Speaker
Description
The near-Earth space environment is strongly influenced by the solar wind and embedded interplanetary magnetic field. Therefore a thorough understanding of the upper atmosphere response during the passage of geoeffective solar wind transients, such as high-speed streams/stream interaction regions (HSS/SIR) and interplanetary coronal mass ejections (ICMEs) is crucial for accurate space weather predictions. A key mechanism in dissipating the solar wind energy in the upper atmosphere is auroral Joule heating, which causes thermal expansion of the thermosphere, increasing the thermospheric density and causing low Earth orbiting (LEO) satellites to experience more drag. Applying a novel method for determining the Joule heating using AMPERE, SuperMAG and SuperDARN data, we study the northern hemispheric Joule heating and global thermospheric neutral density enhancements at Swarm and GRACE satellites during 231 geomagnetic storms between 2014 and 2024 by using superposed epoch analysis. It is found that the Joule heating in the ionospheric E-region and thermospheric neutral density enhancements at the altitude of the Swarm and GRACE satellites (350 – 550 km) show characteristics which depend on the geomagnetic storm driver. The Joule heating has a fast increase at the beginning of the storm main phase when the storm is initiated by a HSS/SIR or by the sheath region of ICMEs. In comparison, a more gradual and longer lasting increase is found in storms driven by magnetic clouds within ICMEs. This is in line with previous results of the total field-aligned and ionospheric currents during storms (Pedersen et al., 2021, 2022). The thermospheric neutral density as referenced to 450 km altitude increases gradually during the storm main phase to about 120% of the quiet time density, and the enhancements are typically largest and longest-lasting for storms driven by magnetic clouds. This is likely because of the prolonged interval of increased Joule heating during magnetic cloud-driven storms.
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