Generalized moist potential vorticity and its application in the analysis of atmospheric flows

Potential vorticity(PV)serves as an important dynamic tracer for large-scale motions in the atmosphere and oceans.Significant pro-gress has been made on the understanding and application of PV since the work of Hoskins et al,who introduced an"IPV thinking"of a dynamical system in a purely dry atmosphere.In particular,there has been a substantial amount of work done on the PV in a general moist atmosphere.In this paper,the generalized moist potential vorticity(GMPV)and its application in the mesoscale meteorological fields are reviewed.The GMPV is derived for a real atmosphere(neither completely dry nor saturated)by introducing a generalized potential temperature instead of the potential temperature or equivalent potential temperature.Such a generalization can depict the moist effect on PV anomaly in the non-uniformly saturated atmosphere.The effect of mass forcing induced by rainfall on the anomaly of GMPV is also reviewed and a new dynamic variable,the convective vorticity vector(CVV),is introduced in connection with GMPV.2008 National Natural Science Foundation of China and Chinese Academy of Sciences.Published by Elsevier Limited and Science in China Press.All rights reserved.     

一次典型MCC卫星云图及雷达回波特征分析

2010年6月19日夜间,贵州北部普降暴雨及大暴雨,分析认为,这是由位于贵州中北部、重庆南部的一个中尺度对流复合体(MCC)造成的.利用常规的micaps观测资料、自动站资料及卫星tBB和雷达资料分析了这次MCC的云图和回波特征,结果表明,这次MCC系统造成的降水范围大、雨强强、分布较集中,卫星云图上tBB最小值达-90℃以下,-80℃冷云区面积和MCC的总降水量存在一定的正相关,-80℃冷云区面积越大,MCC总降水量也越大.MCC在雷达回波上表现出一条类似飑线的带状回波和零星的块状回波,带状回波造成的降水强度大,常常造成暴雨和大暴雨.     

A stochastic method for convective storm identification, tracking and nowcasting

The convective storm identification, tracking and nowcasting method is one of the important nowcasting methodologies against severe convective weather. In severe convective cases, such as storm shape or rapid velocity changes, existing methods are apt to provide unsatisfied storm identification, tracking and nowcasting results. To overcome these difficulties, this paper proposes a novel approach to identify, track and short-term forecast （nowcast） of convective storms. A mathematical morphology-based storm identification method is adopted which can identify storm cells accurately in a cluster of storms. As for the difficult tracking problem, sequential Monte Carlo （SMC） method is utilized to simplify the tracking process. It is not only inherently suitable for handling complicated splits and mergers, but also capable of handling the case of storm-missing detection. In order to provide more accurate forecast of a storm position, this method takes the advantages of the cross-correlation method. The qualitative and quantitative evaluations show the efficiency and robustness of the proposed approach.     

Diagnostic analysis of the asymmetric structure of the simulated landfalling typhoon "Haitang"

The landfalling processes of Typhoon "Haitang" near Lianjiang of Fujian Province of China from 00 UTC 19 to 12 UTC 20 July 2005 were reproduced by using the nesting non-hydrostatic WRF model and data assimilation technology (Level II Doppler radar data of Changle of Fujian Province are assimilated to the simulation every one hour from 01 to 06 UTC 19 July 2005).The mesoscale structure and evolution of the typhoon before,during,and after its landfall were discussed.The simulation data show that the assimilation experiment with the high temporal-and-spatial-resolution radar radial velocity and reflectivity data can produce much better simulation of the typhoon track,intensity evolution and landfalling location than the control experiment without assimilating radar data.By using the assimilation experimental data,the mesoscale fine-mesh structure and evolution before and after typhoon landfall were analyzed.Because of the influence of sea-land thermodynamic difference,two asymmetric convective regions were located at ocean and land,respectively.To better understand and investigate the asymmetric-structure characteristics of the landfalling typhoon,several dynamical diagnostic tools,the helicity (H),the moist potential vorticity (MPV),the convective vorticity vector (CW),the moist vorticity vector (MVV),which are associated with the development of strong convections,are introduced.Further analysis illuminates that the distributions of these physical diagnostic parameters are totally asymmetric,and subsequently,the associated convections also show distinct asymmetry.     

Kuo(1965,1974)和Anthes(1977)对流参数化方案对降水影响的数值研究

本文应用11层原始方程模式和一次实际降水个例对 Kuo(1965)、Kuo(1974)以及Anthes(1977)对流参数化方案进行了初步试验,结果表明:考虑对流参数化后降水强度增加,但对降水落区影响很小,其中 Anthes(1977)方案对降水的增加最多,Kuo(1965)方案增加最少.在三种参数化方案中,Kuo(1974)方案模拟出的对流降水比重最高,Anthes(1977)方案的对流降水比重最低,但是 Anthes(1977)方案的反馈作用却最大,其影响的大尺度降水比不考虑对流作用时高出近10倍.由于模式还不够完善,降水的模拟与实况相比还有一定差距,但初步的结论是 Anthes(1977)对流参数化方案效果较好,Kuo(1974)方案次之,不考虑对流作用时模拟的降水强度与实际相比太小。     

同心圆柱体间旋转气隙内对流换热的数值模拟研究

本文利用商用CFD软件对发电机气隙简化模型——同心旋转圆柱体间环形气隙内流体对流换热情况进行数值模拟,得到了不同泰勒数Ta下流场的速度分布、温度分布和热流密度分布。将模拟得出的平均努赛尔数Nu与经验公式的计算值进行了对比,误差在合理的范围之内,证明了数值模拟的有效性。计算结果表明,受流场中泰勒涡的影响,速度、温度、以及热流密度沿轴向的分布呈现周期性波动,波动频率与泰勒涡的数量相同,其中,速度与温度分布波动的变化趋势相同,热流密度波动的变化趋势与前两者相反;泰勒数Ta越大,流场的平均努赛尔数Nu越大,流场的对流换热性能越好。另外,本文还对带凹槽气隙模型进行了流动模拟,分析了泰勒-库特流能够强化传热传质的原因,为后续发电机环形气隙对流换热特性的模拟做准备。     

五种太阳能设备跟踪器及其涉及的物理背景分析

本文选择介绍了我们研制或设计的五种赤道式太阳能设备跟踪器。它们不仅适用于广阔的中纬度地带亦可用于南北回归线之间地区,其中的一种已应用于地下建筑天然采光工程。文章还着重分析了应用这些设备所涉及的物理背景,如多维非稳态热传导,对流换热等并给出初步结果。     

基于贝叶斯方法的中尺度对流系统移动方向研究

在朴素贝叶斯分类的基础上建立了一种增强型分类器系统,并在对1997～2002年夏季青藏高原上MCS(Mesoscale Convective System)进行自动追踪的基础上,对MCS的移动方向与其周边环境物理量场的分布特征进行了分类研究.进而,将分类结果与决策树、人工神经网络分类方法进行了比较.研究表明,与其他分类方法相比,使用增强型的贝叶斯分类器预测MCS的移动路径具有较好的效果,这为揭示高原上MCS的移动规律、提高长江中下游地区灾害天气预报的准确率提供了一种有效的方法.     

贵州2次MCC暴雨诊断和触发机制对比分析

用FY2-D卫星红外云图云顶亮温(TBB)、常规观测资料和NCEP1°×1°格点再分析资料对2008年5月29—30日(“0529”)与2010年6月16—17日(“0616”)贵州2次MCC暴雨天气过程进行诊断分析和触发机制讨论.结果显示:2次MCC发展的历程不同,“0529”MCC最初由多个较小的对流系统合并发展形成中β尺度对流系统,“0616”MCC却由单个对流系统迅速发展形成.2次MCC过程大气低层的影响天气系统明显不同,“0529”MCC天气过程中冷空气占据主导地位,“0616”MCC天气过程中,西南低空急流起到了关键性的作用.诊断分析发现:“0529”MCC,大气低层的动力条件和水汽辐合剧烈,因此对流和短时强降水更强.“0616”MCC,动力条件和水汽辐合垂直方向伸展的高度高,水汽的输送持续,形成了较广范围的暴雨天气.利用锋生函数针对2次MCC过程触发机制的讨论显示:“0529”MCC,受冷锋影响,加大了经向风的东西向切变,Af伸长变形明显;同时形成θse密集区,有利的热力锋生条件,使得锋生加强.“0616”MCC,低空急流的建立和加强,形成有利的动力锋生条件,使得伸长变形Af和切变变形Bf均对锋生作出明显贡献.     

翅片管束传热及阻力特性的三维数值模拟

在实验的基础上,利用计算流体力学FLUENT软件对空气外掠管束时管外流动和放热性能进行了数值模拟,得到了两种不同管束布置时的对流换热准则关联式及阻力函数关系式。并且通过与前人经过实验而得到的准则关联式相比较,发现文中通过数值模拟得到的准则关联式与其吻合性较好。还总结出了在Re较高时,管束采用叉排布置是不经济的。