The STRATEOLE experiment is designed to study the wintertime Antarctic lower stratosphere polar vortex and its springtime breakdown. To this end, it is planned to fly a large number (around 200) of long-lived (3 months), small isopycnic drifting balloons instrumented with temperature and pressure sensors, GPS and transmitters. The main goal of STRATEOLE experiment is to provide an unprecedented documentation of the wind in the vicinity of the vortex edge in order to study vortex porosity and erosion, filimentation and mixing properties of the air masses. In addition, by the use of other sensors on some gondola, like radiometers and tuneable laser diodes, STRATEOLE will also provide in situ and/or column-integrated trace species measurements (like NO2, O3, CH4, H2O, aerosols...) and information on the radiation budget of the Antarctic lower stratosphere during this period. This will permit to obtain a better understanding of mechanisms responsible for ozone depletion occurring during the springtime vortex dilution.

An algorithm using NOAA-12 AVHRR (Advanced Very High Resolution Radiometer) solar reflectance measurements for retrieving cloud droplet size and optical thickness has been applied to a boundary layer stratocumulus cloud in the vicinity of the Azores on 12 June 1992 during the Atlantic Stratocumulus Transition Experiment (ASTEX). This day was particularly advantageous for validations because of the absence of cirrus or other higher-level clouds during the satellite overpass and the existence of a large relatively uniform stratus cloud deck. Uncertainty estimates for the retrievals are presented along with a discussion of the algorithm. An in-flight absolute calibration of AVHRR channel 1, necessary for accurate optical thickness retrievals, was done concurrently with the retrievals through comparison with a visible radiometer flown on the National Aeronautics and Space Administration's ER-2 and using the stratus cloud as the common reflectance target. Results are compared with in situ microphysical measurements taken with the Particulate Volume Monitor (PVM-100) and Forward Scattering Spectrometer Probe (FSSP-100) instruments on the University of Washington C-13A aircraft. Satellite retrievals of both optical thickness and droplet size lie within the values measured by the two in situ instruments.

Rayleigh-scattering cross sections and volume-scattering coefficients are computed for standard air; they incorporate the variation of the depolariztion factor with wavelength. Rayleigh optical depths are then calculated for the 1962 U.S. Standard Atmosphere are for five supplementary models. Analytic formulas are derived for each of the parameters listed. The new optical depths can be 1.3% lower to 3% higher at midvisible wavelengths and up to 10% higher in the UV region compared with previous calculations, in which a constant or incorrect depolarization factor was used. The dispersion of the depolarization factor is also shown to affect the Rayleigh phase function slightly, by approximately 1% in the forward, backscattered, and 90 degree scattering-angle directions.

Aircraft measurements of solar flux in the cloudy tropical atmosphere reveal that solar absorption by clouds is anomalously large when compared to theoretical estimates. The ratio of cloud forcing at an altitude of 20 kilometers to that at the surface is 1.58 rather than 1.0, as predicted by models. These results were derived from a cloud radiation experiment in which identical instrumentation was deployed on coordinated stacked aircraft. These findings indicate a significant difference between measurements and theory and imply that the interaction between the clouds and solar radiation is poorly understood.