TROPOSPHERE-TO-STRATOSPHERE TRANSPORT IN THE LOWERMOST STRATOSPHERE FROM MEASUREMENTS OF H2O, CO2, N2O AND O-3

The origin of air in the lowermost stratosphere is investigated with m easurements from the NASA ER-2 aircraft. Air with high water vapor mix ing ratios was observed in the stratosphere at theta similar to 330-38 0 K near 40 N in May 1995, indicating the influence of intrusions of t ropospheric air. Assuming that observed tracer-tracer relationships re flect mixing lines between tropospheric and stratospheric air masses, we calculate mixing ratios of H2O (12-24 ppmv) and CO2 for the admixed tropospheric air at theta=352-364 K. Temperatures on the 355 K surfac e at 20-40 N were low enough to dehydrate air to these values. While m ost ER-2 CO2 data in both hemispheres are consistent with tropical or subtropical air entering the lowermost stratosphere, measurements from May 1995 for theta<362 K suggest that entry of air from the midlatitu de upper troposphere can occur in conjunction with mixing processes ne ar the tropopause.