SABER observation of storm�time hemispheric asymmetry in nitric oxide radiative emission

The nitric oxide (NO) 5.3 mu m radiative emission is the dominating and most efficient cooling agent in the thermosphere above 100 km. The NO 5.3 mu m radiative cooling is an important parameter, particularly during geomagnetic storm events, to quantify the energy budget within the magnetosphere-ionosphere-thermosphere system. We utilize the TIMED (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics)/SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) observations of NO radiative cooling to investigate the storm-time hemispheric asymmetry during 2002-2018. The auxiliary parameters such as NO density, atomic oxygen density, thermospheric temperature, and the meridional wind are obtained from the TIEGCM (Thermosphere-Ionosphere-Electrodynamics General Circulation Model) simulations. We analyze the events that occurred close to (or during) the equinox periods to get rid of the effect of seasonal asymmetry. The TIEGCM-simulated NO density and meridional wind show hemispheric asymmetry during geomagnetic storm event. Almost no hemispheric variation in TIEGCM-atomic oxygen and -thermospheric temperature is noticeable. The SABER-observed and the TIEGCM-simulated radiative flux exhibits higher values in the northern and southern hemispheres, respectively, during the events close to (or during) March and September equinox. Our analysis shows that the storm-time meridional wind could play an important role resulting in the hemispheric asymmetry by changing the density and temperature.