Simulation of rain attenuation time series

The simulation of a fine space-time structure of rain has great potential applications in many fields of research such as radar-meteorology, hydrology, and telecommunications. A rainfall simulator has been developed based on simple assumptions on the release of raindrops from cloud bases, and on a model of raindrop interarrival time and size distributions at ground level, derived from a statistical analysis of actual measurements using CETP's disdrometer over more than a year. Among the simple assumptions used, the probability of precipitating drops follows an exponential law related to the drop size. This Monte-Carlo simulation can be performed in two dimensions giving the spatial distribution of rain drops in a vertical plane. From this simulation, time series of rain rates, but also of microwave attenuations at a given frequency and elevation angle can be derived. The simulator is designed so that the main characteristics of rain observed on the ground are preserved: size distribution, interarrival time distribution and autocovariance of drop sizes. Results show that quantities derived from the series of raindrops generated by the simulator, such as time series of rain rate or attenuation, are in good agreement with observations.