The role of nitric oxide in thermospheric response to different storm drivers

When present in the lower atmosphere nitric oxide (NO) is considered a pollutant, however, NO in the thermosphere plays a pivotal role in thermal balance. It is effectively nature's thermostat for controlling the upper atmosphere response to extreme energy deposition from solar and geospace storms. Emissions from NO at 5.3 μm, NO+ at 4.3 μm, and CO2 at 4.3 and 15 μm are the largest sources of IR radiative energy dissipation. Several mechanisms produce NO in the upper atmosphere. Photoelectrons created by solar soft X-rays, and auroral energetic particle precipitation and Joule heating enhance NO density. Shortwave photons and auroral particles ionize and dissociate N2. The resultant excited N atoms combine with O2 producing NO that peaks around 110 km. Enhanced auroral Joule heating drives a temperature‐sensitive reaction of ground state N with O2 which is the main NO production mechanism at altitudes > 140 km. We report on several upper atmospheric heating events where the cooling effects of NO were in direct competition with various sources of energy input. We show that knowing which source of NO is actively cooling and when it is doing so, is key to forecasting thermospheric expansion associated with satellite drag.