Distribution of Precipitating Clouds up to the Meso-.ALPHA. Scale in Radar Echo Composite Charts over Japan.

Abstract

A radar echo composite chart (RECC) displays precipitation intensity levels in 5 Â 5-km grids for a composite region of digitized radars covering more than 2 Â 10 6 km 2 . 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-b and meso-a-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.

Long-term Changes in the Spatial Concentration of Daily Precipitation in Japan

“…A possible index of spatial concentration of precipitation may be the variance and/or maximum precipitation amount within a precipitation area (Misumi 2002;Suzuki 2006). However, such approach requires determining the 'shape' and 'boundary' of precipitation area, which is difficult in the present study because spatial coverage of data network is too limited to capture complicated precipitation patterns.…”