Keywords:Horizontal temperature gradients, polar MLT, sodium LIDAR, EISCAT, Tromsoe
Based on about 2700 hours of temperature data obtained with the Tromsoe sodium LIDAR, we have investigated horizontal temperature differences (i.e. temperature gradient) in the polar MLT region between October and March. The sodium LIDAR operated at the EISCAT Tromsoe site (69.6 deg. N, 19.2 deg. E) has a capability of simultaneous five-beam observations; i.e. temperature and sodium density data are obtained simultaneously with good time and altitude resolutions (3 min/500m). In addition to vertical observations, the sodium LIDAR observed volumes of four different directions with azimuth and elevation of (0 deg., 77.5 deg.), (90 deg., 77.5 deg.), (180 deg., 77.5 deg.), and (270 deg., 77.5 deg.) between October 2013 and March 2017, while the elevation angle of 60 degree was set between October 2012 and March 2013, and between October 2017 and March 2018. These configurations allow us to derive horizontal temperature difference between about 80 and 107 km.
We have analyzed (so far) about 184 nights of temperature data sets. The horizontal temperature gradient is found to be in range from about 0.5 K/km to -0.5 K/km for northward and eastward directions, and on average (nighly mean) in range from about 0.05 K/km to -0.05 K/km. We will report temporal and altitude variations of the tempetarure gradient, changes of nightly mean temperature gradients in accordance with SSWs, and comparison with GAIA calculations.