Some characteristics of electric field momentum coupling with the neutral atmosphere

It has been shown earlier that thermally driven winds due to Joule heating in the auroral zones can account for observed global scale composition effects in the thermosphere during magnetic storms. These winds are relatively small in comparison with wind fields attributed to E×B ion drifts. Using mode theory to describe the interaction of this momentum source, some response characteristics of thermospheric temperature, composition, and winds are discussed. E×B ion drifts induce horizontal winds that are predominantly divergence free and as such are, by comparison with thermally driven winds, more than a factor of 10 less effective in generating temperature and density variations. The momentum source signatures in composition (inferred from theory) reveal that all atmospheric species, including He, O, N 2 , and Ar, vary in phase with one another and are out of phase with T g above 150 km, in striking contrast to the atmospheric signatures resulting from Joule heating. While the large wind velocities at higher latitudes are thus primarily produced by the ion drift momentum source, the smaller contribution from Joule heating may still be the principal cause of the observed density variations. The momentum source is relatively more effective in the lower thermosphere and, on occasion, may even produce signatures at higher altitudes as suggested from isolated satellite measurements.