Gaoyuan qixiang (Dec 2022)
Low-Frequency Characteristics of Large-Scale Persistent Low Temperature Events in Winter in China and its Relation to Atmospheric Low-frequency Oscillation
Abstract
Based on the daily air temperature data from more than 2000 stations by the National Meteorological Information Center and NCEP/NCAR daily reanalysis data from 1980 to 2017， the effects of low-frequency oscillation on three types （nationwide， northeastern and eastern） of large-scale persistent low temperature events （short for events） in winter over China are compared and studied.The results show that there are more events since the 1980s to the early 1990s and the 2000s， and the winter temperature has a significant period of 10~30 days.By analyzing the atmospheric circulation field， it is found that the low-frequency Siberian high （SH） is the main influence system of the three types of events in the lower level.The low-frequency Siberian high is the strongest in the national type events， and the weakest in the northeast type events.The range of the Siberian high is the largest in the national type events， with its southern boundary can reach the south of the Yangtze River， and it is tilted to east in both the northeast and east type events.In addition， the low-frequency Aleutian low （AL） to the west is also one of the main low-frequency systems affecting the northeast type events.In the middle troposphere， both the national and east type events have the process of the low-frequency transverse trough turning vertically and merging with the East Asian trough， and the transverse trough has a larger zonal scale in the national type events， while the northeast type events are mainly affected by the northeast cold vortex.In the upper troposphere， we can find that the temperate jet stream as a whole continued to be weak and the subtropical jet stream as a whole continued to be strong in the national type events.Temperate jet stream is strong in the west and weak in the east， while the subtropical jet stream is weak in the west and strong in the east in the northeast type events.The temperate jet stream in the eastern type events continue to be weak， but the degree of weakness is greater than that of the national type events， and the subtropical jet stream is strong in the west and weak in the east.In addition， the western forecast signals of -12 days （national type）， -9 days （northeast type） and -10 days （eastern type） and the eastern signal of -12 days （national type） at low-frequency 500 hPa height field should be paid attention to respectively.
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