【作者】 傅敏宁；

【导师】 郑有飞；

【作者基本信息】 南京信息工程大学 ， 大气物理学与大气环境， 2013， 博士

【摘要】 鄱阳湖是我国最大的淡水湖,由于其复杂的地形和水陆地表性质的不均匀性,影响了边界层的温湿结构和物理过程,进而对湖区过境天气系统变化产生影响,以致于该区域严重的灾害性天气时有发生。因此,研究鄱阳湖的边界层特征及对区域天气气候的影响很有必要。本论文通过应用鄱阳湖地区铁塔观测资料、常规气象观测资料以及再分析资料等,采用资料分析、数值模拟等方法,对鄱阳湖湖效应降水特征、鄱阳湖对过境典型天气的影响以及鄱阳湖地区典型天气条件下的近地面层特征进行了分析研究。论文的主要研究内容和结论为：(1)鄱阳湖湖效应降水特征。通过1980-2008年期间气象资料分析,发现鄱阳湖地区发生湖效应降水事件33次。湖效应降水发生条件为,低层为干冷的西北或偏北气流从较暖的水面经过,使气流变暖、变湿,不稳定发展导致降水。其天气背景概念模型主要有2类：一类是槽型(TR型),这是主要的类型,约占88%,主要出现在11月-次年6月；另一类是热带气旋型(TC型),这种类型主要发生在8-9月,所占比例较小,约为12%。(2)鄱阳湖对典型过境天气的影响。分析了鄱阳湖对过湖强天气系统具有加强和减弱作用的2个典型个例,发现这种加强和减弱作用是由于鄱阳湖在不同季节呈现冷源和热源作用造成的。6月底前鄱阳湖主要以热源作用为主,进入7月则以冷源作用为主。除了季节变化影响外,由于水陆比热差异导致的湖温和气温的昼夜变化差异亦会使鄱阳湖对过湖天气系统产生影响,表现为白天鄱阳湖呈冷源作用,夜间呈热源作用。个例一分析了2007年7月23日白天午后到傍晚期间位于鄱阳湖西面的幕阜山脉生成的对流云团在经过鄱阳湖主湖体后产生了明显减弱。原因是盛夏季节鄱阳湖因冷源作用使对过境对流云团产生减弱影响。模拟结果表明,鄱阳湖对过境对流云团的减弱作用就是通过湖体冷源作用激发的反气旋性环流导致的辐散下沉作用造成的。个例二分析了鄱阳湖对2010年6月19-20日江西中北部暴雨过程的影响。模拟结果表明,叠加鄱阳湖地形数据的试验模拟降水结果与实况基本一致。在垂直输送和水汽输送方面,鄱阳湖对降水有明显的增幅作用。这种正反馈主要是由于鄱阳湖表现的热源作用导致的。(3)强降水天气过程的近地面边界层特征。通过分析2011年6月5日夜间至6日早晨鄱阳湖北部的一次局地性强降水天气过程发现,鄱阳湖为强降水提供了充足的水汽条件,加强了近表面层不稳定性的发展。强降水过程中来自鄱阳湖地表的感热和潜热通量向上输送,近地面层湍流动能增加。降水发生前,近表面层中尺度动量通量占主要地位,且逐渐转为向上输送：但在降水过程中,湍流动量通量呈显著加强趋势。(4)冷空气大风过程的近地面边界层特征。通过对2010年2月25日一次影响江西的强冷空气过程边界层特征进行分析,发现随着冷锋过境,鄱阳湖地区近地面层风速符合幂指数函数规律,高度越高风速越大,强风爆发越早。强风期间有系统性下沉运动存在。通过对阵风动量通量和湍流动量通量的比较发现,冷空气大风过程加强了近地面层的湍流,加剧了地表与上层大气的相互作用。更多还原

【Abstract】 Poyang Lake is one of the largest freshwater lakes in China, due to its complexity of terrain and the inhomogeneity of water-land surface, significantly influences the structures of temperature and humidity of local boundry layer and the physical process, which can eventually influences the development of the weather system passing over the Lake. Therefore, it is of great scientific signifcane to research and analyze the characteristics of boundary layer over Poyang Lake and the lake effects on transitting weather system. In this paper, the methods of data analysis and numerical simulation have been employed to analyze the characteristics of the Poyang Lake-effect on precipitation, the surface layer over Poyang Lake under typical weather condition, and the Poyang Lake effect on the transitting weather system. The mian contents and results are as follows:(1) Characteristics of Poyang Lake-effect on precipitation.Through the data analysis we found there exists Lake-effect precipitation over Poyang lake. During such events, winds from the north to northwest advect cold and dry air over Poyang Lake, which rapidly warms and moistens the overlying air mass, finally resulting precipitations. Two synoptic weather patterns are favorable for lake-effect precipitation events:a trough-type pattern (～88%of events) from November to June, and a tropical-cyclone-type pattern (～12%of events) from August to September.(2) Characteristics of Poyang Lake-effect on the transiting weather systems. Here, this paper analyaed two typical examples of transitting weather systems that was strenghened or reduced accordingly, it is indicated that such functions of strenghenning or reducing were caused by the functions of cool source or heat source displayed by Poyang lake seansonally. There exists key thransitting point between cool season and hot season upon the end of June and the early of July, before the end of June Poyang lake plays the role as heat source and after the early July palys the role as cool source, this transit is coincided with the time that is the terminal of rainfall period by the end of June and start of hot and dry period.One example analyzed the phenomenon that the convective clouds generated in Mufu Mountains were remarkably weakened or dissipated after passing over Poyang Lake. It is explained that during hot summer the transiting convective clouds were weakened by the function as cool source produced by Poyang lake. The simulating result show that this weakening function by Poyang lake on the transiting convective clouds were caused by the anti-cyclonical circulations, which is initiated by the cool source of Poyang lake, that will cause atmosphere submerging and diverging.Other example analyzed the influence on a heavy precipitation process occurred in north central Jiangxi during19-20June2010. The simulating result shows that it is identical with the real situation when the Poyang lake geographical data added to the experiment of numerical simulation. On views of the vertical transportation and vapor transportation, Poyang Lake could positively feedback the local anomalous increase of precipitation. This kind of positive reaction majorly generated by the heat source function of Poyang lake.(3) Characteristics of surface layer during a heavy rainfall process. By analyzing a local heavy rainfall process over Poyang Lake region,it is found that Poyang lake provided enough water vapor for strong strengthened the unstable development of nearing surface layer. During the heavy rainfall, the sensible and latent heat fluxes, the horizontal and vertical turbulent momentum fluxes increased rapidly; In addition, the turbulent kinetic energy increased greatly. Before the heavy rain occurrence, the mesoscale momentum flux was larger than the turbulent momentum flux, however, during the heavy rainfall, the turbulent flux increased remarkably.(4) Characteristics of near surface layer during a strong wind process. Through the analysis of the characteristics of near surface layer during a strong wind process,it is found that with the passage of cold air front, the wind speed of near surface layer is obeyed under the rule of power exponent, and the wind speed increases with the height of the surface layer, more earlier and stronge wind more produced quickly. And there exists a systematic descending movement. Though the comparison between gusty momentum flux and turbulent momentum flux, it is indicated that the porcess of strong wind from cool air could strenghen the turbulence of near surface, and could strenghen the mutual function between the surface and up atmosphere.更多还原