Balloon borne observations of backscatter, frost point and ozone in polar stratospheric clouds at the South Pole

Abstract

Concurrent backscatter and ozone measurements were made with near‐simultaneous frost point soundings over the South Pole when the center of the 1990 winter vortex was at or very near that location. The initial water vapor concentration in the stratosphere was ∼5ppmv and decreased to ∼1.5–2.0 ppmv as cooling took place. By mid‐July the stratospheric temperature had decreased to the frost point and heavy polar stratospheric cloud (PSC) activity was observed presumably due to the condensation of water vapor. The lowest water vapor concentrations observed correspond to saturated air at the lowest temperatures encountered. The slow recovery of the water vapor concentration during spring warming indicates that the 12 to 22 km altitude region in the vortex is not readily penetrated by outside air.The observed large decrease in PSC backscatter above ∼14 km before the stratosphere began to warm is consistent with loss of particles by sedimentation leading to significant dehydration and denitrification, The region of PSC activity in July is noted to be in the same region in which ozone depletion and the persistent dehydration is observed later in the year. At the end of August heavy PSC activity was observed in the lower stratosphere and upper troposphere, consistent with earlier observations from NASA aircraft. These lower clouds were in a region that apparently was still experiencing cooling. No compelling evidence was found supporting earlier claims that PSC layers are anti‐correlated with ozone inside the vortex.