Thermosphere Ionosphere Electrodynamics General Circulation Model Research Articles

SABER Observation of Storm‐Time Hemispheric Asymmetry in Nitric Oxide Radiative Emission

AbstractThe nitric oxide (NO) 5.3 μm radiative emission is the dominating and most efficient cooling agent in the thermosphere above 100 km. The NO 5.3 μm radiative cooling is an important parameter, particularly during geomagnetic storm events, to quantify the energy budget within the magnetosphere‐ionosphere‐thermosphere system. We utilize the TIMED (Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics)/SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) observations of NO radiative cooling to investigate the storm‐time hemispheric asymmetry during 2002–2018. The auxiliary parameters such as NO density, atomic oxygen density, thermospheric temperature, and the meridional wind are obtained from the TIEGCM (Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model) simulations. We analyze the events that occurred close to (or during) the equinox periods to get rid of the effect of seasonal asymmetry. The TIEGCM‐simulated NO density and meridional wind show hemispheric asymmetry during geomagnetic storm event. Almost no hemispheric variation in TIEGCM‐atomic oxygen and ‐thermospheric temperature is noticeable. The SABER‐observed and the TIEGCM‐simulated radiative flux exhibits higher values in the northern and southern hemispheres, respectively, during the events close to (or during) March and September equinox. Our analysis shows that the storm‐time meridional wind could play an important role resulting in the hemispheric asymmetry by changing the density and temperature.

On the Effects of Mesospheric and Lower Thermospheric Oxygen Chemistry on the Thermosphere and Ionosphere Semiannual Oscillation

AbstractThis study quantifies mesosphere/lower thermosphere (MLT) oxygen chemical contributions to the global thermosphere‐ionosphere (T‐I) semiannual oscillation (SAO) using a series of numerical experiments from the National Center for Atmospheric Research (NCAR) thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model (TIME‐GCM) that isolate essential chemical processes affecting O and O2 in the MLT region. We track the vertical dynamical, diffusive, and chemical fluxes of O and O2 in and out of two control volumes between ∼80 and 130 km using a finite volume approach to the individual species continuity equation to investigate their relative importance on the global T‐I SAO. TIME‐GCM results indicate that the global T‐I SAO amplitude and phase is fairly insensitive to significant changes in odd oxygen chemical reaction rates in the MLT. While chemistry has an appreciable effect on O in the MLT region, sensitivity to changes in odd oxygen and odd hydrogen chemical rates appear to be offset by a consequent adjustment in the vertical bulk wind and eddy diffusive transport of O locally, rendering their effects inconsequential to the global T‐I SAO aloft. The implications of our findings for reproducing a self‐consistent global T‐I SAO in the NCAR thermosphere‐ionosphere‐electrodynamics general circulation model (TIE‐GCM) with a lower boundary near ∼100 km are discussed. Specifically, including latitude‐season variations in O, O2, and N2 from NRLMSIS® 2.0 at the lower boundary of the TIE‐GCM near ∼100 km improves its representation of the climatological T‐I SAO. However, reformulating the TIE‐GCM temperature lower boundary condition could further improve its ability to simulate the T‐I SAO from first‐principles.

A Comparative Study of Ionospheric Day‐To‐Day Variability Over Wuhan Based on Ionosonde Measurements and Model Simulations

AbstractIonospheric day‐to‐day variability is essential for understanding the space environment, while it is still challenging to properly quantify and forecast. In the present work, the day‐to‐day variability of F2 layer peak electron densities (NmF2) is examined from both observational and modeling perspectives. Ionosonde data over Wuhan station (30.5°N, 114.5°E; 19.3°N magnetic latitude) are compared with simulations from the specific dynamics Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (SD‐WACCM‐X) and the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM) in 2009 and 2012. Both SD‐WACCM‐X and TIEGCM are driven by the realistic 3 h geomagnetic index and daily solar input, and the former includes self‐consistently solved physics and chemistry in the lower atmosphere. The correlation coefficient between observations and SD‐WACCM‐X simulations is much larger than that of the TIEGCM simulations, especially during dusk in 2009 and nighttime in 2012. Both the observed and SD‐WACCM‐X simulated day‐to‐day variability of NmF2 reveal a similar day‐night dependence in 2012 that increases large during the nighttime and decreases during the daytime, and shows favorable consistency of daytime variability in 2009. Both the observations and SD‐WACCM‐X simulations also display semiannual variations in nighttime NmF2 variability, although the month with maximum variability is slightly different. However, TIEGCM does not reproduce the day‐night dependence or the semiannual variations well. The results emphasize the necessity for realistic lower atmospheric perturbations to characterize ionospheric day‐to‐day variability. This work also provides a validation of the SD‐WACCM‐X in terms of ionospheric day‐to‐day variability.

GNSS-based hardware-in-the-loop simulations of spacecraft formation flying with the global ionospheric model TIEGCM

Low-earth-orbit (LEO) spacecraft formation flying (SFF) simulated on the Virginia Tech Formation Flying Testbed (VTFFTB) demonstrated the feasibility of detecting simplified ionospheric electron density (Ne) structures (i.e., one-dimensional equatorial plasma bubbles/EPBs) utilizing a differential total electron content (TEC) method. The Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) is used to greatly enhance the ionospheric Ne simulation capability and fidelity (e.g., dimension, resolution, more realistic space weather processes) of GNSS-based hardware-in-the-loop (HIL) simulations in the current work. An algorithm is developed to incorporate TIEGCM 4D ionospheric Ne profiles into the VTFFTB HIL infrastructure by simulating the TEC impacts on multi-band GNSS signals. First, a series of first-principle analyses on ionospheric Ne retrieval accuracy are presented using software-based LEO SFF simulations in the TIEGCM ionosphere. Subsequently, two HIL ionospheric space weather observation simulation test cases, EPB and Tongues-of-Ionization (TOI), are simulated on the VTFFTB to demonstrate the enhanced 4D ionospheric simulation capability and evaluate the Ne retrieval characteristics. The Ne retrieval techniques are validated and characterized in the TIEGCM ionosphere via both software and HIL simulations. In principle, the technique developed is expected to be applicable to other similar simulation platforms, as well as other global or regional ionospheric models. This is advantageous for future GNSS testing, HIL simulations, and technology developments.

Azimuthal averaging–reconstruction filtering techniques for finite-difference general circulation models in spherical geometry

Abstract. When solving hydrodynamic equations in spherical or cylindrical geometry using explicit finite-difference schemes, a major difficulty is that the time step is greatly restricted by the clustering of azimuthal cells near the pole due to the Courant–Friedrichs–Lewy condition. This paper adapts the azimuthal averaging–reconstruction (ring average) technique to finite-difference schemes in order to mitigate the time step constraint in spherical and cylindrical coordinates. The finite-difference ring average technique averages physical quantities based on an effective grid and then reconstructs the solution back to the original grid in a piecewise, monotonic way. The algorithm is implemented in a community upper-atmospheric model, the Thermosphere–Ionosphere Electrodynamics General Circulation Model (TIEGCM), with a horizontal resolution up to 0.625∘×0.625∘ in geographic longitude–latitude coordinates, which enables the capability of resolving critical mesoscale structures within the TIEGCM. Numerical experiments have shown that the ring average technique introduces minimal artifacts in the polar region of general circulation model (GCM) solutions, which is a significant improvement compared to commonly used low-pass filtering techniques such as the fast Fourier transform method. Since the finite-difference adaption of the ring average technique is a post-solver type of algorithm, which requires no changes to the original computational grid and numerical algorithms, it has also been implemented in much more complicated models with extended physical–chemical modules such as the Coupled Magnetosphere–Ionosphere–Thermosphere (CMIT) model and the Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (WACCM-X). The implementation of ring average techniques in both models enables CMIT and WACCM-X to perform global simulations with a much higher resolution than that used in the community versions. The new technique is not only a significant improvement in space weather modeling capability, but it can also be adapted to more general finite-difference solvers for hyperbolic equations in spherical and polar geometries. Highlights. The ring average technique is adapted to solve the issue of clustered grid cells in polar and spherical coordinates with a finite-difference method. The ring average technique is applied to develop a 0.625∘×0.625∘ high-resolution TIEGCM and more complicated geoscientific models with polar and spherical coordinates as well as finite-difference numerical schemes. The high-resolution TIEGCM shows good capability in resolving mesoscale structures in the ionosphere–thermosphere (I–T) system.

Observations and Simulations of the Peak Response Time of Thermospheric Mass Density to the 27‐Day Solar EUV Flux Variation

AbstractIn this study, the mass densities from Challenging Minisatellite Payload and Gravity Recovery and Climate Experiment satellites and the simulation results from the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) have been used to systematically explore the peak response time (or time delay hereafter) of thermospheric mass density to the 27‐day solar extreme ultraviolet (EUV) flux variation. The TIEGCM can generally reproduce the observed time delay of thermospheric mass density to the 27‐day solar EUV flux changes. The simulation results suggest that the delay of the peak of thermospheric mass density to that of the 27‐day solar EUV flux variation is about 0.9 days. However, geomagnetic activity can significantly affect the derivation of the time delay of thermospheric mass density from the pure solar EUV flux impact. Additionally, the delay of thermospheric mass density to the 27‐day solar EUV flux changes with altitude, latitude, and local time.

Nighttime meridional neutral wind responses to SAPS simulated by the TIEGCM: a universal time effect

The present work uses the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM), under geomagnetically disturbed conditions that are closely related to the southward interplanetary magnetic field (IMF), to investigate how the nighttime poleward wind (30°–50° magnetic latitude and 19–22 magnetic local time) responds to subauroral polarization streams (SAPS) that commence at different universal times (UTs). The SAPS effects on the poleward winds show a remarkable UT variation, with weaker magnitudes at 00 and 12 UT than at 06 and 18 UT. The strongest poleward wind emerges when SAPS commence at 06 UT, and the weakest poleward wind develops when SAPS occur at 00 UT. A diagnostic analysis of model results shows that the pressure gradient is more prominent for the developing of the poleward wind at 00 and 12 UT. Meanwhile, the effect of ion drag is important in the modulation of the poleward wind velocity at 06 and 18 UT. This is caused by the misalignment of the geomagnetic and geographic coordinate systems, resulting in a large component of ion drag in the geographically northward (southward) direction due to channel orientation of the SAPS at 06 and 18 UT (00 and 12 UT). The Coriolis force effect induced by westward winds maximizes (minimizes) when SAPS commence at 12 UT (00 UT). The centrifugal force due to the accelerated westward winds shows similar UT variations as the Coriolis force, but with an opposite effect.

Magnetosphere‐Ionosphere Coupling via Prescribed Field‐Aligned Current Simulated by the TIEGCM

AbstractThe magnetosphere‐ionosphere (MI) coupling is crucial in modeling the thermosphere‐ionosphere (TI) response to geomagnetic activity. In general circulation models (GCMs) the MI coupling is typically realized by specifying the ion convection and auroral particle precipitation patterns from for example, empirical or assimilative models. Assimilative models, such as the Assimilative Mapping of Ionospheric Electrodynamics, have the advantage that the ion convection and auroral particle precipitation patterns are mutually consistent and based on available observations. However, assimilating a large set of diverse data requires expert knowledge and is time consuming. Empirical models, on the other hand, are convenient to use, but do not capture all the observed spatial and temporal variations. With the availability of Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) data, there is an opportunity for employing field‐aligned currents (FAC) in GCMs to represent the MI coupling. In this study, we will introduce a new method which enables us to use observed FAC in GCMs and solve for the interhemispherically asymmetric electric potential distribution. We compare Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM) simulations of a geomagnetic storm period using the new approach and two other often‐used methods for specifying MI coupling based on empirical and assimilative high latitude electric potentials. The comparison shows general similarities of the TI storm time response and improved temporal variability of the new method compared to using empirical models, but results also illustrate substantial differences due to our uncertain knowledge about the MI coupling process.

Modelling diurnal variation magnetic fields due to ionospheric currents

SUMMARY Accurate models of the spatial structure of ionospheric magnetic fields in the diurnal variation (DV) band (periods of a few hours to a day) would enable use of magneto-variational methods for 3-D imaging of upper mantle and transition zone electrical conductivity. Constraints on conductivity at these depths, below what is typically possible with magnetotellurics, would in turn provide valuable constraints on mantle hydration and Earths deep water cycle. As a step towards this objective, we present here a novel approach to empirical modelling of global DV magnetic fields. First, we apply frequency domain (FD) principal components analysis (PCA) to ground-based geomagnetic data, to define the dominant spatial and temporal modes of source variability. Spatial modes are restricted to the available data sites, but corresponding temporal modes are effectively continuous in time. Secondly, we apply FD PCA to gridded surface magnetic fields derived from outputs of the physics-based Thermosphere–Ionosphere–Electrodynamics General Circulation Model (TIEGCM), to determine the dominant modes of spatial variability. The TIEGCM spatial modes are then used as basis functions, to fit (or interpolate) the sparsely sampled data spatial modes. Combining the two steps, we have a FD model of DV band global magnetic fields that is continuous in both space and time. We show that the FD model can easily be transformed back to the time domain (TD) to directly fit time-series data, allowing the use of satellite, as well as ground-based, data in the empirical modelling scheme. As an illustration of the methodology we construct global FD and TD models of DV band source fields for 1997–2018. So far, the model uses only ground-based data, from 127 geomagnetic observatories. We show that the model accurately reproduces surface magnetic fields in both active and quiet times, including those at sites not used for model construction. This empirical model, especially with future enhancements, will have many applications: improved imaging of electrical conductivity, ionospheric studies and improved external field corrections for core and crustal studies.

GNSS-based simulation of spacecraft formation flight: A case study of ionospheric plasma remote sensing

Future space weather missions using spacecraft formation flying can provide more robust, flexible, sustainable, and low-cost observational capability on multi-scale ionospheric plasma structures. The Virginia Tech Formation Flying Testbed (VTFFTB), a hardware-in-the-loop simulation testbed using multi-constellation, multi-frequency global navigation satellite systems (GNSS), has recently been developed to simulate closed-loop, real-time spacecraft formation flight with a group of 2 or 3 satellites at low Earth orbits (LEO). Onboard GNSS receivers are used for formation navigation as well as ionospheric plasma irregularities measurements. In a VTFFTB simulation, the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) was integrated to simulate Equatorial plasma bubbles (EPB) and study the EPB impacts on GNSS signals tracked by LEO formation satellites. This case study demonstrates the VTFFTB application to study the ionospheric plasma impacts on GNSS-related technologies using global space weather models and facilitates development of new ionospheric remote sensing techniques.

An investigation of mid-latitude ionospheric peak in TEC using the TIEGCM

A local maximum value of ionospheric total electron content (TEC) in midlatitude regions, named midlatitude ionospheric peak in this study, has been frequently observed during both the daytime and nighttime. We have carried out a modeling study of midlatitude ionospheric peaks in TEC using the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) to investigate possible mechanisms driving these peaks. Comparisons between model results and Global Position System (GPS) TEC observations in the solar minimum year of 2009 show that TIEGCM can reproduce the nighttime and daytime midlatitude ionospheric peaks. Model results indicate that midlatitude ionospheric peaks in the daytime and nighttime are likely caused by different mechanisms. Nighttime midlatitude ionospheric peaks are attributed to the downwards-moving plasma ambipolar diffusive flux from the plasmasphere. However, the daytime upwards-moving plasma ambipolar diffusive flux and poleward meridional winds, which can cause ionospheric depletion, might play dominated roles in producing midlatitude ionospheric peaks in the early morning in the winter season.

Importance of Regional‐Scale Auroral Precipitation and Electrical Field Variability to the Storm‐Time Thermospheric Temperature Enhancement and Inversion Layer (TTEIL) in the Antarctic E Region

AbstractA dramatic thermospheric temperature enhancement and inversion layer (TTEIL) was observed by the Fe Boltzmann lidar at McMurdo, Antarctica during a geomagnetic storm (Chu et al. 2011, https://doi.org/10.1029/2011GL050016). The Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM) driven by empirical auroral precipitation and background electric fields cannot adequately reproduce the TTEIL. We incorporate the Defense Meteorological Satellite Program (DMSP)/Special Sensor Ultraviolet Spectrographic Imager (SSUSI) auroral precipitation maps, which capture the regional‐scale features into TIEGCM and add subgrid electric field variability in the regions with strong auroral activity. These modifications enable the simulation of neutral temperatures closer to lidar observations and neutral densities closer to GRACE satellite observations (~475 km). The regional scale auroral precipitation and electric field variabilities are both needed to generate strong Joule heating that peaks around 120 km. The resulting temperature increase leads to the change of pressure gradients, thus inducing a horizontal divergence of air flow and large upward winds that increase with altitude. Associated with the upwelling wind is the adiabatic cooling gradually increasing with altitude and peaking at ~200 km. The intense Joule heating around 120 km and strong cooling above result in differential heating that produces a sharp TTEIL. However, vertical heat advection broadens the TTEIL and raises the temperature peak from ~120 to ~150 km, causing simulations deviating from observations. Strong local Joule heating also excites traveling atmospheric disturbances that carry the TTEIL signatures to other regions. Our study suggests the importance of including fine‐structure auroral precipitation and subgrid electric field variability in the modeling of storm‐time ionosphere‐thermosphere responses.

On the Assessment of Daily Equatorial Plasma Bubble Occurrence Modeling and Forecasting

AbstractPredicting the daily variability of Equatorial Plasma Bubbles (EPBs) is an ongoing scientific challenge. Various methods for predicting EPBs have been developed, however, the research community is yet to scrutinize the methods for evaluating and comparing these prediction models/techniques. In this study, 12 months of co‐located GPS and UHF scintillation observations spanning South America, Atlantic/Western Africa, Southeast Asia, and Pacific sectors are used to evaluate the Generalized Rayleigh‐Taylor (R‐T) growth rates calculated from the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). Various assessment metrics are explored, including the use of significance testing on skill scores for threshold selection. The sensitivity of these skill scores to data set type (i.e., GPS versus UHF) and data set size (30, 50, 60, and 90 days/events) is also investigated. It is shown that between 50 and 90 days is required to achieve a statistically significant skill score. Methods for conducting model‐model comparisons are also explored, including the use of model “sufficiency.” However, it is shown that the results of model‐model comparisons must be carefully interpreted and can be heavily dependent on the data set used. It is also demonstrated that the observation data set must exhibit an appropriate level of daily EPB variability in order to assess the true strength of a given model/technique. Other limitations and considerations on assessment metrics and future challenges for EPB prediction studies are also discussed.

English

Ionosphere region is the part of atmosphere layer where radio waves reflect for telecommunication. This is due to its composition in particles. Solar radiation hit particles in ionosphere. This phenomenon causes an ionization of particles in the ionosphere. According to the particles density in this region, radio waves emitted in telecommunication can pass through this region or be reflected. The ionization of ionosphere depends on solar cycle phase, season, and local time that are all closely linked to solar activity. Many models are developed to carry out ionosphere parameters. They are all focused to find a better approach of ionosphere behavior. The present study uses Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) to investigate ionosphere region, during solar maximum and minimum phases. The critical frequency of F2-layer (foF2) and the total electron content (TEC) parameters are carried out by running the model. The values of the parameters are represented on a three-axis graph to give an overview of their time profiles. The seasonal and annual results obtained from this study show a good correlation between TIEGCM and International Reference Ionosphere (IRI) model predictions in the same conditions. The study confirms that particles density in ionosphere behaves as an obstacle for waves transmission. During solar maximum, characterized by a high solar activity, ionization of ionosphere is higher than that at solar minimum. This is similar to what is observed between nighttime and daytime. The study also highlights the “winter anomaly” phenomenon. Key words: Thermosphere-Ionosphere-electrodynamics general circulation model (TIEGCM), international reference ionosphere (IRI), solar cycle phase, solar activity, critical frequency of F2-layer (foF2), total electron content (TEC).

Different Peak Response Time of Daytime Thermospheric Neutral Species to the 27‐Day Solar EUV Flux Variations

AbstractPrevious work suggested that the peak response time of the mass densities of atomic oxygen (O) and molecular nitrogen (N2) in the thermosphere had more than a 1‐day difference relative to the peak of the 27‐day periodic variation of solar extreme ultraviolet (EUV) flux. In this study, we used the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) to explore the physical mechanisms responsible for the different peak response times of the daytime thermospheric neutral species. It was found that the peak response time of O or N2 mass density corresponds to the time of equilibrium between the contributions from the barometric effect and the change in its abundance. The peak response time of O is shorter than that of thermospheric temperature Tn, due to a dynamic change in the circulation that acts to cancel out the contribution from the barometric process prior to the peak of Tn. On the contrary, the change of N2 abundance contributes further to a decrease of N2 mass density on a constant pressure surface when the thermosphere is expanding. The change of chemical loss leads to a longer peak response time of N2 abundance than that due to barometric motion. Therefore, an equilibrium is reached after the barometric effect turns from expansion (contraction) to contraction (expansion), so that the peak response time of N2 is longer than that of Tn. Moreover, the meridional circulation in the thermosphere modulates the latitudinal dependence of the peak response time of thermospheric neutral species.

Influence of Nonmigrating Tides and Geomagnetic Field Geometry on the Diurnal and Longitudinal Variations of the Equatorial Electrojet

AbstractIn this study, equatorial electrojets (EEJs) simulated by the Thermosphere‐Ionosphere Electrodynamics General Circulation Model (TIE‐GCM) were compared with those observed by ground‐based magnetometers and the Challenging Minisatellite Payload (CHAMP) satellite. Simulations were performed with or without nonmigrating tidal forcing at the lower boundary and in the frame of the International Geomagnetic Reference Field (IGRF) or dipole field. The model forced by the nonmigrating tides could qualitatively reproduce the local time and longitudinal variation of an EEJ in the frame of the IGRF with accuracy. The tides were important in causing the later local time occurrence of the EEJ peak in the Peruvian sector, and they favored the occurrence of the morning counterelectrojet (CEJ) in the frame of the IGRF. The difference in the EEJ peak intensity between the Peruvian and Indian stations was enhanced due to the tidal effect. The net effect of the tides on the two‐station difference was almost doubled in the dipole field compared with that in the IGRF. The TIE‐GCM with a tidal input could reproduce a Wavenumber‐4 longitudinal structure of the noontime EEJ, but it underestimated the peak EEJ in the East Asia sector. The magnetically eastward electric field and the neutral zonal wind at noontime in the E region in the TIE‐GCM were both weak in the East Asia sector. This model‐data discrepancy was at least partly due to insufficient lower boundary forcing in this longitudinal sector.

Variations of Lower Thermospheric FUV Emissions Based on GOLD Observations and GLOW Modeling.

Here we compare the global‐scale morphology of Earth's the Far‐Ultraviolet (FUV) emissions observed by NASA's Global‐scale Observations of Limb and Disk (GOLD) mission to those modeled using the Global Airglow (GLOW) code with atmospheric parameters provided by Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM). The O 5S oxygen (135.6 nm) and N2 Lyman‐Birge‐Hopfield (LBH) emissions are observed over the Western hemisphere every 30 min by the GOLD instrument. The FUV brightness of the thermosphere‐ionosphere is expected to vary in systemic ways with respect to geophysical parameters, solar energy input from above, and terrestrial weather input from below. In this paper we examine the O 5S oxygen emission and the N2 LBH emission brightnesses with local time, latitude, season, tides, geomagnetic activity, and solar activity based on GOLD observations and GLOW modeling. Early GOLD observations indicate that the model effectively reproduces the brightness variations with local time and latitude but is biased low in magnitude. However, the TIEGCM is unable to accurately represent the extraordinary nighttime equatorial ionization anomaly observed by GOLD. It is also expected from these results that the signal from geomagnetic storms may obscure tidal signals.

Planetary Wave (PW) Generation in the Thermosphere Driven by the PW‐Modulated Tidal Spectrum

AbstractThe National Center for Atmospheric Research thermosphere‐ionosphere‐electrodynamics general circulation model (TIE‐GCM) is used to conduct numerical experiments that isolate and elucidate a substantial modification of the quasi‐6‐day wave (Q6DW) above 110 km due to presence of the planetary wave (PW)‐modulated tidal spectrum. A two‐stage nonlinear tidal interaction is proposed, and its role in vertical coupling by the Q6DW is quantified. The theory enables calculation of net Q6DW accelerations and heating rates in the height‐latitude domain (90–300 km; ±75°) due to wave‐wave interactions of up to 10 ms−1 day−1 and 8 K day−1, respectively. The Global‐Scale Wave Model (GSMW) is used to demonstrate that these forcings produce Q6DW zonal and meridional wind amplitudes, and temperatures, of order 5–20 ms−1, 5–15 ms−1, and 5–10 K, respectively. Notably, Q6DW thermal forcing in the GSWM accounts for near‐doubling of the wind magnitudes calculated with momentum forcing alone. The computed values are comparable to the 10–22 ms−1, 3–12 ms−1, and 4–12 KQ6DW amplitudes calculated with lower‐boundary forcing of the Q6DW also included. The proposed two‐stage interaction plausibly impacts other PW wind structures in the dynamo region and thus how PW in general participate in atmosphere‐ionosphere coupling.

Equatorial plasma bubbles developing around sunrise observed by an all-sky imager and global navigation satellite system network during storm time

Abstract. A large number of studies have shown that equatorial plasma bubbles (EPBs) occur mainly after sunset, and they usually drift eastward. However, in this paper, an unusual EPB event was simultaneously observed by an all-sky imager and the global navigation satellite system (GNSS) network in southern China, during the recovery phase of a geomagnetic storm that happened on 6–8 November 2015. Observations from both techniques show that the EPBs appeared near dawn. Interestingly, the observational results show that the EPBs continued to develop after sunrise, and they disappeared about 1 h after sunrise. The development stage of EPBs lasted for at least about 3 h. To our knowledge, this is the first time that the evolution of EPBs developing around sunrise was observed by an all-sky imager and the GNSS network. Our observation showed that the EPBs drifted westward, which was different from the usual eastward drifts of post-sunset EPBs. The simulation from the Thermosphere–Ionosphere–Electrodynamics General Circulation Model (TIE-GCM) suggest that the westward drift of EPBs should be related to the enhanced westward winds at storm time. Besides this, bifurcation and merging processes of EPBs were observed by the all-sky imager in the event. Associated with the development of EPBs, an increase in the peak height of the ionospheric F region was also observed near sunrise, and we suggest the enhanced upward vertical plasma drift during the geomagnetic storm plays a major role in triggering the EPBs near sunrise.

Thermosphere‐Ionosphere Modeling With Forecastable Inputs: Case Study of the June 2012 High‐Speed Stream Geomagnetic Storm

AbstractForecasting conditions in the thermosphere and ionosphere is a key outcome expected from space weather research. In this work, we perform numerical simulations using the first‐principles models Global Ionosphere‐Thermosphere Model (GITM) and Thermosphere‐Ionosphere Electrodynamics General Circulation Model (TIE‐GCM) to address the reliability of thermospheric‐ionospheric forecasts. When considering forecasts applicable to periods of geomagnetic activity, careful consideration is required of model inputs, which largely determine how the models will simulate disturbed conditions. We adopt an approach to drive the models with solar wind parameters and the 10.7 cm solar radio flux. This aligns our investigation with recent research and operational activities to forecast solar wind conditions on the Earth a few days in advance. In this work, we examine a weak geomagnetic storm, the June 2012 high‐speed‐stream event, for which we drive GITM and TIE‐GCM with observed solar wind and F10.7 values. We find general agreement between the simulations and observation‐based Global Ionospheric Maps of the total electron content (TEC) response. However, overestimated TEC response is found in the middle to low latitudinal region of the American sector and surrounding areas for both GITM and TIE‐GCM during similar time periods. By conducting numerical modeling experiments and comparing the modeling results with observational data, we find that the overestimated TEC response can be almost equally attributed to the solar wind driving and F10.7 driving during the June 2012 event. We conclude that the accuracy of the high‐latitude electric field and the solar irradiance is crucial to reproduce the TEC response in forecastable‐mode modeling.