Thermosphere Ionosphere Electrodynamics General Circulation Model Research Articles

A numerical study of noontime bite-outs in F2-region electron density

Noontime bite-outs in ionospheric F2-region electron density in the geomagnetic equatorial, low, and middle latitudes have been reproduced in this study using the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM). The different driving mechanisms of F2-region noontime bite-outs at different latitudes were further verified by modeling simulation. In the geomagnetic equator, the upward ExB plasma drifts are the main process to produce the noontime bite-outs in ionospheric electron density. In the geomagnetic low latitudes, both the electrical fields and poleward meridional winds play a crucial role in forming the noontime bite-outs. In contrast to the case at the geomagnetic equator, a weaker fountain effect might be an favorable condition for the noontime bite-outs to occur at low latitudes. For geomagnetic middle latitudes, an upward plasma flux and poleward meridional winds are the dominated drivers in producing the noontime bite-outs. Modeling results show that a large upward plasma flux and poleward meridional winds make the noontime bite-outs to occur and observable over middle latitudes.

Interplanetary Control of High‐Latitude Thermospheric Winds: Results From HIWIND and Model Simulations

AbstractBased on the observations from the balloon‐borne instrument High‐altitude Interferometer WIND experiment (HIWIND) and the simulations from the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM), the Grid Agnostic MHD Environment for Research Applications (GAMERA)‐TIEGCM (GT), and the GAMERA‐TIEGCM‐RCM (GTR), we investigate the variations of summer high‐latitude thermospheric winds and their physical mechanisms from 25 to 30 June, 2018. HIWIND observations show that the meridional winds were the largest at midnight and exhibited strong day‐to‐day variations during the 6‐day period, which were generally reproduced by those three models. The day‐to‐day variations of winds were mainly associated with the interplanetary magnetic field (IMF) perturbations, while the magnetic latitude variations also contributed to the large day‐to‐day variations of the winds seen in the observations. Meanwhile, the zonal winds were mostly westward during the daytime, and the wind speed became large, especially in the afternoon, which is related to the westward ion drift velocity. The observed meridional winds tend to turn equatorward during the daytime on some days, while the simulated winds blow mostly poleward except for simulations by the GTR model on 26 June. The GTR model revealed that the equatorward meridional winds on 26 June were associated with strong and negative IMF conditions, which tilts the convection pattern to the prenoon sector. The simulations also revealed that the ring current could contribute to affecting the neutral wind variations, especially under geomagnetically active conditions.

Multiresolution Data Assimilation for Auroral Energy Flux and Mean Energy Using DMSP SSUSI, THEMIS ASI, and An Empirical Model

AbstractWe apply a multiresolution Gaussian process model (Lattice Kriging) to combine satellite observations, ground‐based observations, and an empirical auroral model, to produce the assimilation of auroral energy flux and mean energy over high‐latitude regions. Compared to a simple padding, the assimilation coherently combines various data inputs leading to continuous transitions between different datasets. The multiresolution modeling capability is achieved by allocating multiple layers of basis functions with different resolutions. Higher‐resolution fitting results capture more mesoscale (10–100 s km) structures such as auroral arcs, than the low‐resolution ones and the empirical model. To better reconcile different datasets, two preprocessing steps, temporal interpolation of satellite data and spatial down‐sampling of low‐fidelity data, are implemented. The inherent smoothing effect of the fitting, which causes an unrealistic spreading of the aurora, is mitigated by a post processing step: the K Nearest Neighbor (KNN) algorithm. KNN identifies the probability of a region with significant aurora and thereby eliminates those regions with low values. Thereby, this methodology can be used to maintain realistic and mesoscale auroral structures without boundary issues. We then run the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) driven by the high‐ and low‐resolution auroral assimilations and compare total electron contents (TECs). TIEGCM driven by data assimilation produces enhanced TECs by a factor of ∼2 than the one driven by the empirical aurora, and high‐resolution results show mesoscale structures. Our study shows the value of incorporating realistic auroral inputs via assimilation to drive ionosphere‐thermosphere models for better understanding the consequences of mesoscale phenomena.

On the significant impact of the 17 March 2015 St. Patrick’s Day geomagnetic storm on the ionosphere over Indian region

The response of the ionosphere in the Indian region to the extreme space weather events of 17–19 March 2015 is studied using Global Positioning System (GPS) Total electron Content (TEC) measurements, Thermosphere Ionosphere Electrodynamics-General Circulation Model (TIE-GCM) simulations and High Frequency (HF) Radar observations. The data from Thiruvananthapuram (8.5° N, 77° E geographic, 0.3° N magnetic latitude) and northern hemispheric midlatitude station Hanle (32.80° N, 79° E geographic, 23.9° N magnetic latitude) have been analyzed for the above event. The TEC over Thiruvananthapuram, a dip equatorial location exhibits a decrease during the post sunset hours on 17 March 2015 and is followed by the generation of F region irregularities at an altitude of 600 km, as observed by HF radar as well as TEC scintillations. The TEC over the mid latitude station of Hanle decreased during the storm recovery phase on 18March 2015 in response to negative storm effects. The extent of decrease in TEC as observed during the recovery phase could not be simulated by TIE-GCM over Hanle. This difference is attributed to the enhanced Joule heating taking place in the polar region during St. Patrick’s Day storm and the associated composition changes. An anomalous heating scenario was introduced and the simulated TIE-GCM results were found to match the observations. The present study clearly brings out the impact of 17 March 2015, St. Patrick’s Day geomagnetic storm on the ionization distribution over equatorial as well as mid latitude stations over the Indian region using observations as well as TIE-GCM simulations and the evolutionary features of ionospheric irregularities over equatorial location using TEC and HF radar observations. The role played by thermosphere ionosphere coupling in modulating the ionization variability over equatorial as well as mid latitude region during periods of extreme geomagnetic forcing is highlighted.

Explaining Solar Flare‐Induced Ionospheric Ion Upflow at Millstone Hill (42.6°N)

AbstractPrevious studies have shown that solar flares can significantly affect Earth's ionosphere and induce ion upflow with a magnitude of ∼110 m/s in the topside ionosphere (∼570 km) at Millstone Hill (42.61°N, 71.48°W). We use simulations from the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM) and observations from Incoherent Scatter Radar (ISR) at Millstone Hill to reveal the mechanism of ionospheric ion upflow near the X9.3 flare peak (07:16 LT) on 6 September 2017. The ISR observed ionospheric upflow was captured by the TIEGCM in both magnitude and morphology. The term analysis of the F‐region ion continuity equation during the solar flare shows that the ambipolar diffusion enhancement is the main driver for the upflow in the topside ionosphere, while ion drifts caused by electric fields and neutral winds play a secondary role. Further decomposition of the ambipolar diffusive velocity illustrates that flare‐induced changes in the vertical plasma density gradient is responsible for ion upflow. The changes in the vertical plasma density gradient are mainly due to solar extreme ultraviolet (EUV, 15.5–79.8 nm) induced electron density and temperature enhancements at the F2‐region ionosphere with a minor and indirectly contribution from X‐ray (0–15.5 nm) and ultraviolet (UV, 79.8–102.7 nm).

Unusual Enhancement of Midlatitude Sporadic-E Layers in Response to a Minor Geomagnetic Storm

This study investigates the variations of middle and low latitude sporadic-E (Es) layers in response to a geomagnetic storm. Es layers are observed by five ionosondes located in the Eastern Asian sector. The critical frequencies of Es layers (foEs) at six stations increased in sequence from high latitude stations to low latitude stations after IMF/Bz turning southward. Lomb–Scargle analysis shows the amplification of semidiurnal oscillation amplitude in the vertical height of Es layers during geomagnetic disturbance. Modeling results of the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) show the enhancement of the wind field in the mesosphere and the lower thermosphere (MLT) region. Our study provides evidence that the enhanced wind field in the MLT region during the storm period could result in the enhancement of Es layers at middle and low latitude.

The Effects of IMF By on the Middle Thermosphere During a Geomagnetically “Quiet” Period at Solar Minimum

AbstractNumerical simulations using the National Center for Atmospheric Research (NCAR) thermosphere‐ionosphere‐electrodynamics general circulation model (TIE‐GCM) are performed to elucidate the effects of the interplanetary magnetic field (IMF) on the middle thermosphere composition during a “geomagnetically quiet” period from the day of year (DOY) 110–111 in 2019 (when the Auroral electrojet (AE) index never exceeded 300 nT and the Kp never exceeded 2). In particular, this paper aims to examine how the Global‐scale Observations of the Limb and Disk (GOLD) mission observed daytime thermospheric O and N2 column density ratio (∑O/N2) depletion at mid‐latitudes originated under such a “geomagnetically quiet” condition. A comparison of electric potential, Joule heating rate per unit mass, ion velocity, neutral temperature and winds in the middle thermosphere (∼160 km) between real IMF and without the IMF east‐west component (By) indicates that a By dominant condition can enhance their strengths under this “geomagnetically quiet” condition. Consequently, ∑O/N2 depletion with a stronger magnitude (30% compared with ∼8% without By) and larger disturbed area was introduced in the post‐midnight sector at high‐latitudes due to strong and localized upwelling associated with the enhanced Joule heating rate per unit mass. The ∑O/N2 depletion was transported equatorward and corotated from local post‐midnight to early morning, and was observed by GOLD at middle latitudes during daytime.

Solar Flux Dependence of Post‐Sunset Enhancement in Vertical Total Electron Content Over the Crest Region of Equatorial Ionization Anomaly

AbstractBased on 10 years' of vertical total electron content (VTEC) data in solar cycle 24 from Ahmedabad (23.0°N, 72.6°E, dip angle 35.2°), a station under the crest region of equatorial ionization anomaly (EIA), it is shown that both the integrated residual and total post‐sunset enhancements in VTEC are conspicuous during Equinox and December solstice when solar flux level exceeds 110 solar flux unit (sfu) with the exception of the year 2012–2013. The post‐sunset enhancements are absent in June solstice at this local time even if the solar flux level exceeds 110 sfu. The integrated residual and total VTEC enhancements during post‐sunset hours are found to be linearly correlated with the solar flux level in Equinox and December solstice. It is noted that a parabolic fit works better for the integrated total VTEC enhancement during December solstice suggesting a possible saturation of VTEC enhancements at high solar flux levels. Based on these observations and Thermosphere Ionosphere Electrodynamics‐General circulation model (TIE‐GCM) outputs, it is argued that the pre‐reversal enhancement (PRE) in the equatorial F region zonal electric field works in tandem with latitudinal gradient in the F region plasma density to determine the degree of VTEC enhancement over the EIA crest region during post‐sunset hours. These results highlight the solar flux dependence of the post‐sunset enhancement of VTEC over the crest region and show that sudden stratospheric warming events in 2012–2013 suppressed these enhancements in December solstice even if solar flux levels exceeded 110 sfu.

Significant Variations of Thermospheric Nitric Oxide Cooling during the Minor Geomagnetic Storm on 6 May 2015

Using observations by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument on board the TIMED (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics) satellite and simulations by the TIEGCM (Thermosphere-Ionosphere-Electrodynamics General Circulation Model), we investigate the daytime variations of thermospheric nitric oxide (NO) cooling during the geomagnetic storm on 6 May 2015. The geomagnetic storm was minor, as the minimum Dst was −28 nT, the maximum Kp was 5+ and the maximum AE was 1259 nT. However, significant enhancements of peak NO cooling rate and prominent decreases in the peak NO cooling altitude were observed from high latitudes to low latitudes in both hemispheres on the dayside by the SABER instrument. The model simulations underestimate the response of peak NO cooling and have no significant variation of the altitude of peak NO cooling rate on the dayside during this minor geomagnetic storm. By investigating the temporal and latitudinal variations of vertical NO cooling profiles inferred from SABER data, we suggest that the horizontal equatorward winds caused by the minor geomagnetic storm were unexpectedly strong and thus play an important role in inducing these significant daytime NO cooling variations.

Three‐Dimensional Reconstruction of Tongue of Ionization During the 11 October 2010 Geomagnetic Storm and Evolution Analysis With TIEGCM

AbstractThe three‐dimensional computerized ionospheric tomography (3DCIT) technique that fused multisource data is used to reconstruct the spatial distribution of tongue of ionization (TOI) appeared over Greenland during a moderate geomagnetic storm on 11 October 2010. The reconstruction results are validated with observations from the constellation observing system for meteorology, ionosphere, and climate radio occultations and two ionosonde stations, which show good agreements. The 3DCIT images indicated a zone of high electron density (magnitude of ∼5 TECU) that crossed northern Greenland and electrons were input into the polar region in the anti‐sunward direction after aggregating at midlatitudes, which formed a TOI. The images also revealed that the TOI magnitude was larger in the upper ionosphere ssand lower at 300 and 500 km but still noticeable. Below 300 km, the TOI was difficult to detect. The simulation result of the Thermosphere‐Ionosphere‐Electrodynamic General Circulation Model (TIEGCM) also showed the same TOI structure. Then, we combined the measured ionospheric data and term‐by‐term analysis of the ion continuity formula in TIEGCM to further identify the principal TOI formation mechanisms. We assume that the dominant TOI formation mechanism is electric field transport, which is offset by ambipolar diffusion and neutral wind transport. Furthermore, the uplift of electrons and the insignificant effect of other physical processes explained the insignificant TOI in lower ionosphere.

The geoeffectiveness of TIE-GCM simulations of ionospheric critical frequency foF2 at the equatorial station of Thiruvananthapuram in the Indian sector

An extensive intercomparison of ionospheric foF2 observations and NCAR Thermosphere-Ionosphere ElectrodynamicsGeneral Circulation Model(TIE-GCM)simulations has been carried out for the dip equatorial location of Thiruvananthapuram. Ionosonde measurements for geomagnetically quiet days of 2002, 2006 and 2008, representing solar maximum, solar minimum and deep solar minimum conditions have been used for the analysis.In general TIE-GCM simulations reproduced the temporal and seasonal characteristics of foF2 over Thiruvananthapuram reasonably well for all the three solar activity conditions. Seasonally the difference between the measured and the simulated foF2 tended to be higher during winter (maximum of 25%). Additionally, it is found that TIE-GCM is not reproducing the reduction in the foF2 values in the noon hours i.e. the bite out, which is very prominent in the foF2 observations predominantly during 2002. A detailed analysis revealed that, there is good agreement between the modeled and measured values for the whole observation period, with an R value of 0.81. From the comparison it is clear that the model underestimates the observations in general but for the periods when bite out is prominent, the model gives an over estimation.The comprehensive comparisons during different solar activity conditions have shown that the difference between modeled and measured ionospheric peak densities lies in the range of.10 to −25%. This study brings out the efficacy of the model in simulating the temporal seasonal and solar cycle variability of ionospheric foF2 over the equatorial Indian region.

Effects of Subauroral Polarization Streams on the Equatorial Electrojet During the Geomagnetic Storm on 1 June 2013: 2. The Temporal Variations

AbstractUsing ground‐based magnetic field measurements and numerical simulations from the Thermosphere‐Ionosphere Electrodynamic General Circulation Model (TIEGCM), a first paper (Zhang, Yamazaki, et al., 2021, doi: https://doi.org/10.1029/2021JA029681; under review) introduced the potential roles of disturbance dynamo electric field due to subauroral polarization streams (SAPS) on the equatorial electrojet (EEJ) during a moderate geomagnetic storm on 1 June 2013. Our second study investigated the temporal responses of equatorial electrojet to SAPS. At noon, the residual EEJ (ΔEEJ) owing to SAPS flows westward, that is, counter equatorial electrojet (CEJ). The temporal variation of CEJ excited by the dynamo electric field was basically consistent with that by SAPS, and the effects of zonal wind were larger than those of meridional wind. The relative time delay of CEJ and SAPS was related to the propagation time of disturbance wind from mid‐latitudes to low‐latitudes. It took 2–3 hr for SAPS‐related disturbance wind to propagate to the equatorial region and change the polarity of EEJ. The influence of meridional winds on the temporal variations of ΔEEJ is related to the generation of eastward currents at mid‐latitudes, which can accumulate the positive charges at dusk terminator and then generate a westward electric field at lower latitudes.

Geomagnetically Induced Currents at Middle Latitudes: 1. Quiet‐Time Variability

AbstractGeomagnetically induced currents (GICs) at middle latitudes have received increased attention after reported power grid disruptions due to geomagnetic disturbances. However, quantifying the risk to the electric power grid at middle latitudes is difficult without understanding how the GIC sensors respond to geomagnetic activity on a daily basis. Therefore, in this study the question “Do measured GICs have distinguishable and quantifiable long‐period and short‐period characteristics?” is addressed. The study focuses on the long‐term variability of measured GIC, and establishes the extent to which the variability relates to quiet‐time geomagnetic activity. GIC quiet‐day curves (QDCs) are computed from measured data for each GIC node, covering all four seasons, and then compared with the seasonal variability of thermosphere‐ionosphere‐electrodynamics general circulation model (TIE‐GCM)‐simulated neutral wind and height‐integrated current density. The results show strong evidence that the middle‐latitude nodes routinely respond to the tidal‐driven Sq variation, with a local time and seasonal dependence on the direction of the ionospheric currents, which is specific to each node. The strong dependence of GICs on the Sq currents demonstrates that the GIC QDCs may be employed as a robust baseline from which to quantify the significance of GICs during geomagnetically active times and to isolate those variations to study independently. The QDC‐based significance score computed in this study provides power utilities with a node‐specific measure of the geomagnetic significance of a given GIC observation. Finally, this study shows that the power grid acts as a giant sensor that may detect ionospheric current systems.

Ionospheric Plasma Vertical Drift and Zonal Wind Variations Cause Unusual Evolution of EPBs During a Geomagnetically Quiet Night

AbstractPrevious studies show equatorial plasma bubbles (EPBs) mainly occur after sunset and usually drift from west to east. In this work, two EPBs occurred after midnight and lasted to sunrise, and were observed by multi‐instruments (two all‐sky imagers (ASIs), global positioning system, Swarm satellite, and a digisonde) during a geomagnetically quiet night of December 18–19, 2018. Our observations also show that plasma depletion structure (PDS) also occurred at that night. EPBs occurred in the region of PDS and showed a special evolution process during the night. Those PDS gradually disappeared with time, but strip‐like EPBs remained clearly in airglow images. Near sunrise, new PDS appeared to merge with those EPBs to form large PDS. Meanwhile, EPBs showed different zonal drifts within a very narrow longitudinal zone (∼2°). One EPB remained stationary while the other showed a small eastward drift. These results are different from post‐sunset EPBs in previous studies. During the lifetime of those ionospheric plasma irregularities, upward and downward motion of the peak height and virtual height of the ionospheric F region was observed by a digisonde, which indicates that the evolution of EPBs should be related to the vertical drift of ionospheric plasma. Besides, based Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM) simulations, we suggest the different zonal drifts of those EPBs might related to plasma zonal drifts caused by zonal winds.

English

The study deals with determining ionosphere parameter at low latitudes during the maximum of solar cycle 22 on quiet days. It uses Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) to carry out Total Electron Content (TEC) parameter in the ionosphere region. TEC time variability on summer and winter highlights a seasonal anomaly, a phenomenon observed since 1965 and which appears while radiations coming from the sun are more intensive in summer than in winter under low latitudes. A mathematical approach integrating the time values of TEC parameter is developed to calculate TEC total value during all the season. The study shows that the seasonal anomaly phenomenon is not observed at every time between summer and winter. Comparison of the rate of electrons production matches with solar radiation intensity between summer and winter during a short period. Apparition of winter anomaly phenomenon shows that ultraviolet and X-rays emitted from the Sun are not the only causes of ionization of particles in ionosphere. Other chemical or physical phenomena also contribute to enhance the concentration of electrons in the atmosphere. The estimation of the rate of TEC production in ionosphere F2-layer enables a comparison of summer and winter behavior in ionosphere layer. The study offers a good knowledge of winter anomaly phenomenon.   Key words: Total electron content, thermosphere-ionosphere-electrodynamics general circulation model, winter anomaly, maximum of solar cycle, quiet day.

Understanding the Total Electron Content Variability Over Europe During 2009 and 2019 SSWs

AbstractThe nature of the variability of the Total Electron Content (TEC) over Europe is investigated during 2009 and 2019 Northern Hemisphere (NH) SSW events in this study by using a combination of Global Navigation Satellite System (GNSS) based TEC observations and Thermosphere‐Ionosphere Electrodynamics General Circulation Model (TIE‐GCM) simulations. To simulate the SSW effects in TIE‐GCM, the dynamical fields from the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X) simulations of 2009 and 2019 SSWs are specified at the TIE‐GCM lower boundary. The observed and simulated TEC are in overall good agreement and therefore the simulations are used to understand the sources of mid‐latitude TEC variability during both SSWs. Through comparison of TIE‐GCM simulations with and without geomagnetic forcing, we find that the TEC variability during the 2019 SSW event, was predominantly geomagnetically forced, while for the 2009 SSW, the major variability in TEC was accounted for by the changes in vertically propagating migrating semidiurnal solar (SW2) and lunar (M2) tides. By comparing the TIE‐GCM simulations with and without the SW2 and M2 tides, we find that these semidiurnal tides contribute to 20%–25% increase in the quiet background TEC.

The Impact of Perturbing Eddy Diffusion and Upper Boundary on the Ionosphere EnKF Assimilation System

AbstractAccurate representation of ensemble members of coupled Ionosphere‐Thermosphere (I‐T) is crucial to the ionosphere forecast in the ensemble Kalman filter (EnKF) data assimilation system. In this paper, besides the model drivers used in previous studies, including the solar 10.7 cm radio flux (F10.7), auroral hemispheric power (HP) and cross‐tail potential drop (CP), the eddy diffusion coefficient (ED), and nighttime vertical O+ flux at the top boundary are also perturbed to generate ensemble members. Based on our developed EnKF data assimilation system, the impact of perturbing different model external forcing parameters on ensemble generation and forecast capability of ionosphere and thermosphere has been investigated in detail through a series of sensitivity tests and data assimilation experiments. This system uses the National Center for Atmospheric Research (NCAR) Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) as a background model. The findings are summarized as follows: (a) Associated with perturbing two additional model forcing parameters, better ensemble members of ionosphere and thermosphere states of the background model can be generated during both daytime and nighttime. (b) The improvement of the forecast capability of the ionosphere and thermosphere variables can be further enhanced. This study can provide a reference for ensemble generating strategy for the coupled I‐T EnKF data assimilation in the future.

The Solar Eclipse Effects on the Upper Thermosphere

AbstractTheoretical studies have shown that the solar eclipse can have significant impacts on the thermospheric mass density, which, however, has not been confirmed from the observational perspective. In this study, we present direct observations of the thermospheric density responses to three solar eclipses based on the measurements of Gravity Recovery and Climate Experiment (GRACE) and Gravity field and steady state Ocean Circulation Explorer (GOCE). It was observed that the eclipses induced about 20% and 25% density depletions at GRACE altitudes (360 and 480 km, respectively) and about 10% depletions at GOCE altitudes (∼270 km). Moreover, the eclipse could generate large‐scale traveling atmospheric disturbances (TADs), which propagate globally even from the duskside to the dawnside after the eclipse ended. Those thermospheric responses could be generally reproduced by Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). However, the simulated densities recover more rapidly than the observations at the duskside. This study provides observational evidence to validate the results from theoretical models and further bring insights into the mechanism of eclipse effects on the ionosphere‐thermosphere system.

Towards probing Earth\u2019s upper mantle with daily magnetic field variations: exploring a physics-based parametrization of the source

The electromagnetic (EM) field variations capable of probing the electrical conductivity of the upper mantle and mantle transition zone have a period range between a few hours and 1 day. At these periods, the dominant source of the EM signals is the ionospheric current system, which has a complex spatial and temporal structure. A concept of global-to-local (G2L) transfer functions can handle spatially complex source by relating global source expansion coefficients with locally measured magnetic (or/and electric) fields. When estimating the G2L transfer functions, the source is commonly expanded into spherical harmonics (SH). In this paper, we explore an alternative parametrization of the source based on a principal component analysis (PCA) of the Fourier transformed output from the physics-based Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM). Specifically, we investigate whether magnetic fields computed in the realistic three-dimensional conductivity model of Earth excited by the PCA-based source agree better with observatory data than those computed in the same model but induced by the SH-based source. Using PCA to capture the source current compared to SH parametrization, we find that agreement with the observatory data is better during magnetically disturbed times and at shorter periods. Vice versa, it is poorer during magnetically quiet times and at longer periods.

Longitudinal Variations of Equatorial Ionospheric Electric Fields Near Sunrise

AbstractIn this work, we carry out a comprehensive modeling study, using the Thermosphere–Ionosphere–Electrodynamics General Circulation Model, to explore the physical processes by which the longitude‐dependent geomagnetic field drives the longitudinal variations of the sunrise enhancement of the zonal electric fields at the dip equator near the June solstice. Numerical experiments and diagnostic analyses of the electrodynamics equation show that the longitudinal differences of the equatorial zonal electric fields near sunrise are primarily associated with the longitudinal variations in the zonal wind dynamo, with those from the meridional wind dynamo contributing secondarily. Furthermore, the longitudinal differences of the wind dynamo near sunrise are mainly related to the longitudinal variations of and conductance, which are caused primarily by the direct influence of the longitudinal structures of magnetic field declination and strength. Meanwhile, the longitudinal variations of neutral winds, which also result in moderate longitudinal variations, play a secondary role in the longitudinal variations of the neutral wind dynamo, while plasma density, which has minor longitudinal differences near sunrise, contributes slightly by modifying the conductance. Overall, the sunrise enhancement in June is more significant at the longitudes where the magnetic field strength and distortion are larger or the magnetic field declination is smaller in the Northern Hemisphere.