Tropical thin cirrus and relative humidity viewed by the Atmospheric Infrared Sounder

We explore vertical and horizontal distributions of tropical oceanic thin cirrus optical and microphysical properties observed by the Atmospheric Infrared Sounder (AIRS) in the Tropical Tropopause Layer (TTL). AIRS cirrus occurrence, optical and microphysical parameters will be compared to observations from CALIPSO and MODIS and in-situ aircraft observations from recent field campaigns. Cirrus properties are related to relative humidity (RH) distributions within the clouds derived from the AIRS. A spatial and temporal climatology of joint cirrus and RH distributions will be presented and related to previous work. Relationships between cirrus geographical and temporal distribution, optical depth, effective diameter, cloud top temperature, and upper tropospheric water vapor are explored. The implications of these observations for understanding the formation and maintenance of cirrus clouds in the TTL are discussed Similarities and differences will be highlighted in the context of instrument sensitivity, spectral, spatial and temporal sampling, and algorithm differences.