兰州大学机构库 >大气科学学院
东亚典型极端低温事件中大尺度环流系统组合性异常特征研究
Alternative TitleINTEGRATED CIRCULATION ANOMALIES OF THE IMPACTING LARGE-SCALE SYNOPTIC SYSTEM OF EXTREME LOW-TEMPERATURE EVENTS IN EAST ASIA
王嘉禾
Thesis Advisor李艳
2018-05-01
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword极端低温事件 西伯利亚高压 阻塞高压 组合性异常 WRF模式
Abstract

极端低温天气气候事件近些年在我国频频发生,造成了巨大影响。本文利用了1970-2016年我国地面台站观测资料,用百分位法定义了我国极端低温事件的阈值,计算了我国1970-2016年春季以及1970-2015年秋、冬季极端低温事件的频次、强度与站点发生率,分析了频次与强度的时间空间分布。然后选择两次典型极端低温事件-2008年低温雨雪冰冻灾害和2016年“霸王级”寒潮,利用NCEP/NCAR再分析资料,采用西伯利亚高压指数、平流层极涡指数与阻塞高压指数等定量化表征指数,分析了两次极端低温过程期间西伯利亚高压、阻塞高压与平流层极涡等大尺度系统的组合性异常特征。最后,利用WRF数值模式模拟了2016年“霸王级”寒潮,探索用模式模拟结果能否准确定量化表征天气系统的组合性异常特征。得到结论如下:

(1)针对我国极端低温天气气候事件的分析显示,1970-2016年间,春、秋与冬季全国极端低温事件的发生频次、强度与站点发生率均呈减小趋势。频次减小的速率冬季最大,秋季次之,春季最小;强度减小速率秋季最大,春季次之,冬季最小;台站发生率减小速率三个季节相差不大。冬季的极端低温事件频次、强度与站点发生率近些年出现上升趋势,反映出新的年代际变化特征。极端低温事件强度的空间分布与季节关系不大,受纬度与地形的影响很大。整体随纬度呈带状分布,体现出北强南弱的特征。对极端低温事件的频次与强度的EOF分析结果显示,主模态第一模态的空间分布均体现为全国大部分地区负值,青藏高原部分地区为正值的特征;对应的时间系数在1990年代前后有一个较明显的负值往正值的转折点,印证了极端低温频次和强度减少的趋势特征。

(2)选择两次典型的极端低温事件,研究期间大尺度系统组合性异常特征发现:与1970-2005年的气候平均态相比,2016年西伯利亚高压偏强16.8hPa,阻塞高压频率偏高约60%,极涡偏强约296gpm;而2008年西伯利亚高压偏强8.7hPa,阻塞高压频率偏高50%,极涡偏强190gpm,说明2016年过程中三个大尺度天气系统的异常比2008年的过程更显著。分析两次极端低温过程中三个大尺度系统的组合性异常特征发现,与1970-2005年气候平均态相比,2016年过程期间极涡偏强,北极高空有较强冷空气,北极地表爆发性增温配合中高纬阻塞高压的发展,使大量极寒冷的空气在西伯利亚地区积聚,在高空气流的引导下向我国爆发,从而使我国大部分地区的温度短时间内急剧下降。而2008年平流层极涡能量下传,使得阻塞高压长期维持,西伯利亚高压主体也长时间维持,但分裂出小股冷空气不断东移南下,一方面使我国南方维持长时间的低温,另一方面与来自南方的暖湿气流交汇,形成长时间的雨雪冰冻天气。

(3)利用WRF数值模式模拟了一次典型寒潮天气过程(2016年霸王级寒潮)发现,WRF模式能够很好的模拟出寒潮天气模型中大尺度系统的组合性异常特征,即较强的极涡、深厚而强大的阻塞高压和较强的西伯利亚高压。对于定量化指数的模拟发现,WRF模式对于极涡的面积指数模拟较好,但对于极涡强度指数模拟偏小;对于阻塞高压指数的中心位置和强度的模拟显示,WRF模式能够较好模拟出此次低温过程中较强阻塞高压的起止时间,但基本模拟不出前期的一次弱阻高过程;此外,对于较强的那次阻高过程阻高中心位置和强度的模拟也与NCEP再分析数据有所偏差;对于西伯利亚高压指数的模拟偏小,但能够反映西伯利亚高压在寒潮天气过程中的强弱变化,即WRF模式能够模拟出寒潮天气过程的转折期。

Other Abstract

Extreme low-temperature events have occurred frequently in China in recent years, resulting in a great impact. In this paper, the threshold of extreme minimum- temperature events is determined by the percentile method. By using the surface observation station data during 1970-2016, the frequency, intensity and site frequency of extreme minimum-temperature events in spring, autumn, and winter are calculated, and the time and space distribution of frequency and intensity is analyzed. Then, choosing two typical extreme cold wave events, i.e., the extended snow storm in 2008 and the strong cold wave in 2016, by using NCEP/NCAR reanalysis data, quantitative characterization index of the Siberian high, blocking event, and the stratosphere polar vortex are calculated to analyze the integrated circulation anomalies during extreme cold events. Finally, this study uses the WRF model to simulate the strong cold wave in 2016, to evaluate the model simulation ability of predicting the integrated circulation anomalies of the large-scale synoptic systems. The main conclusions are as follows:

1)Under the background of global warming, the frequency, intensity and site frequency of extreme minimum temperature events in spring, autumn, and winter tend to decrease. The frequency, site frequency, and intensity of extreme minimum- temperature event in winter increased in recent years, showing characteristics of decadal variation. The distribution of the intensity of extreme minimum-temperature events is greatly influenced by latitude and topography rather than the season, which is characterized that the intensity is strong in the north and weak in the south and there are different manifestations in special terrain areas. The frequency and intensity of extreme minimum-temperature events in the three seasons are analyzed by the EOF analysis. The first models all show negative values in most areas of China but negative values in the Tibetan Platau, while the corresponding time coefficient turns around 1990, reflecting the trend of warming.

(2)The quantitative index analysis show that during the extreme minimum temperature event in 2016, Siberian high is 16.8hPa stronger, blocking frequency is 60% higher, and polar vortex is 296gpm stronger than the 1970-2016 climatological mean. While during the event in 2008, Siberian high is 8.7hPa stronger, blocking frequency is 50% higher, and polar vortex is 190gpm stronger than the climatological mean. This means that the anomalies of the three large scale systems in 2016 are more obvious than that in 2008. As for the integrated circulation anomalies of such three systems during the two events, results show that polar vortex is stronger during the event in 2016 than the climatology and there is strong cold air in the Arctic. Explosive warming in Arctic and the development of mid-latitude blocking send heavy cold air to the Siberia and airflow at 500hPa leads the cold air to China, which makes temperature in most areas of China decrease sharply in a short time. While during the event in 2008, the anomalies of stratosphere polar vortex propagate downward and affect the troposphere. Then blocking sustains for a long time, as well as the Siberian high. The cold air moves to the south and the east constantly, maintaining a low temperature in southern China for a long time, and leading to cryogenic freezing rain and snow weather, with the help of southern warm and humid air.

(3)The WRF model is used to simulate the typical cold wave process in 2016. The result show that the WRF model can simulate the integrated circulation anomalies of large scale systems well. In other words, WRF model can reproduce the stronger polar vortex, blocking high, and the Siberian high during the extreme low-temperature event. As for the quantitative index, results show that the simulation of the position index of the polar vortex is good and the simulation of polar vortex intensity index is smaller than that of the NCEP/NCAR. There are some problems with the center position and strength of the blocking index, but the model simulation can describe the start and end time of the blocking process. The simulation of the Siberia high pressure index is smaller than that of the NCEP/NCAR, while it can show the trend of strength and weakness in the course of the cold wave.

URL查看原文
Language中文
Document Type学位论文
Identifierhttp://ir.lzu.edu.cn/handle/262010/200199
Collection大气科学学院
Recommended Citation
GB/T 7714
王嘉禾. 东亚典型极端低温事件中大尺度环流系统组合性异常特征研究[D]. 兰州. 兰州大学,2018.
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