Lower Atmospheric Sources of Observed Thermosphere Medium Scale Traveling Atmospheric Disturbances Over Alaska During the 2012-2013 Winter Months

This paper investigates the lower-to-upper atmosphere coupling at high latitudes (>60 degrees N) during the northern winter months of 2012-2013 years, which includes a period of major Sudden "Stratospheric" Warming (SSW). We perform statistical analysis of thermosphere wind disturbances with periods of 30-70 min, known as the medium scale traveling atmospheric disturbances (MSTADs) in atomic oxygen green line (557.7 nm) near similar to 120 km and red line (630.0 nm) emissions near similar to 250 km observed from Scanning Doppler Imagers (SDIs) over Alaska. The SDI MSTADs observations (60 degrees-75 degrees N) are interpreted in conjunction with the previous daytime medium-scale traveling ionospheric disturbance (MSTID) observations by SuperDARN midlatitudes (35 degrees-65 degrees N) radars in the F-region ionosphere and western hemisphere, which confirm findings from the SDI instruments. Increases in MSTAD activity from SDIs show correlations with the increasing meridional planetary wave (PW) amplitudes in the stratosphere derived from MERRA2 winds. Furthermore, a detailed study of the lower atmospheric conditions from MERRA2 winds indicates that the lower atmospheric sources of MSTADs are likely due to the stratospheric generated Gravity Waves (GWs) and not orographic GWs. Favorable stratospheric propagation conditions and polar vortex disturbances resulting from the increased PW activity in the stratospheric region both appear to contribute to increased MSTAD activity in the thermosphere. Additionally, the results show that the MSTID activity from SuperDARN HF radars at mid latitudes during the January 2013 SSW is lower than the MSTAD activity in SDI winds at high latitudes. Plain Language Summary The objective of this paper is to investigate how Atmospheric Gravity Waves (GWs) contribute to the vertical coupling of the atmosphere-ionosphere system. When propagating from below, GWs can create medium-scale traveling atmospheric disturbances (MSTADs) in the thermosphere, which in turn generate medium-scale traveling ionospheric disturbances (MSTIDs) in the ionosphere. This study examines the coupling between the lower and upper atmosphere at high latitudes (>60 degrees N) during the winter of 2012-2013, including a period of Sudden "Stratospheric" Warming (SSW) and quiet geomagnetic conditions. The analysis of MSTAD day-to-day activity observed using Scanning Doppler Imagers that measure airglow emissions in Alaska confirms similar MSTID activity in observed ion density from SuperDARN mid-latitudes radars. The study also confirms that the increased MSTAD activity in the lower-to-upper thermosphere is due to stratospheric-generated GWs, rather than orographic GWs, and is linked to increased planetary wave activity in the stratospheric meridional winds and polar vortex disturbances. Therefore, the paper not only highlights the global characteristics of thermosphere GW-like variations in the western hemisphere but also their connection to lower atmosphere dynamics.