A discussion on D and E region winds over Europe - Winds and temperatures in the auroral zone and their relations to geomagnetic activity

Abstract

Measurements of neutral wind velocity and neutral atmospheric temperature above 90 km in the auroral zone have shown distinct correlations with local and global geomagnetic activity respectively. Individual magnetic substorms have been observed to produce neutral wind speeds of over 500 m -s at 130 to 150 km. Ion-neutral particle drag is a likely accelerating mechanism with enhanced meridional electric fields and electron density. These wind disturbances can theoretically propagate to mid-latitudes in the night hemisphere and produce anomalously high neutral wind speeds on a global scale especia y during geomagnetic storm conditions. Such anomalously high wind speeds have been observed on several occasions at mid-latitude sites during disturbed conditions. Neutral temperature values in the auroral zone show a positive correlation with geomagnetic activity with a relatively slow decay following heating. The temperature dependence upon the G9 index (which is representative of jQ) is altitude dependent, increasing from a value near to the global mean (25 K per unit C9) at 140 km to an enhanced value of 50 K per unit G9 at 165 km. Auroral zone measurements are only possible during the period September to April inclusive; however, in this period, during quiet geomagnetic conditions and between 130 and 200 km, there is a decrease of neutral temperature of 150±50K between mid-latitudes (30° N) and the aurora zone (70° N) which is significantly greater than the polewards decrease of temperature predicted from satellite drag density data.