Daytime thermospheric disturbance winds, transients and transport 2019-2021

Geomagnetic storms affect Earth’s middle to low-latitude ionosphere through processes that occur in the magnetosphere-ionosphere-thermosphere system over short and longer-term (hours and days) time scales. In particular, storm-time transients in high-altitude Joule heating and ion circulation can change the thermospheric wind, causing large scale gravity waves (GWs) with periods of 60-90 minutes and horizontal wavelengths of 1000-2000 km. These waves carry large transient winds (>100 m/s) that can drive ion motion and transient electric potentials. The duration and magnitude of the high altitude heating can lead to longer period changes in mean winds over hours to days, extending globally. If the disturbances extend to the daytime equatorial region and into the E-region wind dynamo (110-160 km), they can modify the dense daytime ionosphere. We analyze three years of ICON mission data and identify dozens of geomagnetic events that travel north or south along magnetic meridians from the poles, driving GWs to the equator in the F-region. Many such events were associated with changes in the mean meridional winds, which indicate an effect on global circulation. A smaller number of storms have changes in zonal mean winds, which are most effective in generating electric fields that can modify the ionosphere. Our results show that the running sum of Ae is a better proxy for low-middle latitude wind disturbance than magnetic indices.