变性台风“麦德姆”(1410)环流中的锋生现象及其对降水的影响

利用中国气象局热带气旋年鉴、FY-2D（0.1°×0.1°）云顶亮温、逐时自动气象站降雨量、常规观测资料和NCEP/NCAR再分析资料,运用锋生函数对台风“麦德姆”（Matmo,1410）影响辽东半岛和山东半岛期间的降水特征进行了诊断分析。结果表明：1）Matmo影响辽东半岛和山东半岛期间,其低压环流与西风带高空槽相互作用,在其西侧和东北侧分别有冷锋和暖锋锋生,两条锋带均向东移。强锋生区首先在低层生成,随后尽管高空锋区向下延伸,但并未与低层冷锋重合,低层冷锋锋生强度减弱。2）山东半岛和辽东半岛的降水均发生在台风低压环流的锋生过程中,但山东半岛的降水明显多于辽东半岛。这与锋生强度密切相关,辽东半岛的锋生强度和垂直运动较山东半岛明显偏弱。3）强降水与台风环流内冷、暖平流活动密切相关,冷暖平流交汇之处对强降水有较好的示踪作用。山东半岛始终处于冷暖平流交汇处,其西侧斜压不稳定加强,上升运动发展,强降水出现在冷锋带上暖平流区内;而辽东半岛由冷平流转为暖平流时,对流运动向其东北方向发展,强降水位于辽东半岛东北部。     

Cyclone Phase Space Characteristics of the Extratropical Transitioning Tropical Cyclones over the Western North Pacific

The cyclone phase space (CPS) method has been utilized to evaluate the extratropical transition (ET) of tropical cyclones (TCs) in many recent publications. However, these studies mainly focused over the North Atlantic basin. In this paper, the CPS characteristics of all the cyclones over the western North Pacific are investigated and discussed, with three parameters calculated from the best-track data of the Regional Specialized Meteorological Center in Tokyo and the Japanese 25-yr reanalysis data. It is concluded that most TCs over the western North Pacific possess the non-frontal and warm-core structure, while a larger number of cyclones that have undergone ET hold the frontal and cold-core structure. The spatial pattern of the CPS parameters indicates that the areas of tropical and extratropical cyclone activities could be demarcated by 30°N. The composite and individual series of three parameters of the CPS indicate that the transformation of −V _T^U from positive to negative leads to the start of ET, and could be considered as a potential predictor in operationally forecasting an ET event.     

NUMERICAL STUDY ON THE DYNAMIC AND THERMODYNAMIC EFFECTS OF THE QINGHAI-XIZANG PLATEAU ON THE SEASONAL TRANSITION IN THE EARLY SUMMER IN EAST ASIA

By employing a five-layer seasonal numerical weather prediction model and utilizing the National MeteorologicalCenter (NMC) objective analysis data on May 10,1991 as the initial field,three numerical experiments——diabatic withorography,adiabatic with orography and adiabatic without orography——have been carried out to investigate the dy-namic and thermodynamic effects of the Qinghai-Xizang Plateau (hereafter the Plateau) on the seasonal transition inthe early summer in East Asia.The results show that the typical seasonal transition features such as the northward shiftof the subtropical westerly jet stream,the adjustment of the long-wave in middle and high latitudes and the changes ofthe circulation in the lower troposphere can be well simulated,if the dynamic and thermodynamic effects of the Plateauare both considered in the model as in the experiment adiabatic with orography.In other two experiments,it is failed tosimulate out the seasonal transition features.The results also show that the thermodynamic effect of the Plateau acts on the atmosphere as a gradually enhancedheating source in the early summer,which makes the air temperature in 500 hPa over the Plateau increase by nearly 10℃in a month and accelerates the northward shift of the subtropical westerly jet stream about seven latitudes more north-ward in twenty days and helps the shifted jet maintain at the northern periphery of the Plateau.It is also helpful to theformation and maintenance of the Lake Balchas trough and the northward and westward extension of the Pacificsubtropical high.On the other hand,the dynamic effect of the Plateau weakens the northward shift of the subtropicalwesterly jet stream and barricades the westward extension of the Pacific subtropical high.If only the dynamic effect ofthe Plateau is considered in the model without consideration of the thermodynamic effect of the Plateau,not only theshifted jet withdraws southward but also the simulated Lake Balchas trough is 10 longitudes more eastward than that inthe diabatic experiment,and the simulated Pacific subtropical high is more eastward and northward.However,the dy-namic effect of the Plateau strengthens the vertical movements in the west and east of the Plateau and makes thelow-level jet maintain in the southeast of the Plateau.The path of the cold air and the tunnel of the water vapor in thelower troposphere during the seasonal transition period in the early summer in East Asia are determined by the couplingof the dynamic and thermodynamic effects of the Plateau.     

MODEL STUDY OF THE EFFECT OF SOIL NO EMISSIONS ON SURFACE OZONE*

The effect of soil NO emissions on surface ozone in autumn in East China has been studied by using TCTM(Troposphere Chemical Transport Model)with the input of meteorological variables from RAMS.The chemical mechanism for ozone variation caused by soil emissions has also been investigated.The model results reveal that soil NO emissions are important to regional ozone formation and distribution and the effect of soil NO emissions shows spatial inhomogeneity.Ozone over most areas in northern China decreases with maximum average decrement reaching 5 ppb while it increases over most areas of central and southern China with maximum average increment reaching 7 ppb caused by soil NO emissions.This situation of ozone variation is mainly determined by nonlinear photochemical mechanism.For the low NOx areas(≤3 ppb),ozone increases as NOx increases;for the high NOx areas(>3 ppb),ozone decreases as NOx increases.The effect of soil NO emissions on ozone depends on the transition value and NOx concentrations.     

季节转换期间副热带高压带形态变异及其机制的研究Ⅱ:亚洲季风区季节转换指数

在“季节转换期间副热带高压带形态变异及其机制的研究Ⅰ :副热带高压结构气候学特征研究”的基础上 ,进一步讨论亚洲夏季风爆发与当地对流层中上层东西向暖脊的经向位置变化关系。亚洲夏季风相继在孟加拉湾、南海和南亚爆发期间 ,除了对流层高、低空风场及深对流活动在季风爆发前后具有反相的变化以外 ,副热带高压脊面附近大气经向温度梯度亦具有明显的反相特征。对流层中上层 (2 0 0～ 5 0 0hPa)脊面附近建立的北暖南冷的温度结构 ,能够反映亚洲各季风区夏季风爆发共同的本质特征 ,根据季节转换的热力学基础 ,指出对流层中上层经向温度梯度作为度量季风爆发的指标是合理可行的。文中提出了以副热带高压脊面附近对流层中上层大气经向温度梯度作为表征季节转换的指数 ,给出了确定季节转换开始日期的具体定义以及历年季节转换日期序列 ,同时给出由85 0hPa纬向风和OLR表征的季风爆发日期序列。相关分析表明 ,85 0hPa纬向风只是个区域性指标 ,而南北温度梯度具有一定的普适性     

ANALYSIS OF EXTRATROPICAL TRANSITION OF TROPICAL CYCLONE OVER MAINLAND CHINA

~~ANALYSIS OF EXTRATROPICAL TRANSITION OF TROPICAL CYCLONE OVER MAINLAND CHINA@朱佩君$Key Laboratory of Severe Storm Research, Department of Atmospheric Sciences, Physics School, Peking University, Beijing 100871 China @郑永光$Key Laboratory of Severe Storm Research, Department of Atmospheric Sciences, Physics School, Peking University, Beijing 100871 China @陶祖钰$Key Laboratory of Severe Storm Research, Department of Atmospheric Sciences, Physi…     

热带气旋的温带变性过程对中纬度下游环流的影响

用WRF模式对变性台风(TC)马勒卡进行模拟,研究了在台风的变性过程(ET)的作用下中纬度下游环流特别是中纬度急流的发展,对台风的强度及其相对上游槽位置的敏感性。结果表明:TC与中纬度系统的相互作用会使得中纬度急流处的斜压不稳定性增大,急流增强。下游环流的发展对TC强度及TC与西风带上游槽的相对位置非常敏感。若TC增强,TC溢出流作用于中纬度急流,使之不稳定性增强,强度也增强,从而导致中纬度下游急流的强度、范围都增强,下游槽脊更显著。若台风减弱则反之。类似的,若TC靠近上游槽,其对中纬度急流的作用得到进一步加强和提前,急流的不稳定性增加,强度增强,下游的急流和槽脊也得到增强。若TC远离上游槽,则反之。     

Transition from the southern mode of the mei-yu front cloud system to other leading modes

Based on normalized six-hourly black body temperature （TBB） data of three geostationary meteorological satellites,the leading modes of the mei-yu cloud system between 1998 and 2008 were extracted by the Empirical Orthogonal Function （EOF） method,and the transition processes from the first typical leading mode to other leading modes were discussed and compared.The analysis shows that,when the southern mode （EOF1） transforms to the northeastern mode （EOF3）,in the mid-troposphere,a low trough develops and moves southeastward over central and eastern China.The circulation pattern is characterized by two highs and one low in the lower troposphere.A belt of low pressure is sandwiched between the weak high over central and western China and the strong western North Pacific subtropical high （WNPSH）.Cold air moves southward along the northerly flow behind the low,and meets the warm and moist air between the WNPSH and the forepart of the low trough,which leads to continuous convection.At the same time,the central extent of the WNPSH increases while its ridge extends westward.In addition,transitions from the southern mode to the dual centers mode and the tropical-low-influenced mode were found to be atypical,and so no common points could be concluded.Furthermore,the choice of threshold value can affect the number of samples discussed.     

高原季节转换时期大气环流变化特征

利用1961～ 2007年NCEP/NCAR的再分析逐日资料,分析高原主体上空大气环流的季节变化和受到高原影响的东亚大型环流系统的季节变化,以此证明本文得到的“高原普适性划分方法”的合理性.得到的初步结论概括如下：高原主体上空的位势高度、风场、高空温度、降水的季节变化和高原普适性季节划分方法划分的高原四季变化一致,高原南亚高压、副热带高压、副热带西风急流的三个特征指数季节变化和高原普适性季节划分方法划分的高原四季变化一致,这些结论都说明高原普适性季节划分方法划分的高原四季是合理的;风场季节率（500hPa、100hPa）显著区随高度升高向赤道靠近,风场季节率的变化主要和东亚季风的变化有关,大气环流系统季节率的显著说明了大气环流的季节变化,同时也证明了高原普适性季节划分方法的合理性.     

热带气旋变性过程客观判别方法在“海马”变性过程中的应用

介绍了一种判别热带气旋变性过程的客观方法.此客观方法使用三个判别参数: 对流层低层热力非对称参数B、高低层的热成风、对变性过程进行诊断判别.此方法使用格点的数值预报产品,计算简单、使用方便,便于业务化.同时针对2004年影响我国的0421号热带风暴"海马",使用NCEP再分析资料对其变性过程进行了分析验证,结果表明:此客观方法所定义的三个判别参数B、、在"海马"的变性过程中有很好的指示作用.