兰州大学机构库 >大气科学学院
ENSO与超长波对欧亚阻高的影响及乌山阻高热动力特征研究
Alternative TitleThe Impacts of ENSO and Ultra Long Waves on Eurasian Blockings and Study of Thermodynamic Characteristics of Ural Blocking Highs
路瑶
Thesis Advisor李艳
2018-05-15
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword阻塞高压 极端天气气候事件 两类ENSO事件 超长波 动量通量
Abstract

欧亚关键区阻塞高压(简称:阻高)是影响我国天气气候的重要天气系统之一,其活动异常往往会导致高温、洪涝、冰冻等极端天气气候事件,对人民的生命财产安全产生极大的威胁。本文使用1979-2017年的再分析数据,借助国际上通用的T&M方法及客观分析法检索阻高,系统研究阻高的气候统计特征;探究其与主要的内部因素(超长波波动)及外强迫(两类ENSO)的关系;最后对与我国冬季天气气候有紧密联系的乌山阻高进行热、动力特征诊断。主要结论如下:(1)冬季乌拉尔山(简称:乌山)及鄂霍次克海(简称:鄂海)地区是阻高多发区,贝加尔湖(简称:贝湖)地区阻高频次相对较少,“双阻型”是中纬度大气环流的主要形势。乌山及鄂海阻高平均持续时间偏长,约为6.6天,贝湖的只有4.9天。整体来说,无论从阻高累积天数、累积频次,还是平均持续时间冬季乌山、贝湖、鄂海地区阻高均在1979-2005年呈现不同程度的下降趋势,尤其在1990s年代以来更为明显,但近10年阻高有增多增强的趋势。乌山及鄂海地区阻高累积天数呈现明显的年际周期变化,贝湖地区阻高的周期变化不显著。乌山阻高在1980 年代初到1990 年代末有明显的4~6年变化周期,鄂海阻高的5~7年变化周期在20世纪80年代末到21世纪初较活跃。(2)东太平洋La Niña冷事件(Eastern Pacific-La Niña,简称:EP-LN)会致欧亚地区瞬时阻高偏多,暖事件(Eastern Pacific-El Niño,简称:EP-EN)会使瞬时阻高偏少。但是乌山(60°E)以西及鄂海(140°E)以东瞬时阻高受中太平洋El Niño事件(Central Pacific-El Niño,简称:CP-EN)影响较大,致阻高偏多。EP-LN事件及中太平洋冷事件(Central Pacific-La Niña,简称:CP-LN)使乌山阻高事件持续时间分别偏多28%、25%,但会造成鄂海阻高偏少。EP-EN 及CP-EN事件会使鄂海阻高生命期偏长14%,18%,但会造成乌山阻高生命期偏短。冬季,当EP-EN事件发生时,乌山及鄂海地区位势高度(Geopotential Height,简称:GPH)有负异常,阻高偏弱;当发生EP-LN事件时,乌山及贝湖西部偏北地区500hPa上GPH有正异常,阻高偏多;当发生CP-EN事件时,欧亚3个关键区GPH都有不同程度的偏强,说明CP-EN事件利于阻高的生成;在CP-LN事件下,乌山及贝湖地区GPH偏高,这为阻高的发生、发展提供良好的条件。(3)北半球中纬度地区1-8波波谱比重在0.93-0.96变化,其中1-3波波谱比重超过0.5,表明1-3波(超长波)是大气运动中最主要的组成部分。1-8波和1-3波的波谱比重均有准2个月的周期变化,且冬季较夏季振荡更为显著。当1-3波波谱比重偏强时,乌山地区GPH明显偏低,贝湖地区的偏高,鄂海地区GPH变化不明显;反之,鄂海地区GPH偏强,其他两个区域GPH变化不显著。当60°N上1-3波波谱比重异常时,GPH异常表现更为突出。60°N上1波振幅与乌山阻高指数呈正相关关系,与鄂海的呈负相关,但是3波振幅与乌山阻高指数呈负相关,与鄂海的呈正相关。当乌山阻高持续时间从4天增加至7天时,30°N上1波振幅增加,2波振幅减小。阻高年均生命期由4天增加至7天时60°N上1波、2波振幅增加了43%,1.86倍。但冬季乌山阻高生命期由4天增加至7天时,1波振幅缩小了25%,2波振幅从112gpm增加至130gpm。2波振幅的激增可能会导致乌山阻高持续时间变长。(4)针对冬季乌山阻高整个生命期的热动力特征诊断显示:在“Day -3”前,中纬度定常温度T*随着高度的增加在减小,并沿着阻高南缘向下输送。在“Day -3”前中纬度对流层中定常热量通量{v*T*}呈“哑铃状”分布。同时20°-70°N区域均被正的(向北)定常动量通量{u*v*}控制,2个极大值中心分别位于30°N,250hPa和55°N,300hPa。从“Day -3”至“Day 0”,中纬度地区400hPa以下温度梯度减小致热成风减小,进而中纬度西风气流减小。同时在中纬度对流层中层出现负的(向南){v*T*}输送,这样在中纬度有热量的辐合,为阻高的建立提供了足够的热量。同时在中纬度有大量{u*v*}向北输送,最大值中心位于55°N附近,70°N以北{u*v*}是向南输送的,所以在70°N有动量通量的辐合,这有助于极锋急流的加强。热量通量的输送导致中纬度温度梯度减小,西风气流减弱,中纬度定常动量通量向北输送为极锋急流提供能量。至“Day +3”高层冷空气已经输送至地面使西伯利亚高压(Siberian High,简称:SH)加强,对流层中层向赤输送的定常热量通量消失,同时动量通量迅速减小有恢复至平常态的趋势。在500hPa上乌山阻高在“Day 0”定常热量、动量通量异常输送的方向是向北的,崩溃时输送方向是向南的,并且在热量通量异常输送中非线性作用起主要作用,但在定常动量通量异常输送中线性及非线性作用都很重要。

Other Abstract

As one of the most serious weather systems which extrodinarily impact on climate and weather of East Asia, the blocking highs in key Eurasian regions will result in anomalously hot weather, flood, freezing, and other severe weather climate events and pose a great threat to people's lives and property. By using reanalysis data in 1979-2016 and methods of T&M, objective analysis which are widely accepted to identify blocking highs, we study the climatic characteristics of blockings in key Eurasian areas, the relationships between blockings and internal factor (ultra long waves), external forcing (two types of El Niño Oscillation (ENSO) ), and thermodynamic characteristics of Urals blocking highs systematically. The main conclusions are as follows:(1) The Ural and Okhotsk regions were areas of high probability of blocking highs, while there was relatively low frequency of blocking highs in the Baikal regions. The “twin blocking type” was the main situation of atmospheric circulation at mid-latitudes. The average duration of blocking highs in the Ural and Okhotsk regions was relatively long with about 6.6 days, and that was only 4.9 days in Baikal regions during winter. As a whole, the blockings in three key Eurasian regions during the winter showed a decreased trend from cumulative days, cumulative frequency, or average duration during 1979-2005, especially since the 1990s. However, during nearly 10 years there was an upward trend of frequency of blocking highs. Significant interannual change was observed in the cumulative days of blockings in Ural and Okhotsk regions, yet there was no obvious change in the cycle blockings of the Baikal areas. There was a clear 4~6 year cycle of changes of Ural blocking highs in the early 1980s to the end of the 1990s, while 5~7 year cycle of changes of blocking highs in Okhotsk regions was more active from the late 1980s to the early 21st century.(2) The Eastern Pacific-La Niña (EP-LN) event would lead to more transient blockings in Eurasian regions, while East Pacific-El Niño (EP-EN) would cause transient blocking highs fewer. However, the instantaneous blocking highs in west of Ural Mountains (60°E) and the eastern part of Sea of Okhotsk (140°E) were greatly affected by the Central Pacific-El Niño (CP-EN), where there were more and stronger blockings. The EP-LN incident and the Central Pacific-La Niña (CP-LN) event led to the average duration of blockings in Ural regions increase by 28% and 25%, respectively, however caused blocking highs in Okhotsk areas to decrease. The EP-EN and CP-EN incidents made the average duration of the blocking highs in Okhotsk areas increase by more than 14% and 18%. The blockings of Ural regions would reduce in EP-EN and CP-EN incidents by some degree. In winter, when the EP-EN event occurred, the geopotential height (GPH) in the Ural and Okhotsk regions was negative anomaly, indicating the blocking highs were weak. The positive anomaly of 500hPa GPH in the Ural and north of Baikal areas occurred which made the blockings higher under EP-LN event. When the CP-EN events occured, the 500hPa GPH in the three key regions of Eurasian was stronger in different degrees, indicating that the CP-EN event were conducive to the generation of blocking highs. Under the CP-LN incident, the little higher GPH of the Ural and Baikal areas provided good conditions for the occurrence and development of the blocking highs.(3) The proportion of the 1-8 wave spectrum in the mid-latitudes of the Northern Hemisphere varied from 0.93 to 0.96, and the proportion of 1-3 wave spectrum exceeded 0.5, which demonstrate that the ultra-long wave is the most important component of atmospheric motions. There was a quasi-two-month periodic variation of proportions of the 1-8 wave and 1-3 wave spectra at 30°N or 60°N , which oscillation in winter was more significant than it in summer. When the proportion of 1-3 wave spectrum was strong, the GPH in Ural areas was low, and the GPH in the Baikal areas was high, but the changes of GPH in the Okhotsk areas were not significant. Conversely, as the proportion of 1-3 wave spectrum was weak, the GPH in the Okhotsk areas was high, yet the changes of GPH in other two regions were not obvious. In addition, when the 1-3 wave spectrum was abnormal at 60°N, the anomalies of GPH were more significant. The amplitude of 1 wave was positively related to the blocking indexes of the Ural regions, and negatively related to blocking indexes in Okhotsk areas. But the correlation between amplitude of 3 waves and the blocking highs in Ural Mountains regions was negative, yet amplitude of the 3 waves was positively related to the blockings in the Okhotsk areas. When the duration of blockings in Ural areas increased from 4 days to 7 days, the amplitude of 1 wave increased, but the amplitude of 2 waves decreased at 30°N, meanwhile the amplitude of 1 wave and 2 waves at 60°N increased by 43% and 1.86 times. The amplitude of 1 wave was reduced by 25% and the amplitude of 2 waves was increased from 112gpm to 130gpm as the duration of blockings in Ural regions increased from 4 days to 7 days in winter. The sharp increase of the amplitude of 2 waves might lead to a longer duration of blocking highs.(4) When we studied the thermodynamic characteristics of blockings in Ural regions during the whole life process in winter, it was found that before the “Day -3”, the stationary temperature T* at middle latitudes decreased with height. The high-level T* was transported downward along the southern edge of the blockings. Before the "Day -3" the stationary heat flux in overall troposphere at the mid-latitudes was distributed as "dumb-bell" shape, i.e. At the same time, the areas of 20°-70°N were controlled by positive (northward) stationary momentum flux {u*v*}, and the two maximum centers were located at 30°N, 250hPa and 55°N, 300 hPa, respectively. From “Day -3” to “Day 0” the temperature gradient (-∂T/∂y) below 400 hPa decreases, which led to thermal winds weak. The westerly winds at mid-latitudes would also be reduced. Meanwhile, the negative (southward) stationary heat flux {v*T*} occurred at mid-latitudes in the middle of troposphere, which showed that heat flux was converged at the mid-latitudes.That provided sufficient heat for blocking establishment. At the same time, the positive stationary momentum flux at mid-latitude became stronger with maximum value center located near 55°N. The stationary momentum flux {u*v*} was transported southward in north of 70°N.That showed that there was a convergence of momentum flux at 70°N, which contributed to the strengthening of the polar front jet. The transportation of heat flux led to a decrease in the temperature gradient at mid latitudes, which made a decrease of westerly. The stationary momentum flux at mid-latitudes was transported northward that caused the polar front jet to be stronger. Until “Day +3”, the cold air from upper troposphere was transported down the ground to strengthen the Siberian High. The negative stationary heat flux in the middle atmosphere disappeared at the same time.The stationary momentum flux rapidly decreased to return to the normal. At the time of establishment of the blockings at 500 hPa, the transportation direction of anomalous heat and momentum flux was northward, while direction in collapse periods was southward. In addition, the non-linear effects played the most important role in the anomalous heat flux {v*T*}’ transportation. However, linear and non-linear both were siginificant in the transportation of anomalous momentum flux {u*v*}’.

URL查看原文
Language中文
Document Type学位论文
Identifierhttp://ir.lzu.edu.cn/handle/262010/200167
Collection大气科学学院
Recommended Citation
GB/T 7714
路瑶. ENSO与超长波对欧亚阻高的影响及乌山阻高热动力特征研究[D]. 兰州. 兰州大学,2018.
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