High Resolution Dynamics Limb Sounder observations of polar stratospheric clouds and subvisible cirrus

The High Resolution Dynamics Limb Sounder (HIRDLS) cloud detection and cloud top determination algorithm is described and applied to 2005-2007 HIRDLS radiance profiles. Statistical averages of HIRDLS and correlative cloud data are highly correlated. The 1998-2005 Halogen Occultation Experiment (HALOE) and HIRDLS time averaged cloud top pressures have a correlation coefficient of 0.87 and 0.93 in the tropics and midlatitudes, respectively. Time series of the temperature T < 195 K hemispherical area, on the 450 K potential temperature surface, and the total number of polar stratospheric clouds observed by the HIRDLS experiment in January and February 2005 have a correlation coefficient of 0.92. HALOE and HIRDLS normalized distributions of cloud counts, expressed as a function of outgoing longwave radiation (OLR), have a correlation coefficient of 0.99. Tropical averages of 1998-2005 HALOE and HIRDLS cloud occurrence frequencies at 82 and 100 hPa are within 25% of each other, and the morphology of latitude-longitude contour maps of cloud frequency are similar. Colocated Stratospheric Aerosol and Gas Experiment (SAGE III) and HIRDLS cloud top pressure values in 2005 have a correlation coefficient of 0.85 when the distance between observations is less than 100 kin and the time difference is less than 6 h. Correlations between colocated GE III and HIRDLS cloud top pressures improve as space and time differences decrease.