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In the upper atmosphere (ionosphere), plasma with two electron populations is very common. The cold electrons ( T e ∼ 1 eV) usually originate in the ionosphere, while the hot electrons ( T e ∼ 100 eV) come from the magnetosphere. In addition to these two electron populations, there may be a beam of electrons streaming along the magnetic field lines. These electrons are responsible for exciting various electrostatic wave modes. In this article, we provide a systematic insight in the evolution of the system, based on the beam energy. With an increase in beam velocity, the beam temporarily recovers a portion of its initial energy as well as a higher saturation energy. The wave energy is lost significantly before saturation and after linear growth at a relatively modest beam velocity. In addition, the low beam velocity generates BGK electron holes in the phase space, which are missing at higher beam velocities. We also present the analysis of the condition of sustained electron holes in the phasespace. [ABSTRACT FROM AUTHOR]

High-resolution thermospheric mass density low Earth orbit (LEO)-based measurements are valuable for accurately estimating short-term atmospheric abrupt disturbances triggered by solar flux forcing. To investigate the enhancing status of solar cycle 25 between August 29 and December 31, 2020, we processed Gravity Recovery and Climate Experiment Follow-on (GRACE-FO) 10-s accelerometer-derived thermospheric mass density (TMD) measurements normalized at 500 km altitude by the NRLMSIS-2.0 empirical model. These 4-month enhancing disturbance observations suggest a shift from relative quiescence to a much more active solar phase, revealing unexpected dependencies on temporal and spatial characteristics. The results indicated that the dominant driver is solar extreme ultraviolet radiation (EUV) during this ascending phase. Density enhancement was symmetric in both hemispheres around the autumn equinox. After the equinox, the neutral density enhancement intensity in the Southern Hemisphere surpasses that in the Northern Hemisphere. Density maxima occurred from high to low latitudes, accompanied by a 2–3 h time lag. The Wygant function was applied to model the response to solar wind geomagnetic field changes and quantify the impact of geomagnetic activities on upper atmosphere density, verifying the time lag of density disturbances. All these findings could potentially improve our understanding of the solar cycle and LEO orbital drag. [ABSTRACT FROM AUTHOR]

Atomic oxygen (AO) is the most abundant species in the terrestrial thermosphere at altitudes of 180 to 700 km and plays a crucial role in numerous upper atmospheric processes. The drag encountered by a spacecraft is directly influenced by the background atmospheric density, making AO a notable contributor in this regard. The objective of this study is to analyze the variability of the density of AO in the near-Earth space environment under different solar activity conditions, as well as during severe space weather events. The analysis is primarily focused on the altitude range of 300 to 500 km in the Earth's thermosphere across the globe, which is a crucial operating region for a large number of Low Earth Orbiting satellites. AO exerts significant drag on the Low Earth Orbit (LEO) satellites and reacts with the materials of the satellite body and in situ probes mounted therein, causing considerable degradation to both. Additionally, AO interferes with measurements made by optical instruments through phenomena such as 'shuttle glow'. Analysis based on NRLMSIS 2.0 model revealed that the concentration of AO displays significant seasonal variations primarily due to the asymmetry in solar insolation. The highest concentration of AO was observed during the spring equinoctial month of the solar maximum year, while the lowest concentration was noted during the winter solstitial month of the solar minimum year. The enhancement seen in AO density contours show an asymmetry in the zonal direction at approximately 50 ∘ N in June and 50 ∘ S in December. Similarly, during geomagnetically disturbed days, the AO density shows enhancements along various longitudes, as indicated by the elongated contours. During geomagnetic storms, the heightened Joule heating in the polar region modifies the meridional circulation, which in turn affects the global distribution of AO density. Similarly, an analysis of thermospheric neutral winds obtained from the HWM93 model reveals that the zonal winds exhibit a strong westward acceleration over the region where AO density is enhanced. Furthermore, such an increase in AO density during geomagnetic storms has been found to cause orbital degradation ranging from a few tens of meters to a few hundred meters, depending on the strength and geo-effectiveness of the storms. This study emphasizes the critical contribution of AO density to satellite drag force, necessitating in situ measurements for an accurate estimation of the altitude decay of the spacecraft. [ABSTRACT FROM AUTHOR]

• Filtering OH rotational temperature estimates perturbations having periods of 0.7–8.2 h. • Statistical approaches allow subtracting uncorrelated random noise. • Seasonal and interannual variations of residuals reflect climatology of correlated wave processes. Ground-based observations of the natural hydroxyl (OH) nightglow at altitudes of 85–90 km are used for deriving the rotational temperature of excited OH, which is close to the neutral atmospheric temperature. For filtering of mesoscale perturbations, we use differences between pairs of measured values of OH rotational temperature separated with fixed time intervals in the range of 0.5–2 h. The filtering is applied for studying mesoscale variations of temperature near the mesopause according to the data of spectral OH nightglow measurements at observatories of Zvenigorod (56°N, 37°E.) in the years 2004–2016, Tory (52°N, 103°E) in 2012–2017 and Maymaga (63°N, 130°E) in 2000–2015. Monthly-mean values and variances of temperature disturbances with periods 0.7–8.2 h are determined. Semiempirical and statistical approaches are used to estimate and subtract variances of the instrumental dark current noise and uncorrelated in time fluctuations. Seasonal and interannual variations in standard deviations of correlated in time mesoscale perturbations of the OH rotational temperature at the considered observational sites are studied. They can give information about multiyear changes in the activity of atmospheric acoustic-gravity waves propagating through the OH layer near the mesopause. [ABSTRACT FROM AUTHOR]

• Ionospheric F2 Layer on QTP is studied by multi-station collaborative method. • The altitude of the F2 layer on QTP has significant regional variations. • The causes of abnormal variations of the F2 layer on QTP are analyzed. The Qinghai-Tibet Plateau (QTP) region is the largest plateau in China and the highest altitude in the world, with a unique geographical environment. Based on the observation data of the 24th solar cycle from six sites on the QTP and its surrounding areas, the multi-station joint detection method is adopted to analyze the temporal variation and spatial distribution characteristics of the critical frequency of the F2 layer(f o F 2) and the bottom height of the F2 layer (h'F 2). The results indicate that the critical frequency of the ionospheric F layer in the QTP is controlled by solar illumination conditions, and conforms to the ionospheric variation law of middle and low latitudes. The height of the F layer has significant regional characteristics, and the F layer height variation in Kunming and Chongqing is particularly drastic, and the average height of the F layer in Chongqing is significantly higher than that in Kunming, which is at a lower latitude, and Lhasa, which is at the same latitude as Chongqing. This phenomenon may be attributed to the unique geographical environment of the QTP, which has an influential effect on the motion of the lower atmosphere, and through the coupling mechanism between the lower and upper atmosphere, has a substantial impact on the F2 layer. The research findings of this article are of great interest to the study of the coupling mechanism between the upper and lower atmosphere. [ABSTRACT FROM AUTHOR]

• We propose spaceborne snapshot GNSS receivers to estimate thermospheric density. • We show that these receivers (<0.1 mW) have a position accuracy 100 superior to TLEs. • We show (T_s ∼ 8 hrs) a relative density accuracy like from TLEs or geodetic receivers. • This improves the time update rate of density values from TLEs by a factor of 9. This paper proposes a novel concept of using highly efficient Snapshot Global Navigation Satellite Systems (GNSS) receivers to provide precise position fixes of single or multiple satellites in Low-Earth Orbit (LEO) to improve upper atmospheric modeling and thus contribute to superior space situational awareness (SSA). While tracking of LEO satellites and the use of onboard GNSS receivers for drag measurements and upper atmosphere modeling are well-established techniques, the expected advent of snapshot GNSS receivers for spaceborne scientific applications will allow massive improvements on the GNSS sensor's Size, Weight, Power and Cost (SWaP-C). With chip-size dimensions of 4x4 mm2, a mass of less than 5 gr, an average power level below 0.1 mW, snapshot receiver technology is expected to provide position fixes in space with an accuracy of ∼19 m (3D r.m.s.), which will surpass the accuracy of Two-Line Elements (TLE) provided by the US Joint Space Operations Center (JSpOC) by at least two orders of magnitude. Equally important to their SWaP-C benefits, Snapshot GNSS receivers will allow mission and spacecraft designers to trade onboard-processing requirements versus payload downlink requirements, leading to either minimum onboard processing or a minimum amount of downlinked data. In this research, we establish the concept and architectural overview of using snapshot GNSS receivers for SSA, including the role of using them in a Distributed Space System (DSS), and detail their characterization and performance in terms of the required GNSS hardware and the impact of these payload on the power budget, the link budget and the OnBoard Data Handling (OBDH) budget of a satellite. It will be shown that these receivers lend themselves especially to their use on femto-, pico- and nano-satellites, although integrated snapshot modules may be flown as auxiliary payloads on micro- or mini-satellites as well. While this work focuses on the implications of the use of snapshot GNSS receivers on spacecraft design for the use of upper atmosphere modeling and SSA, their use may open up other science applications which avoid the need for expensive high-grade GNSS receivers. [ABSTRACT FROM AUTHOR]

• We characterized the pressure wave produced by the Tonga volcano using cosmic rays. • We believe this is the first time that a Lamb wave is studied using cosmic rays. • Our high-altitude data provides additional information about this unique event. High-energy cosmic rays that hit the Earth can be used to study large-scale atmospheric perturbations. After a first interaction in the upper parts of the atmosphere, cosmic rays produce a shower of particles that sample it down to the detector level. The HAWC (High-Altitude Water Cherenkov) gamma-ray observatory in Central Mexico at 4,100 m elevation detects air shower particles continuously with 300 water Cherenkov detectors with an active area of 12,500 m2. On January 15th, 2022, HAWC detected the passage of the pressure wave created by the explosion of the Hunga volcano in the Tonga islands, 9,000 km away, as an anomaly in the measured rate of shower particles. The HAWC measurements are used to determine the propagation speed of four pressure wave passages, and correlate the variations of the shower particle rates with the barometric pressure changes. The profile of the shower particle rate and atmospheric pressure variations for the first transit of the pressure wave at HAWC is compared to the pressure measurements at the Tonga island, near the volcanic explosion. By using the cosmic-ray propagation in the atmosphere as a probe for the pressure, it is possible to achieve very high time-resolution measurements. Moreover, the high-altitude data from HAWC allows to observe the shape of the pressure anomaly with less perturbations compared to sea level detectors. Given the particular location and the detection method of HAWC, our high-altitude data provides valuable information that contributes to fully characterize this once-in-a-century phenomenon. [ABSTRACT FROM AUTHOR]

Satellite drag modeling remains the largest source of uncertainty affecting space operations in low Earth orbit. The uncertainty stems from inaccurate models for mass density and drag coefficient. Drag coefficient modeling also impacts scientific knowledge on the physics and dynamics of the upper atmosphere through the estimation of high-fidelity mass density from measurements of acceleration on-board satellites. Efforts over the last decade have pushed drag coefficient modeling in the right direction, however, have resulted in multiple methods and tools. We provide a comprehensive review of the drag coefficient modeling methods and tools. Current scale differences between thermospheric data sets mostly originate from errors in the aerodynamic modeling, specifically in the modeling of the satellite outer surface geometry and the gas-surface interactions. Enhancing these models' accuracy is intrinsically connected to the satellite drag fidelity for science and operations. A team of invested scientists recently met under the community-driven International Space Weather Action Teams (ISWAT) initiative to discuss and consolidate the efforts towards a drag coefficient modeling baseline for consistency in science and operations. In this paper, we compare the available methods for drag coefficient modeling, their impact on the derived density estimates, and make recommendations for adoption of baseline methods for science and operations. Results show that the differences in derived densities estimates can reach tens of percent at altitudes above 4̃50 km during solar minimum conditions resulting mainly from differences in the modeling of gas-surface interactions. As a result, we conclude and recommend that robust uncertainty quantification be an integral part of any modeling efforts that employ the high-fidelity accelerometer derived density estimates. We also conclude and recommend that gas-surface interaction models that account for impact of altitude and solar variations be employed moving forward. Finally, we recommend future science missions to improve our understanding of gas-surface interactions and eventually the upper thermosphere variability. [ABSTRACT FROM AUTHOR]

New instrumental developments based on a floating-mode avalanche photodiode (APD) combined with an electrostatic energy-per-charge analyzer were conducted for comprehensive and accurate plasma measurements in wide energy ranges in future space plasma explorations. The advantages of APD, namely, rough energy analysis capability, low dark count, compact dimension, and lightweight, are promising as an advanced in-situ measurement technique. We conducted several types of electron/ion beamline experiments under different floating voltage conditions in order to investigate the properties of particle detections and energy analyses using the floating/normal-mode APD combined with/without the electrostatic energy-per-charge analyzer. The electron/ion post-acceleration associated with the operation of APD in floating mode reduces the lowermost energies detectable by APD. Applying a high voltage of ∼ ±5 kV to electrostatically float APD in the combination with an electrostatic analyzer, we can attain wide energy coverages (∼ eV – 100's of keV for electrons, ∼ 5 keV/q – 100's of keV/q for ions) with proper energy resolutions, noise reduction due to double energy discrimination, and ion mass discrimination capability particularly to distinguish energetic He2+ components of solar wind origin. This technique would also be useful to distinguish the terrestrial-origin O+ from H+ in energies of > a few tens of keV if the ions outflowing from the Earth's upper atmosphere significantly affect the plasma population after some energization processes in the magnetosphere. When these advanced in-situ measurement techniques are employed in future exploration missions, wide-energy/angular distributions of both electrons and ions in space could be captured simultaneously by a single sensor head with triple-dome structure on spin-stabilized satellite. [ABSTRACT FROM AUTHOR]

• The ST-ResNet model effectively characterizes the spatial and temporal characteristics of TEC. • The consistency in the results indicate the use of suitable exogenous IMF parameters: IMF B y , IMF B z , Vp and Np. • The RMSE estimates for the entire study region for solar maximum and minimum years are 3.13 TECU and 1.23 TECU respectively. • The RMSE estimates for the mid-latitude region for solar maximum and minimum years are 2.31 TECU and 1.58 TECU respectively. Since the ionospheric total electron content (TEC) exhibits complex spatial and temporal behaviour including the seasonal and solar activity dependencies, resulting in large scale differences across different regions of the world, developing an effective deep-learning-based predictive model, capturing the complex behaviour of TEC is much needed. We present a novel deep learning-based model to predict the TEC using the spatio-temporal residual network (ST-ResNet). The TEC data used in the study were obtained from 185 GPS receiver locations, covering the latitude region from 10° N to 80° N and the longitude region from 110° W to 34° E. We considered TEC data of 154 days each corresponding to the solar maximum (2014) and the solar minimum (2020) years for training the network together with the exogeneous interplanetary magnetic field (IMF) data, including the magnetic field components By, Bz, plasma flow speed (Vp), and proton density (Np). A total of 44,352 maps (collected at the rate of 288 maps per day) were pre-processed by grouping them into closeness, period, and trend channels, which associate with the near-time, short-term, and long-term trends in the TEC data, respectively. After training, the model was tested for one day. The objectives of the study are: i) To develop and evaluate the performance of the ST-ResNet model, ii) to assess its performance on TEC data corresponding to mid-latitude region, under different solar conditions and iii) to compare the ST-ResNet model with other predicted models. For the entire study region, the root mean squared error (RMSE) was found to be 3.13 TECU for the solar maximum year and 1.23 TECU for the solar minimum year. Similar trends were observed in the mid-latitude region (30° N-60° N), with RMSE values of 2.31 TECU and 1.58 TECU for the solar maximum and solar minimum years, respectively. ST-ResNet model showed an improved accuracy over the long short-term memory (LSTM) deep learning network by about 23% and 31% for the entire study region and by 49% and 19% for only mid-latitude region, during the solar maximum and minimum years respectively, suggesting the superior performance of ST-ResNet over the LSTM network. A comparative observation of results of ST-ResNet model with those of back propagation and international reference ionosphere-2016 (IRI-2016) model also showed the superiority of the former. Results confirm the suitability of the ST-ResNet model for predicting the spatial and temporal behavior of TEC across different locations during various solar conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] The climate effects of atmospheric aerosols remain highly uncertain. Part of the uncertainty arises from the fact that scattering and absorbing aerosols have distinct or even opposite effects. Thus their relative fraction is critical in determining the overall aerosol climate effect. This study combines observations and global model simulations to demonstrate that changes in the fraction of scattering and absorbing aerosols play an important role in driving the monsoon precipitation decrease over northern India since the 1980s, especially over the Gangetic Basin. Increased aerosol scattering, or decreased aerosol absorption, manifested as a significant increase of aerosol single scattering albedo (SSA), causes strong cooling in the upper atmosphere. This suppresses vertical convection and thus reduces precipitation. Further analysis of the Couple Model Intercomparison Project Phase 6 multi-model-mean historical simulation shows that failing to capture the SSA increase over northern India is likely an important cause of the simulated precipitation trend bias in this area. [ABSTRACT FROM AUTHOR]

Long-term stereoscopic observations of aerosol, NO 2 , and HCHO were carried out at the Yangmeikeng (YMK) site in Shenzhen. Aerosol optical depths and NO 2 vertical column concentration (NO 2 VCD) derived from MAX-DOAS were found to be consistent with other datasets. The total NO 2 VCD values of the site remained low, varying from 2 × 1015 to 8 × 1015 mol/cm2, while the HCHO VCD was higher than NO 2 VCD, varying from 7 × 1015 to 11 × 1015 mol/cm2. HCHO VCD was higher from September to early November than that was from mid-late November to December and during February 2021, in contrast, NO 2 VCD did not change much during the same period. In January, NO 2 VCD and HCHO VCD were both fluctuating drastically. High temperature and HCHO level in the YMK site is not only driving the ozone production up but also may be driving up the ozone concentration as well, and the O 3 production regime in the YMK site tends to be NO x -limited. At various altitudes, backward trajectory clustering analysis and Potential Source Contribution Function (PSCF) were utilized to identify possible NO 2 and HCHO source locations. The results suggested that the Huizhou-Shanwei border and the Daya Bay Sea area were the key potential source locations in the lower (200 m) and middle (500 m) atmosphere (WPSCF > 0.6). The WPSCF value was high at the 1000 m altitude which was closer to the YMK site than the near ground, indicating that the pollution transport capability in the upper atmosphere was limited. [ABSTRACT FROM AUTHOR]

• Mg II index was implemented in IRI-2016 to assess foF2 but results do not provide a clear improvement of the model performance. • IRI-Plas with Mg II option to assess foF2 provides a slightly better performance than IRI-2016. To assess upper atmosphere parameters, current models use different variables to account for solar activity levels. Studies that evaluate the most recent solar cycles have shown that when dealing with the ionospheric F2 layer, and in particular with foF2, the Mg II index is a better choice than other solar activity proxies to account for solar EUV variation. The International Reference Ionosphere, version 2016 (IRI-2016), a model widely used by the scientific community, uses the Ionosonde Global (IG) index to assess foF2. A most recent and expanded version, IRI-Plas, allows selecting a solar activity proxy among 7 options including IG and Mg II. In the present work, the performance of IRI considering Mg II to assess foF2 is analyzed, comparing three modeling cases: IRI-2016 with its default solar activity index (IG), IRI-2016 with Mg II instead of IG, and IRI-Plas choosing Mg II as the solar proxy option. This model comparison was evaluated in terms of their agreement with measured foF2 data from four stations located in Japan (Northern Hemisphere), and four in Australia (Southern Hemisphere). Monthly medians for the 24 h, along two periods of three years were considered: 2000–2002 and 2008–2010, which correspond to epochs of maximum and minimum solar activity levels, respectively. Based on goodness-of-fit statistics, our results show that in the case of IRI-2016, the Mg II implementation does not reveal a significant improvement for foF2 assessment, and the IRI-Plas performance with the Mg II option is only slightly better than the other two options. Dispersion diagrams between measured and modeled foF2 also evince a similar performance between the three models. All models show the same over- and underestimation patterns, except in the nighttime case during the minimum activity level period for both Australian and Japanese stations where IRI-Plas outperforms the other two model options. The comparable performances of the three options might be attributed to a stronger variation in the evaluated periods which could be related to seasonal changes rather than to solar EUV proxies. Future studies considering time series over several years, covering at least a complete solar activity cycle, are required to determine stronger model performance differences. [ABSTRACT FROM AUTHOR]

Procedures are developed for accelerated laboratory tests of spacecraft polymers for resistance to long-term exposure to hyperthermal atomic oxygen (AO) with the use of high-energy AO ions of a rarefied plasma and Kapton-H polyimide as the reference material. The parameters that characterize physico-chemical, thermo-optical, and aerodynamic AO – Kapton-H interaction (surface roughness, solar absorptance, and normal infrared emittance) are determined at different values of the AO fluence. To do this, use was made of the data of tests onboard spacecraft in the Earth's atmosphere and the authors and others' laboratory tests. The normal and the tangential momentum transfer coefficient and the energy transfer coefficient are reported as a function of the AO bombardment angle. The obtained data on the AO-induced degradation of the parameters that characterize AO–polyimide dynamic interaction allow one to predict the behavior of the polyimide thermo-optical and aerodynamic properties during a long-term service in the Earth's upper atmosphere and ionosphere. • Physical modeling conditions for spacecraft – atomic oxygen interaction are given. • Atomic oxygen to polyimide momentum and energy transport coefficients are measured. • Atomic oxygen induced polyimide degradation parameters are determined. [ABSTRACT FROM AUTHOR]

Foreground emission, mainly airglow and zodiacal light, is a significant contributor in an ultraviolet observation especially from low earth orbit. Its careful estimation and removal are tedious yet unavoidable processes in the study of diffuse UV radiation and by extension interstellar dust studies. Our analysis of deep GALEX observations show that airglow is not only a function of Sun angle but also a strong function of Solar activity at the time of observation. We present here an empirical model of airglow emission, derived from GALEX deep observations, as a function of 10.7 cm Solar flux and Sun angle. We obtained the model by training machine learning models on the data using a variant of the regression algorithm that is both resilient toward outlier data and sensitive to the complexities of the provided data. Our model predictions across various observations show no loss in generalization as well as good agreement with the observed values. We find that the total airglow in an observation is the sum of a baseline part (AG c) that depends on the Solar flux and Sun angle, and a variable part (AG v) that depends on the Sun angle and the time of observation with respect to local midnight. We also find that the total airglow can vary between 85 – 390 photon units in FUV and 80 – 465 photon units in NUV. [ABSTRACT FROM AUTHOR]

The idea that a tropospheric heat source generating waves can be replaced with a surface source of pressure oscillations on the Earth's surface is proposed and analyzed. In the surface source, atmospheric pressure fluctuations caused by a tropospheric source are used. The discrepancies due to the replacement of the tropospheric heat source by the surface one are estimated using experiments with a high-resilution numerical model of acoustic-gravity waves. It is shown that at frequencies of infrasound, the wave amplitudes in the upper atmosphere are very close for both tropospheric heat and surface pressure sources. At frequencies of internal gravity waves, the time-spatial structure of the wave fields are close in the upper atmosphere, but wave amplitudes for the surface pressure generation could be larger (up to two times) than those for the respective tropospheric heat sources. This discrepancy is explained and some corrections to the surface pressure source are proposed, which provide better agreement and may be applied for modeling of waves from tropospheric sources, based on the data of atmospheric microbarometer measurements. [ABSTRACT FROM AUTHOR]

Q-SAT, a small spherical satellite designed and developed by Tsinghua university, was successfully launched on Aug 6, 2020 at Jiuquan satellite launch center in China. The mission of Q-Sat is the joint measurement of long-wavelength Earth gravity field and upper atmosphere density, which is of great significance for improving spacecraft orbit prediction and promoting the development of satellite gravity measurement technology. The satellite is designed in spherical shape innovatively and deploys high dynamic dual-frequency GPS as the main payload. On-orbit data shows that the atmospheric density detection precision is in the order of 10−14kg/m3 and the gravity recovery precision achieves the level of 30 orders. All mission success criteria and objectives were achieved. This paper presents the design, space mission, key technologies, science capabilities and preliminary results of the satellite. • Q-SAT, a spherical satellite for the joint measurement of long-wavelength Earth gravity field and upper atmosphere density, was launched in 2020. • An electromagnetic separation system with point connection-release structure is designed for the Q-Sat. • As secondary payload a powerful GPU module is implemented to validate artificial intelligence computing capabilities in orbit. • Modifications for the Jacchia-Roberts atmospheric density model are proposed in the paper. [ABSTRACT FROM AUTHOR]

We analyze periodic features in the F10.7 cm solar radio flux and the Ap geomagnetic index to examine solar-terrestrial coupling in Earth's atmosphere above 100 km. The coupling is indicated by the same periodic features observed in the global infrared power radiated by Nitric Oxide (NO) and Carbon Dioxide (CO 2). The infrared power data have been measured by the SABER instrument on the NASA TIMED satellite since January 2002. A strong dominant feature for the length of the solar cycle (≈11 years) can be observed in all the datasets. The length of this periodicity can vary from 9.95 years to 12.25 years for different solar cycles. Periodic features larger than the length of the solar cycle are also observed in the F10.7 and Ap index (≈22 years and ≈44 years). A strong 180-day periodic feature can be observed in the Ap index which corresponds to the well-known Russell-McPherron effect. Additionally, the NO power and the Ap index exhibit statistically significant periodic features for shorter periods (e.g., 27, 13.5 and 9 days). This similarity indicates a strong link between the thermosphere's infrared energy budget and the geomagnetic conditions of the upper atmosphere. • LNP analysis has been applied to detect periodic features of solar activities. • F10.7 index, Ap index and SABER infrared measurements have been investigated. • A strong periodic feature for the solar cycle (≈11 years) exists in the datasets. • Larger (≥22 years) and shorter (≤365 days) periodic features are also present. • Earth's infrared radiated energy and geomagnetic behavior have a strong coupling. [ABSTRACT FROM AUTHOR]

• This paper discusses the results from the ship-borne aeronomy experiments from the Indian region. • Thermospheric airglows near the geographic equatoron certain daysexhibited Midnight brightness. • The simulations using a quasi-2D model suggest that it could be associated with the MTM phenomenon. This paper discusses the results from the aeronomy experiment carried out using a multiwavelength photometer operated onboard Sagar Kanya ship from the Indian region, which covered a latitude region from 14.5 N to 2S (7° to −10° Dip latitudes) along the same longitude region (∼72-75E). It has been found that the thermospheric airglows, especially the OI 630.0 nm emission near to the geographic equator exhibits 'Midnight Brightness' on different days of observations. Though the magnitudes were found to be less, the OI 777.4 nm and OI 557.7 nm emissions also exhibited intensity variations on those days, indicating a common causative mechanism for the same. The simulation studies using a quasi-two dimensional ionospheric model, revealed that such an enhancement could be due to the F-region collapse associated with the Midnight Temperature Maximum (MTM) phenomenon. [ABSTRACT FROM AUTHOR]

Previous works have shown that dust particles can be accelerated to marginally relativistic velocities in supernova. In this paper we consider the observational signatures of the interactions of such particles with the Earth's atmosphere. We develop a hydrodynamic and radiative model to explore the detectability of ≳ 1 mm sub-relativistic meteoroids. We find that a large fraction of the meteoroid energy during its passage through the Earth's upper atmosphere powers the adiabatic expansion of a hot plasma cylinder, giving rise to acoustic shocks. Additionally, a global network of several hundred all-sky optical cameras with a time resolution of ≲ 10 - 4 s would be capable of detecting ≳ 1 mm sub-relativistic meteoroids. [ABSTRACT FROM AUTHOR]

Tropical cyclones are one of the potential sources of gravity waves, which can transport energy and momentum to higher heights through their vertical propagation and interaction with the background flow and thereby influence the dynamics of the upper atmosphere. High-resolution wind data acquired by the Medium Frequency (MF) radar at Kolhapur (16.69°N, 74.24°E) are utilized to study the high frequency gravity waves (20–60 min) associated with the tropical cyclone named "Vayu" formed in the Indian Arabian Sea in June 2019. An enhancement of the gravity wave (GW) activities in the meridional wind is observed during 13–15 June 2019. The source of the gravity wave is the tropical Vayu cyclone of category 2 storm. We employed the gravity wave variance data from NASA's Atmospheric Infrared Sounder (AIRS) satellite for our analysis over stratospheric heights. The enhancement of gravity wave variance in both the stratosphere mesosphere heights and the low values of OLR indicate the strong convection associated with cyclone, the source of observed gravity waves. In the present study we analyzed the horizontal propagation direction of the cyclone generated gravity waves using perturbation ellipse, it is found to be in the north–south plane. The temperature profiles obtained from the SABER instrument on board TIMED satellite indicate the presence of mesospheric inversion layer with an amplitude of nearly 40 K on the day of large gravity wave variance (June 13, 2019). These results indicate the cyclone can generate gravity waves which can propagate to higher heights and modify the MLT thermal structure, providing evidence for the vertical coupling between lower and upper atmosphere. • High-frequency GW activity in meridional wind associated with Tropical Cyclone "Vayu". • Studied cyclone generated high-frequency gravity waves (GWs) over Kolhapur. • Anticorrelation of GW activity with OLR reveals tropospheric convection associated with cyclone as a source. [ABSTRACT FROM AUTHOR]

• Latitudinal distribution in OI 630.0 nm dayglow emissions presented. • The effects of the equatorial electrodynamics on dayglow emission show small variations with magnetic latitudes. • Dayglow emission rates respond to meridional winds positively near to dip equator and negatively away from equator. Earth's upper atmosphere over low latitudes is influenced by the equatorial electrodynamics. Its influence can also be modulated by the thermospheric winds. The effect of these two forces on the thermospheric neutral behaviour in the daytime can be investigated by measuring the variations in the OI 630.0 nm dayglow emission rates as these serve as effective tracers of the altitude region of their origin. The capability to measure dayglow emissions over a large field-of-view presents a unique opportunity to investigate the upper atmospheric behaviour over large spatial extents. Diurnal measurements of OI 630.0 nm dayglow emission rates have been carried out from two different locations in India using multi-wavelength imaging echelle spectrographs, MISE, which, together cover a spatial range from 5 ° -18 ° magnetic latitude. These investigations have been carried out during January-February 2020 (winter season) when solar flux variation was nearly negligible (varied only by 4 solar flux unit from 68–72 solar flux unit). Therefore, latitudinal variations in the daily averaged oxygen dayglow emission intensities have been analyzed to assess their response to the variations in the strength of the equatorial electrodynamics and the meridional winds. The results reveal that these forces show varying effects with the poleward meridional wind contributing to an enhancement in the OI 630.0 nm dayglow emission rates closer to the magnetic equator and a decrement as one moves away from the equator. The equatorial electric field effect, however, continues to be equally effective in the low-latitudes region under consideration. [ABSTRACT FROM AUTHOR]

• The daytime nitric oxide vibrationally excited levels are studied numerically. • Chemical processes are considered including suprathermal electrons precipitation. • NO 5.3 μm volume emission rate results corroborate SABER satellite data. The nitric oxide vibrationally excited levels in the daytime are studied, at altitudes between 80 and 200 km. For that, we use a coupled 1D Boltzmann kinetic-fluid model to find density profiles of the major ions: O 2 + ; N 2 + ; NO + ; N + ; O + , nitrogen atoms: N ( 4 S) ; N ( 2 D) and vibrationally excited levels: NO (v ⩽ 7). A variety of processes are included in the model calculations that are neutrals chemistry, ions chemistry, photoabsorption, energetic electrons acting on the neutral atmosphere, molecular diffusion, and turbulent diffusion transport. The vibrational excitation of the nitric oxide is under strong solar control, reaching its maximum value near noon, when the solar zenith angle has the smallest value and then decreases away from noon. Data measurements of NO 5.3 μ m volume emission rate (VER) provided by SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) satellite instrument corroborate our numerical results. [ABSTRACT FROM AUTHOR]

The seasonal and temporal variability of the OI 630.0 nm nightglow emissions were observed over Cachoeira Paulista (22.7oS, 45oW; dip latitude −35°) in Brazil by multichannel photometer during 2014 and 2015. The temporal variation of the OI 630.0 nm nightglow intensity shows a peak during post-midnight hours (∼ 25 h 00 LT) during the summer. During autumn, this peak is shifted towards pre-midnight at ∼ 22 h 00 LT. It is noticed that this peak again shifted towards post-midnight at 26 h30 LT and 25 h30 LT during winter and spring, respectively. The intensity increases by a factor of 2–4 in the summer than that observed in other three seasons. The modelling of the nightglow measurements in 2015 is carried out by calculating the excitation rate, emission rate and intensity of OI 630.0 nm nightglow emission in the upper atmosphere at low latitudes. Our calculation suggests that the dissociative recombination of O 2 + with electrons is the main source for the OI 630.0 nm nightglow emission. We report that the model intensities are in good agreement with the measurements at Cachoeira Paulista for all four seasons and the model reproduces all features of peak intensities very well. [ABSTRACT FROM AUTHOR]

This study contains predictions for mass spectrometry and plasma instrument measurements during upcoming Venus flybys of BepiColombo and Solar Orbiter and discusses the possibility of a phosphine detection with mass spectrometry in Venus' upper atmosphere. The results extend the ones published previously in Gruchola et al. (2019) , where predictions for the proposed ESA mission EnVision and the Venus flyby of JUICE were included. Both the Venus flyby of BepiColombo and the one of Solar Orbiter will take place in August 2021, only 1 day apart. BepiColombo, carrying the neutral mass gas spectrometer STROFIO, could probe the atmosphere around closest approach and obtain data on the thermal and hot neutral particle populations in the upper atmosphere. According to this study, the thermal hydrogen population as well as the hot species H, C, N and O, including isotopes, should be visible to STROFIO. Especially data on the abundance of the hot species would yield important insight into the planetary escape processes. The Solar Orbiter on the other hand carries the plasma instrument SWA-HIS, designed to measure the energetic solar wind ions. During its second Venus gravity assist it will traverse the magnetosheath, the region between bow shock and ion composition boundary, where in addition to the solar wind ions energetic planetary ions are present. The planetary pickup ions can be measured by SWA-HIS, providing important information on the outflow of planetary ions and the ionization processes in the upper atmosphere itself. The recent reports of phosphine in Venus' cloud decks with an abundance of 20 ppb at 80 km probably overestimate the actual PH 3 abundance, as the data are currently being reanalyzed (Greaves et al., 2021). However, even with this upper limit of 20 ppb a phosphine detection with a mass spectrometer e.g. on-board ESA's proposed EnVision mission, seems unlikely. To resolve the PH 3 peak and the 16O18O peak a mass resolution of almost 10'000 is required, and the PH 2 D peak is masked by the Cl fragment peak of HCl. Furthermore, NGMS on-board Pioneer Venus with a mass resolution of around 440 did most likely not detect phosphine, as it scanned only a few masses in the mass range of interest where more abundant species than phosphine are present. [ABSTRACT FROM AUTHOR]

• PAD of magnetospheric trapped particles is studied using test-particle simulations. • When adiabatic invariants are conserved, particles follow butterfly-type PAD. • All three adiabatic invariant violate when gyro-radius of trapped particles is large. • Particles follow Gaussian type PAD when adiabatic invariants are not conserved. • Theoretically estimated bounce/drift period is invalid as adiabatic invariant violate. This article aims to understand the pitch angle distributions (PADs) of the charged particles in the Earth's inner magnetosphere using test-particle simulations. The emphasis is on characterizing the variation in pitch angle of the charged particles trapped along the Earth's magnetic field lines. These charged particles undergo gyration, bounce, and azimuthal drift motions in the Earth's inner magnetosphere. They are trapped until their pitch angle falls into the loss-cone to get lost into the upper atmosphere. We have developed a three-dimensional test-particle simulation model in which the relativistic equation of motion is solved numerically to track these trapped particle's trajectories. We have examined the pitch angle distributions of the electron, proton, and oxygen for the cases where adiabatic invariants are conserved and non-conserved. For this purpose, we have considered the particle's trajectory in the latitudinal range of [ - 40 ° , 40 ° ] for one complete drift around the Earth. We found that when adiabatic invariants are conserved, the particles possess butterfly-type pitch angle distributions. Whereas, when adiabatic invariants are not conserved, the particle's pitch angle distribution bunches toward the 90°-peaked distribution. The situation of non-conservation of adiabatic invariants demonstrated in the present simulation is arising due to larger gyro-radius (few Earth radii) over which the ambient magnetic field is not constant. We have noticed that in the static dipolar magnetic field, all three, 1st, 2nd, and partly 3rd adiabatic invariants are non-conserved when gyro-radius is larger. The information on the change in the pitch angle distribution pattern from butterfly-type to 90°-peak distribution will be useful to understand the pitch angle distributions observed by the recent spacecraft in the Earth's radiation belts. [ABSTRACT FROM AUTHOR]

• New polar caps emerge at lower latitudes with axial non-dipolar magnetic fields. • Axial non-dipolar magnetic fields have more polar caps and auroral zones but may cover smaller areas. • Total area of auroral zones is larger than the area of polar caps with axial degrees larger than 3. • Latitudes of auroral zones and polar caps adjacent to the geographical poles increase with degree. The geomagnetic field, modified by the solar wind, determines the shape, area and location of polar caps and auroral zones, among other magnetosphere and upper atmosphere characteristics. Since the field varies greatly with time it is of interest to analyze polar caps and auroral zones variations linked to magnetic field variations of intensity and pattern. Polar caps and auroral zones locations and areas for various single harmonic axial field configurations are obtained analytically assuming a simple magnetopause model. As the axial degree n increases, the polar caps and auroral zones total number, given by n + 1 and 2n respectively, also increase. However, their total areas decrease from a larger value in the case of an axial dipole to a minimum for an axial octupole (n = 3), and then increase for increasing degrees. The increasing rate is much higher in the auroral zones case to the point that it exceeds the dipolar value at n = 5 while in the polar caps case this occurs at n = 8. The absolute latitudes of the auroral zones and polar caps that reside around the geographical poles increase with axial degree. Our results represent an end-member case of the evolution of auroral zones and polar caps during polarity reversals if the transition involves axial dipole energy cascade to higher axial degrees. Evidence for such an energy transfer is found in the historical record of the geomagnetic secular variation. [ABSTRACT FROM AUTHOR]

• The first time that underground production of 81Kr was detected in geological formations. • A novel model was developed that describes the dynamics of production and emanation of radionuclides in rocks. • The difficult to measure independent spontaneous 81Kr fission yield of 238U was constrained based on a natural analogue. • The importance of underground production of 81Kr for groundwater dating is reassessed. Radiokrypton dating using the long-lived natural isotope 81Kr has been developed for determining the age of ancient groundwater. 81Kr is attractive for this purpose because it is generally thought to be produced solely in the upper atmosphere. Its 229,000-year half-life, a spatially homogeneous distribution in the atmosphere, and the absence of anthropogenic sources makes it an ideal tracer to determine ages up to ∼1.3 million years. As a noble gas, it is inert and thus not subject to interfering geochemical reactions that may alter the age information. We sought to date groundwater samples collected from deep (0.6–1.9 km) rock fractures in the Kaapvaal Craton, South Africa. Previous studies using other dating methods have estimated groundwater ages at these sites in the 1–100 million year range. Surprisingly, three of the four samples collected from flowing boreholes in gold and diamond mines showed 81Kr isotopic abundances at 2–5 times the atmospheric value. This is the first time that underground production of 81Kr has been detected, indicating that 81Kr can be generated underground in measurable quantities in contrast to the long-held paradigm that such production is insignificant in natural rocks. A radionuclide production and release model is proposed in order to quantify the importance of different factors that affect the concentrations of 81Kr in the groundwater. It is not only the high effective uranium content of the rock but also a higher 81Kr fission yield than previously anticipated that are likely causing the elevated 81Kr values in this case. In less extreme environments with average crustal composition (i.e. moderate U concentration), however, we anticipate that the underground production minimally affects groundwater 81Kr dating as demonstrated. [ABSTRACT FROM AUTHOR]

The atmosphere of Titan is a unique natural laboratory for the study of atmospheric evolution and photochemistry akin to that of the primitive Earth, with a wide array of complex molecules discovered through infrared and sub-mm spectroscopy. Here, we explore high resolution visible spectra of Titan (obtained with VLT-UVES) and retrieve an empirical high resolution list of methane absorption features at high resolution, (R = 100. 000) between 5250 Å and 6180 Å, for which no linelists are yet available. Furthermore, we search for the predicted, but previously undetected carbon trimer, C 3 , on the atmosphere of Titan, at its 4051 Å band. Our results are consistent with the presence of C 3 at the upper atmosphere of Titan, with a column density of 1 0 13 cm−2. This study of Titan's atmosphere with high-resolution visible spectroscopy presents a unique opportunity to observe a planetary atmosphere where CH 4 is the main visible molecular absorber, from which CH 4 optical proprieties can be studied. It also showcases the use of a close planetary target to test new methods for chemical retrieval of minor atmospheric compounds, in preparation for upcoming studies of cold terrestrial exoplanet atmospheres. • Study of Titan's visible spectrum with VLT-UVES in very high spectral resolution. • Absorption lines Doppler Shift allow distinction between Solar and Planetary origin. • CH 4 visible absorption bands in Titan are studied in very high resolution. • 97 absorption lines are detected and characterised in CH 4 visible bands below 620 nm. • Absorption features are consistent with the existence of C 3 in Titan's atmosphere. [ABSTRACT FROM AUTHOR]

The habitability of Earth significantly depends on the evolution of its atmospheric properties, which are strongly influenced by escape processes. Polar outflow, which encompasses the atmospheric escape of ions through the open field lines of the Earth's magnetosphere, is the dominant escape process for modern Earth and likely played a significant role in Earth's early history as well. In this article, we investigate the evolution of Earth's polar outflow during the Archean eon 3-4 gigayears (Ga) ago for an N 2 -CO 2 atmosphere. For this, we use a kinetic direct simulation Monte Carlo (DSMC) particle code to simulate the interactions between the solar wind and the Earth's upper atmosphere. We explore the effects of different CO 2 mixing ratios (10%, 25%, 50%, 75%, 99%) on the polar outflow escape rates of oxygen, nitrogen and carbon. Using the ion production rates as an estimate for polar outflow, our results indicate that during the time 3.6-4.0 Ga ago, a CO 2 mixing ratio larger than 25% may have been necessary to avoid excessive escape via polar outflow. Close to 4 Ga ago, even 50% CO 2 may have been necessary due to the stronger solar winds. Our results align with other studies also suggesting a similarly high CO 2 mixing ratio in the early Archean. • Polar outflow is a non-negligible atmospheric escape process for magnetized planets • Early Archean Earth may have had 25%-50% CO 2 to prevent excessive polar outflow • Studies on thermal and non-thermal escape suggest similar levels of necessary CO 2 [ABSTRACT FROM AUTHOR]

Recent observations using the Wind and Ulysses spacecrafts and the Solar Occultation For Ice Experiment (SOFIE) during the period between 2007 and 2020 indicate a total cosmic dust influx at Earth ranging from 22 to 32 tonnes per day. Much is still unclear about the formation, evolution, and propagation of this cosmic dust throughout our Solar System, as well as the transport and chemical interaction of such particles within our own atmosphere. Studying meteoroids, which are particles small and fast enough to ablate in the Earth's upper atmosphere producing meteor plasma detectable by meteor radars, offers an opportunity to better understand these processes. While meteor radars provide a powerful tool to detect meteoroids, they are limited to detecting particles that produce a sufficient amount of plasma within the instrument's field-of-view, and thus most of their trajectory remains undetected. In this work, we report a novel methodology, using new polarization measurements as well as two state-of-the art models, to determine the pre-atmosphere dynamical characteristics of the detected particles, before they suffer any significant ablation or deceleration. We present the results for 20 meteor detection case studies, and find that for the majority of particles, at least 80% (typically 95%) of the particle mass has already been lost at the time of detection. In addition, while all particles experienced deceleration by the time of detection, this was typically small (≤ 4% of their initial velocity). Future work will implement this new methodology to automatically determine the initial mass and velocities of individual meteors. This will help provide more precise meteor orbits and characterization of parent source populations, as well as the identification of potential interstellar particles. • Meteoroids offer tool to better understand processes within Earth's upper atmosphere. • Meteor radars provide powerful detection tool but have detection limits. • Much of particle's trajectory remains undetected — initial mass and velocity unknown. • Methodology utilizes new polarization measurements and two state-of-the-art models. • Determines pre-atmosphere dynamical parameters prior to significant ablation. [ABSTRACT FROM AUTHOR]

Radio occultation (RO) has proved to be a powerful tool for weather forecasting and ionospheric modelling. It is a truly global technique for the observation in the lower as well as in the upper atmosphere. With the evolution of radio occultation technique, the data inversion algorithms used to extract data from the raw RO measurements also evolved over the period of last two decades. In this work, a thorough investigation has been conducted on the performance of model-assisted inversion technique proposed by Shaikh et al. (2017). A combination of low, mid and high latitude geographical locations was chosen to analyze the performance of the technique. It has shown that the proposed technique has significantly improved the data inversion results in high solar activity conditions when the horizontal gradients of the ionosphere are expected to be stronger than normal (for example 24% at King Salmon and 21% at Jeju in high solar activity). The longitudinal sector-wise analysis shows that the American longitudinal sector has slightly weaker performance measures for model-assisted inversion compared to the Asian longitudinal sector. [ABSTRACT FROM AUTHOR]

• F 10.7 cannot describe the hmF 2 behavior in the 24th SA cycle. • hmF 2 behaves during the " v ague" period similarly to foF 2. • The reduction of atomic oxygen in the thermosphere is concluded. The measurements of the F 2-layer height, hmF 2, at Juliusruh station during 1958–2018 are analyzed by the method developed by the authors earlier and used to determine long-term trends in parameters of the F 2 layer. It is found that, in the same way as for the behavior of the critical frequency described by the authors in the previous publication, peculiarities in the hmF 2 behavior are observed after 2002–2003. If the solar activity index F 10.7 is used, an increase in the Δ hmF 2 value is observed and provides a positive trend in hmF 2 that contradicts to the available ideas on the continuing process of cooling and contraction of the upper atmosphere. If the F 10.7 index corrected by other SA indices (the sunspot number Rz or the Lyman-alpha line intensity) is used, as it has been done for the foF 2 trends in the previous publications by the authors, the picture of changes in the hmF 2 trends is obtained similarly to the changes in the foF 2 trends. A well pronounced negative trend in hmF 2 is observed to 2002–2003, and then it is substituted by a chaotic change in Δ hmF 2 during the "vague" period, whereas during the last analyzed years it becomes negative again. Analysis of the slope s of the foF 2(hmF 2) dependence shows that there is a systematic decrease in s with time. That confirms the conclusion of the authors on a decrease in the oxygen amount in the thermosphere. [ABSTRACT FROM AUTHOR]

Since 1988 the Upper Atmosphere Physics unit of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) has provided maps of Maximum Usable Frequency (MUF) and skip distance over a European area extending in latitude from 34°N to 60°N and in longitude from 5°W to 40°E. Anyhow, these maps suffer the following restrictions: (1) they are provided with two months in advance and so they are not suitable for space weather purposes; (2) they are represented with few isolines; (3) they are centred only on Rome (41.8°N, 12.5°E) and generated in black and white; (4) MUF are calculated with a really simple algorithm. In order to overcome these restrictions, a new software tool was developed to get climatological maps (up to three months in advance) and quasi real-time maps, (nowcasting) limited to the sector extending in latitude from 34°N to 48°N and in longitude from 5°E to 20°E, which includes the whole Italian territory. In order to achieve a greater accuracy, MUF and skip distance maps are generated combining the Simplified Ionospheric Regional Model (SIRM) and its UPdated version (SIRMUP) with the Lockwood algorithm. Climatological maps are generated every hour on the basis of the predicted 12-months smoothed sunspots number. Nowcasting maps are generated every 15 min exploiting fo F2 and M (3000)F2 data autoscaled at the ionospheric stations of Rome and Gibilmanna (37.6°N, 14.0°E). Nowcasting maps constitute the most important novelty because they let High Frequency (HF) users know in quasi real-time the radio propagation conditions over Italy. This turns out to be very valuable in terms of reliable radio links, especially in case of adverse space weather events. [ABSTRACT FROM AUTHOR]

The Atmospheric Effects of Precipitation through Energetic X-rays (AEPEX) mission is a 6U CubeSat that will monitor energetic electron precipitation from the radiation belts into the upper atmosphere. The primary instrument will image energetic (50–300 keV) X-rays produced in the atmosphere by bremsstrahlung, providing a near-direct signature of electron precipitation. An energetic electron detector will measure the precipitating electron spectrum, while the X-ray observations will be used to determine the absolute flux. X-ray images will be produced with 10-s time resolution and 50–100 km spatial resolution. The 6U spacecraft uses flight heritage spacecraft bus subsystems, including the attitude determination and control, electrical power, and command & data handling systems. AEPEX is designed to be operated from low-Earth orbit at ~ 500 km altitude with a high inclination in order to cover the outer radiation belt. AEPEX will be the first spacecraft mission to measure X-rays in the 50–300 keV energy range emitted by Earth's atmosphere in response to radiation belt precipitation, and the first to image that precipitation from above. [ABSTRACT FROM AUTHOR]

The second Miniature X-ray Solar Spectrometer (MinXSS-2) CubeSat, which begins its flight in late 2018, builds on the success of MinXSS-1, which flew from 2016-05-16 to 2017-05-06. The science instrument is more advanced – now capable of greater dynamic range with higher energy resolution. More data will be captured on the ground than was possible with MinXSS-1 thanks to a sun-synchronous, polar orbit and technical improvements to both the spacecraft and the ground network. Additionally, a new open-source beacon decoder for amateur radio operators is available that can automatically forward any captured MinXSS data to the operations and science team. While MinXSS-1 was only able to downlink about 1 MB of data per day corresponding to a data capture rate of about 1%, MinXSS-2 will increase that by at least a factor of 6. This increase of data capture rate in combination with the mission's longer orbital lifetime will be used to address new science questions focused on how coronal soft X-rays vary over solar cycle timescales and what impact those variations have on the earth's upper atmosphere. [ABSTRACT FROM AUTHOR]

Cherenkov Telescope Array (CTA) is an upcoming instrument that will start a new generation of atmospheric Cherenkov telescopes. CTA is expected not only to provide an unprecedented sensitivity in the tens of GeV to hundreds of TeV range, but also to considerably improve the systematic uncertainties of the measurements. We study the images registered by Cherenkov telescopes from low energy gamma rays with its first interaction in the upper parts of the atmosphere. The images show a characteristic separation due to the deflection of the first e − e + pair in the Geomagnetic Field. We evaluate the performance of the standard stereoscopic analysis for such events. We derive also a novel method for energy estimation of V-shaped events based purely on geometrical properties of the image. We investigate the potential of combining the classical energy estimation and the novel method for independent validation of the systematic shifts in the energy scale of Cherenkov telescopes and discuss the limitations of such analysis. [ABSTRACT FROM AUTHOR]

In this article, we estimate the influence of the atmospheric-ionospheric interaction and the differences in the location of the geographic and geomagnetic poles on the longitudinal variability of the ionospheric electric field in the vicinity of the geomagnetic equator. For the study, we applied the upper atmosphere model (GSM TIP) and the recently created entire atmosphere model (EAGLE). The simulation results confirm that the four-peak structure of the longitudinal variation and the pre-reversal enhancement of the eastward electric field at the equator are caused by the atmosphere-ionosphere coupling. The role of F-region dynamo in the formation of pre-reversal enhancement of the eastward electric field is beyond the scope of this paper. These structures appear during the minimum of solar activity periods and are formed by the longitudinal variations of the horizontal thermospheric wind and the Pedersen conductivity arising from the action of the mesospheric tides. During solar activity minimum periods, the difference in the locations of geographic and geomagnetic poles leads to some complication and smoothing of the obtained picture of longitudinal variations in the electric field. We suggest that mesospheric tides have a significant effect on the longitudinal variation of the Pedersen conductivity, while the longitudinal variation of the Hall conductivity is mainly determined by the mismatch of geographic and geomagnetic poles. The amplitudes of the equatorial electric field longitudinal variations are three to four times smaller than the amplitudes of their diurnal variations, however, they can have a significant impact on the spatial distribution of the electron density in the F region of the low-latitude ionosphere. [ABSTRACT FROM AUTHOR]

Total Electron Content (TEC) has become one of the most widely used observable parameters of the ionosphere. IRI-Plas is an empirical climatic model of the ionosphere and plasmasphere that extends up to GPS orbital height of 20,000 km. The purpose of the study is to reveal whether the winter anomaly (a phenomenon where the mid-latitude daytime NmF2 (or foF2) is greater in winter than in summer at approximately the same solar activity level) occurs in TEC over the Asian sector and how well it is "captured" by IRI-Plas. The study is based on GPS-TEC data derived from Global Ionospheric Maps (GIM-TEC) for January and July months of high (2000), low (2009) and moderate (2012) levels of solar activity. Ionosonde data recorded at a number of mid-latitude Russian and Kazakhstan ionospheric stations in winter and summer seasons for different levels of solar activity are used along with corresponding IRI-Plas calculations to illustrate some specific features of seasonal variations of the midlatitude ionosphere. A comparative study made between IRI-Plas-foF2 and ionosonde foF2 indicates that the IRI-Plas-foF2 variations are found to be in good agreement with the observations showing similar structures, similar magnitudes reflecting the winter anomaly in the diurnal variations. When the IRI-Plas-TEC values are examined for the difference between winter and summer seasons, it is found that their variations are mainly similar to those of IRI-Plas-foF2. Different from that of IRI-Plas-TEC, the winter anomaly in GIM-TEC is not so strong, appears for both high and moderate levels of solar activity, and it is more pronounced at higher latitudes. In low solar activity, the winter anomaly in GIM-TEC is almost absent at the region considered. Finally, the comparison of the IRI-Plas-TEC and GIM-TEC results for winter conditions show that the IRI-Plas-TEC values are significantly larger than those of daytime GIM-TEC at all locations of Russia and Kazakhstan and for all levels of solar activity that coincides with results of previous studies. However, unlike the previous studies, in summer solstice, IRI-Plas-TEC systematically underestimates the GIM-TEC values during high solar activity year and mostly overestimates them for low solar activity. In moderate solar activity year, IRI-Plas-TEC and GIM-TEC values are practically comparable. Thus, the IRI-Plas-TEC model represents the seasonal anomaly observed in foF2 in mid-latitude region for all levels of solar activity but there is a certain deviation from the behavior of GIM-TEC. One of the main reasons of this discrepancy may be the difference of the model Ne(h)-profile from a realistic profile in the upper ionosphere and plasmasphere, that demands additional updating of models for those upper atmosphere regions. [ABSTRACT FROM AUTHOR]

The results of the study of the gas-dust cloud of solid fuel combustion products dynamics formed under a rocket stages separation are presented. The sequence of the digital images obtained in the twilight condition at a distance of ∼1500 km from the missile trajectory was analyzed. The height of the cloud center reaches up to ∼900 km, and its diameter is ∼2000 km. The glow of the cloud is determined by the scattering of sunlight on dispersed particles of the combustion products. The obtained data allow to specify the dispersed composition of the cloud and dynamic parameters of its development. The proposed methodology can be used to clarify the physical picture of the interaction of the combustion products of solid propellant with the environment, as well as environmental conditions and processes in the upper atmosphere. • The height and diameter of the gas-dust cloud were measured. • The expansion velocity of the cloud is practically constant. • Calculated luminosity of the cloud is in satisfactory agreement with the measurement results. [ABSTRACT FROM AUTHOR]

Dust particles are hazardous to human health and severely affect the city operations. However, there is few research on the topographic dynamic removal of near-surface dust particles. In this study, the surface meteorological and aerosol monitoring data if such an event was analysed. The event took place on March 27–29, 2018 in Beijing, China. Given the special topographic conditions in Beijing, various parameters, such as wind profile line data, four-dimensional variation Doppler radar data, and aerosol lidar data were used to determine the dynamic effects of easterly wind. The event could be divided into four stages. In Stage 1 (Dust aerosol transfer), the dust particles at higher elevation were transferred to upper atmosphere of Beijing through northern wind. These dust particles gradually moved to the lower atmosphere. The temperature inversion layer hindered the settlement of dust particles on the near-surface atmosphere. The dust particles could not penetrate the temperature inversion layer and moved to the near-surface layer. Anthropogenic aerosols of high concentrations were retained below the height of 1 km. In Stage 2 (development of dust particles), following the dynamics of easterly wind, the temperature inversion phenomenon gradually disappeared. The high-concentration dust particles in the higher atmosphere were transferred to the near-surface layer and settled down, thus mixing with the anthropogenic aerosol particles. In Stage 3 (decreasing dust aerosol concentration in the middle troposphere), the easterly wind clearly strengthened in the middle troposphere. Above this layer, the easterly wind weakened with height and formed uplifting airstreams, which coupled with the southerly airstream formed by the upper trough above Beijing. Furthermore, high-concentration aerosols were lifted to a certain height and could not spread to the upper atmosphere because of sinking airflow. In Stage 4 (removal of dust particles), the easterly wind reached the strength of low-level jet streams. The south-westerly wind was present above 2.5 km height. The high aerosol concentrations at the height of 2.0 km and below were lifted to the upper atmosphere and blown downstream by the strong south-westerly wind and the easterly wind coming from clean-ocean air masses, thereby concluding the dust particles' event. Image 1 • Topographic dynamic removal of airborne dust particles are revealed for the first time in Beijing. • Airborne dust particles could not penetrate the temperature inversion layer from high layer to low layer. • Easterly winds destroy the inversion temperature and dust aerosol mixes with anthropogenic aerosol near the surface layer. • Easterly wind strength approaches low-level jet streams and aerosols rise to the upper atmosphere. [ABSTRACT FROM AUTHOR]

"Flyby, orbit, land" has been the guiding philosophy of planetary exploration. This systematic approach has been highly successful in addressing the most fundamental questions of the origin, evolution, and habitability of the solar system. For the giant planets, entry probes take the place of "landers", since the "land" of the gas and icy giant planets, their solid core, lies some tens of thousands of kilometers beneath their cloud tops, hence impractical to reach. On the other hand, during a planet's accretionary heating phase the volatiles trapped in the core material would have been released, forming the atmosphere, together with the most volatile of the gases, hydrogen, helium and neon, that were captured gravitationally when the core became massive enough. Those atmospheric volatiles would thus be accessible by entry probes deployed to relatively shallow depths in the upper troposphere, allowing the determination of the abundances and isotopes of at least the most critical of the "heavy elements" (mass greater than helium). The heavy elements are key constraints to planetary formation and evolution models [1]. Entry probes are essential to retrieve their abundances, which are feasible only in situ at probe depths. That was the rationale behind NASA's 1995 Galileo probe mission at Jupiter and the Saturn Probe mission in NASA's New Frontier 4 candidate list of science themes. Saturn probe proposals to ESA's Cosmic Vision Program are similarly inspired. In 2015, NASA commissioned an Ice Giant Planets Study to recommend a comprehensive set of science goals and objectives, and further to develop potential mission architectures for accomplishing them in the 2023–2033 decade. The most highly rated mission from that study is an orbiter with probe to either Uranus or Neptune [2]. While remote sensing observations from the orbiter will yield the composition, structure and the distribution of neutral and charged particles in the magnetosphere and the upper atmosphere, the entry probe will determine the abundances and isotopic ratios of the noble gases (He, Ne, Ar, Kr, Xe), H, C, and possibly N and S. The noble gases, in particular, are key to discriminating among formation models, and their values from the probe entry location would represent global values as they are unaffected by meteorology, dynamics or chemistry. We will elaborate on these issues and then briefly discuss possible scenario/s for a mission to the icy giant planets, with particular focus on entry probes. • Heavy elements and isotopic ratios are key to giant planet formation models. • Noble gases provide the most robust constraints to models. • Only entry probes can make measurements of heavy elements and isotopes. • No new technology is required to enable an orbiter-probe mission to icy giants now. • Maturation of certain new technology would allow greater science return. [ABSTRACT FROM AUTHOR]

The development of a Ham-band Radio meteor Observation (HRO) Interferometer (IF) at Kochi University of Technology began in 2003. Meteor orbit calculation system uses multi-site radio observation with global positioning system (GPS) timing combined with 5 channel (5 ch) interferometer. The HRO-IF utilizes forward-scattering of 53.750 MHz continuous radio waves transmitted from the Sabae station, realized in 2012. Since the last development, the observation data has been used to study the upper atmosphere from the meteor phenomenon. Here, we introduce the results of the 2015 Geminid meteor shower recorded by forward-scatter multi-site observations as a low-cost and low-power 24/7 continuous meteor observation system, as well as the concept of a comprehensive radio meteor orbit calculation system. As a result, 20 examples of Geminid meteor shower events with 3 levels of noise signal classification recorded in our observations. The predicted Geminid meteor shower speed is about 34 ± 8.86 km/s based on the average value of 12 meteor shower data group in the minimum noise signal category (class A). • A system of forward scattering radar using 53.750 MHz radio wave is used to observe meteor shower over Shikoku island, Japan. • Speed and trajectory of peak Geminid meteor shower in 2015 were estimated based on the noise level classification. • Meteor observation with the forward scatter method provides an alternative inspiration for low-cost study of meteors. [ABSTRACT FROM AUTHOR]

Anthropogenic polluting substances, mainly CO 2 , affect the lower atmosphere where they excite the well-known greenhouse warming. However, they also affect the upper atmosphere (mesosphere, thermosphere and embedded ionosphere), where they cause long-term trends stronger than those in the troposphere. Calculations of long-term trends in the upper atmosphere suffer from various problems, which may be divided into three groups: (1) natural variability, (2) data problems, and (3) methodology. These problems have often been underestimated in trend calculations, which lead to controversial trend results. Here we briefly treat various problems of long-term trend calculations in the upper atmosphere and some ways how to deal with these problems are suggested. • Calculations of long-term trends in the upper atmosphere suffer from various problems. • Problems caused by natural variability, serious data problems and problems in methodology. • Some guidance is given how to minimize the impact of these problems. [ABSTRACT FROM AUTHOR]

Abstract The description of the cloud vertical structure remains the key source of uncertainty in climate studies. Based on the CloudSat dataset, the differences in cloud vertical structures between the active and break spells of the East Asian summer monsoon are analyzed by using the composite analysis method. During the active spell, more clouds appear, the occurrence frequency of single-layer clouds significantly decreases, and the occurrence frequency of clouds with two and more layers obviously increases. The lowest layer of the cloud is thicker than the higher layer during the active spell, while the highest layer of the cloud is thicker than the lower layer during the break spell. The clouds in the southern region of the study area are thicker than the clouds in the northern region during the active spell and thinner than the clouds in the northern region during the break spell. From the active spell to the break spell, the clouds became sparser in the southern region but more compact in the northern region. During the active spell, the cloudiness anomaly demonstrates an obvious northward-tilting structure from the upper atmosphere to the lower atmosphere because the large value center of high clouds is located in the south of the study area, while the middle and low-level clouds are located in the center of the study area. Both convective precipitation and stratiform precipitation occur in the southern region during the active spell, while the northern region is mainly dominated by convective precipitation. The cloud ice water content increases during the active spell and decreases during the break spell. During the active spell, the cloud liquid water content (LWC) increases in most of the study area, and the positive LWC anomaly exhibits an apparent northward-tilting structure from the upper level to the lower level. During the break spell, the LWC decreases in the northern region, and the negative anomaly tilts northward from the upper level to the lower level. However, the shallow convective clouds in the southern region are not completely suppressed during the break spell, and abundant positive LWC anomalies are observed in the lower troposphere. Highlights • An obvious vertical northward-tilting structure of cloud is found during the active spell. • From active to break spell, the clouds became sparser in the south but more compact in the north of East Asia. • The shallow convective clouds in the southern area are not completely suppressed during the break spell. [ABSTRACT FROM AUTHOR]

In order to detect the distribution of gravity waves in the middle and upper atmosphere, an all-sky airglow imaging spectrometer is designed to measure the airglow. It has the detection advantages of ultrawide field of view (FOV), large relative aperture and high signal-to-noise ratio (SNR). It can obtain the spectral images of OH (715–850 nm / 880–930 nm) and OI (630 nm) in the height range of 87–250 km. The whole design method of telecentric objective splicing relay zoom group is used to effectively suppress the spectral drift less than 0.2 nm, which meets the requirements of narrow bandwidth filters. The field experiments in northwest China show that the all-sky airglow imaging spectrometer can continuously acquire airglow spectral images with high SNR in both OH channel and OI channel without focusing in the temperature range of 0–45 ℃, and the images obtained in OH channel have obvious gravity wave phenomenon after star point removal and geometric correction. [ABSTRACT FROM AUTHOR]

New particle formation (NPF) is one main source of atmospheric aerosols and plays an important role in global climate by contributing up to two thirds of the atmospheric cloud condensation nuclei. Numerous studies on characteristics and mechanisms of near-surface NPF have been conducted in last decades. However, the characteristics of NPF around the top of the planetary boundary layer (PBL) remains unclear due to the limitations of vertical measurements. In this study, a tethered airship onboard with advanced particle instruments was deployed for directly measurement of the NPF exactly above and under the top of the PBL in the Yangtze River Delta (YRD) of eastern China in December 2017. Coupled with the real time ground Lidar observation, we successfully conducted measurement of aerosol size distribution, chemical components of aerosol and gas pollutants with 100 m above/under the top of the PBL. Despite not being observed within the PBL during the flight and at three ground sites in YRD, NPF event with the growth rate of 3.8 nm/h was detected above the PBL. High oxidizing capacity, enough condensable vapors and low condensation sink above the PBL favor the onset of NPF. Model simulation and the aerosol chemical composition result indicate the important role of gaseous sulfuric acid in NPF and its subsequent growth in the upper atmosphere. Our study highlights the potential mechanism of NPF above the PBL and the need of direct vertical measurements to better understand NPF in the atmosphere and its climate effect. • Tethered airship platform made it possible to understand subtle vertical structure. • Model forecast and online measurements can reduce the risk of experiment. • New particle formation was detected only above the planetary boundary layer. • The growth rate above the planetary boundary layer was about 3.8 nm/h. • High H 2 SO 4 values above planetary boundary layer favor the new particle formation. [ABSTRACT FROM AUTHOR]

This review article briefly brings out the historical development of atmospheric sodium (Na) measurements over India and the importance of coordinated measurements with multiple techniques to address physical processes in the Earth's upper atmosphere. These measurements were initiated in the early 1970s by observing Na airglow emission intensities with broad band airglow photometer from Mt. Abu, a low-latitude hill station in India. Considerable amount of night-to-night variations in nocturnal emission intensities of the Na airglow were observed. Later, investigations regarding the dependence with the magnetic activities from the equatorial and low latitudes were carried out and double-humped structures in the nocturnal variation of intensities were reported. With the advent of Na lidar at Gadanki around 2005, the measurements of atmospheric neutral Na atom concentration became possible and more frequent occurrences of sporadic Na layers over the magnetic low latitude station compared to other latitudes were detected indicating the role played by electrodynamics. Later, a possible relationship between E-region field aligned plasma irregularities and the concentration of neutral Na atoms was investigated using coordinated measurements of VHF radar and Na lidar. Further, simultaneous measurements with Na lidar and a narrow band airglow photometer with narrow field of view brought out the importance of coordinated observation wherein the characterization of gravity waves could be carried out and also revealed the importance of collisional quenching due to ambient molecules in the Na airglow emission processes. In addition, combining the ground based measurements of Na lidar and meteor wind radar along with satellite measurements made possible to hypothesize the over-turning Kelvin–Helmholtz billow in the Na layer manifests "C-type" or inverted lambda shape structures in the height-time-concentration map of neutral Na atoms. This review paper presents a synoptic view mostly based on the previously reported observations of Na airglow emission, Na lidar and coordinated Na airglow and Na lidar observations from the Indian sector and highlights the importance of simultaneous measurements of mesospheric Na and its emissions along with satellite-borne measurements to address interesting geophysical processes in the Earth's upper atmosphere. [ABSTRACT FROM AUTHOR]

Abstract We present the results of studying the behavior of temperature and of the atomic oxygen concentration in the mesopause region during the 2013 January major Sudden Stratospheric Warming (SSW). The data on the hydroxyl molecule OH(6-2), 834.0 nm emission intensity and rotational temperature were analyzed. These data were obtained through spectrometric measurements at the Geophysical Observatory of the Institute of Solar-Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences (51.8°N, 103.1°E, Tory), and at the Zvenigorod Station at the Obukhov Institute of Atmospheric Physics of the Russian Academy of Sciences (55.7°N, 36.8 E°). We calculated the concentration of atomic oxygen and its variations by using the data of the OH emission measurements. We revealed, that the response of the mesopause characteristics for two longitudinally spaced mid-latitude regions essentially differs. Thus, from the Tory Station data, the maximal increase in the OH emission intensity (by a factor of ∼2) and in the concentration [O] (by a factor of ∼3) occurred during the sudden stratospheric warming (SSW) evolution, whereas, from the Zvenigorod Station data, the OH emission intensity increase (by a factor of ∼3) and the concentration [O] increase (by a factor of ∼3.5) was observed at the SSW recovery phase. As a result of numerical modeling using the Middle and Upper Atmosphere Model (MUAM), it was shown, that the cause for the revealed effect may probably be longitudinal differences in the diurnal variation in the vertical wind at the mesopause heights over the indicated stations during the SSW. One may elucidate these differences through the generation of non-migrating tides due to a non-linear interaction between the intensified stationary planetary wave 1 (SPW1) and migrating tides and forcing a set of high-frequency PWs at the stratospheric heights. All these waves are capably of propagating into the MLT region and produce observed changes in behavior of the OH emission intensity, temperature and atomic oxygen concentration over Tory and Zvenigorod. Highlights • Effects of 2013 SSW on the MLT for two longitudinally spaced mid-latitude sites are investigated. • Longitudinal differences in the behavior of the mesopause temperature and composition were found. • It may be caused by longitudinal differences in the diurnal variation of vertical wind. [ABSTRACT FROM AUTHOR]

Venus is the closest and most similar planet to Earth in the whole solar system, yet, basic measurements are missing. The atmospheric composition has been studied to some extent with the Pioneer Venus Orbiter mission and the more recent Venus Express, however, the concentration of many species and their isotopic ratios are not yet known with satisfying accuracy. Especially when it comes to the heavy noble gases as Kr and Xe, there is little to no collected data in this field. These elements form a key link to the reconstruction of the atmospheric evolution, which would deliver crucial information on the formation of Earth-like bodies. Knowing the abundances of the noble gases may allow us to answer the question why Venus did not evolve to a potentially habitable planet like its neighbour Earth. This paper presents a meta-study of existing observations of Venus' upper atmosphere and exosphere and an exospheric model of the thermal and hot atmosphere of Venus above the homopause. Mass spectra for possible future Venus missions are predicted, as for example the EnVision mission of ESA. The main focus are the heavy noble gases and requirements for the trajectories are proposed. In addition, mass spectra and recommended integration times for the Venus flyby of ESA's JUICE mission are derived. • Kr and Xe can be measured in Venus' atmosphere during an aerobraking operation. • Xenon is detectable in Venus' atmosphere with a 1 s integration below 123 km. • Krypton is detectable in Venus' atmosphere with a 1 s integration below 135 km. [ABSTRACT FROM AUTHOR]