Storm Time Variation of Radiative Cooling by Nitric Oxide as Observed by TIMED‐SABER and GUVI

Abstract The variation of O/N 2 (reference to N 2 column density 10 17 cm −2 ) and nitric oxide radiative emission flux exiting the thermosphere have been studied over the Northern Hemisphere during the superstorm event of 7–12 November 2004. The data have been obtained from Global Ultraviolet Imager (GUVI) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on board the National Aeronautics and Space Administration (NASA)'s Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) satellite. The NO radiative flux is observed to show an anti‐correlation with O/N 2 on a global scale. Both NO radiative flux and O/N 2 ratio show equatorward motion with maximum penetration in western longitude sectors. A local variation of O, O 2 , and N 2 densities have been calculated using NRLMSISE‐00 model over a midlatitude location (55°N,180°E). On a local scale, model calculated O/O 2 and O/N 2 ratios are found to follow the observations made by GUVI. The collisional excitation of NO with atomic oxygen is the most dominant process for the total cooling rate. The SABER‐retrieved NO cooling rate (CR) at a local site suggests an enhancement during the storm period with the peak emission rate closely correlated to the progression of the storm. The peak emission altitude of NO CR moves upward during the main phase of the storm. The NO abundance has been calculated by using cooling rate and Nitric Oxide Empirical Model (NOEM) model. Both these suggest a vary large (3–15 times) increase in NO density during the storm, which is required to account the changes in NO radiative flux. A similar kind of enhancement in NO abundance is also noticed in Student Nitric Oxide Explorer observations during intense geomagnetic storms.