Perturbations of the upper atmosphere in the cleft region

In the dayside polar region-loosely referred to as the cleft region-particle precipitation and joule heating cause significant perturbations of the upper atmosphere. Here Dynamics Explorer-2 satellite data are used to present a synopsis of these disturbance effects. Documented are an increase in electron temperature and a decrease in electron density: increases in ion drift speed and ion temperature; an increase in the upward-directed ion velocity; increases in zonal wind speed and neutral gas temperature; and changes in the neutral gas composition and mass density. It is suggested that the increase in electron temperature is partly controlled by the decrease in electron density; that the ion upflow velocity mainly depends on the electron temperature, less frequently on the ion temperature; and that the observed decrease in thermospheric mass density is due to a decrease in the atomic oxygen density, which in turn is caused by diverging wind flows. (C) 2008 Elsevier Ltd. All rights reserved.