WATER-VAPOR AND CLOUD WATER MEASUREMENTS OVER DARWIN DURING THE STEP 1987 TROPICAL MISSION

Measurements of stratospheric and upper tropospheric cloud water plus water vapor (total water) and water vapor were made with two Lyman a hygrometers as part of the STEP tropical experiment. The insitu measurements were made in the Darwin, Australia, area in January and February of 1987 on an ER-2 aircraft. Average stratospheric water vapor at a potential temperature of 375 K (the average value of theta at the tropopause) was 2.4 parts per million by volume (ppmv). This water mixing ratio is below the 3.0 to 4.0 ppmv necessary to be consistent with the observed upper stratospheric dryness. Saturation with respect to ice and the potential for dehydration was observed up to theta = 402 K.