Dehydration in the lower Antarctic stratosphere during late winter and early spring, 1987

Measurements of total water were made with Lyman α resonance fluorescence hygrometers mounted on the ER‐2 and DC‐8 aircraft. Direct evidence was obtained for dehydration of the lower stratosphere over Antarctica; minimum values were about 1.5 parts per million by volume (ppmv), compared with values of 3.0 4.5 ppmv immediately outside the region high potential vorticity gradient in the potential temperature range 420<θ<460 K. On one flight, ice crystals large enough to have appreciable sedimentation velocities were observed. The DC‐8 data at 300<θ<320 K frequently showed extensive belts of dry, ozone‐rich air between 60° and 75°S latitude, with the equatorward “edge” in water well correlated with that observed by the ER‐2 some 8–9 km higher. Data from near Punta Arenas and from the ferry flights are used to argue that the effects of dehydration over Antarctica were visible at mid‐latitudes.