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)