Doppler radar observation on the orographic modification of a precipitating convective cloud in its landing

The orographic modification of a precipitating convective cloud, which form ed in association with typhoon 9304 and travelled over the sea, was studied by mainly analyzing the dual-Doppler radar system observational data. From July 24 1900 LST, to July 25 0000 LST, many convective clouds landed at th e southeastern coast of the Kii Peninsula. Although they reached the coast in various stages of development, most of them showed similar features. The ir radar-echoes were intensified 10 to 20 km off the coast before landing, and the radar-echoes were intensified again or broadened over land after th eir radar-echo intensities were reduced near the coast. Before the first in tensification of convective radar-echoes over the sea, the echoes were inte nsified in their upper rear-parts 30 to 40 km off the coast, and intensifie d in their front-parts near the coast. By averaging horizontal winds derive d from the dual-Doppler radar system observational data for about two hours , it was shown that the ambient wind speed decreased near the coast, and th e horizontal convergence zone larger than 10(-4) s(-1) existed along the co ast line about 10 km off the coast. On the basis of these observational res ults the travelling convective clouds orographic modification, and the effi cient formation of precipitation in them were discussed, taking into accoun t the results of numerical experiment about the Kii Peninsula orographic ef fect on ambient winds. It can be inferred that the large rainfall amount re corded in association with the typhoon around the Kii Peninsula coast was c aused as a result of the integration of travelling convective clouds orogra phic modification.