大气中对称不稳定机制的动力学分析及暴雨的分析与预报

用气块法从力学角度对对称不稳定机制及在对称不稳定条件下产生的环流进行分析，更全面地定义了对称不稳定及它的产生机制和中尺度环流形成的过程。对暴雨个例诊断分析表明，有些强降水区在降水前和降水过程中存在着不对称不稳定，说明对称不稳定条件下形成的环流对暴雨有引发和加强作用。在以往研究原基础上，总结出了利用常规观测资料分析对称不是否存在，及其能量大小的方法，用它来预报是否降水及降水的强度，从而提高降水预报准确率。     

混流式转轮中流场的大涡模拟

建立了基于微可压缩流体理论的相对运动的大涡模拟方法,并对混流式转轮流场进行了三维非恒定粘性数值模拟,计算方法采用了有限体积法和预测-校正方法,对固体边壁的处理使用了“壁函数”法。得到了混流式转轮的三维速度场和压力分布,与k-ε模型计算结果进行比较表明,所建立的相对运动的大涡模拟方法对转轮性能预测更加精确、合理,对转轮改型设计具有十分重要的参考价值。     

中尺度数值模式(MM5V3)在沈阳区域气象中心的试用

简单介绍了沈阳区域气象中心在微机上调试和试用中尺度数值模式MM5V3的情况，MM5V3在前、后处理上使用Fortran90编程，与MM5V2有一定差别，利用T106L19资料和常规探空报形成经、纬网格的初值，预处理场和侧边界，代入模式前处理系统中，模式运行完毕后，预报产品直接进入MICAPS、Vis5d、Grads系统，进行图形显示，在2000年汛期试用中发现，MM5V3对东北地区的强降水过程有一定的预报能力，预报评分表明，MM5V3的降水预报结果和MM5V2互有优劣，总体来看，MM5V3的预报质量略高于MM5V2。     

THE MESOSCALE CONVECTIVE SYSTEMS ACROSS THE TAIWAN STRAIT AND NEIGHBORING AREAS DURING IOP608 OF HUAMEX

The paper gives the distributions of the daily mean temperature of black body of satellite infrared images from June 7 to 10, 1998 during HUAMEX and examines 14 meso-α-scale convective systems and a number of meso-b-scale convective systems using the satellite infrared images at 1-h intervals. The mesoscale convective systems on June 7 and 9, which resulted in severe rainstorm over the middle of Taiwan and the estuary region of the Pearl River (Zhujiang R.), are emphatically analyzed. The serial development of mesoscale convective systems is revealed by the distributions of the black body temperature of satellite infrared images. The environmental conditions in which many mesoscale convective systems continuously occurred are diagnosed. The visualizing tool, LiveView, displays the link between the upper and lower horizontal wind fields and the vertical circulations and 3-dimensional trajectories of moist air motions, based on the data of objective analyses.     

The generation of phytoplankton patchiness by mesoscale current patterns

 Elken et al. (1994) suggested that phytoplankton patchiness can be generated by mesoscale eddies in light-limited, nutrient-replete environments. This hypothesis is explored using two ecological models of different physical complexity. The model results support the idea that the coupling of mesoscale eddy circulation and phytoplankton growth leads to differential growth rates and thus generates variability in phytoplankton distributions. The specific circulation of a cyclonic eddy isolates a phytoplankton population in its core. Due to the reduced vertical mixing, a higher growth rate is supported in the core, and phytoplankton concentrations increase compared to the surrounding environment. A one-dimensional model is used to explore the hypothesis in general and to perform sensitivity studies. A more realistic simulation uses a coupled three- dimensional model for the western Baltic Sea. Starting from vertically and horizontally homogeneous distributions for nutrients and plankton, the models generate patchiness due to the proposed mechanism. The described mechanism may apply for other mesoscale variable environments during light-limited growth periods as well, e.g., the frontal region of the Southern Ocean. Received: 31 March 2001 / Accepted: 31 August 2001     

CHARACTERISTICS OF MESOSCALE FLOOD-MAKING TORRENTIAL RAIN SYSTEM SIMULATED BY HIGH RESOLUTION LIMITED AREA MODEL—NUMERICAL SIMULATION OF A HEAVY RAIN PROCESS DURING MEIYU SEASON IN 1991*

An experimental work on the transplant of high resolution limited area model(HIRLAM) isfirstly introduced into China.For the implementation,first of all is to adjust a new geographicalcoordination and to remove the instability caused by the Tibetan Plateau,the roof of the world.Then,we have applied this model to simulate a flood-making torrential rain process which occurredin the Changjiang-Huaihe River Valley in July 1991.That revealed the formation,development andmovement of a mesoseale heavy rain system which had made a disastrous flood event in the middleand lower reaches of Changjiang River Valley.The result encourages us to use the HIRLAM for the researches on the Meiyu belt,the salientfeature of precipitation of East Asia,and the numerical prediction of heavy rains in China.     

A novel ozone sensor for direct eddy flux measurements

A small, lightweight (1.5 kg) and fast-response ozone sensor for direct eddy flux measurements has been built. The basis for detection is the chemiluminescence of an organic dye adsorbed on dry silica gel in the reaction with ozone. The chemiluminescence is monitored with a cheap and small blue-sensitive photomultiplier. At a flow rate of 100 l min^-1 the ozone sensor has a 90% response time of significantly better than 0.1 s with a detection limit lower than 50 ppt at S/N=3. There are no interferences from other atmospheric trace gases like NO_x, H₂O₂ and PAN. Water vapour and SO₂ enhance the chemiluminescence efficiency of the ozone sensor. Since their response times are 22 seconds and 30 minutes, respectively, no correlation between rapid ozone fluctuations and those of these two trace gases is noticed by the ozone sensor when operating at a frequency of 10 Hz.The ozone sensor was tested for several weeks in continuous measurements of ozone fluxes and deposition velocities over different croplands using the eddy correlation technique. Good agreement was found between ozone dry deposition velocities derived from profile measurements and by eddy correlation.     

中尺度数值模式中湿过程参数化的敏感性试验

本文利用一个三维中尺度模式，分别采用两种不同的湿过程处理方案ＦＰＡ和ＮＣＡ模拟同一个洋面冷锋个例，以考察模拟结果对湿过程参数化方案的敏感性。两种方案的区别在于前一种使用了次网格湿对流参数化而后者没有。通过比较分别使用ＦＰＡ和ＮＣＡ方案所进行的模拟ＦＰＳ和ＮＣＳ，发现冷锋结构在两者间出现较大差异。从８５０ hPa等压面|Δθe|等值线图所显示的结构看，ＮＣＳ中冷锋呈现为一长一短两条锋带，而ＦＰＳ中冷锋仅呈现为一条锋带。在相应的冷锋横向垂直剖面中，ＮＣＳ中存在两个相邻的锋面垂直环流，而ＦＰＳ中只有一个。另外，ＮＣＳ中对流不稳定的冷锋区出现垂直运动过分发展的现象，而ＦＰＳ中不存在这个问题。通过与卫星云图比较，我们注意到，ＮＣＳ中尽管出现了垂直运动过分发展的现象，但相对于ＦＰＳ而言，其模拟的冷锋结构与实际较为接近，成功地模拟出云图上显示的双冷锋结构。ＮＣＳ中垂直运动过分发展的一个重要原因是模式中采用的静力平衡近似。ＦＰＳ中次网格对流参数化方案的使用，通过减少甚至消除对流不稳定度，一方面使垂直运动的过分发展倾向受到约束，另一方面也可能使在对流不稳定层结下的锋区环境中本应出现的中尺度结构失去了形成的机会。     

一次MCS的尺度分离动能分析

利用尺度分离动能方法对１９９４年６月１１日０９ＵＴＣ－１２日１０ＵＴＣ影响湖南省的一次ＭＣＳ进行了研究，结果表明：１．大尺度运动中非地转风以及两种尺度间风场与气压的相互作用产生的动能，是这次ＭＣＳ的主要能源；２．中尺度动能以及两种尺度风场相互作物 动勇，随ＭＣＳ发展而增加；３．在ＭＣＳ的整个发展阶段，高层的总体动能锐减。     

Estimation of drag coefficient over the western desert sector of the Indian summer monsoon trough

In the estimation of momentum fluxes over land surfaces by the bulk aerodynamic method, no unique value of the drag coefficient (C _D) is found in the literature. The drag coefficient is generally estimated from special observations at different parts of the world. In this study an attempt is made to estimate drag coefficient over the western desert sector of India using data sets of Monsoon Trough Boundary Layer Experiment (MONTBLEX) during the summer monsoon season of 1990. For this purpose, the fast and slow response data sets obtained simultaneously from a 30 m high micro-meteorological tower at Jodhpur are used. All the observations used in this study are confined to a wind speed regime of 2.5–9.0 ms⁻¹. A comparison of momentum fluxes computed by eddy correlation (direct estimation) with profile and bulk aerodynamic (C _D = 3.9 × 10⁻³, Garratt, 1977) methods revealed that though the nature of variation of the fluxes by all these methods is almost similar, both the indirect methods give an under-estimated value of the fluxes. The drag coefficient is estimated as a function of wind speed and surface stability by a multiple regression approach. An average value of the estimated drag coefficient is found to be of the order of 5.43 × 10⁻³. The estimated value ofC _D is validated with a set of independent observations and found to be quite satisfactory. The recomputed momentum fluxes by bulk aerodynamic method using the estimated drag coefficient are in close agreement with the directly estimated fluxes.