On the responses of mesosphere and lower thermosphere temperatures to geomagnetic storms at low and middle latitudes

Friday, September 14, 2018

Observations from lidars and satellites have shown that large temperature increases and decreases occur in the middle and low latitudes of the mesosphere and lower thermosphere (MLT) region during geomagnetic storms.

Temporal variations of Kp image
(top row) Temporal variations of Kp between 17th and 23rd April, 2002: the black solid line shows the real Kp values during the storm and the red line is a constant Kp value of 3.0 for non-disturbed conditions. The second to bottom rows are the Tn differences at 60°N, 40°N, and 20°N in the height range of 94-110 km between TIMEGCM simulations driven by real Kp values and by a constant value of Kp of 3.0. The left column is for the longitude of 105°W where the geomagnetic storm began at 02:00 LT. The right column is for the longitude of 30°E and the onset of the geomagnetic storm was at 11:00 LT. The left y-axis is pressure levels and the right y-axis is the corresponding altitudes. The red dashed lines indicate the beginning of the geomagnetic storm.

We undertake first-principles simulations of the MLT temperature response to storms using the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIMEGCM) to elucidate the nature and causes of these changes. Temperature variations were not uniform; instead nighttime temperature changed earlier than the daytime temperature; and temperatures changed earlier at high latitudes than at low ones. Furthermore, temperatures increased in some places/times and decreased in others. As the simulation behaves similarly to observations, it provides an opportunity to understand the processes that drive the observed changes. Our analysis has shown that they were produced mainly by the adiabatic heating/cooling that is associated with the vertical winds resulting from global wind circulation changes, with additional contributions from vertical heat advection.

Publication Name: Geophysical Research Letters

First HAO Author's Name: Jingyuan Li