Abstract
A radar echo composite chart (RECC) displays precipitation intensity levels in 5 × 5-km grids for a composite region of digitized radars covering more than 2 × 106 km2. Each continuous precipitation cluster in a RECC is considered a precipitating cloud (p-cloud). At around 400 km, the distribution of the horizontal scale (S) for p-clouds changes. At scales smaller than 400 km, the distribution decreases smoothly with scale. In the distributions of S and maximum precipitation intensity (A) for p-clouds, there is a peak at between 400 and 1,000 km and about 45 mm/h throughout the year. This peak results from large-scale p-clouds accompanying macro-β and meso-α-scale disturbances.
From June to September over land, precipitation is concentrated at scales between 15 and 200 km and intensities exceeding 8 mm/h. This distribution results from cumulus-scale p-clouds, which include a variety of convective clouds initiated by boundary-layer processes. A third type of p-cloud, caused by air-sea interactions, appears with the cold northwesterly flow that follows the passage of extratropical cyclones, especially in winter. This type dominates the weaker intensity side of the cumulusscale p-clouds between 5 and 200 km in the precipitation distribution.
