The natural thermostat of nitric oxide emission at 5.3 μm in the thermosphere observed during the solar storms of April 2002

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment on the Thermosphere-Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite observed the infrared radiative response of the thermosphere to the solar storm events of April 2002. Large radiance enhancements were observed at 5.3 μm, which are due to emission from the vibration-rotation bands of nitric oxide (NO). The emission by NO is indicative of the conversion of solar energy to infrared radiation within the atmosphere and represents a \textquotedblleftnatural thermostat\textquotedblright by which heat and energy are efficiently lost from the thermosphere to space and to the lower atmosphere. We describe the SABER observations at 5.3 μm and their interpretation in terms of energy loss. The infrared enhancements remain only for a few days, indicating that such perturbations to the thermospheric state, while dramatic, are short-lived.