Low latitude thermospheric responses to magnetic storms

Thermospheric density and neutral velocity perturbations associated with three magnetic storms in the autumn season of 2011 are examined using data from the neutral wind meter (NWM) on the Communication/Navigation Outage Forecast System (C/NOFS) satellite. The data from perigee passes near 400km altitude show marked increases in neutral density during the storms and associated increases in horizontal neutral flow speeds. These thermospheric responses are characterized by enhanced meridional neutral flows with peak perturbation amplitudes near 100m/s and relative neutral density enhancements ranging from 50-100%. The increases in the neutral density and meridional flow velocity at equatorial latitudes occur about 5-7h after the initial perturbations are observed in the z component of the interplanetary magnetic field (IMF), and they persist for 20-30h. The perturbations in the neutral density are in good agreement with temperature increases predicted by an empirical model that has been validated using data from the CHAMP and Gravity Recovery and Climate Experiment missions, with a maximum lag time of similar to 1-1.5h between the model temperature increases and the observed density perturbations. The model temperatures are in excellent agreement with ground-based low-latitude temperature measurements during the storms. Ground-based wind measurements during one of the storms provide additional data for comparison with the perturbation wind amplitudes measured aboard the satellite.