台灣地區寒潮個案之研究

A Case Study of Cold Surges in the Vicinity of Taiwan

蔡清彥(Ching-Yen Tsay)

《大氣科學》 8卷1期 (1981/05) Pp. 81-94

摘要

本文在1972年12月中選擇一個強寒潮及一個中寒潮個案，分析寒潮爆發前及當時之天氣結構，並研究中與強寒潮天氣型式之異同。在寒潮爆發前36小時，中與強寒潮之溫度分佈特性十分相似，低壓槽後之溫度冷槽均十分顯著，而中與強寒潮36小時前天氣型式之最大差異在於槽線和氣流走向之不同。強寒潮者，主槽線位於蒙古高原（包括肯特山、杭愛山、阿爾泰山、唐奴烏拉山及薩彥嶺等）中部，槽線呈東北東－西南西走向，槽後吹北或北北西風。而中寒潮者，主槽線亦位於蒙古高原中部，但呈北北東－南南西或南北走向，槽後吹西北或西北西風。此槽線和氣流分佈特性在整個對流層中（包括850mb－200mb）均十分相近。由於氣流走向的不同，造成強寒潮槽後有較強的冷平流。另外在寒潮爆發前36小時，西藏高原東方首次出現地形槽。強寒潮者，此槽線發展較深厚包括850及700mb，而中寒潮者僅發生在700mb上。至於此時之垂直速度之分佈情形則受地形影響甚巨。由於主槽線位於蒙古高原中部一帶，因此地形抬升作用造成槽後之上升運動和槽前之下降運動。此時地形所造成之垂直運動與中緯度綜觀尺度系統本身之槽後下降和槽前上升運動正好相反。在強寒潮個案，850 & 700mb垂直運動主要受地形抬升作用所控制，而500mb至200mb垂直運動則主要受系統本身之次環流所影響。至於中寒潮者，系統本身次環流稍弱，地形抬升作用控制850，700及500mb之垂直運動。在寒潮爆發當時，中與強寒潮之溫度分佈特性亦十分相似，但強寒潮槽後之溫度冷槽較強。而中與強寒潮之槽線及氣流走向亦有顯著之不同。強寒潮槽線呈東北－西南走向，槽後吹北北西－西北風；而中寒潮槽線呈南北走向，槽後吹西北西風。溫度和氣流分佈的差異使得強寒潮槽後有較強之冷平流。至於垂直速度之分佈情形，中與強寒潮者十分相近，主要包括槽前之上升及槽後之下降運動。

並列摘要

A severe and a moderate c old surge case in December of 1972 were selected in the present study to analyze synoptic structures before and during cold-air-outbreaks and to study the simularities and differences between the synoptic patterns.Thirty-six hours before the cold-air-outbreaks occuring in Taipei, the temperature distributions are similar between the severe and moderate cold surges, each cold trough is located behind its corresponding low pressure trough. The major differences between the synoptic patterns of these two cases are the orientation of the trough and that of the flow pattern. In the case of severe cold surge, the major trough is located over the Mongolian Plateau and oriented in east-northeast to west-southwest direction, the wind behind the trough blows either from north or from north-northwest. Although, the major trough is also located over the mongolian Plateau in the case of moderate cold surge, it is oriented in either north-northeast to south-southwest or north to south direction and the wind behind the trough blows either from northwest or from west-northwest. The above mentioned characteristics of the through and flow pattern are found at all levels in the troposphere. As a result, cold advection is stronger in the case of severe cold surge. In addition, a topographical trough to the east of the Tibetan Plateau first appears at 36 hours before the cold-air-outbreaks in both cases. The trough is found at both 850 and 700 mb levels for the severe cold surge case, whereas it is only found at 700 mb level for the moderate cold, surge case. The distribution of vertical motion is controlled by the topography in that area. At that time, the major trough lay over the ridge of the Mongolian Plateau. Therefore, the ascending and descending motions are found behind and ahead of the trough respectively. The topographical controlled vertical motions overcome the secondary circulation of the mid-latitude synoptic-scale system at 850 and 700 mb levels for the severe cold surge case and at 850, 700 and 500 mb levels for the moderate cold surge case. It indicates that the secondary circulation is weaker for the moderate cold surge case.During the cold-air-outbreaks, the temperature distributions as well as the distributions of vertical motion are similar between the severe and moderate cold surges. The orientation of the trough and that of the flow pattern are also the major differences between the severe and moderate cold surges. The northeast to southwest oriented trough for the severe cold surge case is contrast to the north to south oriented trough for the moderate cold surge case. Accordingly, the wind blows from either north-northwest or northwest in the case of severe cold surge whereas, from west-northwest for the moderate cold surge case.