Three‐dimensional GCM modeling of nitric oxide in the lower thermosphere

Abstract

The coupled middle atmosphere and thermosphere (CMAT) general circulation model has been used to predict the global distribution of nitric oxide (NO) in the lower thermosphere. This three‐dimensional (3‐D) model incorporates a complex ion and neutral chemical scheme, high‐resolution solar flux data and variable auroral energy inputs. Comparison of simulated NO densities with those observed by the Student Nitric Oxide Explorer (SNOE) show that the CMAT model is able to recreate large‐scale features in the observed NO distribution under differing geophysical conditions. While previous studies have used 1‐D photochemical models to speculate on the latitudinal extent of aurorally produced NO, we have simulated NO production and transport in three dimensions under both geomagnetically stable and disturbed conditions. We have shown that the spatial and temporal distribution of aurorally produced NO is highly variable with location and local time. CMAT simulations suggest that under moderate geomagnetic conditions, the most equatorward geographic latitudes to be influenced by aurorally produced NO are 30°S and 45°N. Under conditions of high geomagnetic activity, aurorally produced NO is present at latitudes poleward of 15°S and 28°N. The asymmetry in latitudinal extent is attributed to the greater offset between geographic and geomagnetic poles in the southern hemisphere. NO density maxima are predicted to occur between 14 and 48 hours after a period of high geomagnetic activity, their spatial and temporal distribution depending on location with respect to the auroral oval and local time at which auroral forcing occurs.