An organized density (and pressure) structure was recently discovered in the neutral thermosphere at high-latitudes. The structure consists of two to four high- and low-density regions having diameters of 1000 to 2000 km. The density in each region is enhanced or depleted from the hemispheric average by up to 30%. The structure is thus a significant feature of the near-Earth space environment at high-latitudes. We refer to each distinct region of enhanced or depleted density as a density ''cell.'' The cells extend upward from about 120 km into the upper thermosphere, and once formed they remain approximately fixed with respect to the geomagnetic pole. A parametric study of the density cell morphology for different magnetic activity levels is described for equinox solar minimum using the National Center for Atmospheric Research thermosphere ionosphere general circulation model (NCAR-TIGCM). Density data were sought to verify the existence of the structures first predicted by the NCAR model. The TIGCM simulations were used to predict the large density perturbations observed by the S85-1 satellite in a circular sun-synchronous orbit near 200 km altitudes.

The most obvious manifestation of the cells was the presence of density peaks located near 70 ¿&Lgr; on the dayside and nightside, and a density minimum near the magnetic pole. Since high-latitude densities are generally expected to increase during magnetic activity, the low densities over the pole are perhaps the most interesting feature of the cell structure discussed here. The satellite data confirm the existence of the cellular structure over a range of magnetic activity levels. The discovery of the cells is important because the structure provides a unifying framework for the analysis and interpretation of high-latitude data from both past and future experiments. The cells result from various forms of coupling between the ionosphere and thermosphere. The cell formation is quantitatively consistent with concepts from dynamic meteorology. ¿ American Geophysical Union 1996