冬季北大西洋涛动（NAO）的变异及其对欧洲天气的影响机制研究

发布时间：2018-11-21 08:06

【摘要】：北大西洋涛动（North Atlantic Oscillation简称：NAO）是北半球冬季最显著的大气低频偶极子模态。NAO对局地及周边地区的天气气候有着显著的调控作用。已有的大部分的研究主要是关注NAO气候态的平均特征（月平均，季节年平均），但是并不能刻画每个NAO事件生命过程的具体变化特征，因此也无法研究NAO生命过程对欧洲天气的影响，尤其是对低温降雪天气的影响机制。另外，对于时空变异的NAO事件来说，传统的NAO正、负位相（NAO+和NAO-）的分类方法并不能完全刻画其特征。本文针对上述问题，从NAO生命周期分解和NAO事件变异两个主要方面进行了系统的研究。具体结论如下：本文通过将NAO生命过程详细分解为开始阶段（B1），发展阶段（B2），衰减阶段（A1）及结束阶段（A2）四个关键期，分析了不同生命阶段对应的欧洲地区阻塞、温度及降水的分布变化。合成分析发现，阻塞分布明显受到NAO位相的调控作用。受NAO+事件调控，阻塞从大西洋东部至欧洲东北部呈现西南－东北（SW-NE）方向分布；受NAO-事件调控，阻塞从欧洲中部至北大西洋和格陵兰地区呈现东南－西北（SE-NW）方向分布。特别发现，在NAO+（NAO-）事件生命周期中，对应的升温（降温）最明显的阶段为衰减阶段，这主要是由于温度平流对欧洲大陆的延迟影响导致的。物理机制分析发现，NAO-（NAO+）阶段北欧（南欧）阻塞频率的增加与NAO-（NAO+）偶极子结构的西退（东移）密切相关。大西洋中高纬度西风的减弱（加强）与NAO偶极子结构的纬向西退（东移）密切相关，即NAO过程的自我反馈机制。围绕2012年1月～2月欧洲地区发生的一次极端低温（暴雪）事件，结合最近提出的原地型（In-situ）和位相转换型（Transition）NAO事件的分类，指出发生位置变异的偏东型位相转换事件（NAO+转Eastern NAO-简称： NAO+转ENAO-）的发生有利于欧洲爆发低温降雪天气过程。ENAO-事件会给整个欧洲地区尤其是东欧和南欧带来大幅度持续的降温过程，同时在ENAO-环流所对应的南北分支风暴路径的调控作用下，南欧降水（雪）增多。进一步的气候统计分析表明，虽然NAO+（NAO-）会给欧洲带来升温（降温）过程，同时降水分布表现为单支（南北两支）结构，但是NAO事件纬向位置的变异会给欧洲地区的天气气候造成不同的影响。本文中，以NAO偶极子中心的北部中心为标准，判断其位置处在10W经线以东和以西来划分偏东型NAO（EasternNAO简称：ENAO）和偏西型NAO（Western NAO简称：WNAO）事件。分析表明，不论对于In-situ NAO-事件还是Transition NAO-事件，ENAO－给欧洲地区带来的降温幅度和面积要大于WNAO-。另外发现在2005年之后，NAO+转ENAO-事件发生的频率明显增多，，可能是近10年欧洲地区频发极端寒冷暴雪天气的原因。进一步的分析发现，相比WNAO+事件，ENAO+事件会给欧洲带来更加明显的升温作用。同时，ENAO事件对应的阻塞的分布位置也相对偏东。NAO的纬向位置与西风强弱有密切关系，较强的西风会强迫NAO向下游（东）发展变异；如果西风偏弱，NAO位置就会相对偏西。
[Abstract]:The North Atlantic Treaty (NAO) is the most significant low-frequency dipole modality in the northern hemisphere. The NAO has a significant regulatory effect on the weather and climate in the local and surrounding areas. Most of the studies have focused on the average (monthly, seasonal, average) characteristics of the NAO climate state, but it is not possible to describe the specific change characteristics of the life process of each NAO event, so it is not possible to study the effect of the NAO life process on the European weather. in particular to a mechanism for influencing the low-temperature snowfall weather. In addition, the traditional NAO positive and negative phase (NAO + and NAO-) classification methods do not completely characterize the NAO events of space-time variation. In the light of the above-mentioned problems, the research of the system is carried out from the two main aspects of the NAO life cycle decomposition and the NAO event variation. The specific conclusions are as follows: In this paper, through the detailed breakdown of the NAO life process into four key periods of the start stage (B1), the development stage (B2), the attenuation stage (A1) and the end stage (A2), the distribution of the obstruction, the temperature and the precipitation in the European region corresponding to the different life phases is analyzed. The results of synthesis and analysis show that the blocking distribution is obviously affected by the control of the NAO phase. The function is controlled by the NAO + event, blocking the distribution of the southwest-northeast (SW-NE) direction from the eastern part of the Atlantic to the north-east of Europe, and is controlled by the NAO-event to block the direction of southeast-northwest (SE-NW) from the central part of Europe to the North Atlantic and Greenland. Distribution. In particular, in the life cycle of the NAO + (NAO-) event, the most obvious phase of the corresponding temperature rise (cooling) is the attenuation stage, which is mainly due to the influence of the temperature advection on the European continent's delay. The physical mechanism analysis shows that the increase of the blocking frequency of the NAO-(NAO +) phase in the Northern Europe (NO +) phase is close to that of the NAO-(NAO +) dipole structure. Correlation between the weakening (strengthening) of the high-latitude westerly wind in the Atlantic and the weft-to-west (east-shift) of the NAO dipole structure, that is, the self-feedback of the NAO process Mechanism. An extreme low temperature (Blizzard) event that occurred in the European region from January to February 2012, in combination with the recent classification of In-situ and Transition NAO events, it was noted that the east-type bit-phase transition event (NAO + to Eastern N, The occurrence of AO-abbreviation: NAO + (NAO-) is beneficial to the low temperature drop in Europe The process of snow and weather. The ENAO-event will bring a significant and sustained cooling process to the whole European region, especially in Eastern Europe and Southern Europe, while the south-European precipitation is under the control of the north-south branch storm path corresponding to the ENAO-circulation. (snow) increased. The further analysis of climate statistics shows that while NAO + (NAO-) will bring a temperature rise (cooling) process to Europe, the precipitation distribution is shown as a single branch (both north and south), but the variation of the weft-to-position of the NAO event will give the weather gas in the European region In this paper, the north center of the center of the NAO dipole is used as the standard, and the position is determined to be east and west of the 10W warp, and the Eastern NAO and the Western NAO (Western NAO) are divided.: WNAO) events. The analysis shows that, whether for In-situ NAO-event or transition NAO-event, the temperature drop and area of the ENAO-to the European region To be greater than the WNAO-. It is also found that, after 2005, the frequency of NAO + to ENAO-events has increased significantly and may be the most frequent extreme cold in the European region in the last 10 years The reason for the cold snowstorm is that the ENAO + event will bring more to Europe than the WNAO + event. Add a significant temperature rise effect. At the same time, the ENAO event corresponds to a blocked score The position of the cloth is also relative to the east. The latitude position of the NAO is closely related to the strength of the westerly wind. The stronger westerly wind forces the NAO to develop the variation to the downstream (east); if the westerly wind is weak, the NAO
【学位授予单位】：中国海洋大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：P461.2;P732

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