大气环境层结对闪电活动影响的模拟研究

利用一个二维面对称雷暴云起电、放电模式,选取了北京地区3次雷暴过程的环境层结,计算并讨论了不同层结条件下雷暴中动力、微物理过程及其对起电、放电活动的影响。结果表明,上升速度和水汽条件是影响雷暴动力、微物理过程和闪电活动的最重要因子。上升速度的大小决定了雷暴发展到成熟的时间和雷暴的强弱,较强的上升气流有利于雷暴云在较短时间内达到较大的高度。而持续的上升气流和充足的水汽有利于雷暴的成熟期延长从而增强闪电活动。较强的上升速度和充足的水汽可以产生更多的对闪电起电、放电有直接影响的冰相物并能使其持续生成,从而形成较大的电荷浓度。较强的上升速度和不利的水汽条件也可以在某时形成较大的冰相物浓度,但冰相物难以持续生成。而较弱的上升速度和充足的水汽则容易形成暖云过程,对冰相物的生成也有不利影响。上升速度和水汽相互影响,又共同受到环境层结的支配。大气低层潮湿、中层湿度适中,较大的不稳定能量和一定量的对流抑制能量将有利于强闪电活动的发生。表现在大气不稳定参数的取值上,对流性稳定度指数的值小于-10℃(负值表示不稳定),对流有效位能值在1000 J/kg以上,对流抑制能量大于40 J/kg,700 hPa相当位温在340 K以上,700—400 hPa中层平均湿度在35%—85%,有利于强闪电活动的发生。     

气旋爆发性发展过程的动力特征及能量学研究

本文对不同路径的爆发性气旋进行了动力特征及能量学研究。发现高空大值位涡空气的下伸是气旋爆发性发展的一个重要条件。初生气旋逐渐向强位涡区移近并形成上下位涡区相接的形势。使气旋迅速发展。高空急流与气旋发展有密切关系。发展中的气旋明显地向着急流左侧的辐散区移动。急流的突然加强及高空强风动量的不断下传，构成了下层的强风带及上下一致的急流结构。能量学研究指出在气旋发展前气旋内散度风动能向旋转风动能的转换突然增强。散度风动能在爆发气旋发展时有明显增长。     

山西春季层状云系数值模拟及与飞机探测对比

采用中国气象科学研究院 (CAMS) 中尺度云参数化模式对2010年4月20日山西省一次春季层状降水云系的宏微观结构,特别是垂直方向上的微物理结构进行了数值模拟和分析。利用携带云粒子探测设备的飞机对该次层状云系进行了两次云物理探测飞行,并将飞机探测所获取的数据和图像资料与数值模拟结果进行了对比研究。模拟结果显示:该次降水过程以层状冷云降水为主,云中过冷水含量丰富,云系存在明显的3层结构,地面降水主要来自于云中高层冰晶、雪、霰等冰相粒子的融化和低层云水的转化。数值模拟与飞机探测对比分析显示,高空温度、湿度和高度的配置两者基本一致,数值模拟不同高度的云粒子相态、垂直方向云水比含水量与飞机探测获取的云粒子图像和云液态水含量的垂直结构基本吻合,但数值模拟的云中各种水成物粒子出现的高度较飞机探测偏高。     

Elucidating Dominant Factors Affecting Land Surface Hydrological Simulations of the Community Land Model over China

In order to compare the impacts of the choice of land surface model(LSM) parameterization schemes, meteorological forcing, and land surface parameters on land surface hydrological simulations, and explore to what extent the quality can be improved, a series of experiments with different LSMs, forcing datasets, and parameter datasets concerning soil texture and land cover were conducted. Six simulations are run for the Chinese mainland on 0.1° × 0.1° grids from 1979 to 2008, and the simulated mon...     

A Comprehensive Observational Analysis for the Effects of Gas Cannons on Clouds and Precipitation

To analyze the effects of gas cannons on clouds and precipitation, multisource observational data, including those from National Centers for Environmental Prediction (NCEP) reanalysis, Hangzhou and Huzhou new-generation weather radars, laser disdrometer, ground-based automatic weather station, wind profiler radar, and Lin''an C-band dual polarization radar, were adopted in this study. Based on the variational dual-Doppler wind retrieval method and the polarimetric variables obtained by the dual-polarization radar, we analyzed the microphysical processes and the variations in the macro - and microphysical quantities in clouds from the perspective of the synoptic background before precipitation enhancement, the polarization echo characteristics before, during and after enhancement, and the evolution of the fine three-dimensional kinematic structure and the microphysical structure. The results show that the precipitation enhancement operation promoted the development of radar echoes and prolonged their duration, and both the horizontal and vertical wind speeds increased. The dual-polarization radar echo showed that the diameter of the precipitation particles increased, and the concentration of raindrops increased after precipitation enhancement. The raindrops were lifted to a height corresponding to 0 to -20 ℃ due to vertical updrafts. Based on the disdrometer data during precipitation enhancement, the concentration of small raindrops (lgNw) showed a significant increase, and the mass-weighted diameter Dm value decreased, indicating that the precipitation enhancement operation played a certain“lubricating”effect. After the precipitation enhancement, the concentration of raindrops did not change much compared with that during the enhancement process, while the Dm increased, corresponding to an increase in rain intensity. The results suggest the positive effect of gas cannons on precipitation enhancement.     

郑州强对流天气成因分析

对2004年郑州出现的7次强对流天气过程的天气形势、影响系统及稳定度的分析结果表明：华北低涡和NW气流形势下存在着低层升温、高层降温机制,使大气层结趋于不稳定,当测站高低空温差或温度平流差达到一定量值,且近地层存在辐合系统时,易出现强对流; SW气流或高压控制时,大气高温高湿,具有较强不稳定能量,若850 hPa或地面出现辐合系统时,易产生强对流;地面湿度连续数天加大或保持在某一值域,其上空温湿24 h变化呈上趋冷下趋暖或上趋干下趋湿并达到一定量值,预示强对流的发生;700～500 hPa湿度明显减小,24 h温度露点差加大4 ℃以上,或近地层θse≥350K,中低层Δθse≥26 K,θse小值位于700 hPa或500 hPa,其厚度≥2000 m,易出现强雷雨大风; 700 hPa以下t-td≤4.3 ℃,或连续4天850 hPa t-td≤7 ℃、700 hPa t-td≤5 ℃、500 hPa t-td≤9 ℃,PW≥12,可预示短时暴雨的出现.     

An Optical Disdrometer for Measuring Present Weather Parameters

A new present weather identifier（PWI） based on occlusion and scattering techniques is presented in the study. The present weather parameters are detectable by the meteorological optical range（MOR） approximately up to 50 km and by droplets with diameters ranging from 0.125 mm to 22 mm with velocities up to 16 m s-1. The MOR error is less than 8% for the MOR within 10 km and less than 15% for farther distances. Moreover, the size errors derived from various positions of the light sheet by the particles were checked within ± 0.1 mm ± 5%. The comparison shows that the MOR, in a sudden shower event, is surprisingly consistent with those of the sentry visibility sensors（SVS） with a correlation coefficient up to 98%. For the rain amounts derived from the size and velocity of the droplets, the daily sums by the PWI agree within 10% of those by the Total Rain Weighing Sensor（TRwS205） and the rain gauge. Combined with other sensors such as temperature, humidity, and wind, the PWI can serve as a present weather sensor to distinguish several weather types such as fog, haze, mist, rain, hail, and drizzle.     

WRF中土壤图及参数表的更新对华北夏季预报的影响研究

土壤质地及其物理性质的参数化对陆面过程模拟具有明显的影响。研究了土壤质地和土壤水文参数表的更新对WRF（Weather Research and Forecasting）模拟性能的影响。使用北京师范大学土壤属性数据集和修正后的土壤水文参数表替换WRF默认数据,对2017年6—8月华北地区开展数值模拟试验和评估验证。结果表明,模拟结果对土壤类型数据集和水文参数表的更新较为敏感,对地面要素预报有正效果。WRF默认土壤数据集中,中国东部以粘壤土为主,而在北京师范大学土壤数据集里则以壤土为主;修正后的土壤水文参数在Noah陆面过程中增强了裸土潜热蒸发能力。数值模拟试验表明,土壤输入数据和土壤水文参数的更新能够增强陆面向大气的潜热同时减弱感热输送,致使大气底层温度降低而湿度增大。利用华北区域748个地面气象观测站的2 m温度和2 m湿度对2017年夏季的模拟结果进行验证,结果显示更新试验对地面要素的预报偏差有较好的修正作用,能够将2 m温、湿度的预报技巧分别提高3.4%和2.9%。      

A Study On Atmospheric Boundary-Layer Characteristics At Anand, India Using Lsp Experimental Data Sets

An attempt is made to study the planetary boundary layer (PBL) characteristics during the winter period at Anand (22.4°N, 72.6°E), a semi-arid region, which is located in the western part of India. A one-dimensional turbulent kinetic energy (TKE) closure model is used for the study. The structure of the PBL,which consists of profiles of zonal and meridional components of wind,potential temperature and specific humidity, is simulated. A one-dimensional soil heat and moisture transport parameterization scheme is incorporated for the accurate representation of the energy exchange processes at the soil-atmosphere interface. The diurnal variation of fluxes of sensible heat, latent heat, shortwave radiation, net radiation and soil flux, soil temperature at different depths, Richardson number and TKE at the height of the constant flux layer is studied. The model predictions are compared with the available observations obtained from a special Land Surface Processes (LSP) experiment.     

季冻区草炭土非线性K-G模型试验研究

季冻区草炭土是沼泽环境中植物残体在氧化分解作用下,堆积形成的含有大量未分解纤维残体的特殊土。草炭土纤维及其含量对其强度和变形特性具有重要影响,目前考虑纤维含量对草炭土强度和变形特性影响的本构关系研究还相对匮乏。K-G本构模型因其模型参数与土的体积模量和剪切模量能建立直接联系,因此在岩土工程非线性理论和数值计算分析方面广泛应用。以不同纤维含量的草炭土为研究对象,进行三轴剪切试验,研究了草炭土的应力应变曲线,得到了草炭土非线性K-G模型参数,分析了各模型参数随纤维含量的变化规律,建立了模型参数与纤维含量之间的线性函数关系。