Density Variation and Isopycnic Layers

Abstract

A pole-to-pole study of density deviations near the 80th meridian west is presented from the surface to 31 km altitude. Density deviations are greatest at the surface, and under extreme conditions may range from 1.0 to 2.0 kg m?2. Density decreases almost exponentially with altitude and occasionally falls below 0.01 kg m?3 at 31 km. Density deviations decrease from the surface to an isopycnic layer, which varies in height from 6 km in polar regions to 12 km at the equator. Above this isopycnic layer, density variations increase with altitude to a maximum density deviation layer. This maximum density deviation layer occurs along the base of the summer tropopause and is approximately the center of the tropospheric wind maximum. The maximum density deviation layer is parallel to, and 50 per cent higher in altitude than the lower isopycnic layer. A weaker, second isopycnic layer is shown above and parallel to the maximum density deviation layer; this second isopycnic layer is found in tropical regions and near the south pole. Because of large seasonal and latitudinal variations in atmospheric density, no single standard atmosphere can present density data adequate for high speed vehicle operations on a global basis.