A Parameterization for Longwave Surface Radiation from Sun-Synchronous Satellite Data

Abstract

A parameterization has been developed for computing downward, upward, and net longwave radiation at the earth's surface using meteorological data from NOAA's operational sun-synchronous satellites. The parameterization was developed using a narrowband radiative transfer model and a large meteorological database consisting of satellite and in situ soundings. Clear-sky downward flux was represented as a function of surface and lower tropospheric temperatures and water vapor burden of the atmosphere. Cloud contribution to the downward flux was represented in terms of cloud base temperature and water vapor burden of the atmosphere below the cloud. Upward flux was computed directly from the surface temperature. Results obtained with the parameterization were verified against detailed radiative transfer computations for an independent set of satellite and in situ soundings. The parameterization was applied to satellite soundings for the month of April 1982 from a large region in the tropical Pacific Ocean. Averaged net fluxes for this month showed striking similarities with 8-yr averages of monthly-mean values obtained for the same region by an earlier investigator. Sensitivity studies were conducted to estimate random and systematic errors in computed fluxes due to probable errors in TOYS-derived parameters Random errors in fluxes computed for individual satellite soundings were estimated to be 20?25 W m?, but were reduced to <2 W m?2 for monthly averages over 5°?5° regions when fluxes for about 200 soundings were averaged. Biases as large as 8?10 W m?2 could still be present in the results, mainly because of the errors in TOYS-derived cloud parameters. This problem may be rectified in the near future with the availability of data from the International Satellite Cloud Climatology Project.