Thermospheric meridional circulation during sudden stratospheric warming events

Wednesday, 17 December 2014
Fazlul Laskar and Pallam Raju Duggirala, Physical Research Laboratory, Ahmedabad, India
Oxygen dayglow emission intensities, at OI 557.7, OI 630.0, and OI 777.4 nm, over a low-latitude location showed systematic enhancements in intensities throughout the daytime hours during the four sudden stratospheric warming (SSW) events that occurred in the years 2010 – 2013. The arctic latitude lower thermospheric temperatures at around 120 km altitudes obtained from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument are found to be enhanced during SSW events and show a latitudinal gradient (temperature decreasing towards low-latitudes). Commensurately, the Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) Doppler Interferometer (TIDI) measurements showed equatorward winds in the mesosphere lower thermosphere (MLT) altitudes over high latitudes during these events. Both, the high-latitude lower thermospheric temperature enhancements and the MLT region equatorward winds occur simultaneously with the observed enhancements in the OI dayglow emission intensities at all the wavelengths. From these observations and other supporting observational and modeling results it is proposed that a new cell of meridional circulation in the MLT winds is set up during SSW events, which enables transport of atomic oxygen from high-to-low latitudes. Such an additional contribution of oxygen density over low-latitudes interacts with daytime lower thermospheric dynamics and is attributed to be the cause for the observed enhancement in the oxygen daytime optical emission intensities over low-latitudes. These results will presented in the light of experimental evidence to such circulation alluded to by earlier simulation studies.