Global and Seasonal Extent of the Thermospheric Midnight Temperature Maximum as Seen in O(1D) Nightglow by WINDII and Simulated by C-IAM

Abstract:

Manifestations of thermospheric dynamics are observed in the variations of upper atmosphere neutral winds, temperature, density and F-region plasma over a wide time range. These fields are influenced by perturbations propagating vertically from the lower and middle atmosphere (e.g. tides) and from above through variations in the solar and geomagnetic activity. The midnight temperature maximum (MTM) is a large scale neutral temperature anomaly with wide spread influence on the low-latitude thermosphere and ionosphere. Variations in the low latitudes’ nighttime neutral density, termed midnight density maximum (MDM) have also been observed and modeled. Although there is a large body of work on the characteristics of the MTM (& MDM) there are still a few questions which remain to be answered concerning the global scale distribution of the MTM (&MDM), their spatial extent and longitudinal variations, their global seasonal occurrence pattern and amplitude.

The Wind Imaging Interferometer (WINDII) flown on the Upper Atmosphere Research Satellite (UARS) provides among other parameters multiyear observations of O(¹D) nightglow volume emission rates (VER), Doppler temperatures, and neutral winds over the altitude range from 150 to 300 km with continuous latitude coverage from 42°N to 42°S and to 72° in one hemisphere every 36 days. These correlative in time and space data are employed in the study of the global and seasonal extent of the MTM/MDM. The results are compared with simulations by the Canadian Ionosphere and Atmosphere Model (C-IAM). Reasonable agreement is obtained in terms of temporal, solar flux, and solar zenith angle variations.