Abstract

--- - "Although much work has been done to characterize the global response of Earth's upper atmosphere to geomagnetic storms, much is unknown regarding the response on mesoscales (similar to 30-500 km). In order to understand how the nightside, high-latitude ionosphere responds on these scales during storms, we have characterized widths, velocities, and occurrence rates of equatorward and poleward mesoscale flows. We characterized them according to main phase versus recovery phase as well as coronal mass ejection (CME) versus high-speed stream (HSS) storms. Some results include the following: Mesoscale flows are faster during the main phase of the storms. Faster flows >400 m/s are more frequent and probable during CME storms as compared to HSS storms, but more flows occur during HSS storms. Polar cap flows are wider during CMEs than during HSSs. There is a postmidnight preference for polar cap mesoscale flows during storms, especially during recovery phase and during HSSs." - Plain Language Summary Geomagnetic storms are the Sun's most effective way to transport energy from the solar wind into the Earth system. The type of storm and the phase of the storm (its developing vs. its recovering phase) drive Earth's system differently and therefore create different types of disturbances to Earth's nearby space and upper atmosphere. Our study characterizes and contrasts one type of disturbance-30-500 km wide, nightside upper atmosphere plasma flows-during two types of storms and during the two storm phases. We found the flow characteristics are different between the types and phases of storms. For example, more flows occur during one type of storm, but faster flows occur during the other. Plasma flows at these scale sizes have not been studied until recently, but their effects may be very important to the global Earth system. Our results can be input into global models to improve them and to better understand and predict Earth's response to storms.