【作者】 陈莉；

【导师】 吴增茂； 高山红；

【作者基本信息】 中国海洋大学 ， 大气物理学与大气环境， 2010， 博士

【摘要】 大气波导对雷达探测和无线电通讯有重要影响,是世界各国国防关注的热点之一。近年来,我国对大气波导的关注和投入与日俱增。然而,广阔海洋上观测数据严重缺乏与长期连续的大范围观测难以实施等现状,严重制约了大气波导的理论研究。现有针对我国近海大气波导分布特征的统计研究由于时间和空间分辨率较低,与实际应用还存在较大差距。对于大气波导的演变机理,国内研究主要从电波传播理论分析和天气形势诊断角度进行研究,而对大气波导的热力和动力特征演变机理的深入研究相当少。随着大气数值模式的快速发展与广泛应用,高时空分辨率的数值模拟已逐渐成为研究大气波导的重要手段。本文旨在利用大气再分析数据与大气数值模拟结果,统计分析中国近海大气波导的发生规律和分布特征,并在此基础上借助数值模拟详细研究典型天气过程中大气波导的演变机理。本文首先利用2006-2007年NCEP-FNL大气再分析数据对中国近海大气波导的时空分布特征进行了统计分析,探讨了其气候学成因,对我国近海大气波导特征有了较为全面的了解；接着基于大气模式MM5,对2007年全年中国近海大气波导进行了高时空分辨率的数值模拟,根据模拟结果,采用经验正交函数(EOF)分解方法研究了影响我国东部局部海域低空波导形成的天气学特征；同时还利用模拟结果进行了蒸发波导的直接诊断,分析了蒸发波导的季节变化与海洋环流和海面气象条件的相关关系；然后,利用MM5模拟研究了一次黄海海雾过程中大气波导的发生规律；之后,选用比MM5更先进的WRF模式及其三维变分系统(3DVAR),利用尽可能丰富的特性层探空观测数据和卫星遥感数据,进行了一系列的数据同化对比试验,找到了对于大气波导模拟最佳的同化方案,在此基础之上模拟并研究了我国东部和东南沿海海陆风过程中大气波导的演变机理；论文最后讨论了各种大气数值模式在大气波导研究中的优势,对大气波导问题进行了展望。借鉴气象上成熟的研究方法,本文对于大气波导的研究手段有所创新：(1)将EOF方法引入大气波导研究中。本文中依据大气数值模拟结果确定东南海域的低空波导样本,利用EOF方法找出有利于该局部海域波导产生的主要天气形势。此方法可有效应用于其他局部海域。(2)利用成熟的中尺度大气模式,通过合理精细化近海面垂直分层,直接进行蒸发波导的模拟,而不必依赖于蒸发波导模型,避免了对于气象要素输入的敏感性和局地经验参数选择的局限性。本文的主要结论有：(1)中国近海大气波导出现概率及波导类型的变化与东亚季风活动紧密关联,季风是其气候学成因；夏季时渤、黄、东海沿岸海域大气波导明显增多,与海陆风局地环流有关。(2)对于中国东部局部海域,当位于冷高压偏南侧、或热带低压的西北侧、或南部高压与北部低压之间时,依次对应着有利于产生低空大气波导的三种主要天气形势：第一种形势(约占41%)下的波导高度较高(约1300-1500m),第二种形势(约占7%)下的波导强度较大(约17M),它们的共同点是辐散下沉形成稳定逆温层且大气低层较强的水汽平流造成较大的水汽垂直梯度；第三种形势(约占4%)下,平流过程是形成大气波导的主要原因。(3)蒸发波导的空间分布受中国近海海洋环流的强烈影响,存在一个与黑潮区域相一致的带状波导高出现概率区域,台湾暖流、黄海暖流和对马暖流使得在某些季节相应海域蒸发波导出现概率高于其周围海域。(4)大气波导与海雾过程有着紧密联系,对于黄海平流海雾,雾顶水汽垂直梯度可达到50%/100m,而导致大气波导发生在雾顶100～200m的高度内；同时雾体的辐射冷却作用使大气层结稳定度增强,波导层强增大；大气波导比海雾对水汽条件更敏感,一旦发生水汽的垂直混合便迅速消失。(5)受海陆风影响,我国东部和东南沿海大气波导地出现具有显著的日变化规律；海风时,陆地干空气上升并在海上下沉,与低层的潮湿空气形成强烈的水汽梯度,同时空气被压缩增温,形成热内边界层,大气波导就发生在其中；陆风时,海上水汽垂直混合,波导消失,在有地形作用下形成的背风波时,这个过程更加迅速。更多还原

【Abstract】 The research of atmospheric ducts, a world focus of national defense, has a significant influence on radar detections and radio communications. China has paid more attention to the issue of atmospheric ducts in recent years. However, the research of ducts is restricted by lack of observations over vast oceans. There is a gap to practical guiding for the low spatial-temporal resolution of statistics. For mechanisms of ducts, currently, local researchers mainly focus on the theories of radio propagation and the weather situation diagnosis, but rarely on the thermodynamic and dynamic mechanisms of ducts. Fortunately, high-resolution numerical models offer an alternative way of gaining insight into ducts. In this thesis, based on the reanalysis data and numerical simulation results, the distribution features and occurrence frequency of atmospheric ducts over China Seas are statistically analyzed, and the mechanisms of ducts evolution during some typical synoptic processes are also studied by numerical models.First of all, to get an overall understanding, NCEP-FNL reanalysis data is used in statistic analysis of atmospheric ducts and its climate genesis over China Seas; second, meso-scale atmospheric model MM5 with a very high vertical resolution provides an annual variation of simulated ducts. According to the simulation results, the main weather types which are favorable for ducts over a regional sea at east are studied in details using empirical orthogonal function (EOF) decomposition; meanwhile, MM5 results are used to diagnose evaporation duct directly, and the relationship between the seasonal distributions and marine conditions, including ocean oceanic circulations and atmospheric conditions near the sea surface; third, the association of ducts with sea fog over Yellow Sea is analyzed in a case study; fourth, WRF model with its 3DVAR module is chosen for data assimilation tests and development mechanism research of ducts in a sea-land breeze circulation; at last, the advantages of various numerical models are discussed, and some issues of atmospheric ducts are prospected.Referring to methods in meteorology, some ideas for duct research are introduced: (1) EOF for ducts. Based on simulation results, EOF is an effective approach to study synoptic features of atmospheric ducts over a regional sea. (2) Meso-scale model can be used to simulate evaporation duct by refining model vertical levels reasonably, but not depend on evaporation duct model.The results are summarized as follows:(1) there exists a close relationship between the variance of appearance probability and types of the ducts and eastern Asia monsoon activities; coastal zones along the Bohai Sea, the Yellow Sea and the East China Sea have a distinct high occurrence probability during summer. (2)Three top weather situations are favorable for duct occurrence of the regional sea at east: southern to a cold anticyclone, north-western to a tropical low, and between a northern low and a southern high, respectively. In the first situation (accounts for 41%) duct height is relatively high (1300～1600m), and duct strength is much intense (17M) in the second (accounts for 7%). The similarity of these two types is that air divergence and subsidence results in inversion, and strong water vapor advection causes large vertical humidity gradient in lower atmosphere. However, in the third situation (accounts for 4%) advection plays an important role. (3) There obviously exists a belt-region with high evaporation duct occurrence(EDO) along the Kuroshio, and EDO is also relatively higher in some seasons near the regions of Taiwan warm current, the Yellow sea warm current and the Tsushima Warm Current. (4)Ducts occur at the top of sea fog with a height of 100-200m,where relative humidity gradient can be up to 50%/100m; due to the long wave radiation cooling in sea fog, more stable the atmospheric layer is, more intense the ducts are; ducts have a much more rapid response to humidity gradient than sea fogs do. (5) Daily variations of duct occurrences is related to the sea-land breeze in east and southeast coast; sea wind leads to a thermal internal boundary layer where ducts appear in when dry air raising over land and subsidence over sea. The air near sea surface is warming caused by compression and has a huge humidity gradient with upper air. Vertical mixing intense when land air flow over sea and the humidity gradient reduces, then the ducts disappear. This process can be accelerated by lee waves.更多还原