20世纪后30年中国西北西部降水年代际变化机理分析

在全球气候变暖背景下1980年代中期中国西北西部气候发生了年代际突变,降水明显增加且主要是极端降水的贡献. 本文用欧洲中期预报中心再分析资料ERA-40计算了瞬变涡动、环流、水汽输送及其散度等的年代际变化并进行了分解分析. 结果表明, 1987年后大气环流年代际变化形成"东高西低"环流背景场,西风带向该区的水汽输送增加, 水汽辐合增强,其中主要是定常波水汽输送的贡献, 其结果是造成该区及周边空气水汽含量上升, 有利于降水或极端降水的增加. 夏季该区瞬变涡动增强且造成水汽辐合, 增加了降水天气出现的频率; 冬季瞬变涡动减弱, 天气过程减少, 说明降雪增加的原因应该是空气水汽含量增加, 导致降雪强度增加. 因此该区降水的增加即有中高纬度大气变暖变湿的贡献,也有瞬变涡动的动力作用. 未来西北西部降水的趋势主要取决于瞬变涡动与大气水汽含量变化的竞争．     

台风“彩虹”(2015)高分辨率数值模拟及涡旋Rossby波特征分析

采用中尺度数值预报模式对2015年22号台风"彩虹"进行高分辨率的数值模拟,成功地模拟出台风"彩虹"的移动路径、强度和降水分布,尤其是在台风登陆前后,模拟结果与实况比较接近.以此为基础,利用模式输出资料,分析台风的动力、热力精细结构和台风雨带的宏观特征.眼墙处具有低层径向入流、高层径向出流的动力配置.在眼墙附近,同时存在切向风速高值区、垂直上升区、正温度距平区,并随高度向外侧倾斜,雷达回波较强,对流系统比较深厚.次级雨带、主雨带和远距离雨带的雷达回波相对较弱,对流系统垂直厚度略小.再利用尺度分离方法,得到涡旋Rossby波的扰动场资料,进一步分析涡旋Rossby波的特征.1波、2波同时朝切向和径向传播,1波的振幅明显大于2波.研究结果表明,1波、2波正涡度扰动对应强雷达回波,存在强对流活动.降水区上空的垂直涡度扰动呈上正下负的配置,与水平散度扰动的垂直配置相似时,会加强低层辐合和高层辐散,有很强的垂直上升运动,有利于对流系统发展,降水增强.1波、2波扰动的动力配置影响了对流系统的发展,并对降水强度和分布有一定的诊断作用.     

台风莫拉克(2009)暴雨过程中位势切变形变波作用密度诊断分析和预报应用

在水平风场切变形变的基础上引入物理量——位势切变形变, 把水平风场的垂直分量和切变形变与广义位温的空间梯度结合起来. 该物理量的二阶扰动被定义为波作用密度, 在局地直角坐标系中推导了能够描述中尺度扰动系统发展演变的波作用方程. 对2009年登陆台风莫拉克引发的暴雨过程进行诊断分析, 结果表明, 台风中心区切变形变向涡度的转化显著, 该转化通过纬向风的经向梯度实现. 纬向风速的经向梯度与广义位温垂直梯度的耦合引起位涡和位势切变形变之间的转化, 以至于位势切变形变和位涡的异常值区分别位于台风环流的外侧和内侧. 波作用密度因能够描述水平扰动风场的垂直切变和切变形变以及凝 结潜热函数扰动梯度而与观测降水联系紧密. 相关统计分析表明, 2009年夏季波作用密度与6 h观测降水存在明显滞后相关性, 对未来6 h降水有一定的指示意义. 另外, 波作用密度通量散度和扰动非地转风位涡是影响波作用密度局地变化的主要物理因素. 基于波作用密度与观测降水的良好相关性, 建立了波作用密度暴雨预报方程. 2009年登陆台风"苏迪罗", "天鹅", "莫拉菲"和"巨爵"的暴雨预报个例分析和长时间序列的ETS评分计算表明, 波作用密度对台风暴雨具有较好的预报效果, 其预报降水能力略优于美国全球预报系统(GFS)的直接降水预报. 关键词： 位势切变形变 波作用密度 波作用通量散度 台风暴雨     

强降水过程中垂直螺旋度和散度通量及其拓展形式的诊断分析

在垂直螺旋度的基础上,定义了散度通量,水汽垂直螺旋度和水汽散度通量三个宏观物理量.针对两次强降水过程,利用NCEP/NCAR实时分析资料对这些物理量进行诊断分析,结果表明,这些物理量能够比较准确地综合表征强降水系统所共有的典型动力场垂直结构,进而与降水系统的发展演变密切相关.这些物理量垂直积分的异常值区与观测的6 h累积地面降水具有良好的对应关系,表明它们对强降水的落区和降水系统的发展移动具有良好的指示预测意义.NCEP-GFS每日四次6 h预报场资料的计算表明,垂直螺旋度和散度通量及其拓展形式（水汽垂直 关键词： 垂直螺旋度 散度通量 水汽垂直螺旋度 水汽散度通量     

大气水汽探测地基差分吸收激光雷达系统设计与性能仿真

为持续获得对流层低层高精度、高时空分辨率的水汽浓度分布数据,提出了一套改进的大气水汽探测地基差分吸收激光雷达系统方案.详细描述了系统主要组成部分,对主要误差进行了分析与估计,并提出了一种差分吸收截面实时测量装置用于补偿发射激光器带来的测量误差.针对该系统,并结合上海地区不同季节的水汽浓度状况,对935 nm水汽吸收带中四个水汽吸收峰的差分光学厚度、雪崩二极管的倍增系数M与回波信噪比的关系、水汽浓度随机测量误差等进行了详细的仿真与分析.仿真结果表明,根据不同的季节和天气状况,可以选择不同的吸收峰以达到最佳探测效果;在300—5000 m高度范围内,最大可以达到300 m的垂直分辨率与5 min的时间分辨率,水汽浓度随机测量误差不超过18%.     

对气象常用坐标系中位涡形式的探讨

气象常用垂直坐标系中的位涡方程及位涡形式是位涡理论及位涡诊断技术的基础.本文依据坐标转换的观点,分别用两种不同的方法推导出等压坐标和等熵坐标中的位涡方程及相应的位涡表达式.一是从三维矢量运动方程出发,由三维涡度方程、连续方程和热力学方程推导位涡方程;二是直接从等压坐标和等熵坐标中的标量运动方程组出发推导位涡方程.结果表明,用两种方法所得到的等压坐标中的位涡方程和位涡表达式形式有所不同,而等熵坐标中用两种方法所得到的位涡方程和位涡形式相同.对垂直坐标系的物理本质分析表明,采用第一种方法时尽管矢量运动方程中的 关键词： 位涡 坐标转换 等压坐标 等熵坐标     

强对流降水过程动力因子分析和预报研究

利用对流涡度矢量垂直分量,湿热力平流参数和波作用密度等动力因子对2009年7月8日发生在我国华北南部地区的强对流降水过程进行诊断分析,结果表明,这些动力因子能够综合描述降水系统水平风场垂直切变,涡度扰动以及位温平流和广义位温(及其扰动)的经向梯度等动力学和热力学特征,在降水区对流层中低层表现为强信号,在非降水区表现为弱信号.利用美国NCEP/NCAR 0.5度GFS的6 h,12 h,18 h和24 h预报资料计算分析2009年6月2日至10月1日动力因子对观测降水的指示预测作用,结果表明,动力因子对观测 关键词： 对流涡度矢量垂直分量 湿热力平流参数 波作用密度     

平流涡度方程及其在2006年Bilis台风分析中的应用

推导得到气压坐标中的动量叉乘形式的垂直涡度方程,这个动量叉乘形式的涡度方程包含了水平风的平流旋转效应,可称为平流涡度方程.由于水平风场的平流作用可由等压面天气图直观分析得到,因此平流涡度方程可方便用于实际天气分析.对2006年的Bilis台风移动过程中由经典涡度方程和平流涡度方程计算得到的垂直涡度倾向进行对比分析发现,二者计算得到的垂直涡度倾向变化的分布形式接近,但平流涡度方程计算得到的倾向的数值明显大于经典涡度方程的数值,正负涡度倾向区也更集中.对Bilis移动过程中的垂直涡度方程和平流涡度方程中各项的计算分析表明,水平风场的平流旋转作用是Bilis发展移动过程中垂直涡度变化的一个主要因素,是造成垂直涡度增强并发展的主要原因.因此,当水平风场平流旋转效应较强时,平流作用对垂直涡度倾向变化起主导作用,可直接用平流项来近似分析Bilis台风的涡度变化.而平流涡度方程中地转涡度和散度项的变化趋势与Bilis台风的移动路径有较好的一致性,这一项对台风的移动路径预报有更好的指示意义.     

功率高压LED模组在不同应力下的老化实验

对LED进行应力加速老化实验及分析可以对器件可靠性做出最快、最有效的评估。本文将相同的6V高压功率白光LED分为两组,一组施加180 m A电流应力和85℃温度应力进行高温老化实验,另一组施加180 m A电流应力、85℃高温和85%相对湿度进行高温高湿老化实验。在老化过程中,测试了LED光电参数随老化时间的变化规律。实验结果表明:高温大电流应力下的样品的光退化幅度为0.9%~3.4%,高温高湿大电流应力下的样品的光退化幅度为25.4%~27.8%,高温高湿下样品的老化程度远高于高温老化下样品的老化程度,湿度对LED可靠性有显著的影响。退化的原因包括荧光粉的退化和器件内部欧姆接触退化等。     

东亚地区大气环流的季节划分及其时空变化特征

利用NCEP-DOE Reanalysis 2 1979-2009年位势高度场、温度场、湿度场和风场逐日再分析资料,采用考虑面积权重的区域多要素最优分割法,对东亚地区大气环流的季节进行划分,并分析了四季起始时间的时空变化特征.研究结果表明:1)东亚地区春季最早始于中高纬地区的平流层和副热带的对流层中下层;夏季最早始于中高纬的平流层和副热带、中纬度地区的对流层中上层;秋、冬季开始最早的地区集中在东亚地区东部和东北部的对流层中低层,以及中高纬的平流层. 2)季节变化与环流形势密切相关,且对流层各个层次的夏季和冬季起始时间的分布均有较好的垂直一致性,平流层与对流层各季节起始时间分布有较大的差异性,平流层中层和下层也并不一致. 3)华北地区四季平均起始时间距平序列的逐年演变特征表明近30年该地区出现了6个四季起始时间异常偏早的年份,与El Niño活跃年份相一致,反映了海温等外强迫对大气环流季节变化的影响. 关键词： 季节划分 东亚地区 区域多要素最优分割法     

Diagnosis of dynamic process over rainband of landfall typhoon

This paper introduces a new physical parameter - thermodynamic shear advection parameter combining the perturbation vertical component of convective vorticity vector with the coupling of horizontal divergence perturbation and vertical gradient of general potential temperature perturbation.For a heavy-rainfall event resulting from the landfall typhoon ’Wipha’,the parameter is calculated by using National Centres for Enviromental Prediction/National Centre for Atmospheric Research global final analysis data.The results showed that the parameter corresponds to the observed 6 h accumulative rainband since it is capable of catching hold of the dynamic and thermodynamic disturbance in the lower troposphere over the observed rainband.Before the typhoon landed,the advection of the parameter by basic-state flow and the coupling of general potential temperature perturbation with curl of Coriolis force perturbation are the primary dynamic processes which are responsible for the local change of the parameter.After the typhoon landed,the disturbance is mainly driven by the combination of five primary dynamic processes.The advection of the parameter by basic-state flow was weakened after the typhoon landed.     

斜压二层模式框架下的准地转理论及其应用

准地转理论是短期天气预报的理论基础.针对中纬度大尺度运动得到的准地转运动方程组是准地转理论的核心.在斜压二层模式框架下,由准地转运动方程组得出的准地转位势倾向方程和准地转垂直运动方程,可以更为明确地解释高空和地面天气系统的移动和发展.结果显示:500 hPa高空槽的移动取决于本层的涡度平流,500 hPa高空槽的发展取决于本层的涡度平流和250与750h Pa层的微差温度平流;地面气旋系统的移动和发展取决于500hPa的正温度平流,250与750 hPa层的微差涡度平流.由实际天气过程对上述应用进行的分析表明,在斜压二层模式框架下得到的准地转位势倾向方程及准地转垂直运动方程,可以更好地确定中纬度天气尺度斜压发展系统的特征,并有助于对天气系统发展客观规律的了解和对数值预报产品内含的物理依据的认识.     

A phase analysis of vorticity vectors associated with tropical convection

Three new vorticity vectors have been proposed by Gao et al to study the two-dimensional tropical convection. In the present paper, phase relations between surface rain rate and the vorticity vectors are analysed with the calculations of lag correlation coefficients based on hourly zonally-averaged mass-integrated cloud-resolving simulation data. The cloud-resolving model is integrated with the vertical velocity, zonal wind, horizontal thermal and moisture advections, and sea surface temperature observed and derived from tropical ocean global atmosphere - coupled ocean atmosphere response experiment （TOGA-COARE） for 10 days. Maximum local increase of the vertical component of the convective vorticity vector leads maximum surface rain rate by 2 hours mainly due to the interaction between vorticity and zonal gradient of ice heating. While maximum local increase of the vertical component of the moist vorticity vector leads maxfinum surface rain rate by 2 hours mainly because of the interaction between zonal specific humidity gradient and zonal buoyancy gradient. And the maximum local decrease of the zonal component of the dynamic vorticity vector leads maximum surface rain rate by 2 hours mainly due to the interactions between vorticity and vertical pressure gradient as well as vorticity and buoyancy.     

A pseudoenergy wave-activity relation for ageostrophic and non-hydrostatic moist atmosphere

By employing the energy-Casimir method, a three-dimensional virtual pseudoenergy wave-activity relation for a moist atmosphere is derived from a complete system of nonhydrostatic equations in Cartesian coordinates. Since this system of equations includes the effects of water substance, mass forcing, diabatic heating, and dissipations, the derived wave-activity relation generalizes the previous result for a dry atmosphere. The Casimir function used in the derivation is a monotonous function of virtual potential vorticity and virtual potential temperature. A virtual energy equation is employed(in place of the previous zonal momentum equation) in the derivation, and the basic state is stationary but can be three-dimensional or, at least, not necessarily zonally symmetric. The derived wave-activity relation is further used for the diagnosis of the evolution and propagation of meso-scale weather systems leading to heavy rainfall. Our diagnosis of two real cases of heavy precipitation shows that positive anomalies of the virtual pseudoenergy wave-activity density correspond well with the strong precipitation and are capable of indicating the movement of the precipitation region. This is largely due to the cyclonic vorticity perturbation and the vertically increasing virtual potential temperature over the precipitation region.     

Water Vapour Potential Vorticity and Its Applications in Tropical Cyclones

A new tracer is presented to diagnose tropical cyclones （TCs） and their correspondent rainfall. It is defined as water vapour potential vorticity （WPV） by replacing potential temperature with specific humidity in the potential vorticity （PV）. The WPV is compared with PV and moist potential vorticity （MPV） in diagnosing three tropical cyclone cases occurred in North-West Pacific during 10 July to 21 July 2005 （Haitang）, 30 July to 9 August 2005 （Matsa） and 25 September to 3 October 2005 （Longwang） separately. The results show that in tracing the track of TCs, WPV is not nicer than PV but better than MPV. While diagnosing TCs＇ onshore rainfall, WPV is better than MPV in all the three cases. Moreover, the advection of WPV is a good indication of TC rainfall after its landing.     

Vertically nested nonhydrostatic model for multiscale resolution of flows in the upper troposphere and lower stratosphere

Vertical nesting with refined gridding in coupled mesoscale weather research and forecasting (WRF)/microscale models are presented with a particular emphasis on improved vertical resolution in the upper troposphere and lower stratosphere (UTLS). The finest mesoscale nest is coupled with a sequence of microscale nests with finer resolution in both the horizontal and the vertical. The fully three-dimensional, compressible nonhydrostatic Navier–Stokes equations are solved using a time-split method with a refined grid in the vertical, and improved resolution in the UTLS region. For nesting, both lateral and vertical boundary conditions are treated via implicit relaxation in buffer zones where all fields are relaxed to those obtained from the finest mesoscale nest. Computational results are presented demonstrating the ability of microscale nests to resolve multiscale physics of strongly nonlinear interactions and laminated structures observed in the Terrain-induced rotor experiment (T-REX) campaign of field measurements. Very high resolution real case nested simulations are conducted. The microscale nests fully resolve localized shear layers and sharp gradients of vertical velocity and potential temperature near the tropopause and in the lower stratosphere.     

Temperature dependence of the hole concentration in the model of a hole metal with negative-<Emphasis Type="Italic">U</Emphasis> centers

The temperature dependence of the hole concentration is studied within the model of a hole metal with negative-U centers. Different versions of the model with a simplified representation of allowed bands and a quadratic valence-band dispersion law are considered. It is found that the temperature dependence of the hole concentration can acquire different forms, and the regions of the model parameters corresponding to these forms are determined. The results obtained are used in the discussion of the relation between normal to superconducting properties of high-temperature superconductors.     

Morphological evolution of thermal plumes in turbulent Rayleigh-Bénard convection

An experimental study of the morphological evolution of thermal plumes in turbulent thermal convection is presented. Individual sheetlike plumes are extracted and their area, circumference, and "heat content" are found to all exhibit log-normal distributions. As the sheetlike plumes move across the plate they collide and convolute into spiraling swirls. These swirls then spiral away from the plates to become mushroomlike plumes which are accompanied by strong vertical vorticity. The measured profiles of plume numbers and of vertical vorticity quantify the morphological transition of sheetlike plumes to mushroomlike ones and the mixing and merging or clustering of mushroomlike plumes. The fluctuating vorticity is found to have the same exponential distribution and scaling behavior as the fluctuating temperature.