湿涡度、湿散度在一次大范围降水过程中的诊断评价

为获得湿涡度、湿散度的暴雨落区诊断性能,使用ERA-interim全球再分析资料、Micaps实况降水资料,以2016年6月15—23日我国南方的一次大范围降水过程为例,通过对比诊断、TS得分评价对该组参量性能进行了一次系统检验。结果表明:该组新参量较传统涡度、散度及相对湿度可大幅减少空报,相对湿基权重参数是影响这组参量性能的关键,合理选择经验常数k能大大提高其诊断性能。另外,在该次系统检验中,湿涡度、湿散度表现出的诊断性能已接近国家气象中心暴雨预报的业务水平。

湿Q矢量散度场与ω场的比较

结合 1 991年 7月 5日 2 0时至 6日 2 0时一次典型的江淮梅雨锋暴雨过程实况资料 ,系统、细致地比较分析了实时分析的湿 Q矢量散度场与同时次改进后的MM4(MMM4)模式实时分析输出场之间的差异。结果表明 :在整个梅雨锋暴雨过程中 ,湿 Q矢量散度辐合场与同时刻地面雨区之间的对应关系较 ω场优越 ;70 0 h Pa湿Q矢量散度辐合区对同时刻地面降水场有指示作用 ,尤其在梅雨锋暴雨的发展阶段及强盛时期 ,它对实际降水的落区及强度指示作用更为明显 ;

试用湿静能通量散度对雷暴诊断分析

依据能量天气学的观点，从湿静能守恒方程出发，导出局地能变率的表达式，在一定假定条件下得到局地能变率与湿静能通量散度（下用ＥＤＨ表示）的近似相关式。考虑到雷暴等强对流性天气过程所显示出的强烈的能量特性，我们试用ＥＤＨ对雷暴的发生、发展进行了诊断。分析发现ＥＤＨ场的特征先于能量场本身，且雷暴落区在ＥＤＨ场上规律性比较明显。由此认为，若将ＥＤＨ场与湿静能场（Ｅ＿Ｓ表示）结合应用，对提高雷暴的预报准确率将有一定指导意义。

湿度权重方法在西南涡强降水过程的应用研究

利用欧洲中心ERA-Interim数据分析研究一次西南涡东移导致长江中下游强降水事件,首先,利用湿度权重的方法构造出两个新的动力学诊断量:湿权重风暴相对螺旋度(mSRH)和湿权重螺旋度散度(mMHD)。mSRH可以更好的指示强降水的范围,但是最大强度中心相对降水中心偏北。然后随着西南涡东移的发展,mMHD很好指示的降水中心位置,mSRH和mMHD的中心和降水中心相对一致。其次,将反映热带气旋的生成源地的Okubo-Weiss (OW)参数引入西南涡,描述其位置和移动方向。经过湿度修饰后的mOW参数,mOW最大正值中心很好的指示西南涡的中心位置,西南涡位置中心前部存在一个mOW强大的负值区域,对应着西南涡未来6 h时刻的移动位置。

水汽螺旋度及其在一次江淮暴雨分析中的应用

构造了新的诊断量——水汽螺旋度,并对影响水汽螺旋度变化的因子做了分析。利用MM5模式输出资料对2003年7月4日的暴雨过程进行诊断分析,结果表明:水汽螺旋度与暴雨强度和暴雨落区都有较好的相关,螺旋度通量散度和湿螺旋散度对暴雨也有比较明显的指示作用,其中螺旋度通量散度对暴雨落区和强度的指示作用都很好,而湿螺旋散度与暴雨落区对应得稍差。

非地转湿Q矢量分析及其在暴雨过程中的应用

从包含非绝热效应的“P”坐标出发,直接通过方程各项的量级比较,对方程尺度分离后进行简化,引入非绝热加热作用的非地转湿Q矢量概念,并推导出其表达式以及以非地转湿Q矢量散度为唯一强迫项的非地转ω方程。并将其在实际暴雨过程中应用,分析非地转湿Q矢量在降水过程中的可应用性。发现非地转湿Q矢量散度的辐合区与上升运动有较好的对应关系,而且与非地转ω方程的垂直速度相比较能分离出较小的尺度,对暴雨的预报起更好的指示作用。

2019年初浙江罕见连阴雨过程的成因分析

利用浙江省2019年2月地面气象观测资料、FY-2G红外云图资料、NCEP和ERA-Interim再分析资料,对浙江省2019年冬末春初典型的连阴雨天气过程的成因进行了分析,得出以下结论:(1)连阴雨期间500 hPa极涡呈偶极型,主体持续收缩在北极附近,浙江位于700 hPa和850 hPa切变南侧稳定的西南气流及温度正距平中,对流层高层西风急流持续偏强、位置偏北,强度和位置变化超前于降雨;(2)源自孟加拉湾北部至青藏高原、中南半岛到南海的两条水汽通道持续输送水汽至我国华东地区,浙江同时受两条水汽带叠加影响时雨强达到最大,红外卫星云图分析可对水汽输送通道和天气形势作大致判断,提供降雨预报辅助性参考;(3)700 hPa湿Q矢量显著辐合区和850 hPa经向风0 m·s^(-1)等风速线重叠的区域易出现明显降雨,集中降雨时段浙江上空存在很大的低层假相当位温和水汽通量的水平梯度,水汽输送带位于梯度区之上。

江汉平原一次突发性特大暴雨的诊断分析

利用NCEP 1°×1°逐6 h分析资料和湖北省自动气象站雨量资料分析了2006年5月24日夜间江汉平原南部一场突发性大暴雨、局部特大暴雨过程的成因。结果表明,这次强降雨发生之前,高空急流南界先向北移出湖北省上空,伴随着强降雨的发展与减弱,急流南界又重新南扩到湖北南部;急流核在强降雨发生之前在35～40°N之间东移,特大暴雨发生时已位于暴雨区东北方向渤海湾一带。这次特大暴雨发生在边界层中尺度正涡度区合并加强过程中。暴雨过程伴随着高层惯性稳定度的减小与低层位势不稳定的维持;南海西北部到华中地区西南水汽通道的建立是特大暴雨发生的有利条件,水汽输送主要集中在中、低层。特大暴雨发生之前低层正值湿螺旋散度增加明显。

ODMV/ODMD对长江中下游一次暴雨过程的诊断分析

基于欧洲中期数值预报中心(ECMWF)再分析资料(ERA-interim)和长江中下游124站降水资料以及四种业务常用数值模式资料(EC-thin,T639-thin,Grapes和Japan-thin),以2016年6月30日~7月7日长江中下游地区连续性暴雨天气过程为例,详细分析和讨论了四种数值预报模式以及一维湿涡度(ODMV)和一维湿散度(ODMD)对于长江中下游暴雨落区的诊断效果。得到结论如下:(1)无论是主观分析还是与实际降水的空间相似度,ODMV/ODMD对于雨带和强降水中心的把握都明显优于四种数值模式,在空间分布上表现出更高相似性。(2)Japan-thin预报降水显著偏弱,T639-thin则偏强,而EC-thin、Grapes和T639-thin还表现出较大的离散程度,只有ODMV/ODMD对雨带和强降水中心的平均误差和均方根误差都最小,在降水强度上表现出更高准确性。(3)随着降水强度的增加,Japan-thin、EC-thin和Grapes的漏报率增加显著,Threat Score(TS)评分迅速降低;而T639-thin空报率增速较快,TS评分同样下降明显;只有ODMV/ODMD空报率迅速减小,漏报率缓慢增加,TS评分减弱得较慢,至最高标准时(6h≥30 mm),TS评分依然达到0.22,在降水的时间演变上表现出更好的协同性。

2021年4·26华南区域性暴雨过程的特征

利用常规观测资料、ECMWF第5代全球大气再分析逐小时数据集,对2021年4月26日华南区域性暴雨天气过程环境流场、主要影响系统、水汽条件和温湿特征物理量进行分析。结果表明:该次暴雨过程的主要影响系统有高空槽、低涡切变线、弱锋面低槽;暴雨前期中层大气以下水汽含量充沛,水汽来源主要是南海暖湿东南气流和源于孟加拉湾的西南气流;副高加强与南支槽波动触发西南急流突变,是暖式切变低空水汽强烈辐合主要原因;广义湿位涡异常区对暴雨落区有较好示踪作用,暴雨区一般在GMPV水平梯度较大区域附近;具有湿度因子的湿涡度、湿散度物理量能较好描述大气低层水汽辐合辐散状况,对分析低层水汽和动力环境条件有一定意义。

一次西南涡致洪暴雨天气过程诊断分析和数值模拟试验

基于NCEP(National Centers for Environmental Prediction)的FNL(Final Operational Global Analysis)资料和WRF-ARW模式,对2014年7月10—12日西南涡(SWV)暴雨天气过程进行诊断分析和数值模拟试验。研究结果表明,西南涡沿切变线东移发展和低空西南急流的增强是导致此次暴雨过程的主要原因。西南涡的移向和相对风暴螺旋度(SRH)大值区有很好对应关系,SRH大值区对西南涡暴雨过程强对流的落区有较好的指示作用。沿西南涡移动方向,其前部暖平流后部冷平流有利于其前移,沿假相当位温平流场的零等值线可指示西南涡的移向。引入湿螺旋度散度(MHD)来分析西南涡降水的水汽条件发现,模式结果计算的850hPa上MHD值分布与雨区和降雨强度对应较好,但对于降水的定量预测还需考虑MHD大值区延伸的高度。

一次特大暴雨过程的诊断分析

利用NCEP再分析资料、常规资料对2006年7月2日河南中部特大暴雨过程进行诊断分析,结果表明:深厚的湿层和不稳定层结在强降水发生前已形成;在高低空出现的正负涡度柱、散度柱互耦配置和强烈的垂直上升运动,导致不稳定能量快速释放,产生了此次特大暴雨。强降水期湿Q矢量散度负值中心达到最强,与暴雨区对应。

Soil Moisture Content Monitoring Based on ERS Wind Scatterometer Data

The ERS-1/2 wind scatterometer （WSC） has a low resolution cell of about 50 km but provides a high repetition rate （〈4 d） and can make measurements at multiple incidence angles. In order to estimate effective surface reflectivity （related to soil moisture content） over bare soil Using WSC data, an original methodology based on the advance integral equation model （AIEM） is presented, which takes advantage of its multiple view angular characteristics. This method includes two steps. First, a simplified two-parameter surface scattering model is calibrated by AIEM simulated-database over a wide parameter space. Second, regression analyses are carded out using the simulated database to build the relation between those parameters of our model at different incident angles from two observations of Mid and Fore beams. From the model simulated database, our technique works quite well in estimating Г^0. The possibility of applying the model to retrieve soil moisture is investigated using a set of data collected from the Intensive Observation Period field campaign in 1998 of the Asian Monsoon Experiment Tibet （GAME-Tibet）. The retrieved values obtained for the bare land surface are consistent with ground measurements collected in these areas and the correlation coefficient between retrieved soil moisture and the measured one reaches 0.65.

Dependence of Mixed Aerosol Light Scattering Extinction on Relative Humidity in Beijing and Hong Kong

The hygroscopic properties of mixed aerosol particles are crucial for the application of remote sensing products of aerosol optical parameters in the study of air quality and climate at multiple scales. In this study, the authors investigated aerosol optical properties as a func tion of relative humidity （RH） for two representative me tropolises： Beijing and Hong Kong. In addition to the RH data, mass concentrations of PM10 （particulate matter up to 10 utm in diameter） and aerosol scattering extinction coefficient （aext） data were used. The relationship between the mass scattering extinction efficiency （MEE, defined as O＇ext/PMl0） and RH can be expressed by regression func tions asf= 1.52x ＋ 0.29 （re= 0.77）,f= 1.42x ＋ 1.53 （re= 0.58）,f= 1.19x ＋ 0.65 （re= 0.59）, andf= 1.58x ＋ 1.30 （re = 0.61） for spring, summer, autumn, and winter, respec tively, in Beijing. Here, f represents MEE, x represents I/（1-RH）, and the coefficients of determination are pre sented in parentheses. Conversely, in Hong Kong, the corresponding functions are f= 1.98x- 1.40 （r^2= 0.55）,f = 1.32x - 0.36 （r^2 = 0.26）,f= 1.87x - 0.65 （r^2 = 0.64）, and f= 2.39x - 1.47 （r^2 = 0.72）, respectively. The MEE values for Hong Kong at high RHs （RH 〉 70%） are higher than those for Beijing, except in summer; this suggests that aerosols in Hong Kong are more hygroscopic than those in Beijing for the other three seasons, but the aerosol hy groscopicity is similarly high in summer over both cities. This study describes the effects of moisture on aerosol scattering extinction coefficients and provides a potential method of studying atmospheric visibility and ground level air quality using some of the optical remote sensing products of satellites.

Diffusion of Chloride Ions in Soils:I.Influences of Soil Moisture, Bulk Density and Temperature

Diffusion coefficients of chloride ions in four soils of different texture with varying effective moisture content and varying bulk density from 1.1 to 1.6 g cm3 under three different temperatures were determined by the diffusion-cell method using 36Cl-labelled CaCl2 solution. The results showed that activation energy decreased with water content, which indicated that the threshold for diffusion was lower at a higher soil moisture rate. Therefore, the diffusion coefficient (D) of chloride ions in soil increased consistently with soil moisture. Although a near linear increase in the diffusion coefficient with increasing soil moisture or bulk density in all the soils was observed, the increase rate in different soils was not the same. The D value increased with temperature, and with temperature increased by 10℃ in the range from 5 "C to 45℃ theD valve increased by 10%～30%, averaging about 20%.

Coupling effects of influence factors on probability of corrosion initiation time of reinforced concrete

The coupling model of major influence factors such state affecting the chloride diffusion process in concrete is as environmental relative humidity, load-induced crack and stress discussed. The probability distributions of the critical chloride concentration Cc, the chloride diffusion coefficient D, and the surface chloride concentration Cs were determined based on the collected natural exposure data. And the estimation of probability of corrosion initiation considering the coupling effects of influence factors is presented. It is found that the relative humidity and curing time are the most effective factors affecting the probability of corrosion initiation before and after 10 years of exposure time. At the same exposure time, the influence of load-induced crack and stress state on the probability of corrosion initiation is obvious, in which the effect of crack is the most one

Investigation in Mathematical Models of Chloride Diffusion Coefficient in Concrete Exposed to Marine Environment

Degradation of RC （reinforced concrete） in maritime structures has become a worldwide problem due to its excessive costs of maintenance, repair and replacement in addition to its environmental impacts and safety issues. Degradation of both concrete and steel which is the main reason of reduction in the service life of RC structures strongly depends on the diffusion process of moisture and aggressive species. In this paper, the major and popular mathematical models of diffusion process in concrete are surveyed and investigated. Predominantly in these models, the coefficient of chloride diffusion into the concrete is assumed to be constant. Whereas, experimental records indicate that diffusion coefficient is a function of time. Subsequently, data analysis and comparisons between the existing analytical models for predicting the diffusion coefficient with the existing experimental database are carried out in this study. Clearly, these comparisons reveal that there are gaps between the existing mathematical models and previously recorded experimental results. Perhaps, these gaps may be interpreted as influence of the other affecting parameters on the diffusion coefficient such as temperature, aggregate size and relative humidity in addition to the water cement ratio. Accordingly, the existing mathematical models are not adequate enough to predict the diffusion coefficient precisely and further studies need to be performed.

Liquid spreading on a pre-wetted biomimetic surface inspired by a dog's tongue

Liquid film flow widely exists in industries due to its high thermal film is strongly influenced by the properties of the working surface efficiency and low flow flux. The spreading of the liquid A biomimetic surface with multi-scale structures inspired by the skin of a dog＇s tongue is proposed in this paper for the enhancement of heat and mass transfer. The spreading and flow behaviors of a gravity-driven liquid falling down the pre-wetted biomimetic surface are compared with that on the smooth sur- faces, via the combination of numerical simulations using the volume of fluid （VOF） method, and experimental measurements using high-speed imaging. On the pre-wetted smooth substrate, liquid merges with two droplets before the free surface of the liquid slowly develops into a parabolic shape. In contrast, on the biomimetic surface, liquid rapidly and uniformly spreads into a thin film which could effectively enhance mass transfer in both spanwise and streamwise directions. The characteristics and distribution of the microstructures on the proposed biomimetic surface are potentially to be used to guide the design of the surface in high efficiency heat exchangers and reactors.