• 作者： 蔡清彥
• 作者服務機構： 國立臺灣大學大氣科學系
• 中文摘要： 以區域性斜壓模式預報寒潮暴發的天氣型式變化時，我們發現最嚴重的誤差是500 mb槽線
  尾端通過西藏高原的東北角時，正渦旋度中心不合理地往南移動，造成低壓中心不合理的與主槽
  分離而滯留於華中、華南地區。在 850 mb上，亦出現低壓中心不台理滯留於華南地區的現象，
  因而造成蒙古、新彊地區的高壓系統無法往華南伸展。這種誤差可能是由於模式未能考慮西藏高
  原的阻擋及偏向效應所造成的。為了改進預報，本文乃以 5,000 公尺地形等高線為 500, 700 及
  900 mb上的內邊界，利用兩種內邊界條件來模擬西藏高原的阻檔偏向效應。其中A型邊界條件
  假設在內邊界上的流線函數值相等且不隨時間改變；而B型邊界條件則假定高原北邊與南邊各有
  相同的流線函數值，東西兩邊的邊界值各由北向南遞增。這兩種邊界條件均能部份減小 500 mb
  上華中、華南地區不合理低壓的影響範圍，並能部份改進850 mb上高壓系統強度及位移的預報
  。另外，引用B型邊界條件能?消除A型邊界條件所造成 500 mb 上高原地區的不合理正負渦旋
  度中心。但兩種預報結果均仍與實際天氣型式頗有出入，有待進一步研究改進。
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• 英文摘要： We study the prediction of the cold-air-outbreak in Taiwan by a limited-area baroclinicmodel. The most serious error at 500 mb is theunrealistic southward movement of a positivevorticity center during a trough passing overthe northeastern part of Tibetan Plateau. As aresult, an unrealistic low pressure system isseparated from the main trough and stagnatesin the central and southeastern China. At 850mb, an unrealistic low pressure system is alsofound in the southeastern China. Therefore,the high pressure system is not able to extendsouthward to the southern China. This syste-matic error is most likely due to the lack ofblocking effect of Tibetan Plateau in the model.The present paper is devoted to the study ofsimulating the blocking effect of Tibetan Plateauby using the 5000 m topographic contour as aninternal boundary at 500, 700 and 900 mb levels.Two types of internal boundary condition areused. Type A assumes a constant value ofgeopotential height along the internal boundary,while type B allows the geopotential height toincrease southward along the western and easternboundaries and to have two different constantvalues for the northern and southern boundaries.The uses of both types of internal boundaryconditions are able to partly reduce the size ofthe unrealistic low pressure system at 500 mband to partly improve the prediction of the in-tensity and movement of the high pressuresystem at 850 mb. In addition, type B is a betterboundary condition as it does not generate largevorticity values along the internal boundariesas the type A boundary condition does. However,further studies are needed as the predictions byboth methods are still quite different from theobservations.
• 中文關鍵字： --
• 英文關鍵字： --