HIRDLS and CALIPSO observations of cirrus near the tropopause

Thin cirrus forms near, and dehydrates,the tropopause as humid air rises slowly across the tropopause. Structured cirrus also forms due to blow-off from and dissipation of deep convection. Observations of cirrus by the HIRDLS limb emission and CALIPSO lidar are analyzed to determine frequencies of occurrence, and latitude-longitude maps of the cirrus, expressed as a function of cirrus vertical width and distance to deep convection. The analyses uses HIRDLS radiance and preliminary extinction profiles, CALIPSO vertical feature maps, and Climate Diagnostic Center OLR (outgoing longwave radiation) data. We compare our frequencies of occurrence to previous measurements by the SAGE, HALOE, and LITE experiments.