Survey of Thermosphere Joule Heating Locations and Magnetic Disturbance Conditions

Neutral density enhancements as evidence of Joule heating in the thermosphere are frequently observed in the polar cusp. Neutral density enhancements are usually investigated for selected magnetic storm events and certain disturbed magnetic conditions. A different approach is taken in this study. We first conducted a systematic survey of thermosphere heating events using the available CHAMP, GRACE and SETA accelerometer data and then examined their occurrence locations and magnetic disturbance conditions. CHAMP and GRACE data together cover ten years period from 2001 to 2010 at 300 - 500 km altitudes. SETA data are from accelerometers on sun-synchronous, low altitude satellites covering the 170-280 km altitude region during 1982 and 1983. In addition locations of intense energy deposition of Poynting fluxes observed by DMSP satellites during 2001-2005 are used to compare distributions of the neutral density hot spots. The survey indicates that neutral density enhancements were detected not only near the polar cusp but also occasionally in the polar cap region. They were observed over a wide range of magnetic activity. Large Joule heating appears to occur preferentially in the morning sector and the summer hemisphere. The results are discussed for better understanding thermospheric responses of magnetospheric energy transfer and ionospheric heating by field-aligned currents.