Reassessment of the thermospheric response to geomagnetic activity at low latitudes

The present study takes advantage of measurements made at low latitudes by the Cactus accelerometer. From such measurements, the response of several thermospheric parameters to geomagnetic activity can be simultaneously and reliably retrieved: total density, density scale height, vertical density scale height gradient, temperature, O/N2 ratio and mean molecular mass. Their behavior exhibits a diurnal variation, some features of which have not been described, especially in the case of strong geomagnetic storms; the night scale height response appears to be stronger than the day one, while its vertical gradients increase by day and slightly decrease at night. The temperature increase is higher by day while the O/N2 ratio decreases by day, and increases at night at constant pressure level as well as at fixed height. By day, significant vertical temperature gradients are also found. These results as well as others are analyzed in the light of existing theories and compared to the predictions of existing thermospheric models. Strong meridional winds at night, heat transport through thermal conductivity, as well as wave dissipation during the day, might be factors helping to account for such behavior.