DEVELOPMENT AND APPLICATION OF REMOTE-SENSING OF LONGWAVE COOLING FROM THE NOAA POLAR ORBITING SATELLITES

Satellite data have provided considerable information on the radiation budget at the top of the Earth-atmosphere system. However, in order t o maximize the usefulness of these observations, it is necessary to kn ow how the radiative heating and cooling are distributed within the at mosphere and between the Earth's surface and the atmosphere. A techniq ue has been developed to use radiance data from the High Resolution In frared Sounder (HIRS) instrument flown on NOAA operational satellites to obtain estimates of the profile of longwave atmospheric cooling (LC ) and the atmospheric emission to the Earth's surface (downward longwa ve radiation, DLR). Briefly, the DLR and LC are estimated from HIRS ra diance observations using regression techniques on radiative transfer calculations. The technique requires the spectral radiance data from H IRS and the vertical distribution of cloud amount and cloud-base and c loud-top heights. Cloud information is not generally available concomi tantly with the HIRS radiances, and the initial effort has focused on the development of clear sky models. Radiative cooling is calculated f or four layers: surface to 700 mb, 700 to 500 mb, 500 to 240 mb, and 2 40 to 10 mb. Initially, a month-long data set was produced - 15 Decemb er 1990 through 15 January 1991 - for study and technique evaluation. Calculations were global on a 2.5-degrees by 2.5-degrees latitude-long itude grid. Monthly averages and five-day running means were produced. Comparisons were made to the National Meteorological Center (NMC) med ium range forecast (MRF) model fields of LC and DLR. The agreement was generally within values expected from comparisons of calculations fro m the different models, especially for zonally averaged quantities. Th ere were, however, significant differences over specific geographical areas (e.g., Africa and Australia). Analysis of these differences indi cated where improvements were needed in the HIRs and the MRF technique s, resulting in an improved HIRs model for estimating clear sky DLR an d LC. The clear-sky algorithms for the LC and outgoing longwave radiat ion at the top of the atmosphere have been implemented as an experimen tal quasi-operational system for further evaluation. Twelve months of data (June 1992 through May 1993) have been processed to date, and the availability of the data were announced to the international climate community for use and evaluation beginning in January 1993.