冬季西伯利亞高壓移動路徑之分析及其對臺灣寒潮之影響

Abstract

影響東亞地區冬季期間最主要的系統即為西伯利亞高壓，了解與其相關之 高壓的移動路徑為了解東亞地區冬季氣候變化的重要工作之一。為提高研究的 科學再現性，並免除過去主觀追蹤高壓移動路徑的種種不便，本研究使用再分 析資料，經一系列演算法客觀的定義 1948—2017 年間東亞地區高壓移動路徑， 並依其主要行經位置將路徑分為向東移動進入西伯利亞高壓區的西側路徑 (West Tracks)，及自西伯利亞地區發源，並向東移動的東北路徑 (Northeast Tracks)，和東南路徑 (Southeast Tracks) 三類。 經分析後發現 1983—2017 年間，Northeast Tracks 和 Southeast Tracks 的數 量皆較 1948—1982 年間多，但 West Tracks 的數量則以 1948—1982 年間較多。 此外，Southeast Tracks 的數量和西伯利亞高壓強度呈現負相關，當西伯利亞高 壓較弱時，較容易自高壓東南方分裂並形成一向東移動之子高壓。 從天氣尺度上來看，長短不一的寒潮事件為東亞地區冬季期間最常見的天 氣現象，當北方冷空氣經由西伯利亞高壓傳至南邊使該地降溫時即可能發生。 冷空氣南傳的方式主要可分為二種，西伯利亞高壓受其東北方阻塞高壓影響滯 留原地，冷空氣隨高壓東側北風持續南傳使華中及華南地區降溫;另一種冷空 氣南傳的方式為西伯利亞高壓向東南方延伸或分裂子高壓時帶至行經區域令該 地降溫形成寒潮。 為瞭解客觀分析之路徑與臺北地區寒潮間關聯，將 2000—2017 年間臺北所 發生之五十六次寒潮事件依地面氣溫、地面氣溫降溫速率、阻塞高壓存在與否 分成三類: (1) 第一類寒潮(blocking with cold air and temperature drop, BCD)，十 八年間共發生二十五次; (2) 第二類寒潮(blocking with cold air only, BC)，十八 年間僅發生五次; (3) 第三類寒潮(cold air and temperature drop without blocking, CD) ，十八年間共發生二十六次。第一、三類寒潮事件臺北地區皆快速降溫， 其間伴隨 Southeast Tracks 的機率約為 80%，比第二類寒潮事件多了約 20%。The Siberian High has a high impact on weather and climate in East Asia during northern hemisphere winter, so it is important to understand its tracks for the climate change in East Asia. For increasing the scientific reproducibility and avoiding inconvenient processes in subjective tracking, this research uses an objective algorithm to define and track the translation of the Siberian High center in reanalysis data. The tracks are divided into three primary groups: West Tracks, Northeast Tracks, and Southeast Tracks. West Tracks are the tracks of highs from the west merging with Siberian High, while Northeast and Southeast Tracks occurs when a secondary high separates northeastward or southeastward from Siberian High. The numbers of Northeast and Southeast Tracks in 1983—2017 are both more than those in 1948—1982, but the number of West Tracks in 1948—1982 is more than that in 1983—2017. Besides, the Southeast Tracks shows a negative correlation with Siberian High intensity; that is, a secondary high center tends to go southeastward when the Siberian High is weak. Cold surge, a common boreal winter weather phenomenon in East Asia, is usually induced by the cold air outbreak from higher to lower latitudes of Siberian High. The cold air moves southward in two ways. One way is the advection by the northerly on the eastern flank of stationary Siberian High when it is blocked by another high in its northeast; the other is the movement of cold air along with the southward translation of Siberian High. To understand the association between Siberian High tracks and the cold surge at Taipei, the cold surge events at Taipei of 18 winters in 2000—2017 are divided into three groups, type 1 (blocking with cold air and rapid temperature drop, BCD), type 2 (blocking with cold air only, BC), and type 3 (cold air and rapid temperature drop without blocking, CD), which occurs 25, 5, and 26 times, respectively. The type-1 and type-3 cold surge events are featured by a rapid temperature drop; about 80% of them are accompanied by the Southeast Tracks of Siberian High, while the type 2-cold surge, in which the temperature drop is not rapid, has approximately 20% less occurring with the Southeast Tracks.