Abstract: Mesoscale model MM5 is used to examine the orographic effect to the precipitation caused by a Mesoscale Convective System (MCS) over Taiwan. A series of sensitive simulations are carried out to investigate the sensitivity of model resolution and orographic accuracy to precipitation. The results show that model resolution is crucial to the precipitation forecast, and orographic accuracy is found to be essential to both the location and the amount of the precipitation for this case. In order to get reasonable prediction, 6km model grid resolution and 18km accuracy of orography are needed.
      Sensitivity simulations with and without orography of Central Mountain Range (CMR) in the model show there are two kinds of orographic effects to the precipitation in this case, which can be called as "induced" and "modified" effects. CMR in Taiwan blocks the movement of mesoα scale low that associated with the MCS in the lower troposphere, and help to generate local mesoβ scale lows interacting with the mesoα scale vortex at the north of CMR. Severe rainfall brought by these local stationary mesoscale circulation systems is "induced" in northern Taiwan. At the central CMR, where the MCS landed, both rainfall area and its intensity are increased. That means the central CMR only "modified" the rainfall.

Key words: orographic effect, MCS, precipitation

摘要： 利用中尺度模式MM5研究了台湾地形对中尺度对流系统所引起的降雨的影响。通过一系列不同模式分辨率和不同精确度地形高度的敏感性实验， 发现模式的分辨率对降水的预报起决定作用，同时，地形的精确度也可以改变降水的分布和强度。为了得到合理的模拟，6km 的模式分辨率和18km 的地形精确度是必须的。
      去掉台湾地形的敏感性实验表明，台湾中央山脉对降水的影响可以分为两类，即“强迫”和“修正”效应。在对流层低层，中央山脉对中α尺度低压有阻挡作用，并强迫局地中β尺度的低压。中β尺度的低压和中α尺度低压相互作用，在台湾北部“强迫”出暴雨；而在台湾中部，中尺度对流系统登陆的地方，中央山脉对降雨的落区和强度都给予了“修正”。

关键词: 地形影响, 中尺度对流系统, 降雨