Michio Yanai

Response of Deep and Shallow Tropical Maritime Cumuli to Large-scale Processes

Abstract A spectral diagnostic method of cumulus ensemble (Nitta, 1975) is compared with a bulk diagnostic method (Yanai et al., 1973), using the same data set taken in the Marshal Islands area for a 100-day period in 1956. For the total vertical cloud mass flux and mass detrainment, both methods give nearly identical results. Using the spectral diagnostic method, daily spectra of cloud base mass flux as functions of the detrainment height are obtained. The effects of radiative cooling upon the background cloud mass spectrum is examined. Typical radiative cooling rates in the tropics tend to produce a bi-modal distribution of mass spectrum showing deep and shallow clouds. Then the dependence of daily cloud mass spectra on the large-scale vertical motion and the evaporation from the sea is examined by data stratification, by correlation analysis, and by time-spectrum analysis. Under disturbed conditions, the bi-modal distribution is further enhanced. Under suppressed conditions, a uni-modal distribution co...