Near-saturation Conditions at the Tropical Tropopause: Results from Ticosonde

Balloon-borne frostpoint measurements have shown a high frequency of supersaturation near the tropical tropopause, and this has been attributed to forced ascent associated with wavemotions as well as diabatic heating. Long-term profile statistics are typically presented on altitude, pressure or potential temperature surfaces. For example, at Costa Rica long-term mean values of CFH RH at 16.8 km, the mean annual height of the tropopause, range from less than 60 percent in July to over 90% in October. While a plot of the annual cycle vs height shows relatively high humidities in the upper troposphere and especially so as one approaches the tropopause, the overall picture is one of subsaturation. A very different picture emerges,however, if the analysis is done in height relative to the tropopause. Here the long-term average of RH at the tropopause is 94 percent or greater throughout the year. We discuss this paradoxical result in the context of dynamical and cloud processes occurring near the tropical tropopause

The EOS Aura Mission

The Earth Observing System (EOS) Aura satellite is scheduled to launch in the second quarter of 2004. The Aura mission is designed to attack three science questions: (1) Is the ozone layer recovering as expected? (2) What are the sources and processes that control tropospheric pollutants? (3) What is the quantitative impact of constituents on climate change? Aura will answer these questions by globally measuring a comprehensive set of trace gases and aerosols at high vertical and horizontal resolution. Fig. 1 shows the Aura spacecraft and its four instruments