The dawn−dusk asymmetry in mesosphere and lower thermosphere temperature disturbances during geomagnetic storms at high latitude

Utilizing observations by the Sounding of the Atmosphere using Broadband Emission Radiometry(SABER)instrument,we quantitatively assessed the dawn-dusk asymmetry in temperature disturbances within the high-latitude mesosphere and lower thermosphere(MLT)during the main phase of geomagnetic storms in this study.An analysis of five geomagnetic superstorm events indicated that during the main phase,negative temperature disturbances were more prevalent on the dawn side than on the dusk side in the high-latitude MLT region.Results of a statistical analysis of 54 geomagnetic storm events also revealed a notable disparity in temperature disturbances between the dawn and dusk sides.At high latitudes,38.2%of the observational points on the dawn side exhibited negative temperature disturbances(less than−5 K),whereas on the dusk side,this percentage was only 29.5%.In contrast,at mid-latitudes,these proportions were 34.1%and 36.5%,respectively,showing no significant difference.We also conducted a statistical analysis of temperature disturbances at different altitudes,which revealed an increase in the proportion of warming disturbances with altitude.Conversely,the proportion of cooling disturbances initially rose with altitude,reaching a peak around 105 km,and subsequently decreased.These temperature disturbance differences could be explained by the day-night asymmetry in vertical wind disturbances during storm conditions.

Interhemispheric and longitudinal differences in the ionosphere-thermosphere coupling process during the May 2024 superstorm

Geomagnetic storm events have a strong influence on the ionosphere–thermosphere(I-T)coupling system.Analyzing the regional response process of the I-T system and its differences across the northern and southern hemispheres is an important but challenging task.In this study,we used a combination of multiple observations and a model simulation to examine the north–south hemispheric difference in the I-T coupling system in the American and Asian sectors during the geomagnetic superstorm that occurred in May 2024.Observations of the total electron content(TEC)showed that the Asian sector had negative storms in the northern hemisphere and positive storms in the southern hemisphere,a process that exacerbated the hemispheric differences in the TEC.However,both hemispheres of the American sector showed negative storms.The thermospheric composition changes also differed between the two sectors,and their variation could partially explain the hemispheric differences caused by positive and negative storms.Moreover,the influence of the thermospheric density change was less than that of the thermospheric composition.Finally,the dynamic effect of the thermospheric wind and the plasma transport processes strongly modulated the north–south differences in the TEC at nighttime in the American and Asian sectors,respectively,during this superstorm.

An Introduction to Magnetosphere-Ionosphere-Thermosphere Coupling Small Satellite Constellation

A future Chinese mission is introduced to study the coupling between magnetosphere,ionosphere and thermosphere,i.e.the Magnetosphere-Ionosphere-Thermosphere Coupling Small Satellite Constellation(MIT).The scientific objective of the mission is to focus on the outflow ions from the ionosphere to the magnetosphere.The constellation is planning to be composed of four small satellites;each small satellite has its own orbit and crosses the polar region at nearly the same time but at different altitude.The payloads onboard include particle detectors,electromagnetic payloads,auroral imagers and neutral atom imagers.With these payloads,the mission will be able to investigate acceleration mechanism of the upflow ions at different altitudes.Currently the orbits have been determined and prototypes of some have also been completed.Competition for next phase selection is scheduled in late 2015.

Variations of Thermosphere Density Based on Joint Analysis of In-Situ Measurement Data From Shenzhou Spacecrafts

Based on the measurements made by Atmospheric Density Detectors(ADDs) onboard Chinese spacecraft Shenzhou 2-4,the variations of thermosphere density are revealed.During the quiet period,the density at spacecraft altitude of 330~410 km exhibited a dominant diurnal variation,with high value on dayside and low value on nightside.The ratio of the diurnal maximum density to the minimum ranged from 1.7 to 2.0.The ratio shows a positive correlation with the level of solar activity and a negative correlation with the level of geomagnetic activity.When a geomagnetic disturbance comes,the atmospheric density at the altitude of 330～410 km displayed a global enhancement.For a strong geomagnetic disturbance,the atmospheric density increased by about 56%,and reached its maximum about 6～7 hours after the geomagnetic disturbance peak. The density asymmetry was also observed both in the southern and northern hemisphere during the geomagnetic disturbance peak.

A long-range forecasting model for the thermosphere based on the intelligent optimized particle filtering

The uncertainties associated with the variations in the thermosphere are responsible for the inaccurate prediction of the orbit decay of low Earth orbiting space objects due to the drag force.Accurate forecasting of the thermosphere is urgently required to avoid satellite collisions,which is a potential threat to the rapid growth of spacecraft applications.However,owing to the imperfections in the physics-based forecast model,the long-range forecast of the thermosphere is still primitive even if the accurate prediction of the external forcing is achieved.In this study,we constructed a novel methodology to forecast the thermosphere for tens of days by specifying the uncertain parameters in a physics-based model using an intelligent optimized particle filtering algorithm.A comparison of the results suggested that this method has the capability of providing a more reliable forecast with more than 30-days leading time for the thermospheric mass density than the existing ones under both weak and severe disturbed conditions,if solar and geomagnetic forcing is known.Moreover,the accurate estimation of the state of thermosphere based on this technique would further contribute to the understanding of the temporal and spatial evolution of the upper atmosphere.

Calibration of GRACE on-board accelerometers for thermosphere density derivation

Low Earth Orbit satellite on-board accelerometers play an important role in improving our understanding of thermosphere density;however,the accelerometer-derived densities are subject to accelerometer calibration errors.In this study,two different dynamic calibration schemes,the accelerometer parameter-incorporated orbit fitting and precise orbit determination(POD),are investigated with the Gravity Recovery And Climate Experiment(GRACE)satellite accelerometers for thermosphere density derivation during years 2004–2007(inclusive).We show that the GRACE accelerometer parametrization can be optimized by fixing scale coefficients and estimating biases every 60 min so that the orbit fitting and POD precision can be improved from 10 cm to 2 cm in the absence of empirical acceleration compensations and as a result the integrity of calibration parameters may be reserved.The orbit-fitting scheme demonstrates similar calibration precision with respect to POD.Their bias estimates in the along-track and cross-track components exhibit an offset within 0.1%and a standard deviation(STD)less than 0.3%.Correspondingly,a bias of 2.20%and a STD of 5.75%exists between their thermosphere density estimates.The orbit-fitting and POD-derived thermosphere densities are validated through the comparison against the results published by other institution.The comparison shows that either of them can achieve a precision level at 6%.To derive thermosphere density from the rapid-increasing amount of on-board accelerometer data sets,it is suggested to take full advantage of the orbit-fitting scheme due to its high efficiency as well as high precision.

Prediction of the thermospheric and ionospheric responses to the 21 June 2020 annular solar eclipse

On 21 June 2020,an annular solar eclipse will traverse the low latitudes from Africa to Southeast Asia.The highest latitude of the maximum eclipse obscuration is approximately 30°.This low-latitude solar eclipse provides a unique and unprecedented opportunity to explore the impact of the eclipse on the low-latitude ionosphere–thermosphere(I–T)system,especially in the equatorial ionization anomaly region.In this study,we describe a quantitative prediction of the impact of this upcoming solar eclipse on the I–T system by using Thermosphere–Ionosphere–Electrodynamics General Circulation Model simulations.A prominent total electron content(TEC)enhancement of around 2 TEC units occurs in the equatorial ionization anomaly region even when this region is still in the shadow of the eclipse.This TEC enhancement lasts for nearly 4.5 hours,long after the solar eclipse has ended.Further model control simulations indicate that the TEC increase is mainly caused by the eclipse-induced transequatorial plasma transport associated with northward neutral wind perturbations,which result from eclipse-induced pressure gradient changes.The results illustrate that the effect of the solar eclipse on the I–T system is not transient and linear but should be considered a dynamically and energetically coupled system.

Roles of thermospheric neutral wind and equatorial electrojet in pre-reversal enhancement,deduced from observations in Southeast Asia

Previous studies have proposed that both the thermospheric neutral wind and the equatorial electrojet(EEJ)near sunset play important roles in the pre-reversal enhancement(PRE)mechanism.In this study,we have used observations made in the equatorial region of Southeast Asia during March–April and September–October in 2010–2013 to investigate influences of the eastward neutral wind and the EEJ on the PRE’s strength.Our analysis employs data collected by the Gravity Field and Steady-State Ocean Circulation Explorer(GOCE)satellite to determine the zonal(east-west direction)neutral wind at an altitude of~250 km(bottomside F region)at longitudes of 90°–130°E in the dusk sector.Three ionosondes,at Chumphon(dip lat.:3.0°N)in Thailand,at Bac Lieu(dip lat.:1.7°N)in Vietnam,and at Cebu(dip lat.:3.0°N)in Philippines,provided the data we have used to derive the PRE strength.Data from two magnetometers—at Phuket(dip lat.:0.1°S)in Thailand and at Kototabang(dip lat.:10.3°S)in Indonesia—were used to estimate the EEJ strength.Our study is focused particularly on days with magnetically quiet conditions.We have found that the eastward neutral wind and the EEJ are both closely correlated with the PRE;their cross-correlation coefficients with it are,respectively,0.42 and 0.47.Their relationship with each other is weaker:the cross-correlation coefficient between the eastward neutral wind and the EEJ is just 0.26.Our findings suggest that both the eastward neutral wind and the EEJ near sunset are involved in the PRE mechanism.Based on the weak relationship between these two parameters,however,they appear to be significantly independent of each other.Thus,the wind and the EEJ are likely to be influencing the PRE magnitude independently,their effects balancing each other.

Thermospheric mass density measurement from precise orbit ephemeris

Atmospheric drag, which can be inferred from orbit information of low-Earth orbiting （LEO） satellites, provides a direct means of measuring mass density. The temporal resolution of derived mass density could be in the range from minutes to days, depending on the pre- cision of the satellite orbit data. This paper presents two methods potentially being able to estimate thermosphere mass density from precise obit ephemeris with high temporal resolution. One method is based on the drag perturbation equation of the semi-major axis and the temporal resolution of retrieved density could be ~lB0 s for CHAMP satellite. Another method generates corrections to densities computed from a baseline density model through a Kalman filter orbit drag coefficient determination （KFOD） process and the temporal resolution of derived density could be as high as 30 s for CHAMP satellite. The densities estimated from these two methods are compared with densities obtained from accelerometer data of CHAMP satellite. When the accelerometer data based densities are used as reference values, the mean relative accuracy of the densities derived from precision orbit data using the two methods is within approximately 10%. An application of the derived densities shows that the derived densities can reduce orbit predication errors.

VHF meteor radar at King Sejong Station,Antarctica

Since 2002, we have been observing the mesosphere and lower thermosphere （MLT） region over King Sejong Station （KSS; 62.22°S, 58.78°W）, Antarctica, using various instruments such as the Spectral Airglow Temperature Imager （SATI）, All Sky Camera （ASC） and VHF meteor radar. The meteor radar, installed in March 2007, continuously measures neutral winds in the alti- tude region 70-110 km and neutral temperature near the mesopause 24 h.d-1, regardless of weather conditions. In this study, we present results of an analysis of the neutral wind data for gravity wave activity over the tip of the Antarctic Peninsula, where such activity is known to be very high. Also presented is temperature estimation from measurement of the decay times of meteor trails, which is compared with other temperature measurements from SATI and the Sounding of the Atmosphere using Broadband Emis- sion Radiometry （SABER） instrument onboard the Thermosphere Ionosphere Mesosphere Energy and Dynamics （TIMED） satel- lite.

SZ-5 Cabin’s Height Changes during Three Super-storms in 2003

In this work,the daily height variations of SZ-5(Shenzhou-5) cabin from 22 October to 28 November in 2003 are analyzed,which includes the period of the Halloween Storm and the Great November Storm.The significant orbital decays have been observed at the end of October and in late November due to the great solar flares and the severe geomagnetic storms.According to the equation of the air-drag-force on a spacecraft and the SZ-5 orbital decay information,the relative daily average thermospheric density changes during the three 2003 super-storms are derived and the results are compared with the Naval Research Laboratory Mass Spectrometer Incoherent Scatter Radar Extended Model(NRLMSISE-00).The results show that the daily average thermospheric density(at the altitude of SZ-5,about 350 km) in storm time enhances to approximately 200% as much as that in the quiet time but the empirical model may somewhat underestimate the average thermospheric density changes and the daily contributions of geomagnetic storms to the density enhancements during these severe space weather events.

Interaction between Equatorial Plasma Bubbles and a Medium-Scale Traveling Ionospheric Disturbance,observed by OI 630 nm airglow imaging at Bom Jesus de Lapa,Brazil

OI 630.0 nm airglow observations,from a new observatory at Bom Jesus de Lapa,were used to study the interaction between EPBs(Equatorial Plasma Bubbles)and the MSTID(Medium-Scale Traveling Ionospheric Disturbance)over the Northeast region in Brazil.On the night of September 16 to 17,2020,an EPB was observed propagating eastward,in an apparent fossil stage,until it interacted with a dark band electrified MSTID(e MSTID).After the interaction,four EPBs merged,followed by an abrupt southward development and bifurcations.Analysis of the data suggests that an eastward polarization electric field,induced by the dark band e MSTID,forced the EPB into an upward drift,growing latitudinally along the magnetic field lines and then bifurcating.

Formation of Ionospheric Precursors of Earthquakes—Probable Mechanism and Its Substantiation

The purpose of this article is to attract the attention of the scientific community to atmospheric gravity waves (GWs) as the most likely mechanism for the transfer of energy from the surface layers of the atmosphere to space heights and describe the channel of seismic-ionospheric relations formed in this way. The article begins with a description and critical comparison of several basic mechanisms of action on the ionosphere from below: the propagation of electromagnetic radiation;the closure of the atmospheric currents through the ionosphere;the penetration of waves throughout the neutral atmosphere. A further part of the article is devoted to the analysis of theoretical and experimental information relating to the actual GWs. Simple analytical expressions are written that allow one to calculate the parameters of GWs in specific experimental situations. Specificity of GW dispersion properties and features of their propagation are analyzed on this mathematical basis, processes of amplitude amplification and dissipation of GWs with height are investigated, the mechanism of generation of ionosphere-magnetosphere current systems is described and their quantitative characteristics are determined. The experimental part presents an analysis of GWs global distribution in the thermosphere derived from the data of the instrument NACS (Neutral Atmosphere Composition Spectrometer) onboard the satellite DE-2 (NASA, 1981-1983). The statistical association of registered ionospheric disturbances with earthquakes is demonstrated. The results of DE-2 data processing are backed up by comparison with data from the DEMETER satellite (CNES, 2005-2010) whose purpose was to study the ionospheric effects of earthquakes. Specific features of GWs that characterize these waves as a factor of influence on the ionosphere from below are indicated.

Response of the Ionospheric F_2-region Over Irkutsk and Hainan to Strong Geomagnetic Storms

The ionospheric responses to two strong storms on 17-19 August 2003 and 22-23 January 2004 are studied,using the data from Irkutsk(52.5°N,104°E) and Hainan(19.5°N,109°E) ionospheric stations.The analysis of variations in relative deviations of the critical frequency △f_0F_2 revealed that at middle latitudes(Irkutsk) negative disturbances were observed in the summer ionosphere; positive and negative ones,in the winter ionosphere during the main and recovery phases respectively.At low latitudes(Hainan),the disturbances were positive in all the cases considered. Mechanisms of the disturbances were analyzed with the aid of empirical models of the neutral atmosphere NRLMSISE-00 and thermospheric wind HWM07.The main factors determining △f_0F_2 variations at middle latitudes during the storms were demonstrated to be the disturbed equatorward thermospheric wind transporting the disturbed atmospheric composition,the increase in the atomic oxygen concentration,and the passage of internal gravity waves.At low latitudes,the effects associated with neutral composition variations are less significant than those of the thermospheric wind and electric fields.

Thermospheric Density Anomaly in the Polar Cap Region During Geomagnetic Storms

The heating of the ionosphere-thermosphere system at high latitudes is a rather common phenomenon in the space climate.During geomagnetic storm time, Joule-heating enhances at high altitudes.The heating generates atmospheric upwelling causing large changes in thermospheric composition and hence in the total mass density.The CHAMP satellite with its complementary payload and long-duration mission provides an excellent dataset for studying the storm-related heating of the upper atmosphere.Based on the four-year accelerometer measurements,density enhancements in polar cap region are observed

Thermospheric density responses to Martian dust storm in autumn based on MAVEN data

The unique seasonal surface dust storms on Mars have a significant impact on the Martian atmosphere.However,due to the lack of observations,semi-empirical models are difficult to simulate the density changes in the thermosphere with the existence of dust storms in detail.Data from multiple Mars probes now offer new opportunities to study the detailed response of Martian dust storms to the upper atmosphere.In this paper,we use MAVEN accelerometer and mass spectrometer to study the variations of the Martian thermosphere density in autumn between MY32 and MY34(The corresponding Earth dates:February 11,2015 to February 28,2019),and use the seasonal model with dust storm index to fit the annual data of the above three Martian years.The results show that the thermosphere density has a clear response to the surface dust storm activity.Furthermore,the spatial distribution of measured data in autumn(northern hemisphere)is compared with the atmospheric density distribution simulated by the general circulation model(GCM)under specific initial conditions.The model simulation results agree well with the thermospheric density distribution characteristics of each Martian year under the initial strong dust storm conditions.It proves the important role of global dust storm in changing the structure of the Martian thermospheric atmosphere.

Ionospheric longitudinal variations at midlatitudes: Incoherent scatter radar observation at Millstone Hill

Incoherent scatter radar （ISR） extra-wide coverage experiments during the period of 1978-2011 at Millstone Hill are used to investigate longitudinal differences in electron density. This work is motivated by a recent finding of the US east-west coast difference in TEC suggesting a combined effect of changing geomagnetic declination and zonal winds. The current study pro- vides strong supporting evidence of the longitudinal change and the plausible mechanism by examining the climatology of electron density Ne on both east and west sides of the radar with a longitude separation of up to 40% for different heights within 300-450 kin. Main findings include： 1） The east-west difference can be up to 60% and varies over the course of the day, being positive （East side Ne 〉 West side Ne） in the late evening, and negative （West side Ne 〉 East side Ne） in the pre-noon. 2） The east-west difference exists throughout the year. The positive （relative） difference is most pronounced in winter; the negative （relative） difference is most pronounced in early spring and later summer. 3） The east-west difference tends to enhance toward decreasing solar activity, however, with some seasonal dependence; the enhancements in the positive and negative differences do not take place simultaneously. 4） Both times of largest positive and largest negative east-west differences in Ne are earlier in summer and later in winter. The two times differ by 12-13 h, which remains constant throughout the year. 5） Variations at different heights from 300-450 km are similar. Zonal wind climatology above Millstone Hill is found to be perfectly consistent with what is expected based on the electron density difference between the east and west sides of the site. The magnetic declination-zonal wind mechanism is true for other longitude sectors as well, and may be used to understand longitudinal variations elsewhere. It may also be used to derive thermospheric zonal winds.

Thermospheric circulation model in meridian plane (I)——Storm time variations in thermal status and circulation

A thermospheric circulation model in meridian plane (TCMMP) is introduced and a case study on the variations in night side thermosphere caused by energy deposition in auroral oval during a single magnetic substorm is expounded. Calculations show that TCMMP can correctly reflect the thermospheric thermal status and circulation patterns during storm time and the results are in agreement with previous theoretical and observational ones. This paper and other works also show the validity of TCMMP in researches on medium and large scale changes in mid- and low latitude thermosphere. Results also support strongly some related theory about the cause of ionospheric storms, expecially the negative phase storms.

Characteristics and mechanisms of the annual asymmetry of thermospheric mass density

In this paper, globally-averaged, thermospheric total mass density, derived from the orbits of -5000 objects at 250, 400, and 550 km that were tracked from 1967 to 2006, has been used to quantitatively study the annual asymmetry of thermospheric mass density and its mechanism（s）. The results show that thermospheric mass density had a significant annual asymmetry, which changed from year to year. The annual asymmetry at the three altitudes varied synchronously and its absolute value increased with altitudes. The results suggest that there is an annual asymmetry in solar EUV radiation that is caused by the difference in the Sun-Earth distance between the two solstices and the random variation of solar activity within a year. This change in radiation results in an annual change in the thermospheric temperature and thus the scale height of the neutral gas, and is the main cause of the annual asymmetry of thermospheric mass density. The annual asymmetry of mass density increases with altitude because of the accumulating effect of the changes in neutral temperature and scale height in the vertical direction.

Thermospheric mass density derived from CHAMP satellite precise orbit determination data based on energy balance method

In this article, the energy balance method is used to retrieve thermospheric mass density from CHAMP satellite precise orbit determination(POD) data during 2007–2009. The retrieved thermospheric mass densities are compared with those from accelerometer data and an empirical model. The main conclusions are as follows:(1) Thermospheric mass density can be retrieved from POD data by the energy balance and semi-major axis decay methods, whose results are consistent.(2) The accuracy of the retrieved densities depends on the integration time period, and the optimal period for CHAMP density retrieval from POD data is about 20 minutes.(3) The energy balance method can be used to calibrate accelerometer data.(4) The accuracy of retrieving thermospheric density from POD data varies with satellite altitude and local time.