NEW EXPERIMENTAL DATA ON MESOSCALE VARIABILITY OF AIR HUMIDITY NEAR THE EQUATORIAL AND TROPICAL TROPOPAUSE

M. Yu. Mezrin and S. M. Shmeter

Results are discussed of the airborne studies of the humidity field mesostructure at 15—21 km over the Seyshelles (the Indian Ocean). The flights of the Russian stratospheric M-55 Geofizika aircraft were carried out in February—March 1999 within the framework of the International APE-THESEO project. For the humidity measurements, an original Russian high-precision condensational airborne hygrometer designed by M. Yu. Mezrin is used. It is found that in the equatorial and tropical tropopause layer and immediately above, the spatial structure of the mixing ratio m exhibits a fluctuational behavior at least up to the scales of several kilometers. The m values are minimal within the tropopause layer, above which, up to the upper boundary of the layer under study (about 21 km), дm ≥ 0. Mechanisms that can supply the water vapor above the tropopause are determined. The measurements show that in separate volumes in and above the tropopause, there are mesoscale fluctuations of m, causing m changes by factors of tens (sometimes reaching saturation) within layers several hundred meters thick and hundreds of kilometers long. In the saturated zones, layers of supertropospheric clouds can develop.