Scaling characteristics of modelled tropical oceanic rain clusters

The scaling exponents of the distributions of cluster rain amount, R, and cluster size, A, for oceanic rain clusters over the Indian and Pacific warm pools, and the intertropical convergence zones over the eastern Pacific and the tropical Atlantic, were obtained from a set of regional climate model downscaling products. The main aim of the investigation is to compare the model cluster's scaling characteristics with those obtained from observations that have been reported previously. The scaling exponents for the model were found to be different across the ocean basins indicating the lack of universality in the modelled rain cluster distributions. The scaling exponent for the conditional mean of R given A = a, E(R|a), was found to be the same across the different ocean basins, and the estimated value of the exponent agrees with that obtained from satellite-observed rain clusters. However, no crossover in the scaling of E(R|a) in the model for cluster size larger than mesoscale was seen, unlike those reported elsewhere based on observations. The implication is that in the model the intensification of rain with cluster size continues up to synoptic scale. Through simple scaling arguments it is believed that before the break in scaling that has been identified from an observational study elsewhere, the model simulates the fundamental mesoscale dynamics well and thus estimated the E(R|a) in agreement with observations. Whether such a difference in transition of scaling between the modelled and observed rain cluster scaling behaviour depends on the model details, for example the convection parametrization, needs further clarification.