Global cloud cover trends inferred from two decades of HIRS observations

Abstract

Cloud cover information and the frequency of upper tropospheric clouds have been extracted from NOAA/HIRS polar orbiting satellite data from 1979 to 2001. The HIRS/2 sensor was flown on nine satellites from TIROS-N through NOAA 14 during this time forming a consistent 22-year record. CO2 slicing was used to infer cloud amount and height. Trends in cloud cover and high cloud frequency are small in these data. High clouds show small but statistically significant increasing trends in the tropics and northern hemisphere. The HIRS analysis contrasts with that from the ISCCP which shows decreasing trends in both total cloud cover and high clouds during most of this period. The HIRS detection of upper tropospheric thin cirrus creates most of the difference with respect to ISCCP; GLAS observations of high thin clouds are largely in agreement with the HIRS.