10-day cold stream caused by blocking high 強冷十天 原來是阻塞高壓擋住氣流

Wed, Feb 07, 2018 - Page 14

Two strong cold masses in succession hit Taiwan last week, and have remained for ten days, with a strong continental cold air mass and cold stream driving temperatures down. According to Central Weather Bureau (CWB) Weather Forecast Center Director Lu Kuo-chen, the reason the cold temperatures have remained for such a prolonged period is primarily due to the persistence of a “blocking high pressure” channeling dense air southward.

The CWB forecast early last month that two cold air masses would hit Taiwan. On the evening of Jan. 28, a northerly front arrived, bringing with it a strong continental cold air mass. On Saturday, this cold air mass intensified and turned into a cold stream. The forecast was that the cold stream would not abate until today, by which point the cold spell would have lasted for 10 days.

During an interview on Saturday, Lu said that the CWB found the cold spell on this occasion was gradual, as opposed to the strongest cold stream in a decade that hit Taiwan two years ago. That cold stream, caused by Arctic oscillation, delivered strong, cold air in a relatively short period of time, and left after a similarly short duration. The long stay of the cold stream on this occasion is due to the blocking high pressure obstructing the air stream.

Lu said that air flowing from west to east was obstructed by a blocking high formed over the Kamchatka Peninsula, forcing it to be compressed and to flow south, arriving in higher latitude areas such as Japan before moving down to Taiwan. This accounts for the intensity of the cold.

Furthermore, the low-lying and denser nature of the air mass meant that it was able to lift larger volumes of warm air and, with a weather front moving over from southern China progressing in an easterly direction, it affected the north and east parts of Taiwan, bringing snowfall to mountainous areas of altitidues over 1,000m.

(CNA, translated by Lin Lee-kai)

兩波強冷空氣接連影響台灣,時間長達十天,從強烈大陸冷氣團到寒流,一波比一波冷;至於為何冷這麼久,氣象局預報中心主任呂國臣說,這是因為阻塞高壓擋住了氣流,冷空氣變厚、往南竄所致。

中央氣象局一月下旬就預報有兩波冷空氣將襲台,二十八日晚上起鋒面南下後,強烈大陸冷氣團來到台灣,冷氣團強度在上週六增強為寒流。估計本月七日白天起才會漸漸減弱,強冷空氣影響台灣時間前後達十天。

呂國臣週六受訪時說,氣象局分析後發現,這次漸進式的冷,與兩年前霸王級寒流的成因不同──兩年前是北極震盪,快速帶來強冷空氣,影響時間較短;這次時間拉得長,是與氣流受阻有關。

呂國臣說,在堪察加半島有一個阻塞高壓形成,阻擋了由西往東的氣流;因氣流受阻,冷空氣被迫往南移,且愈積愈厚,分批先到日本等緯度較高地區,再流竄到台灣,所以冷空氣才會一波比一波強。

另因冷空氣又深又厚,暖空氣抬升的量更大,且華南雲雨區東移,天氣才會又溼又冷,迎風面的台灣北部、東部更明顯,一千公尺以上的高山都降雪。

(中央社)