Interhemispheric Asymmetries in the Large‐Scale Traveling Atmospheric and Ionospheric Disturbances During the 5–6 August 2011 Geomagnetic Storm

Abstract In this study, we investigate the interhemispheric asymmetry (IHA) in high‐latitude Joule heating during the initial phase of the 5–6 August 2011 storm. We also examine its relationship with IHAs in the large‐scale traveling atmospheric and ionospheric disturbances (LSTADs/LSTIDs) in the American sector. The analysis is carried out using the Global Ionosphere Thermosphere Model (GITM) driven by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) field‐aligned current (FAC) patterns together with a series of ground‐based and satellite observations. First, GITM simulation results indicate that Joule heating during the initial phase in the Northern Hemisphere (NH) is roughly twice that in the Southern Hemisphere (SH) and exhibits pronounced IHAs in terms of spatial distribution. Particularly, at the beginning of the initial phase, Joule heating deposited in the NH is concentrated in the afternoon sector, where the American sector is located, while the SH shows minimal heating in the same sector. Second, the GITM simulation results reveal that the strong NH Joule heating launches an equatorward‐propagating LSTAD/LSTID first. About an hour later, enhanced duskside Joule heating in the SH generates another LSTAD/LSTID. The two disturbances propagate with comparable phase speeds, so the NH one reaches the geomagnetic equator earlier than its SH counterpart. Such IHAs in the LSTAD/LSTID have also been confirmed by the observations. Moreover, observations further reveal an additional NH LSTAD/LSTID likely triggered by regional heating near the onset of the initial phase, which is not reproduced by GITM due to limitations in resolving regional electrodynamic forcings in FAC patterns.