A preliminary study of the formation of precipitation systems under undisturbed conditions during TAMEX
A preliminary study of the formation of precipitation systems under undisturbed conditions during TAMEX
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TAMEX期间原状降水系统形成的初步研究
DOI：
10.1007/bf01044131
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发表时间：
1997
影响因子：
2
通讯作者：
Chuan
中科院分区：
文献类型：
--
作者：
Ching;Chuan
台湾岛的山地对降水系统的发生有着重要的影响，尤其是山地面积占陆地面积的三分之二。这些山平均约3公里高。为了探讨太平洋高压系统影响下降水系统的形成，我们在TAMEX（Taiwan Area Mesoscale Experiment，Kuo and Chen，1990）中选取了五个个例（1987年5月24、25、26日，6月19、20日）。在所有情况下，大部分降雨发生在下午，当自由对流（LFC）的水平在约1公里的高度。若平均风（低于3公里高度）为南风（5月25日及26日），则台湾西部及东部的斜坡地带沿着会有较多的降水。台湾南部和北方也出现降雨。若平均风向为西南风（5月24日），降水型态与5月25日相似，但台湾西南部及东北部平原地区降水量较少;若盛行风向随高度变化不大，平均风向为东南偏南（6月19日），则台湾西北部至中部降水量较多。若平均风向为南风，且风向随高度变化不大（6月20日），则台湾北方及中部雨量较大。一个非静力模式被用来模拟在所有五种情况下的降水系统的形成。模拟结果表明，雨水的混合比可以发生在上游侧的山坡和中部山区，地形抬升的环境风和上坡流由于地面加热是明显的。在山的下游一侧，由于背风面辐合的上升运动和地面加热的上坡运动也有助于降雨的形成。
SummaryThe effect of mountains on the occurrence of precipitation systems on Taiwan island is very significant, especially as mountain areas occupy about two-thirds of the land-mass. The mountains are, on average, about 3 km high. To investigate the formation of precipitation systems influenced by Pacific high pressure systems, we selected five cases (May 24, 25 and 26, June 19 and 20 in 1987) during a field program, TAMEX (Taiwan Area Mesoscale Experiment, Kuo and Chen, 1990). In all cases most of the rainfall took place in the afternoon when the level of free convection (LFC) was at about the 1 km height. If the average wind (below 3 km in height) was from the south (May 25 and 26), higher amounts of precipitation would be found along the sloped areas of western and eastern Taiwan. Rainfall also occurred in southern and northern Taiwan. If the average wind was from the southwest (May 24), the precipitation pattern was similar to that on May 25, except over the plains area in southwest and northeast Taiwan, where the amount was less. However, if the prevailing wind direction changed little with height and the average wind was from the south-southeast (June 19), higher rainfall amounts occurred from northwestern to central Taiwan. If the average wind was from the south and wind direction changed little with height (June 20), higher rainfall amounts took place in northern and central Taiwan. A nonhydrostatic model was used to simulate the formation of precipitation systems in all five cases. Simulation results indicated that the mixing ratio of rainwater could occur on the upstream side of a mountain slope and in the central mountain areas, where topographic lifting from the environmental wind and an upslope flow due to surface heating were evident. On the downstream side of the mountain, upward motion due to lee-side convergence and upslope motion from surface heating would also help rain form.