Drop size spectra and integral remote sensing parameters in the transition from convective to stratiform rain

Several authors have reported the correlation between the shape (mu) and slope (Lambda) of the gamma distribution of raindrops to reduce the number of parameters required to measure rainfall by remote sensing methods. However, we find that there are no well-defined mu-Lambda, or associated relations between reflectivity (Z) and rain rate (R) or differential reflectivity for all storms or portions thereof. Rather, there is a general behavior such that A and b ( in the Z = AR(b) relation) and median volume drop diameter D-o all decrease from convective ( C) to stratiform ( S) to transition ( T) rains. The mu-Lambda correlation of the investigators in question appears to be limited to rainfall events which do not include convective rain; it is biased toward S and T rains. They miss the narrow ( large mu), large D-o DSDs of convective rain that are often found to have equilibrium spectra. The dependence of D-o on the strength of the updraft and the findings of others concerning the association with the physics, dynamics, and climate regime strongly suggests that it is necessary to characterize the physical and dynamic nature of the storms in order to select the appropriate remote sensing algorithms.