Comparison of global diabatic heating rates from FGGE level IIIb analyses with satellite radiation imagery data

Abstract

We evaluate the global distribution of diabatic heating rates based on the thermodynamic energy budget using the ECMWF Level IIIb FGGE analyses. We select the two 15-day periods of 27 January to 10 February 1979, during the FGGE Special Observing Period (SOP)-I, and 7-21 June 1979, in the SOP-II. An effort is made to examine the daily variation of tropospheric diabatic heating in contrast with previous investigations which dealt with the climatological aspect. The daily variations of tropospheric diabatic heating appear to be related to synoptic features of the global circulation, indicating that the diagnosed heating distributions provide useful information related to numerical weather prediction. Nevertheless, a question may be raised regarding the accuracy of the daily variations of diagnosed heating rates, since the calculation of diabatic heating involves an observationally sensitive quantity, i.e., the vertical motion. One way to investigate the accuracy of diagnosed heating rates is to compare the present results with similar calculating using different FGGE datasets. In the Appendix, we present the diagnosed heating rats based on the GFDL Level IIIb data for the SOP-I study period. While comparisons of heating rates calculated from different analyses are revealing, we still lack an independent measure of comparison. We propose, therefore, the use of infrared and visible radiometric imagery data from the TIROS-N to examine the reliability of diagnosed heating and vertical velocity distributions in the tropics. A stratification of radiance data in terms of cloud types helps to establish useful relationships between infrared radiance and diabatic heating (and vertical velocity), suggesting that radiance data may be used to infer the distribution of diabatic heating in the tropics and to improve the analysis of the divergent wind field.