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Using the High attitude Interferometer WIND observation balloon and Antarctic Jang Bogo station high latitude conjugate observations of the thermospheric winds we investigate the seasonal and hemispheric differences between the northern and southern hemispheres in June 2018. We found that the summer (northern) hemisphere dayside meridional winds have a double‐hump feature, whereas in the winter (southern) hemisphere the dayside meridional winds have a single hump feature. We attribute that to stronger summer, perhaps, northern hemisphere cusp heating. We also compared the observation with NCAR Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) model. The TIEGCM reproduced the double‐hump feature because of added cusp heating. The summer hemisphere has stronger anti‐sunward winds. This is the first time we have very high latitude conjugate thermospheric wind observations. Plain Language Summary: Using balloon instrument in the northern hemisphere and ground based instrument in the southern hemisphere, we study the conjugacy of the thermospheric winds of high latitudes. We found that the more summer hemispheric heating alters the thermospheric winds and resulted in a double‐hump feature on the dayside meridional winds. We also used model with cusp heating to simulate the winds and were able to reproduce the double‐hump feature. Key Points: The stronger summer (northern) hemispheric power could be the cause of double hump in the dayside meridional windsThermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) was able to reproduce the double‐hump features seen by the High attitude Interferometer WIND observation, and single hump in the winter hemisphere observed at Jang Bogo stationTIEGCM overestimates the poleward wind on the dayside and equatorward wind on the nightside in the summer hemisphere [ABSTRACT FROM AUTHOR]

The state and variations of the Ionosphere‐Thermosphere (I‐T) system are strongly influenced by dynamical processes, with these effects being amplified during intense space environment disturbances such as geomagnetic storms, producing multi‐scale disturbance features in the I‐T system. The redistribution of energy and momentum through the dynamical processes is currently not well understood. Unfortunately, the dearth of thermospheric observations has yielded limited studies capable of monitoring and analyzing the I‐T dynamical coupling during storms using co‐located measurements. This work examines the responses of the I‐T system during the April 2023 geomagnetic storm based on high‐resolution continuous I‐T system observations at Mohe observatory, a middle latitude station. Both large‐scale features and short‐period oscillations were identified in multiple key parameters of the I‐T system. Similar disturbed patterns in thermospheric winds occurred during the main and recovery phases of the geomagnetic storm. However, the oscillation features in many parameters of the I‐T system are only observed during the main phase. The results of concurrent I‐T system observations unveil the oscillation features of thermospheric winds, temperatures, the ionospheric F2 peak height, electron density, and total electron content. These findings reveal the important influence of wind divergence on thermospheric temperature disturbances and its modulatory effect on ionospheric disturbances. Plain Language Summary: The upper atmosphere is partially ionized to form the ionosphere (I), and the neutral component of the background is known as the thermosphere (T), constituting the I‐T system. The state and variations of the I‐T system are strongly influenced by dynamical processes, especially during intense space weather events like geomagnetic storms. Investigating the response features of the I‐T system during geomagnetic storms would enhance our understanding of the mechanisms and impacts of dynamical processes. However, due to the limited thermospheric observation, most studies are unable to concurrently address the conditions of both the thermosphere and ionosphere, resulting in a nebulous understanding of the involved dynamical processes. Thus, this study investigates the responses of the I‐T system during the April 2023 geomagnetic storm by utilizing high‐resolution, continuous I‐T system observations obtained from the Mohe observatory. The observations identified disturbances on different space‐time scales in the I‐T system and unveiled the correlation between thermospheric wind, temperature, ionospheric peak height, electron density, and total electron content disturbances, revealing the crucial role of thermospheric wind in linking thermosphere and ionosphere disturbances through dynamical processes. Key Points: The multi‐scale ionospheric/thermospheric disturbances during geomagnetic storms were monitored by the co‐located observationsThe adiabatic compression process of the horizontal wind is an important factor for the traveling thermospheric temperature disturbanceIn addition to variation of ionospheric altitude caused by the meridional wind, the divergence of wind also modulates the amplitude of traveling ionospheric disturbancess [ABSTRACT FROM AUTHOR]

Abstract In this study, the neutral wind observations from the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument onboard Ionospheric CONnections (ICON) are used to investigate the longitudinal structure of zonal wind between 100 and 300 km during daytime. The four-peaked structure in the longitudinal distribution between June and August is visually clear in the whole altitudinal range. The longitudinal wavenumber 1–4 patterns (WN1–WN4) are extracted, and the altitude–month distributions of WN1–WN4 and their contributions to the longitudinal structure are compared. The amplitudes of WN3 and WN4 show seasonal dependence, and the amplitude of WN4 exhibits obvious vertical propagation from the mesosphere and lower thermosphere (MLT) to the upper thermosphere in summer and autumn. WN1 is an important contributor to the longitudinal structure, WN4 is the primary contributor in the lower altitude ranges in summer and autumn at three latitudes. The contributions of WN3 (WN1) increase holistically with latitude in summer (spring, autumn, and winter). And the main wave sources of WN1–WN4 are further investigated in the 100–106 km and 210–300 km altitude regions. The main wave sources of WN1 and WN2 have complex variations with altitude, latitude, and season, while WN3 (WN4) is clearly influenced by DE2 (DE3 and SE2). Graphical Abstract

Thermospheric wind observations from high to mid latitudes are compared with the newly developed Multiscale Atmosphere Geospace Environment (MAGE) model for the Nov 3–4 geomagnetic storm. The observation and simulation comparison shows a very good agreement and is better at high latitudes in general. We were able to identify a thermospheric poleward wind reduction possibly linked to a northward turning of the Interplanetary Magnetic Field (IMF) at ~22 UT on Nov 3 and an enhancement of the poleward wind to a southward turning near 10 UT on Nov 4 at high latitudes. An IMF southward turning may have led to an enhancement of equatorward winds at Boulder, Colorado near midnight. Simultaneous occurrence of aurora may be associated with an IMF By turning negative. The MAGE model wind simulations are consistent with observations in these cases. The results show the model can be a very useful tool to further study the magnetosphere and ionosphere coupling on short time scales.

In this study, the neutral wind observations from the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument onboard Ionospheric CONnections (ICON) are used to investigate the longitudinal structure of zonal wind between 100 and 300 km during daytime. The four-peaked structure in the longitudinal distribution between June and August is visually clear in the whole altitudinal range. The longitudinal wavenumber 1–4 patterns (WN1–WN4) are extracted, and the altitude–month distributions of WN1–WN4 and their contributions to the longitudinal structure are compared. The amplitudes of WN3 and WN4 show seasonal dependence, and the amplitude of WN4 exhibits obvious vertical propagation from the mesosphere and lower thermosphere (MLT) to the upper thermosphere in summer and autumn. WN1 is an important contributor to the longitudinal structure, WN4 is the primary contributor in the lower altitude ranges in summer and autumn at three latitudes. The contributions of WN3 (WN1) increase holistically with latitude in summer (spring, autumn, and winter). And the main wave sources of WN1–WN4 are further investigated in the 100–106 km and 210–300 km altitude regions. The main wave sources of WN1 and WN2 have complex variations with altitude, latitude, and season, while WN3 (WN4) is clearly influenced by DE2 (DE3 and SE2). [ABSTRACT FROM AUTHOR]

The design, principles of operation, calibration, and data analysis approaches of the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) on the NASA Ionospheric Connection (ICON) satellite have been documented prior to the ICON launch. Here we update and expand on the MIGHTI wind data analysis and discuss the on-orbit instrument performance. In particular, we show typical raw data and we describe key processing steps, including the correction of a "signal-intensity dependent phase shift," which is necessitated by unexpected detector behavior. We describe a new zero-wind calibration approach that is preferred over the originally planned approach due to its higher precision. Similar to the original approach, the new approach is independent of any a priori data. A detailed update on the wind uncertainties is provided and compared to the mission requirements, showing that MIGHTI has met the ICON mission requirements. While MIGHTI observations are not required to produce absolute airglow brightness profiles, we describe a relative brightness profile product, which is included in the published data. We briefly review the spatial resolution of the MIGHTI wind data in addition to the data coverage and data gaps that occurred during the nominal mission. Finally, we include comparisons of the MIGHTI wind data with ground-based Fabry-Perot interferometer observations and meteor radar observations, updating previous studies with more recent data, again showing good agreement. The data processing steps covered in this work and all the derived wind data correspond to the MIGHTI data release Version 5 (v05). [ABSTRACT FROM AUTHOR]

We analyze horizontal plasma drifts measured by the Defense Meteorological Satellite Program satellites during two intense magnetic storms. It is found, for the first time, that westward plasma flows associated with subauroral polarization streams (SAPS) in the dusk‐evening sector penetrate continuously to equatorial latitudes. The westward ion drifts between subauroral and equatorial latitudes occur nearly simultaneously. The latitudinal profile of the westward ion drifts at low latitudes (approximately within ±30° magnetic latitude [MLat]) is relatively flat, and the westward ion drifts at the magnetic equator reach 200–300 m s−1. In the dawn‐morning sector, eastward ion drifts at subauroral latitudes are also SAPS. The storm‐time dawnside auroral boundary moves to ∼±55° MLat, and the dawnside SAPS penetrate to ∼±20° MLat at 0930 local time. A dawnside SAPS flow channel appears to exist, although it is not as well defined as the duskside SAPS flow channel. Thermospheric wind data measured by the Challenging Minisatellite Payload satellite are analyzed, and zonal disturbance winds are derived. Disturbance winds can reach equatorial latitudes rapidly near midnight but are limited to ±40° geographic latitude or higher near noon. The effects of disturbance winds on the zonal ion drifts at middle and low latitudes are discussed. It is suggested that both the westward ion drifts at middle and low latitudes in the dusk‐evening sector and the eastward ion drifts at middle and lower latitudes in the dawn‐morning sector are caused primarily by penetration of the SAPS and auroral electric fields. Key Points: Horizontal ion drifts from auroral to equatorial latitudes and thermospheric winds are analyzed during two intense magnetic stormsPenetration of westward plasma flows of subauroral polarization streams to equatorial latitudes near dusk is identified for the first timePenetration of auroral and subauroral electric fields to low latitudes near dawn is identified for the first time [ABSTRACT FROM AUTHOR]

The Satellite for Orbital Aerodynamics Research (SOAR) is a CubeSat mission, due to be launched in 2021, to investigate the interaction between different materials and the atmospheric flow regime in very low Earth orbits (VLEO). Improving knowledge of the gas–surface interactions at these altitudes and identification of novel materials that can minimise drag or improve aerodynamic control are important for the design of future spacecraft that can operate in lower altitude orbits. Such satellites may be smaller and cheaper to develop or can provide improved Earth observation data or communications link-budgets and latency. In order to achieve these objectives, SOAR features two payloads: (i) a set of steerable fins which provide the ability to expose different materials or surface finishes to the oncoming flow with varying angle of incidence whilst also providing variable geometry to investigate aerostability and aerodynamic control; and (ii) an ion and neutral mass spectrometer with time-of-flight capability which enables accurate measurement of the in-situ flow composition, density, velocity. Using precise orbit and attitude determination information and the measured atmospheric flow characteristics the forces and torques experienced by the satellite in orbit can be studied and estimates of the aerodynamic coefficients calculated. This paper presents the scientific concept and design of the SOAR mission. The methodology for recovery of the aerodynamic coefficients from the measured orbit, attitude, and in-situ atmospheric data using a least-squares orbit determination and free-parameter fitting process is described and the experimental uncertainty of the resolved aerodynamic coefficients is estimated. The presented results indicate that the combination of the satellite design and experimental methodology are capable of clearly illustrating the variation of drag and lift coefficient for differing surface incidence angle. The lowest uncertainties for the drag coefficient measurement are found at approximately 300 km, whilst the measurement of lift coefficient improves for reducing orbital altitude to 200 km. • The design of the experimental CubeSat SOAR (Satellite for Orbital Aerodynamics) is presented. • SOAR is due to be launched in early 2021 to the ISS and subsequently deployed into orbit. • The mission will perform the aerodynamic characterisation of materials in very low Earth orbit (VLEO). • The aim is to improve understanding of the fundamental gas–surface interactions in the VLEO environment. • Materials able to reduce aerodynamic drag and improve aerodynamics-based control will be tested. [ABSTRACT FROM AUTHOR]

HIWIND (High altitude Interferometer WIND experiment) is a balloon‐borne Fabry Perot interferometer for daytime thermospheric wind observations. In this paper, we examine the summer polar cap thermospheric winds observed by HIWIND with the RISR‐C (Resolute Incoherent Scatter Radar‐Canada) observed ion drifts and electron densities. We also perform National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model simulations to compare with the HIWIND and RISR‐C observations. The standard Thermosphere Ionosphere Electrodynamics General Circulation Model underestimates the high‐latitude electron density and overestimates the thermospheric winds. The discrepancies between modeled and observed meridional winds are large near midnight and noon. After increasing the energy flux in the polar cap drizzle, the simulated electron density is comparable with the RISR‐C observations. However, large discrepancies with the HIWIND‐observed thermospheric winds persist. The cause of the model versus observation discrepancy in winds is probably due to the processes outside the polar cap. Key Points: HIWIND made first polar cap daytime thermospheric wind observationNormal TIEGCM underestimates the polar electron density and overestimates thermospheric windsHIWIND observed slightly equatorwind near the local noon [ABSTRACT FROM AUTHOR]

The CHAMP and GOCE satellites provided high-resolution thermosphere data between 2000 and 2013, improving our knowledge of atmosphere dynamics in the thermosphere-ionosphere region. However, the currently available data sets contain inconsistencies with each other and with external data sets and models, arising to a large extent from errors in the modelling of aerodynamic forces. Improved processing of the wind data for the two satellites would benefit the further development and validation of thermosphere models and improve current understanding of atmospheric dynamics and long-term trends. The first step to remove inconsistencies has been the development of high-fidelity models of the satellite surface geometry. Next, an improved characterization of the collisions between atmospheric particles and satellite surfaces is necessary. In this article, the effect of varying the energy accommodation coefficient, which is a key parameter for describing gas-surface interactions (GSI) is investigated. For past versions of the thermosphere density and wind data from these satellites a value of the energy accommodation coefficient of α E = 0.93 was selected. The satellite accelerometer measurements, from which the thermospheric data are derived, have now been reprocessed using high-fidelity geometries and a wide range of α E values. Lowering the α E value used in the processing leads to an increase in the lift over drag ratio for those satellite panels that are inclined to the flow. This changes the direction of the modelled acceleration, and therefore the interpretation of the measured acceleration in terms of wind. The wrong choice of α E therefore leads to the introduction of satellite attitude-dependent wind errors. For the CHAMP and GOCE satellites, we have found that values of the energy accommodation coefficient significantly lower than 0.93 (0.85 for CHAMP and 0.82 for GOCE) result in increased consistency of the wind data. A comparison between the two missions and an overview of the influence on the results of filtering for solar activity and seasonal and diurnal variations is presented. [ABSTRACT FROM AUTHOR]

Thermospheric zonal winds at altitudes of 140 to 250 km are shown to reverse from eastward to strong westward between 100° and 200° in geographic longitude and 60°S to 70°S latitude in the Southern Hemisphere. The reversal also occurs at the same latitude in the Northern Hemisphere, but from 200° to 340° longitude. The phenomenon has been previously described as a "wind wall." Observations by the Wind Imaging Interferometer (WINDII) on the National Aeronautics and Space Administration's Upper Atmosphere Research Satellite (UARS) and simulations by the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X) are utilized to explore the characteristics of what has been called a wind wall. In order to study the dependence on solar radio flux and geomagnetic activity, the relationships of the maximum zonal wind and F10.7 (the solar radio flux at 10.7 cm) and ap indices are investigated. The results show that WINDII observations and WACCM‐X simulations agree well in describing this wind signature. Moreover, the appearance of the wind wall is found to have a strong dependence on the solar radio flux and geomagnetic activity. In addition, WINDII winds have a stronger response to geomagnetic activity than WACCM‐X winds. Key Points: There are strong westward winds at 140 to 250 km altitude between 100° to 200° longitude and 60° to 70° southern latitudeWINDII observations and WACCM‐X simulations agree well in describing the high‐latitude windThe strong zonal westward wind magnitude depends on the solar radio flux and geomagnetic activity [ABSTRACT FROM AUTHOR]

Daytime thermospheric winds observed by the balloon‐borne instrument HIWIND (High‐altitude Interferometer WIND experiment) during two flights in June 2011 and 2018 from Kiruna (68°N, 20°E), along with simultaneous European Incoherent SCATter radar ion drift data, are analyzed. National Center for Atmospheric Research TIEGCM (Thermosphere Ionosphere Electrodynamics General Circulation Model) simulations for both flights are compared with observations. The observed thermospheric winds from the two flights have many similarities. HIWIND‐observed thermospheric winds tend to be equatorward during the morning hours before noon and close to zero in the afternoon. In contrast, TIEGCM predicts poleward winds before noon and near zero in the afternoon. Southward interplanetary magnetic field Bz, occurring as the balloon passed through morning, was associated with greater equatorward meridional winds. The TIEGCM‐simulated zonal winds have large differences with observations under more active conditions. The second HIWIND flight confirms some important results from the first flight and further shows thermospheric wind variations under different interplanetary magnetic field conditions. HIWIND observations in general provide invaluable data for model validation and highlight deficiencies in current high‐latitude simulations. Key Points: HIWIND‐observed thermospheric winds tend to be equatorward during the morning hoursSouthward IMF Bz leads to more equatorward meridional winds in the morningTIEGCM runs predict poleward winds in the morning [ABSTRACT FROM AUTHOR]

Abstract Thermospheric wind measurements obtained from linear non-gravitational accelerations of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite show discrepancies when compared to ground-based measurements. In this paper the cross-wind is derived from both the linear and the angular accelerations using a newly developed iterative algorithm. The two resulting data sets are compared to test the validity of wind derived from angular accelerations and quantify the uncertainty in accelerometer-derived wind data. In general the difference is found to be less than 50 m/s vertically after high-pass filtering, and 100 m/s horizontally. A sensitivity analysis reveals that continuous thrusting is a major source of uncertainty in the torque-derived wind, as are the magnetic properties of the satellite. The energy accommodation coefficient is identified as a particularly promising parameter for improving the consistency of thermospheric cross-wind data sets in the future. The algorithm may be applied to obtain density and cross-wind from other satellite missions that lack accelerometer data, provided the attitude and orbit are known with sufficient accuracy. [ABSTRACT FROM AUTHOR]

The generation of a large-scale wave in the upper atmosphere caused by a solar eclipse was first predicted in the 1970s, but the experimental evidence remains sparse and comprises mostly indirect observations. This study presents observations of the wind component of a large-scale thermospheric wave generated by the 21 August 2017 total solar eclipse. In contrast with previous studies, the observations are made on the nightside, after the eclipse ended. A ground-based interferometer located in northeastern Brazil is used to monitor the Doppler shift of the 630.0-nm airglow emission, providing direct measurements of the wind and temperature in the thermosphere, where eclipse effects are expected to be the largest. A disturbance is seen in the zonal and meridional wind which is at or above the 90% significance level based on the measured 30-day variability. These observations are compared with a first principles numerical model calculation from the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model, which predicted the propagation of a large-scale wave well into the nightside. The modeled disturbance matches well the difference between the wind measurements and the 30-day median, though the measured perturbation (∼60 m/s) is larger than the prediction (38 m/s) for the meridional wind. No clear evidence for the wave is seen in the temperature data, however. [ABSTRACT FROM AUTHOR]

In situ measurements of the thermospheric wind can be obtained by observing the attitude response of an aerostable spacecraft. In the proposed method, the aerostable spacecraft is left uncontrolled, freely reacting to the aerodynamic torques, and oscillating around its equilibrium attitude. The wind’s magnitude and direction is determined by combining the attitude observations with estimates of the other perturbing torques, atmospheric density, and spacecraft’s aerodynamic properties. The spatial resolution of the measurements is proportional to the natural frequency of the attitude’s oscillation. Spacecraft with high aerodynamic stiffness to inertia ratios operating at low altitudes exhibit higher natural frequencies, making them particularly suited for this method. A one degree-of-freedom case is used to present and illustrate the proposed method as well as to analyze its performance. [ABSTRACT FROM AUTHOR]

Abstract: The relationship between high‐latitude ionospheric currents (Hall current and field‐aligned current) and thermospheric wind is investigated. The 2‐D patterns of horizontal wind and equivalent current in the Northern Hemisphere derived from the CHAMP satellite are considered for the first time simultaneously. The equivalent currents show strong dependences on both interplanetary magnetic field (IMF) By and Bz components. However, IMF By orientation is more important in controlling the wind velocity patterns. The duskside wind vortex as well as the antisunward wind in the morning polar cap is more evident for positive By. To better understand their spatial relation in different sectors, a systematic superposed epoch analysis is applied. Our results show that in the dusk sector, the vectors of the zonal wind and equivalent current are anticorrelated, and both of them form a vortical flow pattern for different activity levels. The currents and zonal wind are intensified with the increase of merging electric field. However, on the dawnside, where the relation is less clear, antisunward zonal winds dominate. Plasma drift seems to play a less important role for the wind than neutral forces in this sector. In the noon sector, the best anticorrelation between equivalent current and wind is observed for a positive IMF By component and it is less obvious for negative By. A clear seasonal effect with current intensities increasing from winter to summer is observed in the noon sector. Different from the currents, the zonal wind intensity shows little dependence on seasons. Our results indicate that the plasma drift and the neutral forces are of comparable influence on the zonal wind at CHAMP altitude in the noon sector. [ABSTRACT FROM AUTHOR]

Ground-based measurements of thermospheric wind and temperature are known to be affected by tropospheric scattering during geomagnetically active times, when horizontal airglow gradients are large. In this work, we present an analysis of the effects during quiet times, when horizontal airglow gradients can be assumed to be negligible, and we derive corrections to be applied to historical and future data sets. These corrections are easy to apply, depending only upon the optical thickness of the atmosphere and the measured wind, not the viewing direction or temperature. If these corrections are not applied, all winds estimated from ground-based observatories are underestimated by about 10% (depending on the optical thickness), and temperatures are overestimated by a couple K. We present observational evidence of the effect of atmospheric scattering on temperature measurements using 5 years of data from the North American Thermosphere Ionosphere Observing Network. We find that the temperatures measured to the east and west are statistically larger than the temperatures measured to the zenith. This is consistent with our analysis of the effect of atmospheric scattering, though the difference in the measurements is slightly larger than the theoretical prediction. [ABSTRACT FROM AUTHOR]

The Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument was built for launch and operation on the NASA Ionospheric Connection Explorer (ICON) mission. The instrument was designed to measure thermospheric horizontal wind velocity profiles and thermospheric temperature in altitude regions between 90 km and 300 km, during day and night. For the wind measurements it uses two perpendicular fields of view pointed at the Earth's limb, observing the Doppler shift of the atomic oxygen red and green lines at 630.0 nm and 557.7 nm wavelength. The wavelength shift is measured using field-widened, temperature compensated Doppler Asymmetric Spatial Heterodyne (DASH) spectrometers, employing low order échelle gratings operating at two different orders for the different atmospheric lines. The temperature measurement is accomplished by a multichannel photometric measurement of the spectral shape of the molecular oxygen A-band around 762 nm wavelength. For each field of view, the signals of the two oxygen lines and the A-band are detected on different regions of a single, cooled, frame transfer charge coupled device (CCD) detector. On-board calibration sources are used to periodically quantify thermal drifts, simultaneously with observing the atmosphere. The MIGHTI requirements, the resulting instrument design and the calibration are described. [ABSTRACT FROM AUTHOR]

Ground-based Fabry-Perot interferometers routinely observe large vertical winds in the thermosphere, sometimes reaching over 100 m/s. These observations, which use the Doppler shift of the 630.0 nm airglow emission to estimate the wind, have long been at odds with theory. We present a summary of 5 years of data from the North American Thermosphere-Ionosphere Observing Network, showing that large apparent vertical winds are a persistent feature at midlatitudes during geomagnetic storms. We develop a radiative transfer model which demonstrates that these measurements can be explained as an artifact of the scattering of light in the troposphere. In addition to the example from midlatitudes, we apply the model to low latitudes, where we show that the postsunset vertical winds routinely measured over Brazil are explained in part by atmospheric scattering. Measurements of the horizontal wind and temperature are also affected, with errors reaching 400 m/s and 200 K in the most extreme cases. [ABSTRACT FROM AUTHOR]

The solar-wind magnetosphere interaction primarily occurs at altitudes where the dipole component of Earth's magnetic field is dominating. The disturbances that are created in this interaction propagate along magnetic field lines and interact with the ionosphere-thermosphere system. At ionospheric altitudes, the Earth's field deviates significantly from a dipole. North-South asymmetries in the magnetic field imply that the magnetosphere-ionosphere-thermosphere (M-I-T) coupling is different in the two hemispheres. In this paper we review the primary differences in the magnetic field at polar latitudes, and the consequences that these have for the M-I-T coupling. We focus on two interhemispheric differences which are thought to have the strongest effects: 1) A difference in the offset between magnetic and geographic poles in the Northern and Southern Hemispheres, and 2) differences in the magnetic field strength at magnetically conjugate regions. These asymmetries lead to differences in plasma convection, neutral winds, total electron content, ion outflow, ionospheric currents and auroral precipitation. [ABSTRACT FROM AUTHOR]

This study shows the horizontal structure of climatology of thermospheric nocturnal winds at a height of approximately 250 km in the Asia-Oceania region for the first time using observations made with Fabry-Perot interferometers (FPIs; optical wavelength of 630.0 nm). The FPIs used in this study were located at Shigaraki (Japan, 34.8°N, 136.1°E), Chiang Mai (Thailand, 18.8°N, 98.9°E), Kototabang (Indonesia, 0.2°S, 100.3°E), and Darwin (Australia, 12.4°S, 131.0°E). The observation data underwent quality control that involved consideration of cloud information, wind speed value, and standard deviation of results obtained from synchronous fringe images; approximately 30 % of the observation data from all the four stations were deemed suitable for use. The nocturnal diurnal changes at Shigaraki according to the local solar time were generally consistent with changes in China at similar latitudes, although the amplitudes were slightly different. All four stations showed the continuous flow pattern of the nocturnal diurnal wind in each season. The Chiang Mai and Darwin stations observed seasonal/diurnal changes similar to those observed by stations at similar latitudes on the North and the South American continents. Although there were fewer samples for Chiang Mai, Kototabang, and Darwin in the rainy season compared to that for Shigaraki, the seasonal climatology reported here can be used to provide a background long-term average status for describing anomalous events and extremes having different causes. [ABSTRACT FROM AUTHOR]

A tiny and low-cost ground-based Fabry-Perot interferometer (FPI) was designed using a filter behind etalon and Galilean telescope system for the thermospheric wind observation with OI 630.0 nm nightglow emissions (~250 km). Based on the instrument, experiments were carried out at Langfang (39.40° N, 116.65° E) site for a rough comparison and Kelan (38.71° N, 111.58° E) site for a detailed validation. Wind results of Langfang experiment are well consistent with measurements of two other FPIs deployed at Xinglong (40.40° N, 117.59° E) and Kelan which are retrieved by the American National Center for Atmospheric Research (A-NCAR). In Kelan experiment, the averaged wind deviation between our FPI and A-NCAR FPI is 11.8 m/s. The averaged deviation of wind measurement error between them is 2.9 m/s. The comparisons suggest good agreement. Then, the analysis of influencing factors was made. The center determination offset has an exponential relation with wind deviation, while the radius calculation offset is linear with wind deviation. [ABSTRACT FROM AUTHOR]

Based on measurements of ground-based GPS station network, differences of the mid-latitude ionospheric TEC in the east and west sides of North America, South America and Oceania have been analyzed in this paper. Results show that for nearly all seasons from 2001 to 2010 and in both sides of the longitudes with zero declination, there exist systematic differences for the mid-latitude ionospheric TEC in the regions mentioned above and the features of these differences markedly depend upon the local time but less depend upon seasons and the level of solar activity. Theory analysis shows that the longitude variations of both declination and zonal thermospheric winds are one of important factors to cause differences of the mid-latitude ionospheric TEC in both sides of the longitudes with zero declination. [ABSTRACT FROM AUTHOR]

Highlights: [•] Weak and short-lived positive deviations were observed during the storm in summer. [•] Strong and long-lived negative trends were observed in the summer storm. [•] Asymmetrical variation of VTEC was observed during the storms in the two equinoctial months. [•] The winter and autumn equinox storms were dominated by positive deviation of VTEC. [Copyright &y& Elsevier]

Previously, we studied the ionospheric effects of the sequence of geomagnetic storms on September 9-14, 2005 using a global self-consistent model 'Thermosphere-Ionosphere-Protonosphere' (GSM TIP). Differences between the predicted and observed effects of the ionospheric storms may be due to the use of the three-hour K index of geomagnetic activity in modeling the time dependence of model input parameters, use of the dipole approximation of the geomagnetic field, and disregard in simulations for solar flares that occurred during this period. We tried to eliminate two of these three reasons. First, we used the A index of geomagnetic activity with minute resolution in modeling the time dependence of the model input parameters. Second, we took into account the effects of solar flares. In addition, GSM TIP model was supplemented by an empirical model describing the precipitation of high-energy electrons. The results of the simulation of the behavior of various ionospheric parameters over the Yakutsk, Irkutsk, Millstone Hill, and Arecibo stations on September 9 and 10, 2005 in the new formulation of the problem, presented in the current work, are in better agreement with the available experimental data than the results of previous calculations. [ABSTRACT FROM AUTHOR]

The thermospheric crosswind velocities at an altitude of 400 km measured by an accelerometer on board of the CHAMP satellite are compared with the results of model calculations performed using the Upper Atmosphere Model (UAM). The results of measurements averaged over the year in 2003 reveal a two-vortex structure of high-latitude winds corresponding to magnetospheric-ionospheric convection of ions in the F2 ionosphere region. A similar picture with similar speed values was obtained in model calculations. A comparison of the crosswind speed obtained in individual measurements on October 28, 2003 with the corresponding model values revealed close agreement between them in some flights and differences in others. Taking into account the dependence of convection electric field on the B component of interplanetary magnetic field sometimes improved agreement between thermospheric crosswind speeds obtained in model calculations and measured using the satellite. [ABSTRACT FROM AUTHOR]

Abstract: The thermospheric neutral wind and ionospheric layer conductance at latitudes higher than 45° (provided from empirical models), as well as the conductivities caused by solar irradiation (deduced from model parameters: neutral temperature, concentration and electron density) are used to calculate the distribution of the electrostatic potential, current and electric field between geomagnetic latitude ±72° and 0–24h MLT in terms of the ionospheric current continuity equation, on June- and December-solstices during strong storms. The driving electric field across the polar cap and the region 2 field-aligned current, caused by the magnetospheric coupling, are taken into account in the calculation. The results represent the complexities and varieties about the coupling between disturbances of the magnetosphere, the thermospheric wind and the distribution of ionospheric conductance. The penetration of disturbed currents from the auroral zone to mid- and low-latitude area is often asymmetrical between the southern and northern hemispheres. Both the intensification of the eastward equatorial electrojet on the day side at the beginning of a storm, and later, the appearance of the westward equatorjet after noon, can be found frequently during storm periods. In the moderate high latitude areas the existence of a eastward electric field in the midnight-dawn region is an expected mechanism, which can be used to explain phenomena found many times in our previous works, due to its E × B upper-ward drift effect. [Copyright &y& Elsevier]

During the American solar eclipse on 21 August 2017, the GNSS network was applied to record the ionospheric responses. Following the lunar shadow, the TEC depletion emerged over the eclipse path. After the eclipse end, the depletion in the north gradually disappeared and then the TEC enhancement emerged. The depletion in the south has continued for a long time. A sharp area between the enhancement and depletion regions appeared at 27°N latitude. Moreover, the depletion region were moving to south with larger and larger TEC decline after the eclipse maximum. The TEC over four selected places with same latitude and different eclipse obscurations is presented. Interestingly, the recovery periods of these TEC values are similar. The f o F2 and h m F2 in the enhancement and depletion regions displayed very different variation tendency. The eclipse-induced thermospheric winds are considered to further reduce the TEC after the eclipse. The formation of the sharp area in TEC may be related to the fountain effect. • The eclipse-induced depletion was moving to south with larger and larger TEC depletion after eclipse maximum. • A sharp area between the enhancement and depletion regions appeared at the latitude of 27° N. • The fountain effect and eclipse induced thermospheric winds may play an important role for the rare phenomena. [ABSTRACT FROM AUTHOR]