一次“北涡南槽”型广西强降水过程的数值模拟

利用MM5V3．6模式对2005年4月25日一次典型的西南涡影响下的广西强降水过程进行了数值模拟，结果表明，MM5V3．6模式对于这次强降水过程具有比较强的模拟能力，能较为准确地模拟出强降水及其系统的发展演变，为更深入的探讨提供高时空分辨率的动力协调资料。     

“96．8”河北大暴雨雨团活动的数值模拟

利用非静力平衡的中尺度模式MM5(v3)对“96．8”河北暴雨进行了48小时数值模拟试验，模拟出的雨团数量和路径与根据稠密的地面观测逐时雨量分析得到的雨团活动相当一致，表明MM5对中尺度雨团有较好的模拟能力。     

一次"北涡南槽"型广西强降水过程的数值模拟

利用MM5V3.6模式对2005年4月25日一次典型的西南涡影响下的广西强降水过程进行了数值模拟,结果表明,MM5V3.6模式对于这次强降水过程具有比较强的模拟能力,能较为准确地模拟出强降水及其系统的发展演变,为更深入的探讨提供高时空分辨率的动力协调资料。     

登陆台风Winnie(1997)的数值模拟研究Ⅰ:结果检验和云系的模拟

用非静力平衡的中尺度模式MM5 (V2 )对 1997年 11号台风Winnie在登陆后演变为温带气旋的过程进行了48h模拟。结果表明 :MM 5不仅比较好地模拟出台风在陆地上的移动路径及其产生的降水 ,而且成功地模拟出了台风登陆后次中心的产生。利用模拟大气中的水物质 (云水、雨水、冰晶、雪水和霰 )模拟了台风云图 ,很好地展示了在卫星实际观测的红外云图上 ,Winnie台风在登陆后其云系的结构从热带气旋的螺旋结构到温带气旋的锋面云系结构的转变过程。因此对Winnie台风的数值模拟可以作为深入研究台风登陆后从热带气旋演变为温带气旋的变性过程的基础。     

1998年“4.18”强沙尘暴分析及数值模拟

对1998年4月18－19日发生在新疆、甘肃、宁夏、内蒙古等地的一次强沙尘暴天气过程从天气事实、天气学成因等方面进行了分析和诊断，然后利用非静力MM5模式对这次沙尘暴天气进行了数值模拟。结果表明，西西伯利亚强冷空气迅速东移，在新疆西部上空形成强锋区，对应的地面冷锋东移至前期增暖显著的新疆、内蒙古、甘肃、宁夏等地形成了本次大风、强沙尘暴天气。用非静力MM5模式较好地模拟出了此次强沙尘暴天气过程的地面强风系统、高空锋区的发生发展。     

2003年春季江淮一次暴雪过程的模拟研究

采用NCEP全球再分析资料和常规地面、高空观测资料，利用非静力中尺度数值模式MM5（V3．6）对2003年2月江淮地区暴雪过程进行了数值模拟。结果表明，MM5能够较好地模拟出地面及中低空大、中尺度环流系统，能够成功模拟出暴雪中尺度低涡的发生、发展及结构演变；低空西南急流与暴雪有着密切关系，对暴雪天气预报有很好的指导作用；对涡度场、散度场和垂直速度场的诊断表明，运动场和热力场的相互配置及耦合关系非常有利于暴雪切变线的发展及暴雪形成与维持。还利用模拟雷达反射率因子检验了模拟的正确性。对温度场的分析可知。降水性质与700hPa、850hPa温度平流有直接关系。     

一次梅雨锋暴雨过程的中尺度对比模拟分析

使用新一代细网格WRF中尺度数值模式和MM5（V3）模式，对2003年7月4～6日发生在江淮流域的一次梅雨锋暴雨过程进行了数值模拟对比分析。结果表明：WRF和MM5都能较好的模拟这次暴雨过程雨带的分布和走向，而WRF能更好的模拟降水中心的位置和雨量；与暴雨过程相联系的低空急流和涡度场等分布特征的模拟，WRF模式亦优于MM5模式。此外，在云贵高原东麓山地，与WRF模式相比，MM5模式在低层模拟出虚假的低压环流，这可能与两模式所采用的垂直坐标差异有关。对WRF的模拟结果分析发现，700hPa湿位涡异常区与暴雨发生区对应很好。     

2003年7月31日固原暴雨天气数值模拟

利用中尺度数值模式MM5。对2003年7月31日宁夏固原暴雨天气过程进行了数值模拟,结果表明：模式能较好地模拟出这次天气过程的影响系统及其演变,揭示了常规观测中无法分析到的中小尺度天气系统。模式输出产品导出的螺旋度、对称不稳定、湿焓、非地转湿Q矢量等物理量。对本次强降水天气具有较好的描述能力和预报指导意义。     

“96·8”华北暴雨数值模拟与稳定性分析

分析1996年8月发生在华北地区的台风暴雨过程的环流形势，发现：副热带高压与台风低压之间的气压梯度很大，宽广的偏南急流源源不断地向北输送水汽和能量，而太行山一带正处于汇合区，构成十分有利的暴雨天气形势。应用MM5数值预报方法对1996年8月4—5日的降雨天气过程进行数值模拟，并依据天气学原理和位涡理论对此过程的稳定性进行分析认为：（1）MM5数值预报模式较好地模拟出了台风暴雨的物理过程。（2）此次降雨的不稳定层结有南高北低现象，同时有对称不稳定和对流不稳定存在；条件性对称不稳定可使环流加速，对降水有一定的增幅作用。     

98.7湖北特大暴雨的天气分析与降水模拟

1998年7月20～23日，湖北省南部发生了一次持续性特大暴雨过程，采用双向嵌套的非静力中尺度数值模式(MM5)对这次强暴雨过程进行初步模拟试验。结果表明，粗、细网格均能较好地模拟出雨带的走向和变动以及武汉地区的暴雨中心，尤其是嵌套域(细网格)模拟的降水强度比粗网格有明显改进，和实际观测结果更接近；另外，对引发这次特大暴雨的对流层低层的中尺度系统也能够很好地模拟出来。     

Wind tunnel evaluation of a rime metering device using a magnetostrictive sensor

A ground-based rime-meter developed by Hydro-Quebec was evaluated in 1992 in the icing tunnel at Université du Québec à Chicoutimi (UQAC) and this instrument is presently used in a network of stations monitoring rime and other iced precipitations in the province of Quebec (Canada). The rimemeter uses, as a sensing element, the probe of the Rosemount icing detector model 871A regulated by an improved programmable controller. The purpose of the evaluation was to characterize the frequency response of the rime-meter mounted with various probes in order to determine their dynamic sensitivity and accuracy under a variety of operating and icing conditions apt to occur in field. The tunnel investigation showed the high sensitivity of the probe to meter ice accumulation. Therefore, it appears feasible under dry conditions, with appropriate calibration, to use this ice sensor as a device for determining the liquid water content. However, its operation in freezing rain near 0°C requires further investigation in the laboratory and in the field.     

初始场和分辨率对WRF模拟对流性降水的影响

文章利用WRF模式分析了2015年7月29日内蒙古中部地区一次典型冷涡过程带来的对流性降水,探讨了初始场和网格分辨率对对流性降水模拟结果的影响。初始场和网格分辨率均会影响模式模拟结果,对于对流性短时强降水而言,在相同的初始场条件下,网格分辨率越高,对降水强度和落区的预报越准确,而在相同的高分辨率网格条件下,初始场的精度越高,模拟不同等级降水的TS评分均较高,表明在高分辨率网格和高精度的初始场条件下,模式对不同等级的降水均有较好的模拟。     

Numerical simulation of pollutant dispersion in a small valley under conditions with supercritical Richardson numbers

The numerical drainage wind model of Wonget al. (1987) is used together with a Lagrangian particle model in the simulation of carbon monoxide (CO) dispersion within a small urban valley in Edmonton, Alberta, Canada. The conditions studied are those of strong static stability when vertical mixing is suppressed. These are conditions with the Richardson number exceeding its critical value (hereafter referred to as supercritical conditions). Observations showed that under such conditions, vertical turbulence is suppressed but horizontal turbulence still exists. The effects of turbulence in the dispersion and transport of pollutants under such conditions are small. However, in the present simulation, a simple turbulence parameterization based on observations is used for supercritical conditions. Some field experiments were performed and the observations are compared with model results. For a location downwind of the CO source, two peaks can be observed during the course of the drainage flow regime. The model results suggest that these represent an initial flux from the drainage flow and a second flux later from drainage wind recirculation. Another main feature of the model-predicted concentration field is zones of maximum concentration at and above the valley floor. There is a drainage wind cell on each side of the valley slope and the cells are effectively decoupled from the prevailing wind above. The present modelling results show that when the prevailing wind exists before the development of the drainage wind, it can be instrumental in transporting CO from one drainage wind cell to the other. Otherwise, the CO released within one drainage wind cell is well contained.     

A framework for the structure of a low windspeed field

In this paper the structure of the wind field in near calm conditions is established. First, the main parameters that characterize the wind field are defined. By considering a bivariate Gaussian distribution for the components of the wind speed, which becomes a circular distribution in low wind speeds, simple relations among those parameters have been obtained. Some experimental evidence supporting the proposed formulation is given.     

Two-dimensional microclimate distribution within and above a crop canopy in an arid environment: Modeling and observational studies

A numerical two-dimensional model based on higher-order closure assumptions is developed to simulate the horizontal microclimate distribution over an irrigated field in arid surroundings. The model considers heat, mass, momentum, and radiative fluxes in the soil-plant-atmosphere system. Its vertical domain extends through the whole planetary boundary layer. The model requires temporal solar and atmospheric radiation data, as well as temporal boundary conditions for wind-speed, air temperature, and humidity. These boundary conditions are specified by an auxiliary mesoscale model and are incorporated in the microscale model by a nudging method. Vegetation parameters (canopy height, leaf-angle orientation distribution, leaf-area index, photometric properties, root-density distribution), soil texture, and soil-hydraulic and photometric properties are considered.The model is tested using meteorological data obtained in a drip-irrigated cotton field located in an extremely arid area, where strong fetch effects are expected. Four masts located 50 m before the leading edge of the field and 10, 30, and 100 m inward from the leading edge are used to measure various meteorological parameters and their horizontal and vertical gradients.Calculated values of air and soil temperatures, wind-speed, net radiation and soil, latent, and sensible heat fluxes agreed well with measurements. Large horizontal gradients of air temperature are both observed and measured within the canopy in the first 40 m of the leading edge. Rate of evapotranspiration at both the upwind and the downwind edges of the field are higher by more than 15% of the midfield value. Model calculations show that a stable thermal stratification is maintained above the whole field for 24 h. The aerodynamic and thermal internal boundary layer (IBL) growth is proportional to the square root of the fetch. This is also the observed rate of growth of the thermal IBL over a cool sea surface.     

Stochastic interpolation as a means to estimate oceanic fields

Abstract

The method of stochastic interpolation (conditional simulation) is introduced as a means to interpolate / extrapolate a scalar or vector field of an oceanic variable, e.g. currents. Conditional simulation produces the synthesis of a random field that is forced to agree with simultaneous measurements in the same time interval and area where the input data are being synthesized. The conditional simulation is applied to the vector field for two California current measurement programs (Coastal Ocean Dynamics Experiment (CODE) and Central California Coastal Circulation Study fccccsj, north and south of San Francisco, respectively). These field programs covered different areas and were characterized by different instrument spacings. The influence of these spatial factors shows up in the quality of the conditional simulations, i.e. a smaller area and a tighter mooring array led to more physically reasonable flow realizations. The various realizations provided by a series of conditional simulations allow confidence intervals to be defined. Other uses for this technique include optimization of current‐meter (or other sensor) placement and the specification of initial or boundary conditions for numerical models. This latter function could be invoked when real data are sparse or when the data that are available are overly smooth and do not contain enough of the variability of the natural system.     

我国华中地区稻田甲烷排放特征

本文主要讨论地处我国华中水稻生态区的湖南红壤稻田的CH4排放特征。稻田CH4排放的日变化都有一致的规律，即在下午16:00左右出现最大值；CH4排放的日变化幅度与天气条件和水稻植物体有关；CH4排放的日变化与温度日变化的相关性很好（R>0.90）。早稻和晚稻的CH4排放季节变化规律有明显的差别，这主要是由于早、晚稻水稻生长期间的天气特别是空气温度变化的差异引起的，早稻CH4排放率在水稻生长中期（6月）略大，而晚稻在水稻移栽后几天内CH4排放就达到整个季节中的最大值，以后随时间逐渐降低；缺水会使CH4排放率明显降低，而且在重新灌水后相当长时间内CH4排放率没有回升；CH4排放在全有机肥的田中最大，然后依次是常规施肥、全沼渣肥及化肥田；尿素、氯化钾和复合肥的多施可降低稻田CH4排放率；不同施肥田中CH4排放率的温度效应不同；施肥是控制CH4排放的一种可行手段；在整个晚稻生长季节中瞬时CH4排放率与瞬时温度呈明显的指数关系；在1991年双季水稻生长季节中，稻田中CH4的排放量为67.96 g·m-2，其中早稻的CH4排放率为0.36 g·m-2·d-1，晚稻为0.48 g·m-2·d-1。     

基于高分辨率中尺度气象模式的实际雷暴过程的数值模拟试验

雷暴数值预报的实际应用离我们还有多远？本文对此进行了尝试, 即利用一个复杂的高分辨率中尺度气象模式驱动一个三维雷电模式, 在只采用常规气象观测资料的条件下, 对北京的一次实际雷暴过程进行模拟试验, 分析了雷暴云的宏观动力、 微物理过程及电结构的时空变化特征以及其可能的相互作用机制。结果表明: 利用高分辨中尺度模式预报出的三维气象场作为雷电模式的初始场, 完全可以不需添加虚假的扰动来触发雷暴云的发展, 高分辨中尺度模式的预报场本身所包含的水平非均匀、 垂直强非静力性及较强的对流不稳定信息足够促发雷暴云的剧烈发展; 用较为真实的三维气象场作为初始场模拟产生的电场分布特征与云微物理分布特征及环境气象要素的分布结构非常协调, 得到的雷暴云的电荷结构特征以及电结构随时间的演变特征更为复杂, 更真实的体现了实际雷暴云本身发展的复杂性, 同时, 模式能够模拟出合理的云闪及正负云地闪, 且模拟的闪电频数随时间发展演变趋势基本与观测实况基本吻合, 从而表现了对雷电天气潜在的预报能力。本次模拟的北京雷暴云在发展过程中, 水物质霰的最大质量比、 最大正电场强度及闪电频数随模拟时间的演变发展趋势非常相似。     

一次强对流天气的多普勒特征分析

利用天气图、卫星云图和5cm多普勒天气雷达的资料，详细分析了一次强对流天气的环流背景、回波发展演变过程和多普勒特征及其风场结构；初步分析了强对流天气瑟下垫面地理特征之间的密切关系。对多普勒天气雷达探测强对流天气的方法进行了初步探讨。