A Simple Model for Atmospheric Density Variations from 200 to 800 km

Abstract

A simple atmospheric density model, based on satellite orbital decay data from four satellites, is derived by assuming that a direct proportionality applies between the 10.7-cm solar-radio-noise flux and the density. The model incorporates effects due to variations of solar activity and time of day in a single table of values from which the density and its variations, from altitudes of 200 to 800 km at low and middle latitudes, can be readily calculated as a function of the 10.7-cm solar flux. The accuracy with which the model represents the data from which it was derived is checked by comparing calculated rates of orbital decay with observed values. As a result of these comparisons, it is concluded that the model has been able to represent the density derived from the four satellites with some degree of success. As the linear relationship between density and radio-noise flux is not likely on a physical basis, it is expected that a more complex relationship will have to be deduced ultimately in order to give good results near sunspot minimum. This analysis demonstrates that great differences in air density exist between day and night in the upper thermosphere and lower exosphere, thus substantiating Jacchia generally. It strongly points up the need for satellite density measurements from the polar regions. The importance of 10.7-cm solar-radio-noise observations as a convenient index of solar ultraviolet radiation is evident, although its exact degree of representativeness over the range of a complete sunspot cycle is unknown.