Observations of Enhanced Semi Diurnal Lunar Tides in the Mesosphere and Lower Thermosphere at Mid and High Northern Latitudes during Sudden Stratospheric Warming Events

Abstract:

In recent years, there have been a series of reported ground- and satellite-based observations of lunar tide signatures in the equatorial and low latitude ionosphere around sudden stratospheric warming (SSW) events. More recently, Pedatella et al. [2014], using the Whole Atmosphere Community Climate Model Extended version (WACCM-X) and the thermosphere-ionosphere-mesosphere electrodynamics general circulation model (TIME-GCM) has demonstrated that the semi-diurnal lunar tide (M2) is an important contributor to the ionosphere variability during the 2009 SSW. Although the model results were focused on the low-latitude ionosphere and compare with Jicamarca electric fields, Pedatella et al. [2014] also reported that the M2 was enhanced in the northern mid and high latitudes (between 30 and 70oN) at mesospheric and lower thermospheric altitudes during the 2009 SSW. Motivated by this finding, we have analyzed winds from 80 to 100 kms obtained with meteor radars from Juliusruh (54^oN) and Andøya (69^oN) stations during five SSWs (2008, 2009, 2010, 2012, and 2013). By fitting the usual solar components (diurnal and semidiurnal and M2, we have been able to identify clearly the enhancement of the M2 as well as the semi diurnal solar tide during all these SSWs. The qualitative agreement with the Pedatella et al. [2014] simulations is very good, i.e., stronger signature at 54^oN than at 69^oN and enhanced around SSW. The analysis of other SSWs not only show the clear relationship with SSWs, but also the different behaviors in strength, time of occurrence, duration, etc., that appear to be associated to the mean wind dynamics as well as the stratospheric planetary wave characteristics.