东亚高空急流协同变化特征及其机理研究

发布时间：2017-12-31 13:19

本文关键词：东亚高空急流协同变化特征及其机理研究　出处：《南京大学》2017年博士论文　论文类型：学位论文

【摘要】：东亚高空急流是北半球重要大气环流系统之一。东亚副热带急流和极锋急流的协同变化既可以反映中高纬度环流系统的作用,又可以反映低纬度环流信号的异常,还能够与大气低频遥相关紧密联系在一起,对东亚天气气候系统的影响起到桥梁或者纽带的作用。本文利用NCEP/NCAR再分析资料,得到冬季东亚陆地上空高空急流的主要模态,揭示出副热带急流和极锋急流位置和强度的协同变化关系,进而研究高空急流协同变化的气候效应。从热力学和动力学两个方面分别讨论急流协同变化的机理。评估AMIP模式对东亚高空急流协同变化的模拟能力,并分析极地增暖对东亚地区急流协同变化的影响。利用局地有限振幅波活动及其能量平衡方程诊断出海冰融化对局地反气旋波活动以及对中纬度地区极端事件的影响机制。全文主要结论如下:一、东亚高空急流位置和强度的协同变化特征东亚地区高空急流包括副热带急流和极锋急流。通过东亚地区急流核的分布确定了陆地上空这两支急流的关键区域。对陆地上空纬向风进行EOF分析发现,东亚陆地上空两支急流变化的主要模态分别对应副热带急流和极锋急流位置和强度的反位相变化特征。当两支急流距离较近,即极锋急流偏南、副热带急流偏北时,两支急流的强度均增强;当两支急流互相远离,即极锋急流偏北、副热带急流偏南时,两支急流的强度均减弱。从对应的大气环流异常来看,当两支急流靠近时,东亚大槽减弱,东亚中纬度地区位势高度增加,太平洋北部西风减弱;而当两支急流远离时,中纬度位势高度减弱,东亚大槽增强。急流位置变化模态对应的500hPa位势高度异常分布在欧亚-太平洋地区呈现出正负正(或负正负)的特征,与中纬度欧亚遥相关型相似;对应的海平面气压场异常分布表现为极地区域与中纬度洋面的反位相变化,与北极涛动相似。二、东亚高空急流协同变化的机制影响急流位置和强度变化的原因除了非绝热加热异常、海温异常等外强迫因子外,大气内部动力学过程也会通过波流相互作用对其产生一定的影响。因此,从热力学和动力学两个方面分析影响急流位置和强度协同变化的可能机制。从热力学方面看,当两支急流距离较近时,从温度平流方程得到非绝热加热以及水平热量输送的作用增加了南北温度梯度,根据热成风原理,增大的经向温度梯度能够增强副热带急流与极锋急流的强度,从而使两支急流的强度增加。当两支急流相距较远时,非绝热加热以及水平热量输送的作用减弱,导致南北温度梯度减小,从而减弱了两支急流的强度。从动力学方面来看,低层斜压性与中纬度天气尺度瞬变活动联系紧密而对副热带地区无显著影响。当两支急流相距较近时,天气尺度瞬变波E矢量在极锋急流区存在辐散中心,加强了该区域纬向风速,从而使极锋急流增强。当两支急流相距较远时,辐散中心减弱甚至转为辐合,从而使极锋急流减弱。除此之外,定常波E-P通量通过增强或减弱纬向风速来改变两支急流的强度。两支急流靠近时,急流区均出现E-P通量辐散中心,增强了两支急流的强度;两支急流远离时,辐散中心的减弱与辐合中心的出现使两支急流强度均减弱。三、极地增暖对高空急流协同变化的影响通过AMIP试验将海冰融化的外源强迫单独分离开来分析海冰融化对东亚地区高空急流的位置和强度协同变化的影响,从AMIP海冰控制试验的模式数据分析海冰融化产生的风场异常可以得到,该模式既能模拟出两支急流强度协同变化,也能模拟出两支急流位置协同变化。海冰融化导致两支急流的强度都存在年际变化,但是整体趋势不显著;极锋急流的位置不仅存在年际变化,还存在明显的年代际变化,整体趋势偏南2.5°左右,而副热带急流位置变化不明显。进一步利用EOF时间序列对纬向风和经向风距平场进行回归可以看出,自20世纪90年代中后期,尤其是21世纪以来,极地增暖致使极锋急流强度减弱,主要表现为纬向风异常减弱,经向风异常增加。四、极地增暖对北半球中纬度极端事件的影响及机制利用有限振幅波活动方法分析500hPa位势高度场得到局地波活动特征,并通过量纲分析将局地波活动分解成平均梯度和涡动扰动尺度两项,分别对应着波活动的热力学变化和动力学变化特征。对再分析资料和AMIP数据中计算出的有限振幅波活动、扰动尺度的趋势分析得出,观测数据中中纬度纬向平均波活动的增加以及波动经向扰动增加的趋势无法在历史模式尤其是海冰控制模式中模拟出来,这说明波活动异常与北极地区的海冰融化无显著的联系,很有可能是由于大气内部变率的作用。但是从局地的波活动变化特征中发现无论是再分析资料还是模式数据,北半球中纬度尤其是欧亚中北部地区局地反气旋波活动均存在显著的增加趋势。而500hPa反气旋波活动往往与阻塞高压等天气系统联系在一起,对局地天气气候的异常产生影响。反气旋活动大值中心南北两侧极端暖事件和极端冷事件概率均有所增加也证实了这个观点。通过能量方程诊断分析发现极地海冰融化较快的巴伦支海-喀拉海地区的反气旋波活动水平输送是欧亚地区反气旋波活动增加的源,与此同时水平输送将极地地区冷空气向南输送造成极端冷事件的发生。
[Abstract]:The Asian jet is one of the important atmospheric circulation systems in the northern hemisphere. Coordinated variation of the East Asian subtropical westerly jet and polar front jet can reflect in the high latitude circulation system, but also can reflect the abnormal signal of the low latitude circulation, but also with the Atmospheric Low-Frequency teleconnection closely linked to the bridge, or the link to the influence of East Asian climate system. The weather by using NCEP/NCAR reanalysis data, the main modes of the winter East Asian jet stream over the land, to reveal the relationship between collaborative subtropical jet and polar front jet location and intensity, and climate effect of high-altitude jet changes. Discuss the mechanism of collaborative jet coordinated changes from two aspects of thermodynamics and dynamics respectively. Simulation capability of collaborative AMIP model to assess changes in the Asian jet, and the analysis of polar warming on the East Asian Jet collaborative change The influence of local. By using the finite amplitude wave activity and energy balance equation on the diagnosis of ice anticyclonic wave activity and on the mid latitude regions of extreme events influence mechanism. The main conclusions are as follows: first, concurrent changes in East Asia westerly jet location and intensity characteristics of East Asia westerly jet including subtropical jet and polar front the key area of land over the rapids. This two jets is determined by the distribution of East Asia. The jet core EOF analysis of zonal wind over the land, anti phase change characteristics of main modes of East Asian over land two jet changes respectively corresponding to the subtropical jet and polar front jet location and strength. When the two jets the short distance, namely the polar front southerly jet, north subtropical jet, strength of two jets increased; when the two jets away from each other, namely the polar front jet north subtropical acute Flow south, strength of two jets were decreased. The atmospheric circulation anomalies corresponding to the view, when close to two jets, the East Asian Trough weakened in mid latitude East Asia geopotential height increase, the North Pacific westerly weakened; and when away from the two jets, mid latitude potential high degree of weakening of East Asia trough enhancement. Jet position change mode corresponding to the 500hPa geopotential height anomaly distribution in Eurasia Pacific region showing a positive negative positive (or negative negative) characteristics, and mid latitude Eurasian teleconnection pattern is similar; the sea level pressure corresponding to the abnormal distribution for the polar regions and in the latitudes of phase, and the Arctic oscillation is similar. Two, the mechanism of the Asian Jet coordinated changes influence the position and intensity of the jet in addition to diabatic heating anomalies, SST anomalies of external forcing factors, internal atmospheric dynamic process will flow through the waves The interaction have a certain impact on it. Therefore, analysis of the impact of the possible mechanism of change of the position and intensity of collaborative jet from two aspects of thermodynamics and kinetics. From the thermodynamic aspect, when the two jet distance, from the temperature advection equation of non adiabatic heating and heat transfer level to increase the role of the north-south temperature gradient and according to the principle of thermal wind, increasing the meridional temperature gradient can enhance the subtropical westerly jet and polar front jet intensity, so that the intensity of two jets increases. When the distance of two jets is far away, the weakening effect of non adiabatic heating and heat transfer level, leading to the north-south temperature gradient decreases, thereby weakening the strength of two a. From the dynamic perspective, low-level baroclinicity and mid latitude synoptic scale transient activity is closely linked to the subtropical regions had no significant effect. When the distance of two a short day, Gas scale transient wave E vector divergence center in the polar front jet region, strengthens the regional zonal wind velocity, so that the polar front jet is enhanced. When the distance of two jets is far away, the divergence center weakened and even to convergence, so that the polar front jet weakened. In addition, Chang Bo E-P the amount of pass through increased or decreased zonal wind velocity to change the intensity of two jets. Near two jets, the jet appeared E-P flux divergence center, enhance the strength of two jets; from two jets, there is weakening and convergence center divergence center of the two jets are strong weakened. Three effects of warming on the polar jet coordinated changes through the AMIP test will be forced to separate exogenous ice separating effect analysis of coordinated changes in East Asia melting sea ice jet location and intensity, from the number of AMIP control test points according to the sea ice The wind of melting sea ice anomalies generated by the model can be obtained, which can simulate the change of collaborative two jet strength, can also simulate two jet location collaborative change. Sea ice melting leads to the strength of two jets have interannual variation, but the overall trend is not significant; the position of the polar front jet not only exist interannual variation there are obvious interdecadal changes, the overall trend of the south of about 2.5 degrees, and the change of position of the subtropical jet is not obvious. The further use of EOF time series of zonal wind and meridional wind anomaly field regression can be seen, since late 1990s, especially since twenty-first Century, the polar warming in polar front jet intensity mainly for the zonal wind anomaly weakened by an abnormal increase in wind. Four, the polar warming effect on the mid latitudes of the northern hemisphere and the mechanism of extreme events using finite amplitude wave activity analysis method 500hPa Potential height field characteristics of bureau ground wave activity, and by dimensional analysis bureau ground wave activities into average gradient and eddy scale two, which corresponds to the thermodynamic changes and dynamic change characteristics of wave activity. The analysis of calculation data and AMIP data in finite amplitude wave activity analysis of disturbance scale trend the increase in the observed data in the mid latitude zonal mean meridional wave activity and fluctuation disturbance increasing trend in history cannot mode especially simulated sea ice control mode, which shows that the wave activity had no significant relationship with the Arctic sea ice melts, it is probably due to the atmospheric internal variability effect. But from the variation of local wave activity found in both reanalysis data and model data, latitudes in the northern hemisphere especially the north central region of the Eurasian anticyclone wave activities are local A significant increasing trend. The 500hPa activity is often associated with anticyclonic wave blocking high weather system together, abnormal weather and climate impact on the anti cyclone activity value centre. The north and south sides of extreme warm events and extreme cold event probability increased also confirmed this point. Through the diagnosis analysis found that the polar energy equation sea ice melts faster the Barents Kara Sea region of the anticyclonic wave activity transportation is anticyclonic wave activity in Eurasia increased, at the same time the level of transmission will polar region cold air southward transport caused by extreme cold events.

【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P442

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