A theoretical study of the responses of mesosphere and lower thermosphere (MLT) winds to geomagnetic storms at middle latitudes

Friday, May 3, 2019

In a recent work, we found that, in the mesosphere and lower thermosphere (MLT) region at middle latitudes, adiabatic heating/cooling and vertical heat advection, both associated with vertical wind changes, are the dominant processes that determine the temperature responses to storms.

Image of meridional acceleration terms
Differences of meridional acceleration terms from 00:00 to 24:00 UT on 17/04/2002 simulated by the TIMEGCM at the location of (40°N, 105°W) from (a) 90-600 km and (b) 94-110 km. The red dashed lines indicate the storm onset time.

However, the cause of MLT vertical wind changes during storms have not been elucidated. Thus there is a compelling need to understand how and why the wind changes during storms in the MLT region. Here we address this question by exploring theoretically the processes that determine the MLT wind response to storms at middle latitudes. During the early phase of the storm, the middle-latitude upper thermospheric wind changes are greater and occur earlier than those in the MLT region. The horizontal wind changes cause vertical winds changes, which are transmitted to the MLT region. The pressure gradient produced by the temperature changes associated with vertical wind changes and the Coriolis force are the dominant processes that drive storm time MLT wind changes at middle latitudes. Momentum advection is minor. As the storms evolve, the enhanced temperatures produce upward vertical winds. The upward vertical winds then lead to a depleted temperature, which consequently alters the horizontal wind pattern again.

Publication Name: Journal of Geophysical Research: Space Physics
First HAO Author's Name: Wenbin Wang