Stratospheric Radiometric Measurements from Constant-Level Balloons

Abstract

Superpressure balloons are used as radiometers to perform in-situ radiometric determinations in the lower stratosphere. The method consists in measuring the temperature of both the lifting gas and the ambient air and then computing the incident fluxes through the thermal balance equation. Data obtained from six flights at the 100 mb level from 1974 to 1978 in the tropics and the Southern Hemisphere are presented. As far as the tropospheric thermal radiation is concerned, the data are in general agreement with previous balloon and satellite measurements, although they show a greater variation with the underlying surface under clear-sky conditions. Over the most extreme conditions (high-level clouds) they demonstrate that the radiation temperature is always higher, by at least 9 K (minimum difference at the equator), than the temperature at 100 mb. The albedo inferred from the solar flux absorbed by a spherical balloon, taking into account the increase of the directional reflectance with zenith angle, is in good agreement with satellite measurements.