关键词: 低空急流, 强降雪, 合成分析

Abstract:

Meteorological observation data and EC reanalysis data were used to analyze the climatic characteristics of heavy snowfalls (24-hour snowfall ≥ 5 mm)in Jinzhou during 2005-2021 and the variations of low-level jets during occurrence and development period of snowfalls under different weather patterns were compared.The results showed that heavy snowfall appears annually from November to March next year with an annual mean occurrence number of 1.6 times and happens most frequently in November and does not appear in January in Jinzhou and occurs more often in the north and south parts and lower infrequently in the central part of Jinzhou.Weather systems of heavy snowfall in Jinzhou are the northward Huabei (11.1%) and Jianghuai cyclone (51.9%) and the eastward Mongolia cyclone (37.0%).Under different weather situations, water resource and energy offered by low-level jets is the key to the occurrence of heavy snowfall.The wind speed of the low-level jet of the eastward Mongolia cyclone is the largest i.e.20 m·s^-1, followed by the Huabei cyclone at 14 m·s^-1 and the Jianghuai cyclone at 12 m·s^-1.The area of the low-level jet of the Mongolia cyclone is the largest, followed by the Jianghuai cyclone and that of the Huabei cyclone is the smallest.Six hours before the snow falls, the low-level jets are all formed, including 96% of southward or southwestward jets and 4% of eastward jets.Two hours before snowfall, low-level jets are maintained and enlarge the impact range, and the vertical rising speed of airflow is(-1.0~-0.5)×10^-3 Pa·s^-1, which can be regarded as the indicator of the beginning of snowfall.During snowfall, the low-level jet at 800~900 hPa emerges, and there is a zone where wind speed is larger than 20 m·s^-1 at 650~850 hPa, the vertical rising speed of airflow at the lower troposphere is increased to(-1.5~-1.0)×10^-3 hPa·s^-1, maintaining and intensifying the snowfall.

Key words: Low-level jet, Heavy snowfalls, Synthetic analysis