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1996年冬季一次南方低温事件的低频特征分析及诊断
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国家重点研发计划项目2018YFC1505804,国家自然科学基金项目41475045


Analysis and Diagnosis of Low-Frequency Characteristics in a Low Temperature Event in Southern China in the Winter of 1996
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    摘要:

    加强大气季节内振荡研究是发展延伸期预报能力的关键之一。研究表明低温形成与冬季风和冷空气的季节内振荡有密切联系。因此,本文利用192站日最低温度观测资料和ERA-Interim再分析环流资料,讨论了偏东路径南下冷空气造成的南方低温事件中准双周振荡特征及低频环流特征,并进行热力学诊断,希望提高对中高纬度地区持续性低温事件中低频信号的认识。结果显示:我国南方地区最低温度存在显著的10~20 d振荡周期,低温事件伴随低频振荡的加强而发生。1996年2月17~24日低温过程前后的低频环流场分析表明,西伯利亚及东亚上空的异常高/低压是影响我国大部分地区冬季温度的关键区,系统沿西北—东南向低频波列向下游移动,东移特征在中纬度带最明显,异常偏北风引导高纬冷空气向南推进是低温事件爆发的根本原因。垂直结构上,内陆以正压性为主,东亚沿岸表现出斜压性。热力学诊断发现温度局地变化主要受平流项和非绝热项作用,冷平流是维持低温过程的关键。

    Abstract:

    Extreme low-temperature events have received considerable interest due to their recurring and catastrophic nature. Several scholars have studied the low-temperature events in China over the past few decades from the perspective of interannual and interdecadal variations. Intraseasonal oscillation has been regarded as one of the basic characteristics of atmospheric activity. One of the keys to the advancement of extended-range forecasting capability is to improve the study of intraseasonal oscillation. Studies have shown that the low-temperature formation is closely related to the winter monsoon and cold air intraseasonal oscillation. Therefore, the authors want to investigate the characteristics of quasi-biweekly oscillation in low-temperature events to improve the understanding of the low-frequency signals of the recurrent 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 southward cold air along the eastern path are discussed with band-pass filtering and SVD (Singular Value Decomposition) decomposition including other methods. Also, the thermodynamic diagnosis is carried out as well. Results showed a significant 10-20 d oscillation cycle at the minimum temperature in southern China and reported 22 sustained low-temperature events in 34 winters during 1979-2013, which occurred with increased the low-frequency oscillation. Analysis of the low-frequency circulation pattern during the low-temperature event in February 1996 shows that the system across Europe is moving downstream along the low-frequency wave line, the eastward change in middle latitude region is most apparent, and the irregular high or low pressure over Siberia and East Asia is the key area closely related to winter temperature in most parts of China. The anomalous northern wind drives the cold air from high latitude to the south is the fundamental cause of cold event in the south. On the vertical structure, systems in the troposphere on the coast of East Asia show the baroclinicity while the interior is mainly barotropic. Thermodynamic diagnosis shows that the local temperature variability is mainly affected by advection term and diabatic heating term because the effect of adiabatic term is too small to be overlooked, and cold advection is the key to maintaining a low-temperature process. The low-frequency oscillation behavior of 10-20 days has a significant contribution to the low-temperature event.

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余汶樯,高庆九.1996年冬季一次南方低温事件的低频特征分析及诊断.大气科学,2020,44(2):257~268 YU Wenqiang,GAO Qingjiu.Analysis and Diagnosis of Low-Frequency Characteristics in a Low Temperature Event in Southern China in the Winter of 1996.Chinese Journal of Atmospheric Sciences (in Chinese),2020,44(2):257~268

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  • 收稿日期:2018-07-07
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  • 在线发布日期: 2020-03-20
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