Tropical tropopause-level thin cirrus coverage revealed by ICESat/GLAS

We analyze cloud-height data obtained at tropical latitudes between Sept. 29 and Nov. 17, 2003 from the Geoscience Laser Altimeter System (GLAS), carried onboard the Ice, Cloud, and land Elevation Satellite (ICESat). The GLAS data show that tropopause-level thin-cirrus clouds occur over most of the tropics. Importantly, we see no preference for them to form in climatologically cold regions of the tropopause. Rather, the distribution of thin cirrus appears to be strongly influenced by the distribution of temperature variability. We seen no evidence that dehydration of air entering the stratosphere is preferentially occurring in the coldest regions of the tropopause; rather, the GLAS data are more consistent with widespread dehydration going on over much of the tropical tropopause.