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Abstract During the second recovery phase of the 13–14 March 2022 storm, intense high‐latitude neutral mass density spikes are detected by satellites at ∼500 km in both hemispheres. These density spikes, accurately modeled by the Global Ionospheric Thermosphere Model (GITM), are identified as high‐latitude neutral mass density anomalies (HDAs). The GITM simulation indicates that these HDAs, which extends over the polar region, are important features in high‐latitude neutral density. Furthermore, GITM reveals that these HDAs are manifestations of transpolar traveling atmospheric disturbances triggered on the dawn side. Moreover, GITM also reveals significant interhemispheric asymmetries (IHAs) in the magnitude, propagation speed, and propagation direction of HDAs, which are linked to the IHAs in the distribution and magnitude of Joule heating deposited as well as the thermospheric background conditions. This study presents a dynamic perspective on the IHA of storm‐time high‐latitude neutral density variations that is particularly helpful to the proper interpretation of satellite observations. 

Abstract High latitude upper atmospheric inter‐hemispheric asymmetry (IHA) tends to be enhanced during geomagnetic storms, which may be due to the complex spatiotemporal changes and magnitude modifications in field aligned currents (FACs) and particle precipitation (PP). However, the relative contribution of FACs and PP to IHA in high‐latitude forcing and energy is not well understood. The IHA during the 2015 St. Patrick’s Day storm has been investigated using the global ionosphere thermosphere model (GITM), driven by FACs from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) and PP from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE). A comprehensive study of the (a) relative contributions of FACs and PP to electric potential and Joule heating and (b) sensitivity of electric potential and Joule heating to the changes in magnitude and distribution of FACs and PP is presented. The results indicate that FACs lead to larger potential and Joule heating changes compared with PP. The spatial variations of potential and Joule heating are also affected by variation in FACs. As for asymmetric magnitude and distribution, it is found that electric potential and Joule heating are more sensitive to changes in the distribution of FACs and PP than the magnitude of FACs and PP. A new spatial asymmetry index (SAI) is introduced, which reveals spatial asymmetric details that are often overlooked by previous studies. This sensitivity study reveals the relative contributions in high‐latitude forcing and emphasizes the importance of obtaining accurate FACs and PP in both hemispheres. 

Inter-hemispheric asymmetry (IHA) in Earth’s ionosphere–thermosphere (IT) system can be associated with high-latitude forcing that intensifies during storm time, e.g., ion convection, auroral electron precipitation, and energy deposition, but a comprehensive understanding of the pathways that generate IHA in the IT is lacking. Numerical simulations can help address this issue, but accurate specification of high-latitude forcing is needed. In this study, we utilize the Active Magnetosphere and Planetary Electrodynamics Response Experiment-revised fieldaligned currents (FACs) to specify the high-latitude electric potential in the Global Ionosphere and Thermosphere Model (GITM) during the October 8–9, 2012, storm. Our result illustrates the advantages of the FAC-driven technique in capturing high-latitude ion drift, ion convection equatorial boundary, and the storm-time neutral density response observed by satellite. First, it is found that the cross-polar-cap potential, hemispheric power, and ion convection distribution can be highly asymmetric between two hemispheres with a clear B_ydependence in the convection equatorial boundary. Comparison with simulation based on mirror precipitation suggests that the convection distribution is more sensitive to FAC, while its intensity also depends on the ionospheric conductance-related precipitation. Second, the IHA in the neutral density response closely follows the IHA in the total Joule heating dissipation with a time delay. Stronger Joule heating deposited associated with greater high-latitude electric potential in the southern hemisphere during the focus period generates more neutral density as well, which provides some evidences that the high-latitude forcing could become the dominant factor to IHAs in the thermosphere when near the equinox. Our study improves the understanding of storm-time IHA in high-latitude forcing and the IT system. 

Abstract The impacts of solar eclipses on the ionosphere‐thermosphere system particularly the composition, density, and transport are studied using numerical simulation and subsequent model‐data comparison. We introduce a newly developed model of a solar eclipse mask (shadow) at extreme ultraviolet (EUV) wavelengths—PyEclipse—that computes the corresponding shadowing as a function of space, time, and wavelength of the input solar image. The current model includes interfaces for Solar Dynamics Observatory and Geostationary Operational Environmental Satellites EUV telescopes providing solar images at nine different wavelengths. We show the significance of the EUV eclipse shadow spatial variability and that it varies significantly with wavelength owing to the highly variable solar coronal emissions. We demonstrate geometrical differences between the EUV eclipse shadow compared to a geometrically symmetric simplification revealing changes in occultation vary ±20%. The EUV eclipse mask is validated with in situ solar flux measurements by the PRoject for Onboard Autonomy 2/Large Yield Radiometer instrument suite showing the model captures the morphology and amplitudes of transient variability while the modeled gradients are slower. The effects of spatially EUV eclipse masks are investigated with Global Ionosphere Thermosphere Model for the 21 August 2017 eclipse. The results reveal that the modeled EUV eclipse mask, in comparison with the geometrically symmetric approximation, causes changes in the Total Electron Content in order of ±20%, 5%–20% in F‐region plasma drift, and 20%–30% in F‐region neutral winds. 

Abstract The geomagnetic storm on February 3, 2022 caused the loss of 38 Starlink satellites of Space‐X. The Global‐scale Observations of the Limb and Disk (GOLD) observations and Multi‐Scale Atmosphere Geospace Environment (MAGE) model simulations are utilized to investigate the thermospheric composition responses to the Space‐X storm. The percentage difference of the GOLD observed thermospheric O and N₂column density ratio (∑O/N₂) between the storm time (February 3, Day‐of‐Year [DOY] 34) and quiet time (DOY 32) shows a depletion region in the local noon sector mid‐high latitudes in the southern hemisphere, which corresponds to the east side of GOLD field‐of‐view (FOV). This is different from the classic theory of thermospheric composition disturbance during geomagnetic storms, under which the ∑O/N₂depletion is usually generated at local midnight and high latitudes, and thus, appear on the west side of GOLD FOV. MAGE simulations reproduce the observations qualitatively and indicate that the ∑O/N₂depletion is formed due to strong upwelling in the local morning caused by strong Joule heating. Interestingly, enhanced equatorward winds appear near local midnight, but also in the local morning sector, which transports ∑O/N₂depletion equatorward. The depletion corotates toward the local afternoon and is observed in the GOLD FOV. The equatorward winds in the local morning are due to the ion‐neutral coupling under the conditions of a dominant positive interplanetary magnetic field east‐west component (B_y) during the storm. 

Abstract In this study, the Global Ionosphere Thermosphere Model is utilized to investigate the inter‐hemispheric asymmetry in the ionosphere‐thermosphere (I‐T) system at mid‐ and high‐latitudes (|geographic latitude| > 45°) associated with inter‐hemispheric differences in (a) the solar irradiance, (b) geomagnetic field, and (c) magnetospheric forcing under moderate geomagnetic conditions. Specifically, we have quantified the relative significance of the above three causes to the inter‐hemispheric asymmetries in the spatially weighted averaged E‐region electron density, F‐region neutral mass density, and horizontal neutral wind along with the hemispheric‐integrated Joule heating. Further, an asymmetry index defined as the percentage differences of these four quantities between the northern and southern hemispheres (|geographic latitude| > 45°) was calculated. It is found that: (a) The difference of the solar extreme ulutraviolet (EUV) irradiance plays a dominant role in causing inter‐hemispheric asymmetries in the four examined I‐T quantities. Typically, the asymmetry index for the E‐region electron density and integrated Joule heating at solstices with F10.7 = 150 sfu can reach 92.97% and 38.25%, respectively. (b) The asymmetric geomagnetic field can result in a strong daily variation of inter‐hemispheric asymmetries in the F‐region neutral wind and hemispheric‐integrated Joule heating over geographic coordinates. Their amplitude of asymmetry indices can be as large as 20.81% and 42.52%, which can be comparable to the solar EUV irradiance effect. (c) The contributions of the asymmetric magnetospheric forcing, including particle precipitation and ion convection pattern, can cause the asymmetry of integrated Joule heating as significant as 28.43% and 34.72%, respectively, which can be even stronger than other causes when the geomagnetic activity is intense.