Thermospheric Composition Research Articles

Plasma transport process in the equatorial/low-latitude ionosphere

The behaviour of the equatorial/low-latitude ionosphere and the transport processes during magnetic disturbed and quiet periods of a high solar activity year, 2014, in the American sector are investigated. Parameters used include vertical drift (Vz), transport term (W), NmF2, hmF2 and scale-height (H). The F2 plasma variations followed the diurnal local solar pattern, being higher at daytime. The sunset maximum and sunrise minimum peaks of hmF2 were directly opposite to the scale height (H) pattern. The plasma distribution was basically controlled by combined actions of the electrodynamic convection/thermospheric composition, which is geomagnetic activity dependent. The annual, semi-annual and winter-anomalies of the F2 parameters were higher at the dip equator in comparison with the low-latitude. The Vz pre-reversal peak magnitude coincided with hmF2 peak and the effects are more pronounced during geomagnetic disturbed conditions. The transport term pattern was similar to that of the scale height and it is suggested as a proxy parameter for quantifying low-latitude plasma irregularities and distribution of thermospheric composition.

Vertical diffusion transport of atomic oxygen in the mesopause region consistent with chemical losses and continuity: Global mean and inter-annual variability

This study describes the vertical diffusion velocity and eddy transport coefficient means derived from the climatological measurements of mesospheric [O] by SABER. Fifty years ago, Colegrove et al. (1967) described a process to transition between the two regions of the atmosphere using transport and continuity equations along with a 1-D composition profile. The two parts of this study are calculations of the downward O diffusion velocities and eddy diffusion coefficients using O densities derived from SABER for: 1) the global mean (±55°) and 2) the inter-annual variation of global and equatorial annual mean O densities. The derived transport diffusion velocities range from ∼1 to 4 cm s−1 at 95-83 km, and kzz varies between ∼9.0–5.0 × 105 cm2 s−1 over the same altitude range. The values of kzz derived here in the 80–100 km region are larger at 98 km than those calculated by Salinas et al. (2016) using SABER CO2 measurements and ∼0.5 times less than Qian et al. (2009, 2013 and TIEGCM model) which were derived from studies of thermospheric O/N2 measurements. Consideration of the kzz altitude profiles in the mesosphere, the mean values for both Salinas et al. (2016) and this study is ∼7. E+05 cm2s-1. The standard deviation of the inter-annual variability in kzz (and downward transport velocities) from globally averaged O profiles is <5%. The deviation is slightly larger (7.4%) at the equator, where a QBO trend is noted at 88 km, although not sufficiently large to be detected in the time history of the mesospheric O column density. The global average column density of O in the mesosphere (80–100 km) had a 0.30% change per sunspot. We suggest that model studies may need to consider higher turbulence (and kzz) in the 100–110 km region in order to satisfy both mesospheric and thermospheric composition.

Understanding the Global Variability in Thermospheric Nitric Oxide Flux Using Empirical Orthogonal Functions (EOFs)

AbstractWe present the first‐ever global assessment of thermospheric nitric oxide infrared radiative flux (NOF) variability. NOF (W/m2) from 100‐ to 250‐km altitude is extracted from 13.7 years of data from the TIMED satellite, Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, and decomposed into four empirical orthogonal functions (EOFs) and their amplitudes. We determine the strongest modes of NOF variability in the data set and develop a compact model of NOF. The first four EOFs account for 83% of the variability in the data. We illustrate the NOF model and discuss the geophysical associations of the EOFs. The first EOF represents 69% of the total variance and correlates strongly with Kp and solar shortwave flux, suggesting that geomagnetic activity and solar weather account for a large portion of NOF variability. EOF 2 shows annual and seasonal variations, possibly due to annual and seasonal thermospheric composition and temperature changes and may represent the chemical breathing mode of NOF. EOF 3 shows annual variations and correlates with solar energetic particle events and X‐flares. EOF 3 may represent winter time solar energetic particle event‐enhanced diurnal tide effects. EOF 4 suggests a meridional transport mechanism at the predawn and postdusk equator after strong storms. The EOF uncertainty is verified using cross‐validation analysis. Quantifying the spatial and temporal variabilities of NOF using eigenmodes will increase the understanding of how upper atmospheric nitric oxide cooling behaves and could increase the accuracy of future space weather and climate models.

Development and Validation of the Whole Atmosphere Community Climate Model With Thermosphere and Ionosphere Extension (WACCM‐X 2.0)

AbstractKey developments have been made to the NCAR Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X). Among them, the most important are the self‐consistent solution of global electrodynamics, and transport of O+ in the F‐region. Other ionosphere developments include time‐dependent solution of electron/ion temperatures, metastable O+ chemistry, and high‐cadence solar EUV capability. Additional developments of the thermospheric components are improvements to the momentum and energy equation solvers to account for variable mean molecular mass and specific heat, a new divergence damping scheme, and cooling by O(3P) fine structure. Simulations using this new version of WACCM‐X (2.0) have been carried out for solar maximum and minimum conditions. Thermospheric composition, density, and temperatures are in general agreement with measurements and empirical models, including the equatorial mass density anomaly and the midnight density maximum. The amplitudes and seasonal variations of atmospheric tides in the mesosphere and lower thermosphere are in good agreement with observations. Although global mean thermospheric densities are comparable with observations of the annual variation, they lack a clear semiannual variation. In the ionosphere, the low‐latitude E × B drifts agree well with observations in their magnitudes, local time dependence, seasonal, and solar activity variations. The prereversal enhancement in the equatorial region, which is associated with ionospheric irregularities, displays patterns of longitudinal and seasonal variation that are similar to observations. Ionospheric density from the model simulations reproduces the equatorial ionosphere anomaly structures and is in general agreement with observations. The model simulations also capture important ionospheric features during storms.

Daytime O/N2 Retrieval Algorithm for the Ionospheric Connection Explorer (ICON).

The NASA Ionospheric Connection Explorer Far-Ultraviolet spectrometer, ICON FUV, will measure altitude profiles of the daytime far-ultraviolet (FUV) OI 135.6 nm and N2 Lyman-Birge-Hopfield (LBH) band emissions that are used to determine thermospheric density profiles and state parameters related to thermospheric composition; specifically the thermospheric column O/N2 ratio (symbolized as ΣO/N2). This paper describes the algorithm concept that has been adapted and updated from one previously applied with success to limb data from the Global Ultraviolet Imager (GUVI) on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission. We also describe the requirements that are imposed on the ICON FUV to measure ΣO/N2 over any 500-km sample in daytime with a precision of better than 8.7%. We present results from orbit-simulation testing that demonstrates that the ICON FUV and our thermospheric composition retrieval algorithm can meet these requirements and provide the measurements necessary to address ICON science objectives.

SAMI3_ICON: Model of the Ionosphere/Plasmasphere System

The NRL ionosphere/plasmasphere model SAMI3 has been modified to support the NASA ICON mission. Specifically, SAMI3 ICON has been modified to import the thermospheric composition, temperature, and winds from TIEGCM-ICON and the high-latitude potential from AMIE data. The codes will be run on a daily basis during the ICON mission to provide ionosphere and thermosphere properties to the science community. SAMI3 ICON will provide ionospheric and plasmaspheric parameters such as the electron and ion densities, temperatures, and velocities, as well as the total electron content (TEC), peak ionospheric electron density (NmF2) and height of the F layer at NmF2 (hmF2).

The Modulation of the Quasi‐Two‐Day Wave on Total Electron Content as Revealed by BeiDou GEO and Meteor Radar Observations Over Central China

AbstractThe ground‐based total electron content (TEC) observations from BeiDou Geostationary Orbit (GEO) satellites provide more accurate temporal ionospheric variations nearly at the fixed ionospheric pierce points as compared with the non‐GEO TEC. BeiDou GEO TEC measurements during 2016, along with the horizontal wind observations from a collocated meteor radar, are utilized to quantitatively study the ionospheric response to the quasi‐two‐day wave (QTDW) in the neutral atmosphere at Meng Cheng (116.6°E, 33.3°N) over central China. The QTDW peaks during July with amplitudes of ~25–30 m/s for both zonal and meridional winds. It is suggested that the nonlinear interactions between the QTDW and tides and their influences on TEC are insignificant for this QTDW event. Nevertheless, the diurnal tide decreases by ~40–60% during the QTDW episode, which is most likely related to the change of background wind induced by the QTDW. Correspondingly, the 24 h oscillations in TEC decrease by ~18%. In addition, the wind perturbations of the QTDW can also possibly modulate the midlatitude electric dynamo and result in a quasi‐two‐day oscillation (QTDO) of ~1.2 total electron content unit (TECU), about ~10% of the background TEC. Our analysis also shows that the background TEC decreases by ~1 TECU (~8%) when the QTDW reaches maximum amplitude. This is probably related to the thermospheric composition changes (e.g., O and N2) induced by the QTDW dissipation.

Equatorial ionospheric disturbances over the East African sector during the 2015 St. Patrick’s day storm

During solar cycle 24, the St. Patrick’s Day storm on 17 March, 2015 was one of the most severe geomagnetic storms. Several research investigations have been done and are still ongoing about this storm since the dynamics of this storm differs on a global scale from one sector to another. This study examines the response of the equatorial ionosphere to the storm in the East African sector. Total electron content (TEC) data from ground stations are used to investigate the evolution of the Equatorial Ionization Anomaly (EIA) during the storm. The TEC observations show a reduced EIA during 18–20 March 2015, consistent with previous studies at other longitudes. Analyses of ground magnetometer data and the thermospheric composition data from the NASA/TIMED satellite reveal that the reduced EIA during the storm can arise from the combined effect of the disturbance dynamo and composition change.

Impact of the lower thermospheric winter‐to‐summer residual circulation on thermospheric composition

AbstractGravity wave forcing near the mesopause drives a summer‐to‐winter residual circulation in the mesosphere and a reversed, lower thermospheric winter‐to‐summer residual circulation. We conducted modeling studies to investigate how this lower thermospheric residual circulation impacts thermospheric composition (O/N2). We found that the upwelling associated with the residual circulation significantly decreases O/N2 in winter and the downwelling in summer slightly increases O/N2. Consequently, the residual circulation reduces the summer‐to‐winter latitudinal gradient of O/N2, which causes the simulated latitudinal gradient of O/N2 to be more consistent with observations. The smaller summer‐to‐winter latitudinal gradient of O/N2 would decrease the ionosphere winter anomaly in model simulations, which would bring the simulated winter anomaly into better agreement with ionospheric observations. The lower thermospheric residual circulation may be a process that has been largely ignored but is very important to the summer‐to‐winter latitudinal gradients, as well as annual/semiannual variations in the thermosphere and ionosphere.

Attribution of interminimum changes in global and hemispheric total electron content

AbstractWe use a new data product of electron column density (total electron content, or TEC) maps to estimate and attribute the interminimum changes (the differences between annual averages centered on the 2008 and 1996 solar minima) in TEC global and hemispheric averages (dividing the globe in three different ways). We attribute the observed changes to corresponding changes in solar and geomagnetic activity. The new TEC map product was constructed with temporally consistent processing, and it resolves some of the apparent inconsistencies of earlier studies. The estimated global average TEC interminimum change is −19.3% ± 1.0% (2σ uncertainty), of which −9.1% is attributable to the interminimum change in solar extreme ultraviolet (EUV) irradiance (as represented by the F10.7 index), −2.2% is attributable to the change in geomagnetic activity (Kp index), and −9.3% remains unattributed. The hemispheric results are very similar to the global results, but the values tend to be slightly larger in the Southern Hemisphere, at low latitudes, and at night, compared to the opposing respective hemispheres. The interminimum changes and temporal variations of thermospheric mass density anomalies (i.e., the difference between the data and the empirical model) are very similar to those of the global and hemispheric TEC residuals, suggesting that they are driven by a common, globally distributed mechanism. Thermospheric composition changes and additional (unobserved) decreases in solar EUV irradiance are possible mechanisms behind the TEC and mass density unattributed changes; we estimate a plausible range of −6% to −13% for the solar EUV irradiance interminimum change.

Positive and negative ionospheric responses to the March 2015 geomagnetic storm from BDS observations

The most intense geomagnetic storm in solar cycle 24 occurred on March 17, 2015, and the detailed ionospheric storm morphologies are difficultly obtained from traditional observations. In this paper, the Geostationary Earth Orbit (GEO) observations of BeiDou Navigation Satellite System (BDS) are for the first time used to investigate the ionospheric responses to the geomagnetic storm. Using BDS GEO and GIMs TEC series, negative and positive responses to the March 2015 storm are found at local and global scales. During the main phase, positive ionospheric storm is the main response to the geomagnetic storm, while in the recovery phase, negative phases are pronounced at all latitudes. Maximum amplitudes of negative and positive phases appear in the afternoon and post-dusk sectors during both main and recovery phases. Furthermore, dual-peak positive phases in main phase and repeated negative phase during the recovery are found from BDS GEO observations. The geomagnetic latitudes corresponding to the maximum disturbances during the main and recovery phases show large differences, but they are quasi-symmetrical between southern and northern hemispheres. No clear zonal propagation of traveling ionospheric disturbances is detected in the GNSS TEC disturbances at high and low latitudes. The thermospheric composition variations could be the dominant source of the observed ionospheric storm effect from GUVI $$\hbox {[O]/[N}_{2}]$$ ratio data as well as storm-time electric fields. Our study demonstrates that the BDS (especially the GEO) observations are an important data source to observe ionospheric responses to the geomagnetic storm.

Analysis of the global ionospheric disturbances of the March 2015 great storm

AbstractThe global ionospheric storm in March 2015 was investigated by using data from over 3000 GPS stations worldwide. In this study, total electron content (TEC), rate of TEC (ROT), and ROT's standard deviation rate of the TEC index, as well as the second‐order difference operator TECT, were considered as main characteristic methods to distinguish ionosphereic disturbances. The results show that (1) based on the multiple methods above, we all observed that for the first time, there were three equatorward traveling ionospheric disturbances (TIDs) in the main phase of this storm. In North America, the disturbance zone expanded to ~40°N; the disturbance periods and AE peak stages were roughly synchronous. We suggest that these three TIDs were induced by the propagation of atmospheric gravity waves to low latitudes under the action of AE. (2) The most intense positive storm occurred over South America and the South Atlantic (over 300% enhancement; 00:00–05:00 UT on 18 March), whereas a negative storm was observed in the corresponding region of the Northern Hemisphere. Such inverse hemispheric asymmetry in intensity and structure can be explained by the variations of the thermospheric composition, the IMF By component, and the geomagnetic intensity. (3) On 18 March, a negative storm dominated globally (except at certain low latitudes), and tended to propagate equatorward and decay with time, which could be largely attributed to the storm circulation theory. And the evolution of the negative storm was further characterized by the foF2 variations of ionosondes.

Conjugate hemisphere ionospheric response to the St. Patrick's Day storms of 2013 and 2015 in the 100°E longitude sector

AbstractThe effects of the St. Patrick's Day geomagnetic storms of 2013 and 2015 in the equatorial and low‐latitude regions of both hemispheres in the 100°E longitude sector is investigated and compared with the response in the Indian sector at 77°E. The data from a chain of ionosondes and GPS/Global Navigation Satellite Systems receivers at magnetic conjugate locations in the 100°E sector have been used. The perturbation in the equatorial zonal electric field due to the prompt penetration of the magnetospheric convective under shielded electric field and the over shielding electric field gives rise to rapid fluctuations in the F2 layer parameters. The direction of IMF Bz and disturbance electric field perturbations in the sunset/sunrise period is found to play a crucial role in deciding the extent of prereversal enhancement which in turn affect the irregularity formation (equatorial spread F) in the equatorial region. The northward (southward) IMF Bz in the sunset period inhibited (supported) the irregularity formation in 2015 (2013) in the 100°E sector. Large height increase (hmF2) during sunrise produced short‐duration irregularities during both the storms. The westward disturbance electric field on 18 March inhibited the equatorial ionization anomaly causing negative (positive) storm effect in low latitude (equatorial) region. The negative effect was amplified in low midlatitude by disturbed thermospheric composition which produced severe density/total electron content depletion. The longitudinal and hemispheric asymmetry of storm response is observed and attributed to electrodynamic and thermospheric differences.

Prompt penetration electric fields and the extreme topside ionospheric response to the June 22–23, 2015 geomagnetic storm as seen by the Swarm constellation

Using data from the three Swarm satellites, we study the ionospheric response to the intense geomagnetic storm of June 22–23, 2015. With the minimum SYM-H excursion of −207 nT, this storm is so far the second strongest geomagnetic storm in the current 24th solar cycle. A specific configuration of the Swarm satellites allowed investigation of the evolution of the storm-time ionospheric alterations on the day- and the nightside quasi-simultaneously. With the development of the main phase of the storm, a significant dayside increase of the vertical total electron content (VTEC) and electron density Ne was first observed at low latitudes on the dayside. From ~22 UT of 22 June to ~1 UT of 23 June, the dayside experienced a strong negative ionospheric storm, while on the nightside an extreme enhancement of the topside VTEC occurred at mid-latitudes of the northern hemisphere. Our analysis of the equatorial electrojet variations obtained from the magnetic Swarm data indicates that the storm-time penetration electric fields were, most likely, the main driver of the observed ionospheric effects at the initial phase of the storm and at the beginning of the main phase. The dayside ionosphere first responded to the occurrence of the strong eastward equatorial electric fields. Further, penetration of westward electric fields led to gradual but strong decrease of the plasma density on the dayside in the topside ionosphere. At this stage, the disturbance dynamo could have contributed as well. On the nightside, the observed extreme enhancement of the Ne and VTEC in the northern hemisphere (i.e., the summer hemisphere) in the topside ionosphere was most likely due to the combination of the prompt penetration electric fields, disturbance dynamo and the storm-time thermospheric circulation. From ~2.8 UT, the ionospheric measurements from the three Swarm satellites detected the beginning of the second positive storm on the dayside, which was not clearly associated with electrojet variations. We find that this second storm might be provoked by other drivers, such as an increase in the thermospheric composition.

Solar wind driving of ionosphere‐thermosphere responses in three storms near St. Patrick's Day in 2012, 2013, and 2015

AbstractWe identify interplanetary plasma regions associated with three intense interplanetary coronal mass ejections (ICMEs)‐driven geomagnetic storm intervals which occurred around the same time of the year: day of year 74–79 (March) of 2012, 2013, and 2015. We show that differences in solar wind drivers lead to different dynamical ionosphere‐thermosphere (IT) responses and to different preconditioning of the IT system. We introduce a new hourly based global metric for average low‐latitude and northern middle‐latitude vertical total electron content responses in the morning, afternoon, and evening local time ranges, derived from measurements from globally distributed Global Navigation Satellite System ground stations. Our novel technique of estimating nitric oxide (NO) cooling radiation in 11° latitudinal zones is based on Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics (TIMED)/Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) measurements. The thermospheric cooling throughout the storm phases is studied with this high latitudinal resolution for the first time. Additionally, TIMED/Global Ultraviolet Imager (GUVI) observations of the dynamical response of the thermospheric composition (O/N2 ratio) are utilized to study negative ionospheric storm effects. Based on these data sets, we describe and quantify distinct IT responses to driving by ICME sheaths, magnetic clouds, coronal loop remnants, plasma discontinuities, and high‐speed streams following ICMEs. Our analysis of coupling functions indicates strong connection between coupling with the solar wind and IT system response in ICME‐type storms and also some differences. Knowledge of interplanetary features is crucial for understanding IT storm dynamics.

Impact of semidiurnal tidal variability during SSWs on the mean state of the ionosphere and thermosphere

AbstractObservations from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites reveal a global reduction in the zonal and diurnal mean F region peak electron density (NmF2) during sudden stratosphere warmings (SSWs). The present study investigates the source of the global NmF2 decrease by performing numerical experiments with the National Center for Atmospheric Research (NCAR) thermosphere‐ionosphere‐electrodynamics general circulation model. The simulations reveal that the NmF2 reduction coincides with a depletion of thermospheric [O]/[N2], indicating that the NmF2 depletion is related to changes in thermospheric composition during SSWs. Numerical experiments further illustrate that the short‐term (∼10 day) enhancement of the migrating semidiurnal solar tide (SW2) during SSWs is the source of the variability in thermospheric composition. In particular, the enhancement of the SW2 during SSWs alters the lower thermosphere zonal mean circulation, leading to a reduction in atomic oxygen in the lower thermosphere. The atomic oxygen reduction propagates into the upper thermosphere through molecular diffusion, leading to a decrease in [O]/[N2] throughout the low‐ to middle‐latitude thermosphere. It is anticipated that the effects of the SW2 on the ionosphere and thermosphere investigated herein will be modulated by SSW related enhancements of the migrating semidiurnal lunar tide (M2). The magnitude of the combined impact of the SW2 and M2 on the ionosphere‐thermosphere mean state will depend on the relative phasing of the solar and lunar tides. The results demonstrate that in addition to modulating the low‐latitude electrodynamics, tidal variability during SSWs can significantly impact the mean state of the ionosphere and thermosphere.

The observation and simulation of ionospheric response to CIR/high‐speed streams‐induced geomagnetic activity on 4 April 2005

AbstractThe ionospheric response to corotating interaction region (CIR)‐induced geomagnetic activity on 4 April 2005 has been studied using in situ electron density measurements, ground GPS‐total electron content (TEC) observations, and numerical simulations of the National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM). The case study resulted that the ionospheric positive response occurred from high to low latitudes. The positive effect at low latitudes could continue for 4 days, whereas at middle to high latitudes the disturbance mainly lasted only for 1 day. The modeled Ne and TEC from TIE‐GCM had a good agreement with those from observations. The simulation results showed that penetration electric fields were responsible for the daytime positive response during the initial and main phases of the geomagnetic storm, while neutral winds were responsible for the presunset positive effects. The long‐lasting positive storm effect during the storm recovery time at low latitudes was related to the thermospheric composition (O/N2) changes during the storm event.

The effects of March 20 2015 solar eclipse on the F2 layer in the mid-latitude

This paper studied the effects of solar eclipse of March 20, 2015 on the F2 layer in the mid-latitude. The diurnal changes in the NmF2 and hmF2 in mid-latitude stations during the spectacular event, as recorded by the ionosonde situated along the path of solar eclipse, which are within the obscuration percentage of 59–90% were investigated. The estimation of the percentage of solar ionizing radiation that remains unmasked during the eclipse window was carried out. The high uncertainty level (i.e. the error is ⩽±0.2), indicates that variation in electron density during eclipse window can be used as proxy parameter for solar ionizing radiation. The NmF2 decreased during the eclipse window, as a consequence of the variation in the local solar radiation. The variation of F2 plasma was dominated by diffusion mechanisms which determine the height at which the F2 peak formed and were related to the changes in thermospheric composition. The downward/upward movements of the plasma correspond with the drifting of the diffusion mechanisms and undergone a comparable variation with the solar ionizing radiation. Our result indicates that eclipse effects increase with increase in latitude and the time lag (the time delay ranges from 11 to 21min) decreases with increase in latitude.

Unusual behavior of the low‐latitude ionosphere in the Indian sector during the deep solar minimum in 2009

AbstractIn this paper we carry out a comparative study of the daytime (7–18 LT) behavior of the near‐equatorial ionospheric F region at the end of the long deep solar minimum (2009) with respect to that of the previous normal solar minimum (1995) in the Indian longitude sector using ionosonde observations of F layer parameters, radar observations of E × B drift, and the IRI‐2012 (International Reference Ionosphere‐2012) model. We investigate the F2 and F3 layer behaviors separately. The results reveal that the peak frequencies of the F layer (fpeak), F2 layer (foF2), and F3 layer (foF3) in 2009 are consistently lower than those in 1995. Maximum difference in fpeak/foF2/foF3 between 2009 and 1995 observations is found in the equinoxes followed by winter and summer. The annual mean, seasonal mean, and 10 day mean peak electron density (corresponding to fpeak) in 2009 were lower than those in 1995 by as much as 34%, 46%, and 65%, respectively. Solar rotation effect is less conspicuous in 2009 than in 1995, consistent with the solar rotation signature in F10.7. Observations also show considerable amount of equinoctial asymmetry in electron density, which is found to be closely linked with the corresponding asymmetry in the vertical E × B drift. Seasonal mean peak electron densities of the F layer (corresponding to fpeak) and the F2 layer (corresponding to foF2) observed during the deep solar minimum of 2009 were smaller than those corresponding to IRI‐2012 model foF2 by as much as 45% and 50%, respectively, underlining the need to incorporate the data collected during the long deep minimum in the IRI model. The unusually weak ionosphere observed in 2009 is discussed in terms of the direct effect of the low solar EUV flux in 2009 as compared to 1995 and its indirect effects on ionospheric electric field, thermospheric composition (or O/N2 ratio), and thermospheric neutral winds.

Day‐to‐day variability in the thermosphere and its impact on plasmasphere refilling

AbstractSatellite drag data showing significant (20%) short‐term variations in atmospheric mass density are presented. These data, along with the Naval Research Laboratory SAMI3 (Sami3 is Also a Model of the Ionosphere) ionosphere/plasmasphere model and the WACCM (Whole Atmosphere Community Climate Model) atmosphere model are used to estimate day‐to‐day variability in thermosphere composition, thermosphere winds, and exosphere temperatures and the effect of this variability on plasmasphere refilling rates. This assessment is guided by SAMI3 modeling showing that modest (20%) decreases in thermospheric density and exospheric temperature can lead to large (60%) increases in plasmaspheric refilling rates and that changes in the thermospheric wind pattern can have a similar effect. Results suggest that day‐to‐day variability in thermospheric wind and composition could affect plasmaspheric refilling rates by 50 to 100%.