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Observations have revealed unique temperature profiles in hot Jupiter atmospheres. We propose that the energy transport by vertical mixing could lead to such thermal features. In our new scenario, strong absorbers, TiO, and VO are not necessary. Vertical mixing could be naturally excited by atmospheric circulation or internal gravity wave breaking. We perform radiative transfer calculations by taking into account the vertical-mixing-driven energy transport. The radiative equilibrium is replaced by the radiative-mixing equilibrium. We investigate how the mixing strength, K zz, affects the atmospheric temperature–pressure profile. Strong mixing can heat the lower atmosphere and cool the upper atmosphere. This effect has important effects on the atmosphere's thermal features that would form without mixing. In certain circumstances, it can induce temperature inversions in scenarios where the temperature monotonically increases with increasing pressure under conditions of lower thermal band opacity. Temperature inversions show up as K zz increases with altitude due to shear interaction with the convection layer. The atmospheric thermal structure of HD 209458b can be well fitted with K zz ∝ (P /1 bar)−1/2 cm2 s−1. Our findings suggest vertical mixing promotes temperature inversions and lowers K zz estimates compared to prior studies. Incorporating chemical species into vertical mixing will significantly affect the thermal profile due to their temperature sensitivity. [ABSTRACT FROM AUTHOR]

We present an atmospheric retrieval analysis of the Y0 brown dwarf WISE J035934.06−540154.6 using the low-resolution 0.96–12 μ m James Webb Space Telescope (JWST) spectrum presented in Beiler et al. We obtain volume number mixing ratios of the major gas-phase absorbers (H2O, CH4, CO, CO2, PH3, and H2S) that are three to five times more precise than previous work that used Hubble Space Telescope (HST) spectra. We also find an order-of-magnitude improvement in the precision of the retrieved thermal profile, a direct result of the broad wavelength coverage of the JWST data. We used the retrieved thermal profile and surface gravity to generate a grid of chemical forward models with varying metallicity, (C/O)atm, and strengths of vertical mixing as encapsulated by the eddy diffusion coefficient K zz. Comparison of the retrieved abundances with this grid of models suggests that the deep atmosphere of WISE 0359−54 shows signs of vigorous vertical mixing with K zz = 109 [cm2 s−1]. To test the sensitivity of these results to our five-knot spline thermal profile model, we performed a second retrieval using the Madhusudhan & Seager thermal profile model. While the results of the two retrievals generally agree well, we do find differences between the retrieved values of mass and volume number mixing ratio of H2S with fractional differences of the median values of −0.64 and −0.10, respectively. In addition, the five-knot thermal profile is consistently warmer at pressure between 1 and 70 bar. Nevertheless, our results underscore the power that the broad-wavelength infrared spectra obtainable with the JWST have to characterize the atmospheres of cool brown dwarfs. [ABSTRACT FROM AUTHOR]

Convective processes are crucial in shaping exoplanetary atmospheres but are computationally expensive to simulate directly. A novel technique of simulating moist convection on tidally locked exoplanets is to use a global 3D model with a stretched mesh. This allows us to locally refine the model resolution to 4.7 km and resolve fine-scale convective processes without relying on parameterizations. We explore the impact of mesh stretching on the climate of a slowly rotating TRAPPIST-1e-like planet, assuming it is 1:1 tidally locked. In the stretched-mesh simulation with explicit convection, the climate is 5 K colder and 25% drier than that in the simulations with parameterized convection(with both stretched and quasi-uniform meshes). This is due to the increased cloud reflectivity—because of an increase in low-level cloudiness—and exacerbated by the diminished greenhouse effect due to less water vapor. At the same time, our stretched-mesh simulations reproduce the key characteristics of the global climate of tidally locked rocky exoplanets, without any noticeable numerical artifacts. Our methodology opens an exciting and computationally feasible avenue for improving our understanding of 3D mixing in exoplanetary atmospheres. Our study also demonstrates the feasibility of a global stretched-mesh configuration for LFRic-Atmosphere, the next-generation Met Office climate and weather model. [ABSTRACT FROM AUTHOR]

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The mass loss rates of planets undergoing core-powered escape are usually modeled using an isothermal Parker-type wind at the equilibrium temperature, T _eq . However, the upper atmospheres of sub-Neptunes may not be isothermal if there are significant differences between the opacity to incident visible and outgoing infrared radiation. We model bolometrically driven escape using AIOLOS, a hydrodynamic radiative-transfer code that incorporates double-gray opacities, to investigate the process’s dependence on the visible-to-infrared opacity ratio, γ . For a value of γ ≈ 1, we find that the resulting mass loss rates are well approximated by a Parker-type wind with an isothermal temperature T = T _eq /2 ^1/4 . However, we show that over a range of physically plausible values of γ , the mass loss rates can vary by orders of magnitude, ranging from 10 ^−5 × the isothermal rate for low γ to 10 ^5 × the isothermal rate for high γ . The differences in mass loss rates are largest for small planet radii, while for large planet radii, mass loss rates become nearly independent of γ and approach the isothermal approximation. We incorporate these opacity-dependent mass loss rates into a self-consistent planetary mass and energy evolution model and show that lower/higher γ values lead to more/less hydrogen being retained after core-powered mass loss. In some cases, the choice of opacities determines whether or not a planet can retain a significant primordial hydrogen atmosphere. The dependence of escape rate on the opacity ratio may allow atmospheric escape observations to directly constrain a planet's opacities and therefore its atmospheric composition.

The James Webb Space Telescope (JWST) is now observing Y dwarfs, the coldest known brown dwarfs, with effective temperatures T eff ≲ 475 K. The first published observations provide important information: not only is the atmospheric chemistry out of equilibrium, as previously known, but the pressure–temperature profile is not in the standard adiabatic form. The rapid rotation of these Jupiter-size, isolated, brown dwarfs dominates the atmospheric dynamics, and thermal and compositional changes disrupt convection. These processes produce a colder lower atmosphere, and a warmer upper atmosphere, compared to a standard adiabatic profile. Leggett et al. presented empirical models where the pressure–temperature profile was adjusted so that synthetic spectra reproduced the 1 ≲ λ (μ m) ≲ 20 spectral energy distributions of brown dwarfs with 260 ≤ T eff (K) ≤ 540. We show that spectra generated by these models fit the first JWST Y dwarf spectrum better than standard-adiabat models. Unexpectedly, there is no 4.3 μ m PH3 feature in the JWST spectrum and atmospheres without phosphorus better reproduce the 4 μ m flux peak. Our analysis of new JWST photometry indicates that the recently discovered faint secondary of the WISE J033605.05-014350AB system has T eff ≈ 295 K, making it the first dwarf in the significant luminosity gap between the 260 K WISE J085510.83-071442.5, and all other known Y dwarfs. The adiabat-adjusted disequilibrium-chemistry models are recommended for analyses of all brown dwarfs cooler than 600 K, and a grid is publicly available. Photometric color transformations are provided in an appendix. [ABSTRACT FROM AUTHOR]

The refraction and extinction in the Earth’s atmosphere depend on the atmosphere’s structure, so it was natural to try to infer that structure from optical observations. Efforts to extract structure from observed refractions led to proof that this is possible only below the astronomical horizon. Direct studies of the real atmosphere show complicated, variable structure. The complex history of relations between structure and refraction is outlined by citing some important works.

Atmospheric ducts could disturb radar detection and radio communication in the Arctic and risk increasing human activities under Arctic warming. It is an urgent need to understand atmospheric ducts in the Arctic, with distinct atmospheric systems and environment. This study attempts to analyze the surface atmospheric ducts over Svalbard, as a critical region in the Arctic Ocean, and discuss the relation to atmospheric and oceanic conditions, based on observation and reanalysis data. The results show an occurrence of 12.6 percent, mean strength of 1.30 MU, and mean depth of 13 m for the surface duct in Svalbard winter from December 2018 to February 2020. The surface duct is characterized as two types: T-type ducts mainly constructed by temperature inversion and H-type ducts constructed by a humidity gradient. The T-type duct dominates the surface duct in Svalbard winter, with an appearance percentage of 80 percent, indicating an importance of temperature inversion in surface duct construction. The surface duct is closely related to atmospheric and oceanic conditions in Svalbard winter, because the T-type duct occurs in colder, drier, and northeasterly weather and the H-type duct occurs in warmer, wetter, and southeasterly weather with higher sea surface temperature.

Constraining L dwarf properties from their spectra is challenging. Near-infrared (NIR) spectra probe a limited range of pressures, while many species condense within their photospheres. Condensation creates two complexities: gas-phase species "rain out" (decreasing in abundances by many orders of magnitude) and clouds form. We designed tests using synthetic data to determine the best approach for retrieving L dwarf spectra, isolating the challenges in the absence of cloud opacity. We conducted atmospheric retrievals on synthetic cloud-free L dwarf spectra derived from the Sonora Bobcat models at SpeX resolution using a variety of thermal and chemical abundance profile parameterizations. For objects hotter than L5 (T eff ∼ 1700 K), the limited pressure layers probed in the NIR are mostly convective; parameterized pressure–temperature (PT) profiles bias results and free, unsmoothed profiles should be used. Only when many layers both above and below the radiative-convective boundary are probed can parameterized profiles provide accurate results. Furthermore, a nonuniform abundance profile for FeH is needed to accurately retrieve bulk properties of early-to-mid L dwarfs. Nonuniform prescriptions for other gases in NIR retrievals may also be warranted near the L/T transition (CH4) and early Y dwarfs (Na and K). We demonstrate the utility of using realistic, self-consistent models to benchmark retrievals and suggest how they can be used in the future. [ABSTRACT FROM AUTHOR]

Photoevaporation is thought to play an important role in early planetary evolution. In this study, we investigate the diffusion limit of X-ray- and ultraviolet-induced photoevaporation in primordial atmospheres. We find that compositional fractionation resulting from mass loss is more significant than currently recognized, because it is controlled by the conditions at the top of the atmosphere, where particle collisions are less frequent. Such fractionation at the top of the atmosphere develops a compositional gradient that extends downward. The mass outflow eventually reaches a steady state in which the hydrogen loss is diffusion-limited. We derive new analytic expressions for the diffusion-limited mass-loss rate and the crossover mass.

The Jovian atmosphere contains a wide diversity of vortices, which have a large range of sizes, colors, and forms in different dynamical regimes. The formation processes for these vortices are poorly understood, and aside from a few known, long-lived ovals, such as the Great Red Spot and Oval BA, vortex stability and their temporal evolution are currently largely unknown. In this study, we use JunoCam data and a citizen science project on Zooniverse to derive a catalog of vortices, some with repeated observations, from 2018 May to 2021 September, and we analyze their associated properties, such as size, location, and color. We find that different-colored vortices (binned as white, red, brown, and dark) follow vastly different distributions in terms of their sizes and where they are found on the planet. We employ a simplified stability criterion using these vortices as a proxy, to derive a minimum Rossby deformation length for the planet of ∼1800 km. We find that this value of L _d is largely constant throughout the atmosphere and does not have an appreciable meridional gradient.

The deep atmosphere of Venus remains mysterious because of the planet’s high, optically thick cloud decks. While phenomena such as the observed decadal fluctuations in sulfur dioxide abundance above the clouds could shed light on conditions below, poor understanding of vertical and horizontal transport limits such an approach. Nightside spectral windows permit observation of trace gas species in the lower atmosphere, but incomplete understanding of the circulation makes the distribution of these species challenging to interpret. We performed two simulations with the Venus Planetary Climate Model including an age of air calculation to investigate tracer transport (a) between the surface and the stagnant lower haze layer and (b) between the cloud deck and the observable upper atmosphere. We find a timescale on the order of many decades for surface-to-lower haze layer transport and ∼1.4 yr from the lowest cloud deck to 101 km. The extreme slowness of transport from the surface to the clouds makes it unlikely that compositional variability at the surface could affect the upper atmosphere sulfur dioxide abundance on observed timescales. Planetary-scale Rossby waves with a zonal wavenumber of 1 in both hemispheres are found to circumnavigate the planet in the deep atmosphere in 36 Earth days. These waves are associated with gyres that collect tracers and areas of upwelling that transport them to higher altitudes, leading to significantly younger air at polar latitudes in the altitude range of 25–45 km. The existence of chemically enhanced traveling Rossby gyres could explain the observed deep atmosphere carbon monoxide variability.

We present vertical profiles of temperature and density from solar occultation (SO) observations by the "Nadir and Occultation for Mars Discovery" (NOMAD) spectrometer on board the Trace Gas Orbiter during its first operational year, which covered the second half of Mars Year 34. We used calibrated transmittance spectra in 380 scans, and apply an in‐house pre‐processing to clean data systematics. Temperature and CO2 profiles up to about 90 km, with consistent hydrostatic adjustment, are obtained, after adapting an Earth‐tested retrieval scheme to Mars conditions. Both pre‐processing and retrieval are discussed to illustrate their performance and robustness. Our results reveal the large impact of the MY34 Global Dust Storm (GDS), which warmed the atmosphere at all altitudes. The large GDS aerosols opacity limited the sounding of tropospheric layers. The retrieved temperatures agree well with global climate models (GCM) at tropospheric altitudes, but NOMAD mesospheric temperatures are wavier and globally colder by 10 K in the perihelion season, particularly during the GDS and its decay phase. We observe a warm layer around 80 km during the Southern Spring, especially in the Northern Hemisphere morning terminator, associated to large thermal tides, significantly stronger than in the GCM. Cold mesospheric pockets, close to CO2 condensation temperatures, are more frequently observed than in the GCM. NOMAD CO2 densities show oscillations upon a seasonal trend that track well the latitudinal variations expected. Results uncertainties and suggestions to improve future data re‐analysis are briefly discussed. Plain Language Summary: The detailed variation of temperature and density with altitude is of paramount importance to characterize the atmospheric state and to constrain the chemistry and dynamics as a whole. The Nadir and Occultation for Mars Discovery (NOMAD) instrument on board the Trace Gas Orbiter (TGO) has among its key targets the characterization of the thermal state with unprecedented vertical resolution. This is the target of this work, where we analyzed transmittance spectra obtained from the NOMAD solar occultation channel, with a state‐of‐the‐art retrieval scheme, adapted from Earth to Mars conditions and geometry. We applied it to the first year of TGO observations, which covered the last two Mars seasons of Mars Year 34. The results permit to study the temperature structure up to 90 km and its seasonal and latitudinal variations, revealing the impact of the MY34 Global Dust Storm, a warm layer at mesospheric altitudes not present in climate models, more frequent cold pockets than in current global climate models, and generally, colder temperature at those altitudes, all of which can be of importance for the validation of these climate models. Key Points: Temperature and density profiles up to 90 km are retrieved from Nadir and Occultation for Mars Discovery (NOMAD) first year of solar occultations, covering two seasons of Mars Year 34NOMAD temperatures agree well with climate model predictions below 50 km but are wavier and globally colder by about 10 K at high altitudesWe report large thermal tides producing warm layers at 80 km in the morning terminator. Also strong warming by the 2018 global dust storm [ABSTRACT FROM AUTHOR]

The methane concentration around urban and suburban areas was studied in terms of (1) CH4 flux/emission, (2) the vertical profile of the air temperature, and (3) land use. Methane flux/emission from automobiles was not negligible in the central area of the industrialized city, although it is not a major contributor globally; furthermore, the contribution from landfill also played an important role related to wind direction. In contrast, in the suburbs, the CH4 flux/emission was a mixture of CH4 from automobiles and paddy fields. The atmosphere in the central area of the city was stabilized at a height of ca. 200 m even in the daytime and even in the summer; this elevated temperature inversion layer prevented air pollutants and air itself from vertical mixing/diffusion/transportation; meanwhile, the atmosphere in the suburbs formed the grounded temperature inversion layer at night in the summer. Interestingly and notably, it was not formed in winter all day, likely because of the strong wind velocity due to the monsoon. Land use also influenced the determination of the CH4 concentration; especially in the suburbs, if paddy fields remained undeveloped, the CH4 concentration discernibly increased from midnight to early morning in the summer, in combined with atmospheric stabilization. [ABSTRACT FROM AUTHOR]

Y dwarfs are the coolest spectral class of brown dwarf. They have effective temperatures less than 500 K, with the coolest detection as low as ∼250 K. They make up the low-mass tail of the star formation process, and are a valuable analog to the atmospheres of giant gaseous exoplanets in a temperature range that is difficult to observe. Understanding Y dwarf atmospheric compositions and processes will thus deepen our understanding of planet and star formation and provide a stepping stone toward characterizing cool exoplanets. Their spectra are shaped predominantly by gaseous water, methane, and ammonia. At the warmer end of the Y-dwarf temperature range, spectral signatures of disequilibrium carbon monoxide have been observed. Cooler Y dwarfs could host water clouds in their atmospheres. JWST spectral observations are anticipated to provide an unprecedented level of detail for these objects, and yet published self-consistent model grids do not accurately replicate even the existing Hubble Space Telescope and ground-based observations. In this work, we present a new suite of 1D radiative-convective equilibrium models to aid in the characterization of Y-dwarf atmospheres and spectra. We compute clear, cloudy, equilibrium chemistry and disequilibrium chemistry models, providing a comprehensive suite of models in support of the impending JWST era of panchromatic Y-dwarf characterization. Comparing these models against current observations, we find that disequilibrium CH _4 –CO and NH _3 –N _2 chemistry and the presence of water clouds can bring models and observations into better, though still not complete, agreement.

A planet’s Ly α emission is sensitive to its thermospheric structure. Here we report joint Hubble Space Telescope and Cassini cross-calibration observations of the Saturn Ly α emission made 2 weeks before the Cassini grand finale. To investigate the long-term Saturn Ly α airglow observed by different ultraviolet instruments, we cross-correlate their calibration, finding that while the official Cassini/UVIS sensitivity should be lowered by ∼75%, the Voyager 1/UVS sensitivities should be enhanced by ∼20% at the Ly α channels. This comparison also allowed us to discover a permanent feature of the Saturn disk Ly α brightness that appears at all longitudes as a brightness excess (Ly α bulge) of ∼30% (∼12 σ ) extending over the latitude range ∼5°–35° N compared to the regions at equator and ∼60° N. This feature is confirmed by three distinct instruments between 1980 and 2017 in the Saturn north hemisphere. To analyze the Ly α observations, we use a radiation transfer model of resonant scattering of solar and interplanetary Ly α photons and a latitude-dependent photochemistry model of the upper atmosphere constrained by occultation and remote-sensing observations. For each latitude, we show that the Ly α observations are sensitive to the temperature profile in the upper stratosphere and lower thermosphere, thus providing useful information in a region of the atmosphere that is difficult to probe by other means. In the Saturn Ly α bulge region, at latitudes between ∼5° and ∼35°, the observed brightening and line broadening support seasonal effects, variation of the temperature vertical profile, and potential superthermal atoms that require confirmation.

We use a two-dimensional (2D) radiative transfer model of Titan, which allows the atmospheric structure to vary in both altitude and latitude, to retrieve the spatial distribution of temperature, haze extinction, and C _2 H _2 , C _2 H _6 , C _3 H _8 , CH _3 C _2 H, C _4 H _2 , and HCN gases, from Cassini Composite Infrared Spectrometer (CIRS) limb-mapping observations over the duration of the Cassini mission. We compare our results with previous analyses of CIRS limb observations using radiative models that only allow the atmosphere to vary in altitude. The temperature, haze, and gas composition retrieved with the 2D model mostly show the same broad spatial and temporal trends as previously published results from 1D models. However, there are some significant differences in the retrieved structure at the fall and winter poles poleward of 60°. Most noticeably, the HCN abundance in the depleted region near 65°N at 350 km in northern winter is stronger in the 2D retrievals than in previous 1D retrievals, and the 2D retrievals show very different structure from earlier 1D retrievals in the north polar C _2 H _2 structure during early northern spring, with a strong depletion around 70°N at 0.02 mbar.

Studies on the atmospheric structure over the Antarctic Plateau are important for better understanding the weather and climate systems of polar regions. In the summer of 2017, an observational experiment was conducted at Dome-A, the highest station in Antarctica, with a total of 32 profiles obtained from global positioning system (GPS) radiosondes. Based on observational data, the atmospheric temperature, humidity, and wind structures and their variations are investigated, and compared with those from four other stations inside the Antarctic circle. Distinguished thermal and dynamic structures were revealed over Dome-A, characterized by the lowest temperature, the highest tropopause, the largest lapse rate, and the most frequent temperature and humidity inversion. During the experiment, a prominent blocking event was identified, with great influence on the atmospheric structure over Dome-A. The blocking high produced a strong anticyclone that brought warm and moist air to the hinterland of the Antarctic Plateau, causing a much warmer, wetter, and windier troposphere over the Dome-A station. Meanwhile, a polar air mass was forced out of the Antarctic, formed a cold surge extending as far as southern New Zealand and affected the weather there. Our results proved that there would be a direct interaction between the atmosphere over the hinterland of the Antarctic Plateau and mid latitudes with the action of a blocking high. Further studies are needed to explore the interaction between the atmospheric systems over the Antarctic and mid latitudes under intense synoptic disturbance, with long-term data and numerical modeling. [ABSTRACT FROM AUTHOR]

This study examines atmospheric structures causing convective development in the events of cloud cluster (CC) over the Korean peninsula using the analysis and forecast data of National Centers for Environmental Prediction (NCEP) climate forecast system reanalysis (CFSR) and observation data. Two CC types—CCs associated with meso-α-scale lows (CCMLs) and mesoscale troughs (CCMTs)—were investigated. The common atmospheric structure for convective development in CC events is comprised of i) a strong southwesterly band (SWB; a region with southwesterly wind speeds >12.5 m s−1) in the lower troposphere upstream of CCs with a mesoscale convergence zone in its exit area, ii) a layer of high-θe air in the lower troposphere near the surface extending from the southwest to SWB exit, iii) elevated height of maximum θe in the lower troposphere near and over the convergence zone, above which a convectively unstable layer exists. Generality of the above-described structure has been demonstrated via examination of composite fields. SWB plays a major role in producing the structure for convective development in CC events over the Korean peninsula mainly through i) advection of high-θe air from the southwest, and ii) significant horizontal convergence in the exit area, which can facilitate convection initiation. The two types of CC show notable differences in atmospheric structure across the boundary between high-θe air from the southwest and low-θe air in the northeast and in the mode of high-θe air transport to the region of convective development. The boundary is generally tilted northeastward with height for CCML cases, whereas it is nearly vertical for the majority of CCMT cases. This study indicates that, despite the above-mentioned differences, convective developments in both CC types can be considered as elevated convection that occurs as air parcels in an elevated layer of convective instability are lifted by upward motion in the convergence zone. For both types of CC, differential θe advection plays the key role for the occurrence of elevated layer of convective instability. And θe front in CCML events indicates the presence of elevated convective instability above it and the possibility of elevated convection provided that a lifting mechanism is available. [ABSTRACT FROM AUTHOR]

Two sets of sea surface temperature/sea ice changes are used to test the sensitivity of tracer transport to the pattern of warming in the doubled CO2 climate. One set (2CO2WT) has greater tropical and high latitude sea surface temperature changes than the other (2CO2), although both fall within the range of plausible response. Simulations were done both with and without interactive ozone. Results show that the SST pattern affects the circulation change throughout the troposphere and middle atmosphere; the ozone interaction affects primarily the upper stratosphere, but through wave-mean flow interaction has effects that extend down into the upper troposphere. Both experiments feature increased tropospheric/stratospheric exchange at low latitudes and greater vertical mixing within the troposphere; only the WT experiments result in increased interhemispheric transport and a more direct circulation in the high latitude stratosphere. Ozone increases in the upper stratosphere and decreases in the lower stratosphere in all the simulations, with greater transport of high latitude ozone into the troposphere in the WT runs. At sea level there is a more positive phase of the Arctic Oscillation (AO)-type oscillation, and this is also true at 100 mbar, but there is no significance in the middle troposphere and the sign is different in the middle stratosphere. Many of these results differ from those generated in older versions of the GISS GCMAM despite the same SST forcing due to differences in control run characteristics, which has implications for model intercomparison experiments.

Precipitation plays a crucial role in the Earth's energy balance, the water cycle, and the global atmospheric circulation. Aerosols, by direct interaction with radiation and by serving as cloud condensation nuclei, may affect clouds and rain formation. This effect can be examined in terms of energetic constraints, that is, any aerosol‐driven diabatic heating/cooling of the atmosphere will have to be balanced by changes in precipitation, radiative fluxes, or divergence of dry static energy. Using an aqua‐planet general circulation model (GCM), we show that tropical and extratropical precipitation have contrasting responses to aerosol perturbations. This behavior can be explained by contrasting ability of the atmosphere to diverge excess dry static energy in the two different regions. It is shown that atmospheric heating in the tropics leads to large‐scale thermally driven circulation and a large increase in precipitation, while the excess energy from heating in the extratropics is constrained due to the effect of the Coriolis force, causing the precipitation to decrease. Plain Language Summary: Precipitation, as the Earth's only natural source of fresh water, is of great importance for society. Climate change, besides changing the mean surface temperature and its distribution, is expected to change the precipitation's temporal and spatial distribution and, to a lesser extent, the global mean precipitation. One important agent in precipitation changes is anthropogenic aerosols. In this paper we study the response of precipitation to aerosol perturbations at different latitudes. Previously, it was proposed that aerosols drive a slowdown of the hydrological cycle. In addition, it was shown that, due to energy budget conservation, absorbing aerosols leads to a reduction in the global mean precipitation. Here we show that the response in the tropics is the opposite of the global mean response and of the extratropical response. Specifically, we show that the same aerosol perturbation generally increases precipitation in the tropics and decreases precipitation in the extratropics. This behavior can be explained by the contrasting ability of the atmosphere to diverge excess dry static energy in the tropics and extratropics. We also show that local aerosol perturbations could affect precipitation in remote regions due to a formation of large‐scale circulation. Key Points: Aerosol effect on precipitation is examined in terms of energetic constraintsAerosol perturbation generally increases precipitation in the tropics and decreases precipitation in the extratropicsThis behavior can be explained by contrasting ability of the atmosphere to diverge excess dry static energy in the two different regions [ABSTRACT FROM AUTHOR]

There is growing evidence that the atmospheric dynamics of the Euro‐Atlantic sector during winter is driven in part by the presence of quasi‐persistent regimes. However, general circulation models typically struggle to simulate these with, for example, an overly weakly persistent blocking regime. Previous studies have showed that increased horizontal resolution can improve the regime structure of a model but have so far only considered a single model with only one ensemble member at each resolution, leaving open the possibility that this may be either coincidental or model dependent. We show that the improvement in regime structure due to increased resolution is robust across multiple models with multiple ensemble members. However, while the high‐resolution models have notably more tightly clustered data, other aspects of the regimes may not necessarily improve and are also subject to a large amount of sampling variability that typically requires at least three ensemble members to surmount. Key Points: Climate models have difficulty representing Euro‐Atlantic regime structure correctlyIncreasing horizontal resolution improves the significance of regime clustering across multiple modelsSpatial patterns and persistence levels of regimes do not necessarily improve with increased resolution [ABSTRACT FROM AUTHOR]

This study analyzes the differences between an objective, automated identification of tropical cyclones (TCs) that undergo extratropical transition (ET), and the designation of ET determined subjectively by human forecasters in best track data in all basins globally. The objective identification of ET is based on the cyclone phase space (CPS), calculated from the Japanese 55-yr Reanalysis (JRA-55) or the ECMWF interim reanalysis (ERA-Interim). The resulting classification into ET storms and non-ET storms underlies the global climatology of ET presented in Part I of this study. Here, the authors investigate how well the CPS classifications agree with those in the best track records calculated from JRA-55 or from ERA-Interim data. According to F1 scores and Matthews correlation coefficients (MCCs), the classification of ET storms in the CPS agrees best with the best track classification in the western North Pacific (MCC > 0.7) and the North Atlantic (MCC > 0.5). In other basins, the correlation between the CPS classification and the best track classification is only slightly higher than that of a random classification. The JRA-55 classification achieves higher performance scores than does the ERA-Interim classification, and the differences are statistically significant in all basins. The lower performance of ERA-Interim is mainly due to a higher false alarm rate, particularly in the eastern North Pacific. Overall, the results show that while the CPS-based classifications are good enough to be useful for many purposes, there is almost certainly room for improvement—in the representation of the storms in reanalyses, in our objective metrics of ET, and in our scientific understanding of the ET process. [ABSTRACT FROM AUTHOR]

Abstract In order to improve the accuracy of fog forecast at Xianyang Airport, microwave radiometer, wind profiling radar and other equipment are utilized to detect fog. With the long term detection data from the equipment mentioned above, this paper analyzes the altitudinal-temporal variation characteristics of wind, temperature, and relative humidity during fog weather. It also tallies up the variation characteristics of the three meteorological factors at different heights as visibility and time changes. The findings are listed as follows. During autumn and winter, fog usually appears between 22:00 BT and 13:00 BT next day at Xianyang Airport, with relatively stable atmospheric structure. During fog, when the height is below 300 m, the average relative humidity is >75%, and the average horizontal wind speed is <3 m/s, along with a weak downdraft. In September and October, there is mainly southwest wind at low levels during fog weather, the height of radiation inversion layer within 300 m. In November, December and January, it is mainly northeast wind at low levels during fog, with rather thick radiation inversion layer. When the visibility is 1500 m in mist, if the temperature drops by 3 °C and the relative humidity rises by 9% in September and October, the visibility decreases to <1000 m accordingly; if the temperature drops by 6 °C in November (or it drops 8 °C in December and January), the inversion layer thickens, the relative humidity increases by 15%, then the visibility reduces to <1000 m. These findings can provide scientific basis to improve the accuracy of fog forecast at Xianyang Airport. Highlights • Microwave radiometer, wind profiling radar and other equipment are utilized to detect fog of Xianyang airport. • By analyzing the characteristics of wind, temperature, and relative humidity, the conceptual models for fog of Xianyang airport are established. • Based on the relationship between wind, temperature, relative humidity and fog formation, the possibility models of fog formation are established. [ABSTRACT FROM AUTHOR]

Impacts of horizontal winds assimilation on thermal tides are investigated by using the Venus atmospheric general circulation model for the Earth Simulator local ensemble transform Kalman filter data assimilation system. The assimilated data are horizontal winds derived from Venus ultraviolet images taken by the Venus Monitoring Camera onboard the Venus Express orbiter. The results show that three‐dimensional structures of the thermal tides are significantly improved not only in the horizontal winds but also in the temperature field, even though the observations are available only at the cloud top level on the southern dayside hemisphere approximately once an Earth day. The reproduced temperature fields agree well with recent radio occultation measurements of the Venus Climate Orbiter Akatsuki. The zonal mean fields of the zonal wind and temperature are also improved globally. This study would enable reanalysis of past Venus observations. Key Points: Three‐dimensional structures of the thermal tides are significantly improved by the data assimilation of horizontal winds derived from Venus UV imagesReproduced temperature fields agree well with those obtained by radio occultation measurements of AkatsukiZonally averaged atmospheric structures are improved globally even though the observations are very limited in space and time [ABSTRACT FROM AUTHOR]

The structure of the upper atmosphere of Mars provides insights into the physical mechanisms that drive escape of species into outer space. Deviations in plasma density profiles with altitude from the theoretical exponentially decaying formulation have been routinely observed for decades yet remain largely unexplained. Proposed mechanisms driving this variability have focused primarily on plasma‐specific processes, as limited by past plasma‐only observations. The Mars Atmosphere and Volatile Evolution mission's Neutral Gas and Ion Mass Spectrometer data set has recently provided unprecedented planetographic coverage for both ions and neutrals in the Martian upper atmosphere. Ion, electron, and neutral density profiles with altitude, collected on the sun‐lit inbound portion of the spacecraft orbit have been analyzed. It was found that neutral species, measured between ~160 and 200 km, behave consistently with the bulk atmosphere and that variations in ion density profiles follow neutral profile variations at the same altitudes in 70% of the observations. In the remaining 30%, additional structure was apparent in the ionized species' profiles that were found to preferentially lie in regions of strong crustal field or to be measured near dawn. A 1‐D ionospheric model was used to show that many observed features in plasma profiles are directly driven by neutral atmospheric features, providing strong evidence for ion‐neutral coupling in the atmosphere of Mars. Key Points: Dayside inbound NGIMS data analyses show strong correlation between ion and neutral density profile structureOne‐dimensional ionospheric model was used to demonstrate and interpret the observed ion‐neutral couplingPlasma‐specific structure shows dependence on crustal field morphology and local time [ABSTRACT FROM AUTHOR]

This paper presents a new algorithm for the joint retrieval of surface reflectance and aerosol properties with continuous variations of the state variables in the solution space. This algorithm, named CISAR (Combined Inversion of Surface and AeRosol), relies on a simple atmospheric vertical structure composed of two layers and an underlying surface. Surface anisotropic reflectance effects are taken into account and radiatively coupled with atmospheric scattering. For this purpose, a fast radiative transfer model has been explicitly developed, which includes acceleration techniques to solve the radiative transfer equation and to calculate the Jacobians. The inversion is performed within an optimal estimation framework including prior information on the state variable magnitude and regularisation constraints on their spectral and temporal variability. In each processed wavelength, the algorithm retrieves the parameters of the surface reflectance model, the aerosol total column optical thickness and single-scattering properties. The CISAR algorithm functioning is illustrated with a series of simple experiments. [ABSTRACT FROM AUTHOR]

Context. GR 290 (M 33/V532 = Romano's Star) is a suspected post-luminous blue variable star located in M 33 galaxy that shows a rare Wolf–Rayet (WR) spectrum during its minimum light phase. In spite of many studies, its atmospheric structure, its circumstellar environment, and its place in the general context of massive stars' evolution is poorly known. Aims. We present a detailed study of this star's wind and mass loss, and a study of the circumstellar environment associated to the star. Methods. Long-slit spectra of GR 290 were obtained during its present minimum luminosity phase with the Gran Telescopio Canarias covering the ∼3600–7500 Å wavelength range together with contemporaneous photometry using B, V, R and I filters. The data were compared with non-local thermodynamical equilibrium (non-LTE) model atmosphere synthetic spectra computed with CMFGEN code and with models for ionized interstellar medium regions computed with CLOUDY code. Results. The current mV = 18.8 mag is the faintest at which this source has ever been observed. The non-LTE models indicate effective temperatures of Teff = 27 000–30 000 K at radius R2/3 = 27−21 R⊙ and mass-loss rate Ṁ = 1.5 × 10−5M⊙yr−1. The terminal wind speed v∞ = 620 km s−1 is faster than ever before recorded, while the current luminosity L* = (3.1–3.7) × 105L⊙ is the lowest ever deduced. The star is overabundant in He and N and underabundant in C and O. It is surrounded by an unresolved compact H II region with dimensions ≤4 pc, from where H-Balmer, He I lines, and [O III] and [N II] are detected. In addition, we find emission from a more extended interstellar medium (ISM) region, which appears to be asymmetric, with a larger extent to the east (16–40 pc) than to the west. Conclusions. In the present long lasting visual minimum, GR 290 is in a lower bolometric luminosity state with higher mass-loss rate. The nearby nebular emission seems to suggest that the star has undergone significant mass loss over the past 104–105 yr and is nearing the end stages of its evolution. [ABSTRACT FROM AUTHOR]

Aims. To understand and compare the 3D atmospheric structure of HD 209458 b and HD 189733 b, focusing on the formation and distribution of cloud particles, as well as their feedback on the dynamics and thermal profile. Methods. We coupled the 3D Met Office Unified Model (UM), including detailed treatments of atmospheric radiative transfer and dynamics, to a kinetic cloud formation scheme. The resulting model self-consistently solves for the formation of condensation seeds, surface growth and evaporation, gravitational settling and advection, cloud radiative feedback via absorption, and crucially, scattering. We used fluxes directly obtained from the UM to produce synthetic spectral energy distributions and phase curves. Results. Our simulations show extensive cloud formation in both HD 209458 b and HD 189733 b. However, cooler temperatures in the latter result in higher cloud particle number densities. Large particles, reaching 1 μm in diameter, can form due to high particle growth velocities, and sub-μm particles are suspended by vertical flows leading to extensive upper-atmosphere cloud cover. A combination of meridional advection and efficient cloud formation in cooler high latitude regions, results in enhanced cloud coverage for latitudes above 30° and leads to a zonally banded structure for all our simulations. The cloud bands extend around the entire planet, for HD 209458 b and HD 189733 b, as the temperatures, even on the day side, remain below the condensation temperature of silicates and oxides. Therefore, the simulated optical phase curve for HD 209458 b shows no “offset”, in contrast to observations. Efficient scattering of stellar irradiation by cloud particles results in a local maximum cooling of up to 250K in the upper atmosphere, and an advection-driven fluctuating cloud opacity causes temporal variability in the thermal emission. The inclusion of this fundamental cloud-atmosphere radiative feedback leads to significant differences with approaches neglecting these physical elements, which have been employed to interpret observations and determine thermal profiles for these planets. This suggests that readers should be cautious of interpretations neglecting such cloud feedback and scattering, and that the subject merits further study. [ABSTRACT FROM AUTHOR]

Guizhou Province, China, experienced several severe drought events over the period from 1960 to 2013, causing great economic loss and intractable conflicts over water. In this study, the spatial and temporal characteristics of droughts are analyzed with the standard precipitation index (SPI), comprehensive meteorological drought index (CI), and reconnaissance drought index (RDI). Meanwhile, historical drought records are used to test the performance of each index at identifying droughts. All three indices show decreasing annual and autumn trends, with the latter particularly prominent. 29, 30, and 32 drought events were identified during 1960–2013 by the SPI, CI, and RDI, respectively. Continuous drought is more frequent in winter–spring and summer–autumn. There is a significant increasing trend in drought event frequency, peak, and strength since the start of the 21st century. Drought duration indicated by CI shows longer durations in the higher-elevation region of central and western Guizhou. The corresponding drought severity is high in these regions. SPI and RDI indicate longer drought durations in the lower elevation central and eastern regions of Guizhou Province, where the corresponding drought severity is also very strong. SPI shows an increasing trend in drought duration and drought severity across most of the regions of Guizhou. In general, SPI and RDI show an increasing trend in the western Guizhou Province and a decreasing trend in central and eastern Guizhou. Comparing these three drought indices with historical records, the RDI is found to be more objective and reliable than the SPI and CI when identifying the periods of drought in Guizhou. [ABSTRACT FROM AUTHOR]

We combine measurements from stellar occultations observed by the Cassini Ultraviolet Imaging Spectrograph (UVIS) and limb scans observed by the Composite Infrared Spectrometer (CIRS) to create empirical atmospheric structure models for Saturn corresponding to the locations probed by the occultations. The results cover multiple locations at low to mid-latitudes between the spring of 2005 and the fall of 2015. We connect the temperature-pressure (T-P) profiles retrieved from the CIRS limb scans in the stratosphere to the T-P profiles in the thermosphere retrieved from the UVIS occultations. We calculate the altitudes corresponding to the pressure levels in each case based on our best fit composition model that includes H 2 , He, CH 4 and upper limits on H. We match the altitude structure to the density profile in the thermosphere that is retrieved from the occultations. Our models depend on the abundance of helium and we derive a volume mixing ratio of 11  ±  2% for helium in the lower atmosphere based on a statistical analysis of the values derived for 32 different occultation locations. We also derive the mean temperature and methane profiles in the upper atmosphere and constrain their variability. Our results are consistent with enhanced heating at the polar auroral region and a dynamically active upper atmosphere. [ABSTRACT FROM AUTHOR]

The longest-lived in-situ measurement platforms at Venus have been the Soviet VEGA balloons in 1985 and the only high-quality pressure/temperature profile in the lowest 10 km of the atmosphere is that from the VEGA-2 lander. Here we review the mission and the resultant literature and report the archival of numerical data from these investigations on the NASA Planetary Data System Atmospheres Node to facilitate their access to the community. We additionally report some new results, including the striking absence of a signature of the planetary boundary layer in the near-surface potential temperature profile from the VEGA-2 lander, in contrast to the well-defined boundaries seen in a comparable profile at Titan. [ABSTRACT FROM AUTHOR]

Receiver aperture averaging technique is employed in underwater wireless optical communication (UWOC) systems to mitigate the effects of oceanic turbulence, thus to improve the system performance. The irradiance flux variance is a measure of the intensity fluctuations on a lens of the receiver aperture. Using the modified Rytov theory which uses the small-scale and large-scale spatial filters, and our previously presented expression that shows the atmospheric structure constant in terms of oceanic turbulence parameters, we evaluate the irradiance flux variance and the aperture averaging factor of a spherical wave in strong oceanic turbulence. Irradiance flux variance variations are examined versus the oceanic turbulence parameters and the receiver aperture diameter are examined in strong oceanic turbulence. Also, the effect of the receiver aperture diameter on the aperture averaging factor is presented in strong oceanic turbulence. [ABSTRACT FROM AUTHOR]

The successive stages of nocturnal atmospheric structure inside a small isolated basin are investigated when a katabatically driven flow on an adjacent tilted plain advects cold air over the basin rim. Data came from Arizona's Meteor Crater during intensive observing period 4 of the Second Meteor Crater Experiment (METCRAX II) when a mesoscale flow above the plain was superimposed on the katabatic flow leading to a flow acceleration and then deceleration over the course of the night. Following an overflow-initiation phase, the basin atmosphere over the upwind inner sidewall progressed through three stages as the katabatic flow accelerated: 1) a cold-air-intrusion phase in which the overflowing cold air accelerated down the upwind inner sidewall, 2) a bifurcation phase in which the katabatic stable layer lifted over the rim included both a nonnegatively buoyant upper layer that flowed horizontally over the basin and a negatively buoyant lower layer (the cold-air intrusion) that continued on the slope below to create a hydraulic jump at the foot of the sidewall, and 3) a final warm-air-intrusion phase in which shear instability in the upper overflowing layer produced a lee wave that brought warm air from the elevated residual layer downward into the basin. Strong winds during the third phase penetrated to the basin floor, stirring the preexisting, intensely stable, cold pool. Later in the night a wind direction change aloft decelerated the katabatic wind and the atmosphere progressed back through the bifurcation and cold-air-intrusion phases. A conceptual diagram illustrates the first four evolutionary phases. [ABSTRACT FROM AUTHOR]

As an additional product of the Japanese 55-year Reanalysis (JRA-55) project, a new global atmospheric reanalysis product, named JRA-55CHS, is under construction. It utilizes quarterdegree sea-surface temperature (SST) as lower-boundary condition with the same data assimilation system as the JRA-55 Conventional (JRA-55C), into which no satellite data is assimilated. The SST data can resolve steep SST gradients along the western boundary currents (WBCs), which are not necessarily well represented in many of the other atmospheric reanalysis products, including the JRA-55C. The present paper briefly documents basic performance of the JRA-55CHS, through comparing it with the JRA-55C and satellite observations in focusing on the major WBC regions. In the JRA-55CHS, mesoscale atmospheric structures along the WBCs are well reproduced in their climatological-mean fields as captured in the satellite observations. Their interannualto decadal-scale variations associated with SST variations are also reasonably reproduced. The corresponding atmospheric features are less obvious in the JRA-55C owing to smoother SST prescribed. Furthermore, comparison between the two reanalysis products reveals that the influence of frontal-scale SST distributions can reach into the middle and upper troposphere, especially in summer. The JRA-55CHS will be useful for deepening our understanding of the nature of midlatitude frontal-scale air-sea interactions. [ABSTRACT FROM AUTHOR]