Lunar tide in the thermosphere and weakening of the northern polar vortex

Abstract

AbstractThe lunar tide and its variability are beginning to be realized as elements of ionosphere‐thermosphere weather. Herein we demonstrate that an enhancement in M2 amplitude at 110 km in the dynamo region is related to the timing and intensity of stratospheric polar vortex weakening (PVW). Timing of the PVW, which typically occurs during January–February, changes on the order of 4–7 d/yr between 2002 and 2013 and the M2 enhancement changes with it, with a time delay of order 2.8 days. The M2 temperature amplitude at 110 km as determined from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) measurements on the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) spacecraft increases linearly from about 20 K to 29 K as the westward zonal mean zonal wind increases from about 10 m s−1 to 80 m s−1 at 70°N and 48 km altitude in accord with PVW events from year to year according to Modern‐Era Retrospective Analysis for Research and Applications (MERRA) data. These relationships point to a level of predictability regarding impacts of the lunar tide on thermosphere and ionosphere densities, winds, and plasma drifts.