Thermosphere Ionosphere Electrodynamics General Circulation Model Research Articles

On the Inverse Correlation Between the Thermosphere Winter Helium Bulge and Solar Activity: Impact of Gravity Wave Drag From the Mesosphere

AbstractUnderstanding the temporal and spatial variations in the ideal inert tracer helium can provide insight into the dynamic evolution of the thermosphere. The magnitude of the thermospheric winter helium bulge was inversely correlated with the level of solar activity. However, this feature has been found to be not reproduced by the Thermosphere‐Ionosphere Electrodynamic General Circulation Model (TIEGCM), and the associated physical mechanisms remain unknown. Using the Thermosphere‐Ionosphere‐Mesosphere Electrodynamic General Circulation Model (TIME‐GCM), we found that mesospheric gravity wave drag (GWD) is a factor contributing to this inverse correlation. Specifically, the summer‐to‐winter circulation in thermosphere becomes the main cause of the helium bulge, as mesospheric GWD can play a role in strengthening this circulation. The GWD contributions to temperature change below the lower thermosphere do not depend prominently on solar activity. However, because the temperature impacts on the pressure gradient force are height‐integrated according to the background temperature of the neutral gas, the higher background temperature in the thermosphere at the solar maximum corresponds to a relatively weaker response in pressure gradient force in the thermosphere. Therefore, the response of the thermospheric circulation that might be expected to accompany increasing solar activity is suppressed due to the influence of mesospheric GWD, which results in a decrease in the magnitude of the winter helium bulge with increasing solar activity. Thus, our results demonstrated that lower atmosphere forcing can play a significant role in the response of thermospheric helium to solar activity.

Effects of Subauroral Polarization Streams on Ionospheric Radial Currents During the Geomagnetic Storm on 23 April 2023

AbstractUsing observations from dual‐spacecraft (dual‐SC, Swarm A and C) and simulations from the Thermosphere‐Ionosphere Electrodynamics General Circulation Model (TIEGCM), this work investigates the ionospheric radial current (IRC) in response to subauroral polarization streams (SAPS) during the geomagnetic storm on 23 April 2023. At noon, a radially inward disturbance IRC (ΔIRC) emerges in response to SAPS, leading to a further intensification of inward IRC. The model simulation indicates that the dynamo current prevails over the polarization current, serving as the primary driver of the inward ΔIRC. Additionally, the significantly enhanced Pedersen conductivity potentially amplifies the inward ΔIRC. At dusk, ΔIRC exhibit a slight outward trend before 21 UT and a pronounced inward trend around 21–24 UT. This temporal variation is attributed to the equatorward propagation of SAPS‐induced thermospheric winds within 3–4 hr. The noontime inward electric field at the dip equator arises from both equatorward winds at low‐mid latitudes and local eastward winds. However, at dusk, the inward polarization electric field primarily stems from local disturbed eastward winds.

Observation of Quiet‐Time Mid‐Latitude Joule Heating and Comparisons With the TIEGCM Simulation

AbstractJoule heating is a major energy sink in the solar wind‐magnetosphere‐ionosphere system and modeling it is key to understanding the impact of space weather on the neutral atmosphere. Ion drifts and neutral wind velocities are key parameters when modeling Joule heating, however there is limited validation of the modeled ion and neutral velocities at mid‐latitudes. We use the Blackstone Super Dual Auroral Radar Network radar and the Michigan North American Thermosphere Ionosphere Observing Network Fabry‐Perot interferometer to obtain the local nightside ion and neutral velocities at ∼40° geographic latitude during the nighttime of 16 July 2014. Despite being a geomagnetically quiet period, we observe significant sub‐auroral ion flows in excess of 200 ms−1. We calculate an enhancement to the local Joule heating rate due to these ion flows and find that the neutrals impart a significant increase or decrease to the total Joule heating rate of >75% depending on their direction. We compare our observations to outputs from the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM). At such a low geomagnetic activity however, TIEGCM was not able to model significant sub‐auroral ion flows and any resulting Joule heating enhancements equivalent to our observations. We found that the neutral winds were the primary contributor to the Joule heating rates modeled by TIEGCM rather than the ions as suggested by our observations.

SubAuroral Red Arcs Generated by Inner Magnetospheric Heat Flux and by SubAuroral Polarization Streams

AbstractSubauroral red (SAR) arcs are commonly observed ionospheric red line emissions. They are usually attributed to subauroral electron heating by inner magnetospheric heat flux (IMHF). However, the role of IMHF in changing the ionosphere‐thermosphere (IT) still remains elusive. We conduct controlled numerical experiments with the Thermosphere‐Ionosphere Electrodynamic General Circulation Model (TIEGCM). Coulomb collisional heat flux derived with the Comprehensive Inner Magnetosphere Ionosphere (CIMI) model and empirical subauroral polarization streams (SAPS) are implemented in TIEGCM. The heat flux causes electron temperature enhancement, electron density depletion, and consequently SAR arcs formed in the dusk‐to‐midnight subauroral ionosphere region. SAPS cause more substantial plasma and neutral heating and plasma density variations in a broader region. The maximum enhancement of subauroral red line emission rate is comparable to that caused by the heat flux. However, the visibility of SAR arcs also depends on the relative enhancement to the background brightness.

Investigation on Chasing and Interaction of Traveling Ionospheric Disturbances Based on Multi‐Instrument

AbstractIn this study, we use multi‐instrument observations (all‐sky imager (ASI), global navigation satellite system (GPS) receivers, digisonde) to study the interaction of nighttime medium‐scale traveling ionospheric disturbances (MSTIDs) on 13 November 2018. The most attractive aspect of this event is that the interaction appeared between two dark bands both propagated southwestward. The airglow observations show that the latter band moved faster and caught up with the former, and these two bands merged into a new one. The propagating characteristics and morphology of the MSTIDs changed during the interaction process. The simulations from the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM) suggested that the ionospheric background zonal winds and electron density distributions could play essential roles in the interaction of the MSTIDs. Moreover, the merging process might be associated with the electrostatic reconnection.

The Nighttime Horizontal Neutral Winds at Mohe Station in Response to the Temporal Oscillations of Interplanetary Magnetic Field Bz

Temporal oscillations in the IMF Bz associated with Alfvén waves occur frequently in solar wind, with a duration ranging from minutes to hours. Using Swarm observations, Fabry–Pérot interferometer measurements at Mohe station, and Thermosphere–Ionosphere–Electrodynamic General Circulation Model simulations, the perturbations of zonal (ΔUN) and meridional (ΔVN) winds due to temporal oscillations in the IMF Bz on 23–24 April 2023 are explored in the following work. ΔUN is strong westward with a speed of greater than 100 m/s at pre-midnight on 23–24 April. This phenomenon is primarily driven by the pressure gradient, offsetting by the ion drag and Coriolis force. On 23 April, ΔVN is weak northward at the pre-midnight and strong southward at a speed of ~200 m/s at pre-dawn. On 24 April, ΔVN is strong (weak) northward at pre-midnight (pre-dawn). It is mainly controlled by a balance between the pressure gradient, ion drag, and Coriolis force.

HIWIND Balloon and Antarctica Jang Bogo FPI High Latitude Conjugate Thermospheric Wind Observations and Simulations

AbstractUsing 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.

Thermospheric nitric oxide energy budget during extreme geomagnetic storms: a comparative study

We selected three superstorms (disturbance storm time [Dst] index less than −350 nT) of 2003–04 to study the thermospheric energy budget with a particular emphasis on the thermospheric cooling emission by nitric oxide via a wavelength of 5.3 μm. The nitric oxide radiative emission data are obtained from the Sounding of the Atmosphere by Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite and the thermosphere ionosphere electrodynamic general circulation model (TIEGCM) simulation. Different energy sources for the magnetospheric energy injection and the thermospheric/ionospheric dissipation processes are calculated using empirical formulations, model simulations, and space-borne and ground-based measurements. The Joule heating rates calculated from different sources showed similar variations but significant differences in the magnitude. The nitric oxide cooling power is calculated by zonally and meridionally integrating the cooling flux in the altitude range of 100–250 km. The satellite observed that cooling flux responds faster to the energy input, as compared to the modeled results. The cooling power increases by an order of magnitude during storm time with maximum radiation observed during the recovery phase. Both the satellite-observed and modeled cooling powers show a strong positive correlation with the Joule heating power during the main phase of the storm. It is found that the maximum radiative power does not occur during the strongest storm, and it strongly depends on the duration of the main phase. The model simulation predicts a higher cooling power than that predicted by the observation. During a typical superstorm, on average, a cooling power of 1.87 × 105 GW exiting the thermosphere is estimated by the TIEGCM simulation. On average, it is about 40% higher than the satellite observation.

Assimilating Space‐Based Thermospheric Neutral Density (TND) Data Into the TIE‐GCM Coupled Model During Periods With Low and High Solar Activity

AbstractThe global estimation of Thermospheric Neutral Density (TND) and electron density (Ne) on various altitudes are provided by upper atmosphere models, however, the quality of their forecasts needs to be improved. In this study, we present the impact of assimilating space‐based TNDs, measured along Low Earth Orbit (LEO) mission, into the NCAR Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM). In these experiments, the Ensemble Kalman Filter (EnKF) merger of the Data Assimilation Research Testbed (DART) community software is applied. To cover various space‐based TND data and both low and high solar activity periods, we used the measurements of CHAMP (Challenging Minisatellite Payload) and Swarm‐C as assimilated observations. The TND forecasts are then validated against independent TNDs of GRACE (Gravity Recovery and Climate Experiment mission) and Swarm‐B, respectively. To introduce the impact of the thermosphere on estimating ionospheric parameters, the outputs of Ne are validated against the radio occultation data. The Data Assimilation (DA) results indicate that TIE‐GCM overestimates (underestimates) TND and Ne during low (high) solar activity. Considerable improvements are found in forecasting TNDs after DA, that is, the Root Mean Squared Error (RMSE) is reduced by 79% and 51% during low and high solar activity periods, respectively. The reduction values for Ne are found to be 52.3% and 40.4%, respectively.

A comparison of ionospheric TEC between the South Atlantic anomaly region and the Indian Ocean region based on TIEGCM simulations in 2002

Using the Thermosphere-Ionosphere-Electrodynamic General Circulation Model (TIEGCM), a comparison of the ionospheric total electron content (TEC) between the South Atlantic anomaly (SAA) and the Indian Ocean (IO) at solar maximum is performed in this study. The results show that the average total electron content in the SAA is greater than that in the Indian Ocean in general. In order to further analyze the difference between the two regions, the empirical orthogonal function (EOF) are used to investigate the temporal and spatial characteristics of TEC. The empirical orthogonal function method separate part of the global four-peak structure (an equatorial ionization anomaly structure, distributed in Southeast Asia, South America, Africa, and central Pacific) and spatial variations in both regions. Moreover, the first mode of EOF shows the different distribution of Equatorial ionization anomaly in South America and central Pacific caused by deviation of geomagnetic field and tides between two regions, and the enhancement of TEC in SAA region at dusk is emphasized, but the enhancement of TEC in IO region at dawn is emphasized. The second mode performs the distribution of EIA in Africa related to solar radiation and E×B drift. The third mode indicates the similar spatiotemporal variations from the geomagnetic field. Besides, the correlation between TEC and Dst in two regions indicate that there are some deficiencies in simulation to the specificity of SAA, and the deficiencies are likely caused by the model’s inaccurate simulation of the magnetic field and particle deposition in the SAA region.

Response Time of Joule Heating Rate and Nitric Oxide Cooling Emission During Geomagnetic Storms: Correlated Ground‐Based and Satellite Observations

AbstractJoule heating is the primary source of the high latitude thermospheric energy dissipation during geomagnetic storm period. The nitric oxide (NO) emission at 5.3 μm accounts for the majority of Joule heating energy due to its radiative nature. It is the dominating cooling agent above 100 km that effectively regulates the thermospheric temperature. We studied the relationship between the response time of NO cooling emission and Joule heating rate during geomagnetic storm periods by using the NO emission observations by Sounding of Atmosphere using Broadband Emission Radiometry (SABER) onboard NASA’s Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics (TIMED) satellite and the Joule heating rate measured by the European incoherent scatter (EISCAT) radar over Tromsø (geographic:69.59°N, 19.22°E), Norway, and the thermosphere‐ionosphere‐electrodynamics general circulation model (TIEGCM) simulation. We selected seven geomagnetic storms during which there were continuous measurements of the Pederson conductivity and electric fields when the TIMED/SABER satellite was in the northview mode. The TIEGCM gives a fair description of NO cooling. However, it was found that the Joule heating rates obtained with the TIEGCM often do not show good agreement with those from EISCAT observations. The Joule heating rate peaks with 3–7 hr of storm' onset. The NO cooling flux takes longer time to respond to the energy input during storm period. The fastest response of the NO cooling emission to the Joule heating rate is found during the strongest storm. The weakest storm does not have the longest response time. No correlation between the response time of NO cooling flux with respect to the Joule heating rate and storm’s intensity was observed.

Controlling Factors of the Seasonal Variation of the Latitudinal Location of the Equatorial Ionization Anomaly Crest

AbstractThe latitudinal location of the Equatorial Ionization Anomaly (EIA) crest has seasonal variation, and there are disagreements on the interpretation of such seasonal characteristic in previous studies. Some studies suggested that this seasonal characteristic is determined by the seasonal characteristic of the equatorial electric field. Others suggested that this seasonal characteristic is determined by the seasonal changes of the thermospheric wind. The current paper uses Total Electron Content (TEC) data and the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) to analyze the seasonal variation of the northern EIA crest in the eastern Asian sector under low solar activity. Our results show that the monthly averaged latitudinal location of the northern EIA crest has a good linear relationship (r = 0.74) with the monthly averaged Equatorial Electrojet (EEJ) intensity, which is a commonly used proxy of the eastward electric field. However, TIEGCM simulations with and without F‐region wind indicate that such a relationship might be attributed to wind effects. Additionally, the linear relationship between the EEJ intensity and the northern‐southern EIA crest distance is not significant (r = 0.47) in the eastern Asian sector. Our results suggest that a good correspondence between the eastward electric field and the latitudinal location of the EIA crest is not assured annually, as the seasonally varying F‐region wind significantly influences EIA evolution.

Evaluation of TIEGCM based on GOCE neutral density

The Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM), as one of the most advanced physical models of the Earth’s thermosphere and ionosphere, is not only widely used in scientific research, but also has essential reference value in aerospace operations. In this study, we use Gravity field and steady-state Ocean Circulation Explorer (GOCE) neutral density to evaluate the accuracy of the TIEGCM. The assessment is performed on both time and spatial scales. The time scales are conducted annually, monthly, and daily, while the spatial scales are carried out in terms of altitude, latitude, and local time. On the time scales, the performance of the TIEGCM on the monthly time scale is better than that on the annual time scale. Also, the performance on the daily time scale is better than that on the monthly time scale. The relative deviation shows a significant seasonal variation, that is, larger in winter and summer and smaller in spring and autumn. In addition, the relative deviation shows a negative correlation with F10.7 and Ap. On the spatial scale, with the increase in altitude, the average relative deviation of the model becomes larger in general. The relative deviation is usually larger at middle latitudes in the Northern Hemisphere and high latitudes in the Southern Hemisphere. Finally, on the scale of local time, the relative deviation changes more dramatically in local morning than at dusk.

Evaluation of the Exospheric Temperature Modeling From Different Empirical Orthogonal Functions

AbstractIn this paper, we constructed the Exospheric Temperature Models (ETM) on the basis of CHAMP and GRACE data using different empirical orthogonal functions (EOFs). The EOFs of the exospheric temperature can be derived either from satellite data directly or from the outputs of the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) and MSIS models by applying the Principal Component Analysis method. Then, the thermospheric mass densities calculated from ETM are used to compare with the observed data in order to evaluate the performance of different ETM models. It was found that all these three models can provide good specification of thermospheric density including day‐night, seasonal, and latitudinal variations. However, the ETM based on CHAMP and GRACE data gives a better performance in modeling the Equatorial Thermospheric Anomaly and the Midnight Density Maximum features than the MSIS‐ETM and TIEGCM‐ETM. Specifically, independent SWARM‐C data comparison showed that the Relative Deviations and corresponding Root‐Mean‐Square‐Errors of our Texo models are less than 8.9% and 22.8%, much better than the MSIS‐00 model.

Statistical models of the variability of plasma in the topside ionosphere: 1. Development and optimisation

This work presents statistical models of the variability of plasma in the topside ionosphere based on observations made by the European Space Agency’s (ESA) Swarm satellites. The models were developed in the “Swarm Variability of Ionospheric Plasma” (Swarm-VIP) project within the European Space Agency’s Swarm+4D-Ionosphere framework. The configuration of the Swarm satellites, their near-polar orbits and the data products developed, enable studies of the spatial variability of the ionosphere at multiple scale sizes. The statistical modelling technique of Generalised Linear Modelling (GLM) was used to create models of both the electron density and measures of the variability of the plasma structures at horizontal spatial scales between 20 km and 100 km. Despite being developed using the Swarm data, the models provide predictions that are independent of these data. Separate models were created for low, middle, auroral and polar latitudes. The models make predictions based on heliogeophysical variables, which act as proxies for the solar and geomagnetic processes. The first and most significant term in the majority of the models was a proxy for solar activity. The most common second term varied with the latitudinal region. This was the Solar Zenith Angle (SZA) in the polar region, a measure of latitude in the auroral region, solar time in the mid-latitude region and a measure of latitude in the equatorial region. Other, less significant terms in the models covered a range of proxies for the solar wind, geomagnetic activity and location. In this paper, the formulation, optimisation and evaluation of these models are discussed. The models show very little bias, with a mean error of zero to two decimal places in 14 out of 20 cases. The models capture some, but not all, of the trends present in the data, with Pearson correlation coefficients of up to 0.75 between the observations and the model predictions. The models also capture some, but not all, of the variability of the ionospheric plasma, as indicated by the precision, which ranged between 0.20 and 0.83. The addition of the thermospheric density as an explanatory variable in the models improved the precision in the polar and auroral regions. It is suggested that, if the thermosphere could be observed at a higher spatial resolution, then even more of the variability of the plasma structures could be captured by statistical models. The formulation and optimisation of the models are presented in this paper. The capability of the model in reproducing the expected climatological features of the topside ionosphere, in supporting GNSS-based ionospheric observations and the performance of the model against the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM), are provided in a companion paper (Spogli L et al. 2024. J Space Weather Space Clim https://doi.org/10.1051/swsc/2024003).

Statistical models of the variability of plasma in the topside ionosphere: 2. Performance assessment

Statistical models of the variability of plasma in the topside ionosphere based on the Swarm data have been developed in the “Swarm Variability of Ionospheric Plasma” (Swarm-VIP) project within the European Space Agency’s Swarm+4D-Ionosphere framework. The models can predict the electron density, its gradients for three horizontal spatial scales – 20, 50 and 100 km – along the North-South direction and the level of the density fluctuations. Despite being developed by leveraging on Swarm data, the models provide predictions that are independent of these data, having a global coverage, fed by various parameters and proxies of the helio-geophysical conditions. Those features make the Swarm-VIP models useful for various purposes, which include the possible support for already available ionospheric models and proxy of the effect of ionospheric irregularities of the medium scales that affect the signals emitted by Global Navigation Satellite Systems (GNSS). The formulation, optimisation and validation of the Swarm-VIP models are reported in Paper 1 (Wood et al. 2024. J Space Weather Space Clim. in press). This paper describes the performance assessment of the models, by addressing their capability to reproduce the known climatological variability of the modelled quantities, and the ionospheric weather as depicted by ground-based GNSS, as a proxy for the ionospheric effect on GNSS signals. Additionally, we demonstrate that, under certain conditions, the model can better reproduce the ionospheric variability than a physics-based model, namely the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM).

Performance evaluation of ionospheric models over equatorial Indian region

An extensive year-long evaluation of Total Electron Content (TEC) obtained from NCAR Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIE-GCM) simulations along with TEC obtained from International Reference Ionosphere (IRI-2020) is carried out with respect to observations made by a GPS TEC receiver over the dip equatorial location of Thiruvananthapuram (8.5° N, 77° E, 0.5° magnetic), in the Indian region during solar minimum period of 2005–2006. The TIE-GCM model and IRI model were run for the period of 2005 (November December) and till October 2006 for each day, and the hourly values of TEC were compared to GPS TEC observations. Overall the temporal and seasonal characteristics of TEC over Thiruvananthapuram were simulated reasonably well by the TIE-GCM model and IRI model. The skill scores of normalized Root Mean Square Error (nRMSE), Prediction Efficiency (P.E), and Ratio between maximum and minimum values were estimated for both models to evaluate their performance. The mean percentage difference between the measured and the simulated TEC was found to be around −25% for IRI, indicating underestimation of the observations, and between −40% and −50% for TIE-GCM again indicating underestimation. A comprehensive analysis revealed that there is good conformity between the modeled and measured values for the whole observation period, with a correlation coefficient R-value of 0.8 and 0.9 for the TIE-GCM and IRI models respectively. This study brings out the competence of the two models in simulating the temporal and seasonal pattern of variability of ionospheric TEC over the equatorial Indian region.

Observations and simulations of large-scale traveling ionospheric disturbances during the January 14-15, 2022 geomagnetic storm

Using the total electron content (TEC) observations from GPS, and simulations from the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM), this work investigates the large-scale traveling ionospheric disturbances (LSTIDs) and the possible involved drivers during the geomagnetic storm on January 14-15, 2022. Based on the term analysis of O+ continuity equation in TIEGCM, it is found that the traveling atmospheric disturbances in equatorward winds are responsible for the LSTIDs, with minor contributions from plasma drifts owing to the prompt penetration electric field. A strong interhemispheric asymmetry of the LSTIDs is observed, which might be attributed to both the equatorward wind disturbances and background plasma. The stronger wind (plasma) disturbances occurs in the winter hemisphere than that in the summer hemisphere. The maximum magnitude of LSTIDs in electron density disturbances occurs at ∼250 and ∼270 km in the northern and southern hemispheres, respectively, owing to both the thermospheric equatorward winds and background plasma. An interesting phenomenon that tail-like LSTIDs occur at the dip equator and low latitudes might be related to the eruption of the Tonga volcano, but it is not well reproduced in TIEGCM that deserves further exploration in a future study.

A Comparative Assessment of the Distribution of Joule Heating in Altitude as Estimated in TIE‐GCM and EISCAT Over One Solar Cycle

AbstractDuring geomagnetically active times, Joule (or frictional) heating in the Lower Thermosphere‐Ionosphere is a significant source of thermal energy, greatly affecting density, temperature, composition and circulation. At the same time, Joule heating and the associated Pedersen conductivity are amongst the least known parameters in the upper atmosphere in terms of their quantification and spatial distribution, and their parameterization by geomagnetic parameters shows large discrepancies between estimation methodologies, primarily due to a lack of comprehensive measurements in the region where they maximize. In this work we perform a long‐term statistical comparison of Joule heating as calculated by the NCAR Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM) and as obtained through radar measurements by the European Incoherent Scatter Scientific Association (EISCAT). Statistical estimates of Joule heating and Pedersen conductivity are obtained from a simulation run over the 11 year period spanning from 2009 until 2019 and from radar measurements over the same period, during times of radar measurements. The results are statistically compared in different Magnetic Local Time sectors and Kp level ranges in terms of median values and percentiles of altitude profiles. It is found that Joule heating and Pedersen conductivity are higher on average in TIE‐GCM than in EISCAT for low Kp and are lower than EISCAT for high Kp. It is also found that neutral winds cannot account for the discrepancies between TIE‐GCM and EISCAT. Comparisons point toward the need for a Kp‐dependent parameterization of Joule heating in TIE‐GCM to account for the contribution of small scale effects.

Polar and Equatorial Ionospheric Electrodynamical Coupling Under a Prolonged Northward Bz Interval

AbstractThe interplanetary magnetic field (IMF) significantly influences the global ionospheric electrodynamics, but it is still largely unknown the high‐ and low‐latitude ionospheric electrodynamical coupling under long‐duration northward IMF Bz (NBz) and By conditions. During the long‐duration NBz and duskward By conditions (Kp < 2, AE < 100 nT, SYM‐H > −25 nT) on 20 August 2014, six pairs of magnetometer data showed that daytime equatorial electrojet (EEJ) underwent strong decreases (reach up to 90%) at wide longitudes. Thermosphere‐ionosphere‐electrodynamics general circulation model (TIE‐GCM) captured well the decrease and the control simulations revealed that both effects of the NBz and By significantly change the plasma convection, Joule heating, and thermospheric winds at high latitudes; and penetration electric field (PEF) due to the NBz plays an important role in the decrease of the equatorial electric field. This study indicates the significant NBz effects on the equatorial ionospheric electrodynamics even during weak geomagnetic conditions, apart from the widely believed meteorological effects. Further study should be taken to disclose the relative contribution between geomagnetic and meteorological effects on the decrease of the equatorial electric field.