Impacts of Different Causes on the Inter‐Hemispheric Asymmetry of Ionosphere‐Thermosphere System at Mid‐ and High‐Latitudes: GITM Simulations

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.

Inter-hemispheric asymmetries in high-latitude electrodynamic forcing and the thermosphere during the October 8–9, 2012, geomagnetic storm: An integrated data–Model investigation

“…All the red and blue lines correspond to the NH and SH, respectively. Following Hong et al (2021), the asymmetry index (AI) is used to quantify the temporal changes of IHA for a given quantity:…”

“…Due to Earth's seasonal dipole tilt, the geomagnetic field configuration, and asymmetric high-latitude forcing (Hong et al, 2021), the storm-time IT responses can be significantly different between the Northern and Southern hemispheres, known as the IT system inter-hemispheric asymmetry (IHA). While all the causes are important, this study focuses on high-latitude forcing since the seasonal effect is considered to be reduced due to the data interval being near the equinox.…”

Investigation of the Southern Hemisphere Mid‐High Latitude Thermospheric ∑O/N2 Responses to the Space‐X Storm

“…The hemispheric asymmetry in solar irradiance (during non-equinoctial periods), asymmetric offset between the geographic and geomagnetic axes in the two hemispheres and non-dipolar terms of the geomagnetic field (Förster & Cnossen, 2013;Laundal et al, 2017) produce hemispheric differences in the momentum and heating sources in the upper atmosphere, which result in significant interhemispheric differences in the thermosphere and ionosphere responses to geomagnetic disturbances (Astafyeva et al, 2020;Hong et al, 2021;Knipp et al, 2021;Wang et al, 2021;Zhu et al, 2022). Notably, the mechanisms of thermospheric composition responses to geomagnetic storms were mainly based on the limited observations in the northern hemisphere (Burns et al, 1991(Burns et al, , 1995Prölss, 1980Prölss, , 2011.…”

Violation of Hemispheric Symmetry in Integrated Poynting Flux via an Empirical Model

“…Förster and Haaland (2015) also find an asymmetry in the appearance of the flow patterns. Also, some authors compare the summer and winter hemispheres (e.g., Papitashvili and Rich (2002)), or dark versus illuminated regions (Liou and Mitchell (2020)), or instantaneous conditions (Hong et al (2021), a model-based study). Although less directly relevant, these kinds of studies provide complimentary information that may be useful in sorting out the causes of asymmetry.…”