1.特变电工新疆新能源股份有限公司 风电工程事业部;2.南京信息工程大学大气科学学院 气候动力学研究中心;3.南京信息工程大学气象灾害教育部重点实验室/气候与环境变化国际合作联合实验室/气象灾害预报预警与评估协同创新中心
1.School of Atmospheric Science,Nanjing University of Information Science &2.Technology
Extreme low-temperature events have attracted wide attention due to their persistence and disastrous nature. Many scholars have analyzed the past few decades'' low-temperature events in China from the perspective of interannual and interdecadal variations. Intraseasonal oscillation has been regarded as one of the basic characteristics of atmospheric activity. Strengthening the study of intraseasonal oscillation is one of the keys to the development of extended-range forecasting ability. The study shows that the formation of low temperature is closely related to the intraseasonal Oscillation of winter monsoon and cold air. Therefore, we want to explore the characteristics of quasi-biweekly oscillation in low temperature events to improve the understanding of the low frequency signals of the persistent extreme low temperature events in the middle and high latitudes. Based on in-situ observed daily minimum temperature from 192 stations in China and ERA-Interim reanalysis data, the characteristics of intraseasonal oscillation and low frequency circulation of the southern low temperature events caused by the southward cold air along the eastern path are discussed with band-pass filtering and SVD decomposition and other methods, the thermodynamic diagnosis is carried out as well. Results show that there is a significant 10-20d oscillation period at the minimum temperature in Southern China and 22 sustained low-temperature events in 34 winters during 1979-2013, which occurred with the enhancement of low frequency oscillation are listed. The analysis of the low frequency circulation pattern during the low-temperature event in February 1996 show that the system over Europe is moving downstream along the low-frequency wave train, the eastward shift is most obvious in middle latitude zone, and the abnormal high/low pressure over Siberia and East Asia is the key area which is closely related to winter temperature in most parts of China. The anomalous northerly wind guides the cold air from high latitude to the south is the fundamental cause of the southern low-temperature cold event. On the vertical structure, systems in the troposphere in East Asian coast shows the baroclinicity while the interior are mainly barotropic. Thermodynamic diagnosis shows the local temperature variation is mainly affected by advection term and diabatic heating term because the effect of adiabatic term is too small to be ignored, and cold advection is the key to maintain a low-temperature process. Therefore, the 10-20 day low frequency oscillation activity has an important contribution to the low-temperature event.