Doppler Radar Observation on the Orographic Modification of a Precipitating Convective Cloud in its Landing

Abstract

The orographic modification of a precipitating convective cloud, which formed 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 250000 LST, many connective clouds landed at the southeastern coast of the Kui Peninsula. Although they reached the coast in various stages of development, most of them showed similar features. Their radar-echoes were intensified 10 to 20km off the coast before landing, and the radar-echoes were intensified again or broadened over land after their radar-echo intensities were reduced near the coast. Before the first intensification of convective radar-echoes over the sea, the echoes were intensified in their upper rear-parts 30 to 40km off the coast, and intensified in their front-parts near the coast. By averaging horizontal winds derived 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 the horizontal convergence zone larger than 10-4 s-1 existed along the coast line about 10km off the coast. On the basis of these observational results the travelling convective clouds orographic modification, and the efficient formation of precipitation in them were discussed, taking into account the results of numerical experiment about the Kui Peninsula orographic effect on ambient winds. It can be inferred that the large rainfall amount recorded in association with the typhoon around the Kui Peninsula coast was caused as a result of the integration of travelling convective clouds orographic modification.

Doppler Radar Study on the Successive Development of Snowbands at a Convergence Line near the Coastal Region of Hokuriku District

“…Many previous studies have noted that the modification of snow clouds before landing plays an important role in the precipitation features in the downwind region (e.g., Isono et al 1966a and b;Takeda et al 1982;Murakami et al 1994;Saito et al 1996). Modifications of convective clouds near the coast are popular phenomena, and are reported in many other regions (e.g., Hsu 1988;Braun et al 1997;Kanada et al 1999). These studies pointed out that differences of temperature, humidity and surface roughness between the sea and the land, and the steepness of the coastal topography directly affect the behavior of convective clouds.…”

Rainfall Enhancement of Band-shaped Convective Cloud System in the Downwind Side of an Isolated Island

“…Ogura et al (1985) stated that extremely concentrated heavy rainfall occurred in the Nagasaki area in 1982 in association with orographic influence on convective systems. The orographic enhancement of rainfall in the upwind slope ofmountains was investigated inmore detail by Kanada et al (1999) by dual-Doppler radar observation. They pointed out that low-level horizontal convergence which formed in the upwind side by orographic effect caused not only the redevelopment of a travelling convective cloud, but also the enhancement of rainfall originated from the convective cloud due to its interaction with low-top clouds which formed in the convergence zone.…”

Kinetic Energy Budget Analysis on the Development of a Meso-β-Scale Vortex Causing Heavy Rainfall, Observed over Aomori Prefecture in Northern Japan on 11 November 2007

“…Moreover, Ogura et al (2008) suggested that the heavy rainfall could be caused by the terrain effect, which can lift low-level air parcels. Heavy rainfall events in Japan are often caused by the terrain effect (e.g., Kanada et al 1999;Arao and Tsuboi 2000;Yoshizaki et al 2000;Kato 2005b;Watanabe 2008). To clarify the terrain effect of Mts.…”