台风“珍珠”(2006)螺旋雨带发展机制的数值模拟研究

基于2 km分辨率的ARW-WRF数值模拟资料,讨论了台风"珍珠"(2006)螺旋雨带中对流单体及内雨带的发展机制。结果表明:模式很好地再现了台风的路径和强度。作为雨带中仅仅存在于眼壁外侧的内雨带,其传播机制与重力波、涡旋Rossby波及混合波没有联系,其可能发展机制仅与低层出流、水平风场和变形场有关。低层出流使得内雨带径向向外运动,而低层的水平风场和变形场使其形成螺旋结构。同时,就螺旋雨带中精细对流单体的发展而言,涡度收支方程定量分析表明,其主要通过两种方式获得垂直涡度:水平涡度倾斜为垂直涡度;上升运动拉伸垂直涡度。随着平流输送,对流单体在眼壁附近合并和汇聚。     

台风“海棠”的螺旋雨带结构及特征

利用中尺度数值模式WRF对2005年7月19—20日台风＂海棠＂登陆前后螺旋雨带的结构及特征进行了模拟和诊断分析。结果表明,本次台风造成的沿海暴雨与主次两条雨带活动有关。主雨带是涡旋Rossby波激发的螺旋雨带,与850 hPa正涡度带有很好的对应关系,降水强度大,辐合层次低,处在温度和切向风速梯度最大处。次雨带辐合层次相对较高,最大温度梯度和相当位温梯度发生在700 hPa以上,无明显切向风梯度配合,其发展主要与台风中心附近的阶梯状相当位温锋区有关。当台风中雨带合并时,易造成降水增幅。台风登陆前后存在螺旋雨带的断裂现象,台风中心西侧及西北侧的中低层的辐散流场使高层的气旋性流场出现和加强,台风在高层的气旋性环流与西部低压结合,使台风西部产生辐合,引起螺旋雨带的断裂,当高层的低压形成明显的气旋式切变时,也可使切变下方螺旋雨带断裂。     

涡旋Rossby波传播和台风切向风速变化的数值研究

设计了一个高分辨率f平面准地转正压涡度方程半谱模式，用以研究非线性对台风切向风速变化，以及不同初始异常条件下台风环流内涡旋Rossby波传播和台风切向风速变化特征。6类(14组)试验的数值结果表明：非线性使台风切向风速的增强减弱，可能使最大风速半径收缩。初始扰动中心位置对涡旋Rossby波传播和台风切向风速变化的影响明显。扰动中心在最大风速半径附近时，台风最大切向风速增强最多；异常中心在台风外区时，使最大切向风速减小。初始异常尺度(范围)减小对台风最大切向风速变化的影响减弱。双涡分布条件下，台风环流外区的涡旋使内区或近眼壁区对流涡旋对台风最大切向风速的影响减弱。     

台风螺旋雨带——涡旋Rossby波

台风中的螺旋云雨带是由多种探测手段被观测到的现象 ,是为大家所共识的不争事实。但是 ,对它的形成、维持的理论解释 ,虽有多种学说 ,一直以来人们都倾向于重力惯性波说。而重力惯性波说有一个致命的弱点 ,即波的相速理论值为 10 1m/s量级 ,它要比螺旋云雨带实测移速只有 10 0 m/s几乎大一个量级。于是从前几年开始 ,人们又回到 30多年前提出的涡旋 Rossby波说那里去寻找合适的解释。经典的Rossby波是 β =(df/dy)作用的大尺度波动 ,而适用于台风中螺旋云雨带的涡旋———Rossby波乃是 f平面 (β =0 )上的中尺度波动。那末 ,对这两类尺度不同和成波机理不同的波动 ,何以均冠予Rossby波一词 ?本文试图从动力学等价原理上 ,对此作统一联系的说明。其结果是 :台风基本气流的涡度 ζ随径向 (r)变化的梯度d ζdr=1rr(r vλ) ,在动力学上等价于科氏参数 f随纬度变化的梯度即β=df/dy ;或者说它们在绝对涡度守恒的前提下 ,作为波扰动的成波机理是等价的     

台风涡旋系统的波动性质及其数值模拟

本文使用柱坐标系下的正压浅水方程组以及斜压扰动方程组,分析得出台风涡旋系统中的涡旋Rossby波划分为两种类型。由于切向基本气流的二阶径向水平切变或者基本气流的垂直涡度在径向方向的变化(β*因子)所导致的涡旋Rossby波称之为第一类涡旋Rossby波(正压涡旋Rossby波),它产生的根本原因是β*因子的作用。这种第一类涡旋Rossby波相对于切向基本气流是单向传播的,其传播方向则与β*因子的正负符号有关。当基本流场垂直涡度-ζz沿着径向r方向增大时,第一类涡旋Rossby波是沿着切向圆周方向逆时针方向传播的;反之则是沿着切向圆周方向顺时针方向传播。如果考虑切向基流的二次垂直切变时,可以得到台风涡旋系统中第二类涡旋Rossby波(斜压涡旋Rossby波)的相速度表达式,第二类涡旋Rossby波产生的物理根源是切向基本流场风速的二次垂直切变或者基本流场径向r方向的平均涡度在空间z方向上的不均匀性(亦即β**因子)。第二类涡旋Rossby波相对于切向基本气流也是单向传播的,当-ζr沿着空间z方向上增大时,第二类涡旋Rossby波就是相对于基本气流-V0是顺时针方向传播的;反之则是相对于基本气流逆时针方向传播。在基本流场的风速-V存在二次径向水平切变或者垂直切变时,台风中的波动可能是混合的涡旋Rossby波——重力波;而当基本流场的风速-V仅仅存在线性切变,不存在二次切变时,此时根本不存在涡旋Rossby波,台风系统中的波动则仅仅是重力惯性波。最后,采用WRF模式对“云娜”台风进行了数值模拟,验证了上述结论。     

台风"云娜"中的涡旋Rossby波研究

运用非静力平衡中尺度模式WRF(V2.03),对2004年14号台风“云娜”在登陆后产生强降水的过程进行了42h模拟,并对螺旋云雨带的涡度场结构进行了分析。分析结果表明,WRF能较好地模拟出台风在陆地上的移动路径,及其产生的台风暴雨的螺旋状分布。台风螺旋云雨带的形成与维持,可以用涡旋Rossby波理论来解释:可以通过改变局地相对涡度径向梯度分布,从而沿台风径向激发出“局地涡旋Rossby波”。     

台风麦莎登陆后粘性摩擦对正压特征波动的影响

本文推导出柱坐标系下含有粘性摩擦项的正压方程组。选取2005年台风麦莎登陆浙江过程中的8月6日15时的WRF(Weather Research and Forecasting)模式输出资料,利用数值差分方法对该正压方程组求特征波解,分析粘性摩擦对台风麦莎内部正压特征波动的影响。结果表明,重力惯性外波在粘性摩擦的影响下,最不稳定波的波数为45左右,波动在摩擦的影响下衰减,波动沿逆时针传播,在半径1000 km处,1波波速为47.43 m/s,在半径r>800 km的范围内,径向风分量扰动加大,辐合辐散运动增强;而摩擦影响下的涡旋Rossby波,2波最不稳定,波动增长率减小,在半径r=200 km处波动相速度为4.282~29.172 m/s,扰动涡度大值区范围减小,涡旋Rossby波的波动区域沿着径向向台风中心收缩。分析包含所有波动时,考虑摩擦后,最不稳定波数在45左右且波动衰减,1波波速在r=1000 km处(外螺旋雨带)为26.374 m/s;在半径r=200 km(内螺旋雨带)为5.275 m/s,考虑径向基本气流后,最不稳定波的波数保持不变,半径r=1000 km处的波速增加为30.324 m/s,r=200 km(内螺旋雨带)处波速为6.065 m/s,摩擦使得径向风分量扰动明显增大,辐合辐散运动加强。     

热带风暴中波动特征的研究进展和问题

在分析热带风暴眼壁和螺旋雨带中尺度波动特征最新研究的基础上，指出这些研究所忽略的问题，其中包括重力惯性波和涡旋Rossby波波解存在的前提条件和约束、理论分析与观测研究存在的差异等。提出一种基于准平衡动力条件下，热带风暴内中尺度扰动涡散运动共存时，区别于标准模混合的不可分的混合涡旋Rossby-重力惯性波，并讨论了位涡守恒条件下这一类不可分混合波的可能成波机制。利用高分辨率的模式大气资料，采用非对称波分量的分解方法分析了Bonnie飓风中的中尺度波动特征，结果表明，热带风暴中1波型扰动既具有涡旋波性质，但也存在散度扰动的变化，而2波型扰动则体现了明显的不可分混合波的特性。     

近几年中尺度动力学研究进展

近几年,中尺度气象由于在逐日天气预报中的重要作用和在气象灾害预报中的显著贡献,已经成为一个热门的研究课题.中尺度气象研究并预测中尺度天气系统的发生发展及其引发的灾害性天气,如暴雨、冰雹、龙卷风等.本文主要总结了2007年以来我国在中尺度研究中取得的显著性成果.主要包括:波动、涡旋、锋面、稳定性、Q矢量和不变量.在波动方面包括重力波的形成和传播的研究,包含旋转Rossby波、混合低频旋转Rossby波和高频惯性重力波在内的台风波动以及考虑水汽作用的中尺度波作用守恒.涡旋部分主要介绍了青藏高原低涡(TPV)和热带气旋内部的涡旋问题.除了涡旋之外,锋面在中国也是一个关键系统.在锋面方面的进展有:梅雨锋中的β中尺度双雨带机制的产生和维持的实验性研究,以及基于广义位温的锋生函数的提出,这些成果使得对锋生过程的描述更接近于实际大气状况.在不稳定问题上,主要介绍了采用Energy-Casimir方法建立的拟能量波作用方程和基本气流具有线性和非线性切变时的横波扰动的不稳定.关于Q矢量,介绍了从地转Q矢量,半地转Q矢量到非地转Q矢量,非地转湿Q矢量的发展,以及由湿地转Q矢量和垂直风切变耦合得到的新型散度方程.最后,讨论了有关质点的两个不变量位温和位涡的相关研究新进展.     

台风麦莎的正压特征波动结构及其稳定性

利用中尺度WRF模式对2005年8月西北太平洋台风麦莎（Matsa）进行了精细的数值模拟。使用模式输出资料,对正压浅水方程组进行了数值差分计算,分析它在最大强度时刻的正压特征波动结构和稳定性。结果表明,台风麦莎内部包含有沿逆时针方向传播的重力惯性外波和涡旋Ross-by波,两种波动的结构和稳定性存在显著性差异。前者主要存在于台风外围,增长率随波长的减小而增加,台风外围的波动相速度为48．9～68．5m／s;后者主要位于距离台风中心200km内,表现为3波最不稳定,半径100km处相速度约为5m／s。此外,重力惯性外波的扰动风场与高度场基本相垂直,扰动散涡比值大于3倍,甚至达到10＾3倍,运动以辐合、辐散为主;涡旋Rossby波的扰动风场基本平行于高度场,扰动散涡比值为10＾-1～10＾-2,涡旋运动是其主要运动,与内螺旋雨带沿着切向圆周方向的传播具有密切关系。     

LOW-FREQUENCY CIRCULATION AND EXTENDED-RANGE FORECAST IN CONNECTION WITH AUTUMN EXTREME HEAVY RAINFALL PROCESS IN HAINAN

Observed daily precipitation data from the National Meteorological Observatory in Hainan province and daily data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis-2 dataset from 1981 to 2014 are used to analyze the relationship between Hainan extreme heavy rainfall processes in autumn (referred to as EHRPs) and 10–30 d low-frequency circulation. Based on the key low-frequency signals and the NCEP Climate Forecast System Version 2 (CFSv2) model forecasting products, a dynamical-statistical method is established for the extended-range forecast of EHRPs. The results suggest that EHRPs have a close relationship with the 10–30 d low-frequency oscillation of 850 hPa zonal wind over Hainan Island and to its north, and that they basically occur during the trough phase of the low-frequency oscillation of zonal wind. The latitudinal propagation of the low-frequency wave train in the middle-high latitudes and the meridional propagation of the low-frequency wave train along the coast of East Asia contribute to the ‘north high (cold), south low (warm)’ pattern near Hainan Island, which results in the zonal wind over Hainan Island and to its north reaching its trough, consequently leading to EHRPs. Considering the link between low-frequency circulation and EHRPs, a low-frequency wave train index (LWTI) is defined and adopted to forecast EHRPs by using NCEP CFSv2 forecasting products. EHRPs are predicted to occur during peak phases of LWTI with value larger than 1 for three or more consecutive forecast days. Hindcast experiments for EHRPs in 2015–2016 indicate that EHRPs can be predicted 8–24 d in advance, with an average period of validity of 16.7 d.     

AN ATTRIBUTION ANALYSIS OF CHANGES IN POTENTIAL EVAPOTRANSPIRATION IN THE BEIJING–TIANJIN–HEBEI REGION UNDER CLIMATE CHANGE

Based on the measurements obtained at 64 national meteorological stations in the Beijing–Tianjin–Hebei (BTH) region between 1970 and 2013, the potential evapotranspiration (ET0) in this region was estimated using the Penman–Monteith equation and its sensitivity to maximum temperature (Tmax), minimum temperature (Tmin), wind speed (Vw), net radiation (Rn) and water vapor pressure (Pwv) was analyzed, respectively. The results are shown as follows. (1) The climatic elements in the BTH region underwent significant changes in the study period. Vw and Rn decreased significantly, whereas Tmin, Tmax and Pwv increased considerably. (2) In the BTH region, ET0 also exhibited a significant decreasing trend, and the sensitivity of ET0 to the climatic elements exhibited seasonal characteristics. Of all the climatic elements, ET0 was most sensitive to Pwv in the fall and winter and Rn in the spring and summer. On the annual scale, ET0 was most sensitive to Pwv, followed by Rn, Vw, Tmax and Tmin. In addition, the sensitivity coefficient of ET0 with respect to Pwv had a negative value for all the areas, indicating that increases in Pwv can prevent ET0 from increasing. (3) The sensitivity of ET0 to Tmin and Tmax was significantly lower than its sensitivity to other climatic elements. However, increases in temperature can lead to changes in Pwv and Rn. The temperature should be considered the key intrinsic climatic element that has caused the "evaporation paradox" phenomenon in the BTH region.     

ANALYSIS OF “BIMODAL PATTERN” STORM ACTIVITY CHARACTERISTICS OF THE BAY OF BENGAL

Storms that occur at the Bay of Bengal (BoB) are of a bimodal pattern, which is different from that of the other sea areas. By using the NCEP, SST and JTWC data, the causes of the bimodal pattern storm activity of the BoB are diagnosed and analyzed in this paper. The result shows that the seasonal variation of general atmosphere circulation in East Asia has a regulating and controlling impact on the BoB storm activity, and the “bimodal period” of the storm activity corresponds exactly to the seasonal conversion period of atmospheric circulation. The minor wind speed of shear spring and autumn contributed to the storm, which was a crucial factor for the generation and occurrence of the “bimodal pattern” storm activity in the BoB. The analysis on sea surface temperature (SST) shows that the SSTs of all the year around in the BoB area meet the conditions required for the generation of tropical cyclones (TCs). However, the SSTs in the central area of the bay are higher than that of the surrounding areas in spring and autumn, which facilitates the occurrence of a “two-peak” storm activity pattern. The genesis potential index (GPI) quantifies and reflects the environmental conditions for the generation of the BoB storms. For GPI, the intense low-level vortex disturbance in the troposphere and high-humidity atmosphere are the sufficient conditions for storms, while large maximum wind velocity of the ground vortex radius and small vertical wind shear are the necessary conditions of storms.     

CHARACTERISTICS AND TRENDS OF CLIMATIC EXTREMES IN CHINA DURING 1959–2014

The spatial and temporal variations of daily maximum temperature(Tmax), daily minimum temperature(Tmin), daily maximum precipitation(Pmax) and daily maximum wind speed(WSmax) were examined in China using Mann-Kendall test and linear regression method. The results indicated that for China as a whole, Tmax, Tmin and Pmax had significant increasing trends at rates of 0.15℃ per decade, 0.45℃ per decade and 0.58 mm per decade,respectively, while WSmax had decreased significantly at 1.18 m·s~(-1) per decade during 1959—2014. In all regions of China, Tmin increased and WSmax decreased significantly. Spatially, Tmax increased significantly at most of the stations in South China(SC), northwestern North China(NC), northeastern Northeast China(NEC), eastern Northwest China(NWC) and eastern Southwest China(SWC), and the increasing trends were significant in NC, SC, NWC and SWC on the regional average. Tmin increased significantly at most of the stations in China, with notable increase in NEC, northern and southeastern NC and northwestern and eastern NWC. Pmax showed no significant trend at most of the stations in China, and on the regional average it decreased significantly in NC but increased in SC, NWC and the mid-lower Yangtze River valley(YR). WSmax decreased significantly at the vast majority of stations in China, with remarkable decrease in northern NC, northern and central YR, central and southern SC and in parts of central NEC and western NWC. With global climate change and rapidly economic development, China has become more vulnerable to climatic extremes and meteorological disasters, so more strategies of mitigation and/or adaptation of climatic extremes,such as environmentally-friendly and low-cost energy production systems and the enhancement of engineering defense measures are necessary for government and social publics.     

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正AIMS AND SCOPE Atmospheric and Oceanic Science Letters (AOSL) publishes short research letters on all disciplines of the atmosphere sciences and physical oceanography. Contributions from all over the world are welcome.SUBMISSIONAll submitted     

A Brief Introduction to Marine Meteorological Science Experiment Base at Bohe Town,Maoming City,Guangdong Province

<正>With the support of specialized funds for national science institutions,the Guangzhou Institute of Tropical and Marine Meteorology,China Meteorological Administration set up in October 2008 an experiment base for marine meteorology and a number of observation systems for the coastal boundary layer,air-sea flux,marine environmental elements,and basic meteorological elements at Bohe town,Maoming city,Guangdong province,in the northern part of the South China Sea.     

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AIMS AND SCOPE
Atmospheric and Oceanic Science Letters （AOSL） publishes short research letters on all disciplines of the atmosphere sciences and physical oceanography. Contributions from all over the world are welcome.     

Information for Authors

AIMS AND SCOPE Atmospheric and Oceanic Science Letters （AOSL） pub- lishes short research letters on all disciplines of the atmos- phere sciences and physical oceanography. Contributions from all over the world are welcome.     

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正AIMS AND SCOPE Atmospheric and Oceanic Science Letters (AOSL) publishes short research letters on all disciplines of the atmosphere sciences