东亚冬季风变率与高空急流的联系及冬季风季节预报

发布时间：2018-03-01 11:35

本文关键词： 东亚冬季风高空急流极冷日数季节预测物理-经验模型　出处：《南京大学》2016年博士论文　论文类型：学位论文

【摘要】：东亚冬季风系统是北半球冬季控制东亚气候最重要的系统,其子成员在经向上涵盖从热带到中高纬,贯穿整个对流层。本文利用NCEP-NCAR再分析资料,从东亚副热带急流和极锋急流协同变化的角度分析高空急流与其它冬季风子成员、东亚地表气温变率的联系,揭示和急流相联系的纬向风切变与其它冬季风成员异常环流的反馈过程；从外强迫和大气内部动力过程的角度分析急流变率模态与冬季风子成员相联系的原因。在东亚冬季风季节预测方面,评估ENSEMBLES计划的耦合模式对温带东亚关键区内平均气温的季节预报能力,并基于外强迫因子影响冬季气温的物理过程以及预报量和预报因子之间的时滞相关,采用建立Physical-Empirical模型的方法,显著提高东亚冬季风关键区的极冷日数和平均气温的季节预报技巧。全文主要结论如下：一、东亚高空急流协同变化与东亚冬季风的联系东亚副热带急流、极锋急流是冬季风系统的子成员。通过对东亚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两个主要变率模态分别对应极锋急流和副热带急流经向位置的移动(急流经向移动模态)和二者强度上反位相变化(急流强度反位相变化模态)。两支急流协同变化的两个主模态分别与东亚冬季风地表气温的北方模态和南方模态相对应。对于急流协同变化第一模态,当极锋急流位置南移时,冬季风系统子成员位置偏西偏北,东亚大槽北段增强并西移；低层西伯利亚高压向西北方扩展,这有利于冷空气进入东亚北部地区。而对于急流协同变化第二模态,当极锋急流强度偏弱时,高原副热带急流偏强,500hPa位势高度场中高纬和中低纬度定常波波列向东传播至东亚,在海平面气压场上为增强的西伯利亚高压和南移的阿留申低压,对应东亚南方为冷冬,反之亦然。从两模态所反映的环流异常来看,与极锋急流、副热带急流分别相联系的纬向风异常通常表现为中高纬西风(东风)异常同时中低纬度东风(西风)异常,对应于对流层高层环流的纬向风切变异常。高层纬向风切变异常是东亚冬季风系统子成员环流异常反馈过程的重要组成部分。与冬季风系统各子成员相联系的异常三维环流通过反馈机制相互耦合：高层纬向风切产生的气旋性涡度使中层位势高度降低,增强的东亚大槽引导冷空气从高纬度南下,冷空气的向南侵入一方面增强西伯利亚高压,高压环流异常将调制与极锋急流相联系的纬向风,另一方面可加强低层经向温度梯度,进而影响热力驱动的副热带急流,这一反馈机制体现了冬季风子成员变率具有一致性特征。与高空急流两个主要变率模态相联系的环流异常均表现出对反馈过程的维持作用。二、东亚高空急流协同变化模态与东亚冬季风相联系的机制研究发现,高空急流变率模态与其它冬季风子成员环流异常相联系的原因有两个。一方面,异常三维环流通过反馈机制而相互耦合,当急流发生变化时,耦合系统的物理反馈过程可调制其它子成员。急流经向移动模态则对应着三维环流耦合异常在中高纬的维持,而急流强度反位相变化模态则反映出环流耦合异常在中低纬度维持。在这一情况下,影响急流变化的因子为来自下垫面的强迫,以及天气尺度扰动的反馈过程和定常波活动。另一方面,高层急流和其它子成员各自分别直接受到北极海冰异常和热带ENSO信号的调制作用,从而导致急流和其它子成员的变化相互联系。秋季巴伦支海海冰异常偏少时,对应海温正异常,极锋急流近极区一侧的低层斜压波活动减弱而近赤道一侧斜压性增强,可调制高层西风异常,同时高纬斜压性改变可阻止气旋东移,气旋减少后有利于西伯利亚沿岸产生反气旋环流异常。秋季巴伦支海增暖延续至冬季时,可以产生500hPa从极区到乌拉尔山的反气旋异常,通过Rossby波传播将导致下游东亚大槽西移加深。与La Nina相联系的热带海洋大陆上空异常降水释放潜热,可产生上升运动和高层向北的辐散风,进而影响高层急流,同时也可以激发经向上向高纬传播的波列,东亚地区显著北传的波通量也有利于500hPa东亚大槽加深。前期秋季热带海温和极地海冰等异常信号影响冬季风的机制为冬季大气环流和地表气温的季节预报提供了科学依据。三、温带东亚关键区冬季极冷日数和平均气温的季节预报本文选取位于东亚冬季风核心区域的温带东亚关键区(TEA,30°-50°N, 110°-140°E),对该区域极冷日数和冬季平均气温进行季节预报研究。通过评估ENSEMBLES计划耦合模式对温带东亚关键区冬季气温的季节预报技巧发现,欧洲中心模式预报技巧高于多模式集合平均,相较其它模式预报结果更为可信,但由于受限于模式水平,当前动力预报技巧仍较低。因此,本文进一步基于外强迫因子影响冬季气温的物理过程以及二者之间的时滞相关,建立Physical-Empirical预报模型,发现关键区极冷日数至少60%左右的变率存在季节可预报性。冬季平均气温和极冷日数的可预报性来源为从秋到冬的持续性物理过程：太平洋发展的ENSO、欧亚大陆北极区域(巴伦支-喀拉-拉普捷夫海)的秋季海温异常,以及欧亚大陆十月份雪盖异常。当前期秋季北极海温偏暖、欧亚大陆雪盖偏多、La Nina发展时,通过调制三维异常环流反馈并影响冬季风系统子成员变化,使得该年冬季温带东亚关键区极冷日数偏多,冬季平均气温偏低。关键区极冷日数的可预报性基础是冷事件频率和平均气温存在高相关性,Physical-Empirical模型为冬季气温和极端冷事件频数提供了更为可靠的季节预测方法。
[Abstract]:The East Asian winter monsoon system is the control system of the northern hemisphere winter climate in East Asia is the most important, the sub member in the meridional direction ranging from tropical to mid high latitude, throughout the troposphere. Using the NCEP-NCAR reanalysis data, from the East Asian subtropical westerly jet and polar front jet collaborative change angle analysis of upper jet and other winter monsoon sub members. Contact surface temperature variability in East Asia, the process of zonal wind shear and reveal the jet associated with other members of the winter monsoon circulation anomaly feedback; analysis of the causes of acute variability and winter monsoon sub modal members connected from the external forcing and atmospheric internal dynamic process perspective. In the prediction of the East Asian winter monsoon season, seasonal forecasting ability ENSEMBLES plans to assess the coupling mode of average temperature of the key area in the Temperate East Asia, and on the basis of external forcing factors affect the physical process and the prediction of winter temperature and pre The correlation between the delay factor reported, using the method of building Physical-Empirical model, significantly improve the seasonal forecast skill of extreme cold days and the average temperature of the East Asian Winter Monsoon key area. The main conclusions are as follows: first, with the East Asian subtropical westerly jet Asian Jet co vary with the East Asian Winter monsoon and polar front jet is a member of the winter monsoon system. Through EOF analysis found on the East Asian zonal wind over the land, the two main East Asia over the land of two jets change rate mode corresponding to the polar front jet and the subtropical jet meridional position (the jet to the mobile phase mode) and two strength (the strength of the jet phase change mode). The two primary modes of two jets coordinated changes correspond to the East Asian Winter Monsoon in northern and southern surface temperature modal mode. For collaborative change in the first mock exam jet State, when the polar front jet position south when winter monsoon sub member position North West, North East Asia trough strengthen and move to the West; the lower Siberia High North West extension, which is conducive to the cold air into the area of North East Asia. And for the second jet coordination change mode, when the polar front jet is weaker, the plateau side a tropical jet is strong, 500hPa geopotential height in high latitude and low latitude stationary wave propagating eastward to the East, the sea level pressure field for the enhancement of Siberia high and south of the Aleutian low, South East Asia corresponding for cold winter, and vice versa. The two mode reflected from the circulation anomaly, and very front jet, the subtropical jet were linked to the zonal wind anomaly is usually westerly (easterly) anomaly and low latitude easterly (westerly) anomaly, corresponding to the upper troposphere circulation variation of zonal wind shear Often. High zonal wind shear anomaly is an important part of the members of the East Asian winter monsoon system sub circulation anomaly feedback process. The abnormal three-dimensional circulation associated with each of the members of the sub winter monsoon system through the feedback mechanism of mutual coupling: high zonal cutting of cyclonic vorticity to middle lower geopotential height, enhanced East Asian Trough guide the cold air southward from the high latitude, the cold air southward into the one hand to strengthen the Siberia high and high pressure circulation anomalies will be modulated with the polar front jet associated with the zonal wind, on the other hand can enhance the low layer meridional temperature gradient, and the influence of the subtropical jet thermal drive, this feedback mechanism reflects the members of winter the wind has consistent characteristics variability. Circulation associated with the two main jet rate mode showed the abnormal feedback process to maintain function. Two, the Asian Jet collaborative change Study on the mechanism of contact mode and the East Asian winter monsoon is found, there are two reasons for high rate of members and other acute rheological modal of winter monsoon circulation anomaly sub linked. On the one hand, the abnormal three-dimensional circulation through the feedback mechanism and mutual coupling, when the jet is changed, the coupling system of the physical process of the other sub modulation feedback the jet to the mobile member. Mode corresponds to maintain the three-dimensional circulation coupled anomalies in the middle and high latitudes, and the intensity of the jet phase mode reflects the anomaly in the low latitude circulation coupled to maintain. In this case, forcing factors influence jet changes from the underlying surface, and the process of the synoptic scale disturbance and feedback Chang Bo. On the other hand, members of high-level jet and other sub respectively by direct modulation of Arctic sea ice anomaly and tropical ENSO signal, resulting in rapids and other Zi Cheng The change of contact with each other. The fall of the Barents Sea ice was extremely scarce, the corresponding positive SST anomaly, polar front jet region near one side of the lower layer baroclinic waves near the equator side weakened baroclinicity enhancement, modulation of high-level westerly anomalies and high latitude baroclinic changes can prevent gas rotating eastward, reduce after cyclone to the coast of Siberia produced an anticyclonic circulation anomaly in the Barents Sea. Autumn warming until winter, can produce 500hPa from the polar anticyclone to mount Ural by abnormal Rossby wave propagation will result in downstream of the East Asia trough westward deepening. Associated with the La Nina tropical marine precipitation anomalies over the mainland release of latent heat, can produce rise the movement and high northward divergence wind, thereby affecting the high-level jet, but also can stimulate the upward propagation of the high latitude wave, was spreading to the North East Asia wave flux is also conducive to the east of 500hPa The sub trough. The early impact of autumn tropical SST and polar sea ice anomaly signal provides a scientific basis for the mechanism of Winter Monsoon Seasonal Forecast of Winter Atmospheric Circulation and surface temperature. Three, seasonal forecasting the key region of temperate zone of East Asian winter cold days and the average temperature of the selected key areas of East Asia is located in the core area of the East Asian Winter Monsoon temperate the (TEA, 30 degrees -50 degrees N, 110 degrees -140 degrees E), studied the seasonal forecasts of the very cold days and the average temperature in winter. By evaluating the plan ENSEMBLES coupling mode to the key area in winter season temperature Temperate East Asia forecast technique, European center model forecast skill than the multi model ensemble. Compared with other forecast results more credible, but due to the limited level of the current model, the forecast skill power is relatively low. Therefore, this paper further based on external forcing physical factors affecting the temperature in winter The delay between the process and the relationship of two, establish the Physical-Empirical prediction model, found around the key areas of extreme cold days at least 60% of the rate of change of seasonal predictability. The average temperature in winter and cold days the predictability of the source of persistent physical process from autumn to winter: Pacific Development ENSO, Eurasia the Arctic region (the Barents Kara Laptev Sea - -) autumn SST anomaly and the Eurasian Snow Cover Anomaly in October. During the fall of the Arctic SST warmer, Eurasian snow cover side, La Nina development, through the modulation of three-dimensional abnormal circulation feedback and influence of the members of the winter monsoon system changes, the key area of temperate winter year East Asia extreme cold days too many, the average winter temperature is low. The key area of extreme cold days predictability is based on cold event frequency and average temperature are high correlation, Physical-Empirical model The winter temperature and the frequency of extreme cold events provide a more reliable seasonal prediction method.

【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P425.42;P457.5

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