Surface Radiation in the Tropical Pacific

Monthly surface radiative fluxes in the tropical Pacific between January 1970 and February 1978 have been calculated using a radiative transfer package which includes detailed treatments of the molecular and droplet absorptions and of the surface and cloud reflections. The input data to the radiation package are surface measurements from the National Climatic Center, climatological temperature and humidity profiles from the National Center for Atmospheric Research, and cloud cover from the University of Hawaii. Results show that the distribution of surface radiation follows closely that of cloudiness and, to a lesser extent, that of humidity. Surprisingly, the distribution of IR radiation can hardly be correlated to the surface temperature. Based upon the expected range of uncertainties in the input data, the rms error in the calculated net surface radiation is estimated to be ∼15 W m−2 with the largest contributions from the uncertainties in cloud cover and humidity. This number is comparable to the interannual variation of the monthly net surface radiation, indicating a need to improve the quality of input data. The sensitivity of surface radiation to input data has also been studied. In order to resolve the interannual variations of the monthly net surface radiation, some accuracy requirements for satellite retrievals of atmospheric and cloud parameters are suggested.