The Midnight Temperature Maximum during Sudden Stratospheric Warmings at Arecibo

Abstract:

The midnight temperature maximum (MTM) is a common nighttime feature in the low latitude thermosphere/ionosphere. The MTM is a local maximum in temperature around local midnight. This feature has been observed for decades but accurately modeling it has proved difficult. More recent modeling efforts have been able to produce a realistic MTM but the different components driving it and its day-to-day variability are not well understood. Specifically, sudden stratospheric warming (SSW) events are known to produce a considerable amount of day-to-day variability in the thermosphere/ionosphere. Further, a previous study using incoherent scatter radar (ISR) observations from Arecibo claimed that the magnitude of the MTM increases 5-10 times its nominal amplitude during a SSW. Therefore, in this work we use a combined data-modeling approach to study the impact of two different SSWs on the MTM at Arecibo. Numerical experiments performed using both a standard and nudged versions of the National Center for Atmospheric Research thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) were compared with ISR data from Arecibo during the January 2010 and 2013 SSWs, and during January 2014 in which no SSW occurred. Prominent initial results to emerge from this work include: (1) Standard TIME-GCM simulations show a consistent MTM every night driven by higher order tidal perturbations but do not produce the day-to-day variability seen in the ISR observations; (2) Constraining the stratosphere and mesosphere of TIME-GCM using Navy Global Environmental Model a high-altitude version (NAVGEM-HA) analyses induce more day-to-day variability in the modeled MTM, but still do not completely reproduce ISR observations at Arecibo; (3) Neither ISR observations nor TIME-GCM simulations support a 5-10 times large MTM amplitude during the January 2010 or 2013 SSW events. Finally, the dynamical mechanisms responsible for driving the MTM are analyzed, and possible improvements in model physics for future thermosphere/ionosphere models to accurately reproduce the MTM are discussed.