In this paper, we will show that the CDR retrieved from 2.1-micrometer channel (hereafter, R21) of the MODIS traces the cloud droplet evolution monotonically (TY. Nakajima et al 2010a, 2010b). In this case, CDR retrieved from 3.7-micrometer channel (R37) is not suitable for this objective because the R37 has a strong sensitivity to the cloud droplet size at the most upper layer where the particle size tends to be small due to evaporation process whereas the R21 has information about cloud droplet size at deeper layer of the cloud and also it has sensitivity to the drizzle particles. We will propose a new approach of constructing the frequency diagram of the radar reflectivity, Contoured Frequency by Optical Depth Diagram (CFODD), which represents typical distributions of the radar reflectivities as a function of COD (TY. Nakajima et al. 2010b, Suzuki et al. 2010). It is quite interesting that the reflectivity profiles in the form of CFODDs, when grouped according to the R21 values, clearly represent every stages of the cloud droplet evolution including cloud, drizzle, and rain modes and the transitions between them. It is also of some interest to find that the CFODDs over ocean and land appear to be different. Drizzle seems to occur in lower layer of the clouds over the ocean than over the land. This possible difference could be explained by the difference in updraft velocity induced by atmospheric stability difference between land and ocean.
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