A study of raindrop size distribution during stratiform rain and development of its parameterization scheme in the framework of multi-parameter observations

A study was carried out to investigate the rain drop size distribution (DSD) characteristics during strong bright band (SBB), weak bright band (WBB) and no bright band (NBB) regimes of stratiform rain by using an L-band wind profiler and Joss-Waldvogel disdrometer at Gadanki (13.5(degrees)N, 79.20(degrees)E), a tropical station in India. The stratiform events with SBB (bright band width >0.49 km) are associated with larger mean drops (D-m) at ground level compared with WBB and NBB situations. Different shapes of raindrop DSDs during these three situations suggest different microphysical processes involved in the evolution of rain DSDs. During SBB regimes, the raindrop spectrum, which is found to be governed predominantly by an aggregation process, is size controlled. On the other hand, during WBB regimes, the raindrop spectrum, which is found to be governed predominantly by a riming process, is number controlled. A new rain DSD parameterization scheme, P (Z, N-0(*)), is proposed in the framework of multi-parameter radar observation. The considered parameters are radar reflectivity factor (Z) and normalized scale parameter (N-0(*)). These two parameters are found to be mutually independent. Reasonable improvement in the estimation of rain intensity is observed by the developed P(Z, N-0(*)) scheme compared with P(Z) and P(Z, D-m). The rain DSDs simulated by the developed P(Z, N-0(*)) scheme are in good agreement with the observed spectrum.