Winds and Temperatures in the Auroral Zone and their Relations to Geomagnetic Activity [and Discussion]
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
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-1 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
... udes in the night hemisphere and produce anomalously high neutral wind speeds on a global scale especially 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 C 9 index (wh ich is representative of KP) is altitude dependent, increasing from a value near to Lhe global mean (25 K per unit C9) at 140 km to an enhanced value of 50 K per unit C9 at 165 km. Auroral zone measurements arc 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 ± 50 K between mid-latitudes (30° N) and the auroral zone (70° N) which is significantly greater than the polewards decrease of temperature predicted from satellite drag density data.