科研之友
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摘要
An intense precipitation system that developed during the rainy season generated an enhanced rainfall event over the northern and lee sides of an isolated elliptical-shaped area (Mt. Halla: height 1950 m, width 35 km, length 78 km) of Jeju Island on 6 July 2007. In this study, we investigate the microphysical structures associated with the developed convective cells interior of the system, which was shown in the vicinities of a terrain, using a cloud-resolving storm simulator (CReSS) that successfully reproduced the intensification of the convective cells. A control experiment simulated the terrain-modified go-around airflow (i.e., the flow of air around Mt. Halla rather than over it) and two localized moist regions (relative humidity %26gt;96%) on the northwestern side and southeastern slope of the island. Regarding the intensification of the convective cell off the northwestern shore of the island, an increase in updraft was seen from the sea surface to an altitude of 1.5 km (maximum at 4.5 km), where the moisture content was high (17 g kg(-1)). Due to the increased updraft and plentiful moisture supply at low altitudes, cloud water increased from the sea surface to reach a maximum at an altitude of 2.7 km. Consequently, the microphysical processes that convert cloud water into raindrops (e.g., collection and conversion) were significant below 43 km, and an increase in rainfall was seen between heights of 1.0 and 42 km; i.e., mainly below the freezing level (4.9 km). With regard to the enhancement of the convective cell on the lee side of the island, an increase in updraft was seen above 1 km (maximum at 5.5 km). The plentiful moisture supply, which was localized on the southeastern slope of the island, was supplied to the convective cell by the southwesterly upslope wind at low altitudes. Driven by the moist updraft above 1.0 km, cloud water increased above 1.5 km, and the microphysical processes that produce raindrops were significantly activated in the region between 1.5 and 53 km in altitude, which extended above the freezing level. Consequently, above the freezing level, the melting rate of graupel decreased while cloud water increased during the intensification of convective cell on the lee side. Off the northwestern shore of the island, most of the hydrometeors increased significantly from the sea surface to below the freezing level as a result of the warm rain process. In contrast, on the lee side, the hydrometeors increased below and above the freezing level due to the action of both stationary terrain-generated convergence, and the southwesterly upslope wind in a moist environment; consequently, both of the active warm and cold rain processes contributed to the generation of the secondary enhancement.
- 出版日期2014-1
