Thermospheric recovery during the 5 April 2010 geomagnetic storm

Thermospheric temperature and density recovery during the 5 April 2010 geomagnetic storm have been investigated. Neutral density recovery as revealed by Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) simulations is slower than observations from the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE), CHAllenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) satellites, suggesting that the cooling processes may not be fully represented in the model. NO radiative cooling rate from TIEGCM is also compared with measurements from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite along satellite orbits during this storm period. It is found that the model overestimates the NO cooling rate at low latitudes and underestimates it at high latitudes. The effects of particle precipitation on the NO number density and NO cooling rate at high latitudes are examined in detail. Model experiments show that while NO number density and NO cooling rate do change with different specifications of particle precipitation, neutral temperature and density recovery remain more or less the same. The latest reaction rates of key NO chemistry are tested as well, and the NO number density between 110 and 150 km is found to be very sensitive to the reaction rate of N(2D) + O2 → NO + O. A temperature-dependent reaction rate for the N(2D) + O2 → NO + O reaction proposed by Duff et al. [2003] brings the TIEGCM NO cooling rate at high latitudes closer to the SABER observations. With the temperature-dependent reaction rate, the neutral density recovery time becomes quite close to the observations in the high latitude southern hemisphere, but discrepancies still exist at low latitudes and in the northern hemisphere, which calls for further investigation.