Joule heating and neutral density enhancements during geomagnetic storms driven by solar wind high-speed streams and coronal mass ejections

Understanding both the spatial and temporal dynamics of the near-Earth space environment is important for successful forecasting of space weather. One example is the auroral Joule heating which causes thermal expansion of the upper atmosphere, increasing the thermospheric density and causing low Earth orbiting (LEO) satellites to experience more drag. This chain of events often begins when geoeffective solar wind transients such as high-speed stream/stream interaction regions (HSS/SIR) or interplanetary coronal mass ejections (ICME) impact Earth’s space environment. Applying a novel method for determining the Joule heating using AMPERE, SuperMAG and SuperDARN data, we study the northern hemispheric Joule heating and global neutral density enhancements at Swarm and GRACE satellites during 231 geomagnetic storms between 2014 and 2024. It is found that the Joule heating in the ionospheric E-region and 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 superposed epoch analysis of the thermospheric density 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.