divergent kinetic energy (RKE and DKE) spectra of geostrophic vortices (Rossby waves; RWs) and inertia‐gravity waves (IGWs) in the global atmosphere are investigated with ERA5 reanalysis. The separation of RWs and IGWs in physical space is based on the normal‐mode decomposition, and the Helmholtz decomposition produces their RKE and DKE spectra at different layers, with a focus on spherical wavenumbers 10 ≤ l ≤ 100. In the upper troposphere and the middle and lower stratosphere, the RKE spectra of the total mode closely resemble the horizontal kinetic energy (HKE) spectra of RWs over most wavenumbers; the DKE spectra of the total mode are more comparable to the DKE spectra rather than the HKE spectra of IGWs, although their slopes are similar. The HKE of RWs is dominated by its rotational component, accounting for more than 80% of the HKE in most ranges of concern. Although the HKE of IGWs is dominated by its divergent component, its rotation component is also significant, with an average percentage exceeding 25% in all three vertical layers analyzed. Care must be taken when employing divergence as a proxy of IGWs, as the DKE may underestimate the HKE of IGWs. With the increase of altitude and the decrease of scale, the contribution of the divergent component increases in the horizontal circulation of both RWs and IGWs. Plain Language Summary: The atmospheric horizontal kinetic energy (HKE) spectrum exhibits a mysterious −5/3 slope at mesoscales, but underlying physical mechanisms are still not fully understood. Evaluating the contributions of geostrophic vortices and inertia‐gravity waves to the HKE spectrum helps us understand this issue. Combining the normal‐mode and Helmholtz decompositions, we investigate the rotational and divergent kinetic energy (RKE and DKE) spectra of geostrophic vortices and inertia‐gravity waves in the global atmosphere with ERA5 reanalysis. Our results verify that the RKE approximates the HKE of the vortex well, but the DKE underestimates the HKE of the wave, especially at larger scales. The HKE of vortices and waves is dominated by their respective rotational and divergent components. However, unlike the negligible divergent component in vortices, the contribution of the rotational component in waves is significant. In the vertically integrated HKE over three selected layers in the upper troposphere and stratosphere, the average percentage of RKE at l = 10–100 exceeds 25%. When using the intersection of RKE and DKE spectra to diagnose the mesoscale transition, it should be noted that the crossing scale of the HKE spectra of waves and vortices may be larger. Key Points: The total rotational kinetic energy (RKE) spectra can be well approximated to the horizontal kinetic energy (HKE) spectra of Rossby wavesThe total divergent kinetic energy (DKE) spectra closely resemble the DKE spectra of inertia‐gravity waves rather than their HKE spectraOn average, the RKE component accounts for more than 25% in the HKE of inertia‐gravity waves at wavenumbers 10–100 [ABSTRACT FROM AUTHOR]

In this paper, we applied a variety of statistical methods to study gravity waves in the troposphere and lower stratosphere in the Brazilian sector, using a large database from Instituto de Controle do Espaço Aéreo (ICEA) of radiosonde measurements carried out in 2014 at 32 locations in the Brazilian territory totaling 49,652 wind and temperature profiles. The average wind profiles were computed and classified by means of a hierarchical cluster analysis. The kinetic and potential energy densities of gravity waves were determined using a detrending technique based on the Least Squares Method and the Fast Fourier Transform. By analyzing the energy density time series it was found that tropospheric average values are consistently larger in the months of winter, late autumn and early spring. Stratospheric average values of variability and kinetic energy density are also consistently larger in this period. A systematic search for quasi monochromatic waves was carried out and their main characteristics such as horizontal/vertical wavelengths and velocities were determined both in the troposphere and lower stratosphere. A correlation analysis between the troposphere and the lower stratosphere based on the measured parameters was used to investigate the wave coupling between the two layers, and no significant correlation was found. Finally, a spatial correlation analysis between energy densities measured at different aerodromes in the same atmospheric layer was carried out, showing that energy densities are spatially correlated for distances less than 3,000–4,000 km. Plain Language Summary: Like waves in the ocean that can be easily seen by any observer in the beach, the atmosphere is also permeated by waves of similar nature, called Gravity Waves (GWs). These waves transport energy through the atmosphere, eventually breaking, reflecting or dissipating at some point. In this work we investigated the characteristics of these waves using weather data retrieved by weather balloons released from several locations in the Brazilian territory in 2014. By analyzing the measurements, we quantified parameters related to GWs, such as the kinetic and potential energy densities. We also investigated GWs that have well defined frequencies, called monochromatic waves, and determined their wavelengths, phases, amplitudes and phase velocities. We did not find correlations between the wave energies in the troposphere and the low stratosphere, which is an evidence of weak coupling between both layers. This result suggests that GWs characteristics are substantially modified in the perturbed, turbulent and windy region between the troposphere and low stratosphere. Moreover, we also identified the prevailing behavior of the winds in each of the studied locations. Key Points: A comprehensive survey on gravity waves using radiosonde data from 32 locations in the Brazilian territory totaling 49,652 profilesThe energy densities of gravity waves are spatially correlated within a region of approximately 3,000 km of radiusIt was found that gravity waves propagating in the troposphere and low stratosphere are uncorrelated in the studied locations [ABSTRACT FROM AUTHOR]

The transport history of tropospheric air masses above the tropical western Pacific (TWP) is reflected by the local ozone and relative humidity (RH) characteristics. In boreal winter, the TWP is the main global entry point for air masses into the stratosphere and therefore a key region of atmospheric chemistry and dynamics. Our study aims to identify air masses with different pathways to the TWP using ozone and radio soundings from Palau from 2016–2019. Supported by backward trajectory calculations, we found five different types of air masses. We further defined locally controlled ozone and RH background profiles based on monthly statistics and analyzed corresponding anomalies in the 5–10 km altitude range. Our results show a bimodality in RH anomalies. Humid and ozone-poor background air masses are of local or Pacific convective origin and occur year-round, but they dominate from August until October. Anomalously dry and ozone-rich air masses indicate a non-local origin in tropical Asia and are transported to the TWP via an anticyclonic route, mostly from February to April. The geographic location of origin suggests anthropogenic pollution or biomass burning as a cause for ozone production. We propose large-scale descent within the tropical troposphere and radiative cooling in connection with the Hadley circulation as being responsible for the dehydration during transport. The trajectory analysis revealed no indication of a stratospheric influence. Our study thus presents a valuable contribution to the discussion about anomalous layers of dry ozone-rich air observed in ozone-poor background profiles in the TWP. [ABSTRACT FROM AUTHOR]