Spatial selection and grouping of raindrops by size in wind gusts

Results that indicate the grouping of droplets of the same size in certain regions of space have been obtained during in situ measurements of the instantaneous structure and spatial and temporal distribution of rains (using methods based on the effect of abnormally high modulation of the scattered light). Calculations that show that such a grouping can be associated with wind gusts and intense turbulence are presented. It is shown that a lateral wind gust leads to the grouping of drops of different sizes in different layers. The processes of spatial selection and grouping are considered for both the laminar flow in the case of droplets and for the turbulent flow regime in the case of the coarse fraction of drops. It is stated that the clustering of particles can lead to a sharp increase in the received signal strength and the anomalous dependence of the backscatter cross section on the wavelength. This means that not only the microstructure of scatterers, but also the dynamic state of the atmosphere should be considered in the interpretation of radar data, e.g., Z-I ratio. The considered clustering mechanism can cause the rapid formation of raindrops in the clouds.