IMPROVED RADIATIVE-TRANSFER CALCULATIONS FROM INFORMATION PROVIDED BYBULK MICROPHYSICAL SCHEMES

Bulk microphysical schemes are providing increasingly detailed informa tion of hydrometeor profiles both within and below clouds. This inform ation can be used to improve radiative transfer calculations with litt le increase in computation time. In the simple context of a single col umn, the work described in this paper uses a relatively complex radiat ion code and a five-category bulk microphysical scheme to investigate simple and computationally efficient methods of utilizing microphysica l information in radiative transfer calculations. The bulk microphysic al scheme used here is typical of many and predicts mixing ratios of l iquid water droplets, rain, ice crystals, snow, and graupel. When all hydrometeors are treated separately in the radiation scheme, improveme nts can be made to the radiative transfer calculations. First, the eff ective radii of the various hydrometeors can be calculated from inform ation provided by the microphysical scheme. Also, adjustments can be m ade to the radiation scheme to allow for the nonspherical shape of ice and snow. The calculation of the effective radius of the various hydr ometeors was simple and fast, and it gave integrated in-cloud thermal infrared heating rates that differed by up to 16% from a scheme that u sed fixed effective radii. Adjusting for the shape of ice crystals and snow was also simple and increased the clouds' albedo, reducing integ rated in-cloud solar healing by similar to 10%. All the links between the bulk microphysical scheme and the radiation code are physically ba sed and do not significantly increase the complexity of the radiation code.