Simulation of a torrential rainstorm in Xinjiang and gravity wave analysis

We used a weather research and forecasting model to simulate a torrential rainstorm that occurred in Xinjiang, China during June 16–17, 2016. The model successfully simulated the rainfall area, precipitation intensity, and changes in precipitation. We identified a clear wave signal using the two-dimensional fast Fourier transform method; the waves propagated westwards, with wavelengths of 45–20 km, periods of 50–120 min, and phase velocities mainly concentrated in the-25 m/s to-10 m/s range. The results of wavelet cross-spectral analysis further confirmed that the waves were gravity waves, peaking at 11:00 UTC, June 17, 2016. The gravity wave signal was identified along 79.17–79.93°E, 81.35–81.45°E and 81.5–81.83°E. The gravity waves detected along 81.5–81.83°E corresponded well with precipitation that accumulated in 1 h, indicating that gravity waves could be considered a rainstorm precursor in future precipitation forecasts.     

基于压电曲壳单元的结构振动最优控制

曲壳结构已广泛应用于航空航天、航海等领域,结构微小的振动会极大地影响部件性能,抑制曲壳结构的振动就很必要。提出了压电曲壳结构的振动最优控制模型,利用空间曲壳单元理论及多点约束方程实现曲壳基结构壳元和压电壳元的耦合,推导了压电曲壳结构动力学有限元方程,并结合线性二次型最优控制理论,实现了压电作动器对曲壳结构的振动最优控制。数值算例表明,对曲壳结构进行动力分析和振动控制时,在达到同样精度及控制效果的情况下,与平壳相比,曲壳单元及作动器所需数目要少得多。     

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     

Effect of a New Eliassen-Palm Flux on Barotropic Basic Flow

We investigate the interaction of eddy and barotropic basic flow in virtue of a new Eliassen-Palm (EP) flux, without introducing residual meridional circulation, by using a multi-scale method. The results show that the evolution of the zonally symmetric barotropic basic flow is completely dominated by the new zonal-averaged EP flux divergence.     

The theory of interaction between wave and basic flow

This paper investigates the interaction between transient wave and non-stationary and non-conservative basic flow. An interaction equation is derived from the zonally symmetric and non-hydrostatic primitive equations in Cartesian coordinates by using the Momentum-Casimir method. In the derivation, it is assumed that the transient disturbances satisfy the linear perturbation equations and the basic states are non-conservative and slowly vary in time and space. The diabatic heating composed of basic-state heating and perturbation heating is also introduced. Since the theory of wave-flow interaction is constructed in non-hydrostatic and ageostrophic dynamical framework, it is applicable to diagnosing the interaction between the meso-scale convective system in front and the background flow.
It follows from the local interaction equation that the local tendency of pseudomomentum wave-activity density depends on the combination of the perturbation flux divergence second-order in disturbance amplitude, the local change of basic-state pseudomomentum density, the basic-state flux divergence and the forcing effect of diabatic heating. Furthermore, the tendency of pseudomomentum wave-activity density is opposite to that of basic-state pseudomomentum density. The globally integrated basic-state pseudomomentum equation and wave-activity equation reveal that the global development of basic-state pseudomomentum is only dominated by the basic-state diabatic heating while it is the forcing effect of total diabatic heating from which the global evolution of pseudomomentum wave activity results. Therefore, the interaction between the transient wave and the non-stationary and non-conservative basic flow is realized in virtue of the basic-state diabatic heating.     

Continuity and momentum equations for moist atmospheres

The moist atmosphere with occurring precipitation is considered to be a multiphase fluid composed of dry air, water vapor and hydrometeors. These compositions move with different velocities: they take a macroscopic motion with a reference velocity and a relative motion with a velocity deviated from the reference velocity. The reference velocity can be chosen as the velocities of dry air, a gas mixture and the total air mixture. The budget equations of continuity and momentum are formulated in the three reference-velocity frames. It is shown that the resulting equations are dependent on the chosen reference velocity. The diffusive flux due to compositions moving with velocities deviated from the reference velocity and the internal sources due to the phase transitions of water substances result in additional source terms in continuity and momentum equations. A continuity equation of the total mass is conserved and free of diffusive flux divergence if the reference velocity is referred to the velocity of the total air mixture. However, continuity equations in the dry-air and gasmixture frames are not conserved due to the mass diffusive flux divergence. The diffusive flux introduces additional source terms in the momentum equation. In the dry-air frame, the diffusive flux of water substances and the phase transitions of water substances contribute to the change of the total momentum. The additional sources of total momentum in the frame of a gas mixture are associated with the diffusive flux of hydrometeors, the phase transitions of hydrometeors and the gasmixture diffusive flux. In the frame of total air mixture, the contribution to the total momentum comes from the diffusive flux of all atmospheric compositions instead of the phase transitions. The continuity and momentum equations derived here are more complicated than the traditional model equations. With increasing computing power, it becomes possible to simulate atmospheric processes with these sophisticated equations. It is helpful to the improvement of precipitation forecast.     

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     

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.     

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     

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.