The Semiannual Thermospheric Density Variation From 1970 to 2002 Between 200-1100 km

摘要

The goal of this study is to characterize the semiannual thermospheric density variation over the last 33 years, covering the height range of 200 to 1100 km. Historical radar observational data have been processed with special orbit perturbations on 13 satellites with perigee heights ranging from 200 to 1100 km. Approximately 120,000 very accurate average daily density values at perigee have been obtained for all satellites using orbit energy dissipation rates. The semiannual variation has been found to be extremely variable from year to year. The magnitude of the maximum yearly difference, from the July minimum to the October maximum, is used to characterize the yearly semiannual variability. It has been found that this maximum difference can vary by as much as 100% from one year to the next. A high correlation has been found between this maximum difference and solar EUV data. The semiannual variation for each year has been characterized based on analyses of annual and semiannual cycles, using Fourier analysis, and equations have been developed to characterize the variation from year to year in the 200 to 1100 km height range.