地形追随垂直运动方程在南疆极端暴雨中的诊断分析

针对2021年6月15～17日发生在昆仑山脉北坡的南疆极端暴雨过程,本文综合考虑地形对暴雨发生、发展的作用后,利用地形追随坐标控制方程并采用Boussinesq近似推导建立了地形追随坐标的非静力平衡广义垂直运动方程。诊断结果表明,经向气压梯度力耦合经向散度项（项一）、垂直气压梯度力耦合纬向散度项（项二）和非绝热加热经向梯度项（项三）是激发暴雨垂直运动发展演变的三个主要强迫项。项一体现了偏北风逐渐增强,在昆仑山脉的阻挡下导致经向辐合增强,触发了垂直上升运动。经向气流辐合始终是对流活动最主要的强迫过程,其次为纬向气流辐合。在地形追随坐标形式下,经向和垂直气压梯度能够增强项一和项二。对流发展阶段,水汽辐合与非绝热加热过程增强了非绝热加热经向梯度,促进了垂直上升运动发展。在地形的影响下,对流层中高层西风过山气流波动特征明显。重力波活动导致的高层辐散进一步促进了山脉迎风坡对流活动。经向和纬向气流辐合、非绝热加热过程以及重力波活动等多个因素共同造成了此次南疆极端暴雨。     

Generation mechanisms of convectively induced internal gravity waves in a three-dimensional framework

The generation mechanisms of convective gravity waves in the stratosphere are investigated in a three-dimensional framework by conducting numerical simulations of four ideal storms under different environmental conditions: one un-sheared and three constant low-level sheared basic-state winds with the depth of the shear layer of 6 km and the surface wind speeds (U_s) of 8, 18, and 28 m s^?1, using the Advanced Regional Prediction System (ARPS) model. The storms simulated under the un-sheared (U_s = 0 m s^?1), weakly sheared (U_s = 8 and 18ms^?1), and strongly sheared (U_s = 28ms^?1) basicstate winds are classified into single-cell, multicell, and supercell storms, respectively. For each storm, the wave perturbations in a control simulation, including nonlinearity and microphysical processes, are compared with those in quasi-linear dry simulations forced by diabatic forcing and nonlinear forcing that are obtained from the control simulation. The gravity waves generated by the two forcing terms in the quasi-linear dry simulations are out of phase with each other for all of the storms. The gravity waves in the control simulation are represented by a linear sum of the wave perturbations generated by the nonlinear forcing and diabatic forcing. This result is consistent with the results of previous studies in a two-dimensional framework. This implies that both forcing mechanisms are important for generating the convective gravity waves in the three-dimensional framework as well. The characteristics of the three-dimensional gravity waves in the stratosphere were determined by the spectral combination of the forcing terms and the wave-filtering and resonance factor that is determined from the basic-state wind and stability as well as the vertical structure of the forcing.     

NUMERICAL STUDY OF TROPICS-EXTRATROPICS INTERACTION

A nonlinear steady-state baroclinic primitive-equation numerical model of atmospheric forced stationarywaves is used to investigate the tropics-extratropics interactions.Newtonian cooling,Rayleigh friction andbiharmonic horizontal diffusion are included in the model.The Eliassen-Palm (EP) cross-section and three-dimensional wave activity flux,which was derived by Plumb (1985) for linear quasi-geostrophic stationarywaves on a zonal flow,are used as diagnostics for the vertical and horizontal propagation of the waves.Results of the numerical experiments and diagnostics analyses suggest that the extratropical influenceon the tropical large-scale motion is important.The mid-latitude orographic forcing,especially of the Qing-hai-Xizang Plateau,and the extratropical thermal forcing make substantial contribution to the main-tenance of the cyclonic circulation over the eastern tropical and subtropical Pacific as well as the inversecirculation over the western Pacific in the upper troposphere.In addition,the longitudinal variation ofdiabatic heating in tropics has a significant influence on the wintertime stationary waves at higher latitudes.     

EFFECTS OF THREE-DIMENSIONAL STRUCTURE OF HEATING FIELD ON THE SUMMER MONSOON CIRCULATION IN ASIA

In this paper,a primitive equation linear wave model is used to examine the effects of three-dimen-sional structure of heating field on the behavior of stationary planetary waves in summer and to comparethe roles of different heating functions for the formation and maintenance of summer monsoon circulationin Asia.It is shown that the aloft heating connected with the latent heating,especially the deep condensationheating associated with the cumulus convection in low latitudes,plays a crucial part in the Asian summer mon-soon and the structures of planetary wave responses are quite sensitive to the vertical distribution of heating.     

加热场的三维结构对亚洲夏季风环流的影响

本文利用原始方程线性波模式考察了加热场的三维结构对夏季定常行星波特性的影响;比较了不同加热方式对亚洲夏季风坏流的形成及维持所起的作用。指出与低纬深厚积云对流相联的凝结加热对亚洲夏季风环流所起的重要作用和大气定常行星波响应对加热场的垂直结构的敏感性。     

青藏高原上空一次重力波过程的识别与天气影响分析

应用再分析资料、多套卫星反演资料和WRF中尺度数值模拟资料,识别了2005年1月10日青藏高原上空一次重力波过程,以及重力波对青藏高原西部降雪的影响。结果表明,此次重力波位于急流出口区的左方,以西南-东北走向覆盖青藏高原大部分地区。大尺度的冷暖平流相间分布和不断增强的非平衡流为重力波的形成提供了有利背景场。小波交叉谱分析显示垂直涡度与水平散度在对流层中层满足重力波的极化性质,在青藏高原西部的上升支对应有降雪过程发生。WRF可以较好地再现这一过程,并且能够模拟出再分析资料中无法分辨的中尺度重力波。数值模拟表明,青藏高原近地面强烈非绝热加热使得低层大气静力不稳定,在近地面暖区触发对流后引起高层凝结释放潜热,低层融化冷却,有利于激发重力波,并在其上升支产生固态凝结物,随后到来的冷气团提供了有利的水汽输送条件,大范围的弱抬升运动取代了原间隔进入降雪区的强对流上升支,使得固态凝结物得以落至地面,最终在青藏高原西部形成本次降雪过程。      

对流和加热对重力惯性波的激发

用线性模型讨论了对流和加热对重力惯性波的激发，分别讨论了初始垂直速度扰动和初始位温扰动及大气内部加热在静态层结大气中激发的重力惯性波，及重力惯性波过程引起的大气温压场的变化。得到的结果可以帮助理解中小尺度系统的发生发展，对流过程与环境大气的相互作用。     

On the Forced Tangentially-Averaged Radial- Vertical Circulation within Vortices Part Ⅰ: Concepts and Equations

将Eliassen建立在平面等压柱坐标系中的径向环流强迫理论（用于研究在摩擦力和非绝热加热过程影响下的静止对称涡旋），推广应用到研究移动非对称气旋或反气旋的径向环流，导出了考虑地球曲面影响的准拉格朗日等压柱坐标系的切向平均径向环流诊断方程，并根据Eliassen的解析解所揭示的涡旋径向环流在涡旋演变中的作用，定 性地讨论了各种热力和动力的作用，这些热力和动力因子除了磨擦力和非绝热加热外，还有平均和涡动形式的惯性力，角动量平流（相当涡度平流），角动量的垂直对流，温度平流，温度的垂直对流（相当绝热加热）等。     

七月中、低纬地区定常波动和加热场的模拟特征

本文利用P-σ混合坐标原始分程球带模式的最新版本,对七月中、低纬地区的定常波动及非绝热加热场进行了数值模拟。结果表明,模式成功地模拟出了北半球夏季对流层中波数为2的定常波动。高层波峰出现在大陆,波谷出现在海洋上,低层则相反。南半球的副热带高压带也模拟出来了。降水量的模拟也是成功的,特别是位于ITCZ中的积云对流性降水。加热场的模拟结果指出,七月份的热源区除了主要分布在北半球的几个主要大陆上,还分布在热带海洋上ITCZ所在区;其余的广大洋面则显示出冷源的性质。其中热带海洋的热源以潜热加热为主(主要分布于大气的中高层),大陆上的热源有的以感热为主(主要分布于大气的低层),有的仍以潜热加热贡献较大。海洋的冷源是由长波辐射冷却造成的。      

非绝热加热对赤道地区平均纬向环流的作用——非线性响应

本文设计了一个两层非线性原始方程模式,做低谱展开,求出非线性方程组的解;讨论了在外参数变化情况下解及其相应环流的演变;并与线性响应作了对比。此外,还讨论了定常解的稳定性。 主要结论是:(1)非绝热加热各分量在非线性响应中能强迫出更为接近实际的赤道地区平均纬圈环流圈。(2)在非线性响应中,潜热加热对纬圈环流的作用是最主要的。随着外参数——湿度的变化,解出现突变现象,其对应的赤道地区平均纬圈环流从一个定常态变到另一个定常态;其中对流潜热的作用最为明显,感热加热的作用是次要的。(3)在非线性响应和线性响应中,辐射加热对环流的作用不同;潜热加热对环流的作用相似,但在前者中它要强得多。      

准平衡和非平衡流对台风百合（2001）内中尺度深厚湿对流的影响

利用台风百合(2001)的高分辨率模式资料, 应用PV－ω反演方法, 在分析台风准平衡和非平衡垂直环流基本特征的基础上, 诊断研究了热力和动力强迫对台风深厚湿对流结构的影响, 结果指出: 准平衡流能够描述台风中具有较长生命史过程的中尺度对流系统的环流结构, 中层大振幅垂直运动主要由准平衡ω方程中凝结潜热释放的热力强迫所决定; 台风低层由动力辐合强迫产生的弱对流, 对眼墙区深厚湿对流的形成起到触发作用; 而高层动力强迫产生的下沉运动则削弱了凝结潜热项的影响, 抑制了垂直运动向高层伸展。非平衡垂直环流结构上呈现的短波振荡和快时间尺度调整的时空分布特征表明, 它是与重力快波频散过程相联系的非定常环流。分析台风中深厚湿对流形成的物理模型可知, 准平衡动力强迫引起的低层弱对流达到一定振幅, 则会引起中层水汽相变引起的凝结潜热反馈, 使得准平衡和非平衡流叠加形成了眼墙区上升运动的大值中心, 加上非平衡垂直环流对动量和热量起到的补偿和调整作用, 构成了台风内中尺度深厚湿对流的组织化过程。     

西北太平洋温带气旋爆发性发展的热力-动力学分析

利用天气、位涡分析和导出的Lagrangian型广义Z－O发展方程的诊断分析,考查了两个西北太平洋温带气旋爆发件发展的主要强迫机制和热力一动力空;司结构。结果表明,热力强迫对爆发性气旋发展起主要控制作用,当反映大气斜乐性的Laplacian温度平流、积云对流和湍流加热为主的热力强迫共同作用使地转相对涡度急剧增长时,气旋便出现了爆发性发展,其中积二尺度的对流加热贡献更大。Laplacian绝热冷却、大气向海洋的感热输送和摩擦效应起阻滞发展的作用,也是控制气旋衰亡的主要过程。爆发性发展启动同子因例而异,涡度平流、Laplacian温度平流和Laplacian大尺度加热均可成为主要启动因子。垂直积分平均分布和垂直结构考查进一步佐证了诊断分析的结果,并揭示了气旋爆发性发展过程中一些重要的热力-动力学分布特征。     

A DIAGNOSTIC STUDY OF AN EXPLOSIVELY DEEPENING OCEANIC CYCLONE OVER THE NORTHWEST PACIFIC

The vertical motions and secondary circulation of an explosively deepening oceanic cyclone,which oc-curred over the Northwest Pacific Ocean and was in conjunction with 200 hPa-level jet stream and hascentral pressure falls of 33.9 hPa/24h,have been computed from seven-level nonlinear balance model and Saw-yer-Eliassen-Shapiro equation for the transverse ageostrophic circulation.The vertical motions are partitionedinto contributions from large-scale latent heat release,effect of cumulus heating,thermal advection,differen-tial vorticity advection,etc.,while the secondary circulation stream function is partitioned into contributionsfrom geostrophic deformation,transfer of momentum and heat in the area of cumulus and diabatic heating.The principal results are the following.Large-scale latent heat release is very crucial to the explosive de-velopment of cyclones.If there is enough transfer of moisture,the positive feedback process between ascentof air and large-scale heating would work.The cumulus heating and the transfer of momentum and heatin the area of cumulus play an important role during the explosively deepening stage.Thermal advection isthe initial triggering condition for large-scale heating and the conditional instability for the convection ofcumulus.     

A new model of tropical waves incorporating momentum mixing by cumulus convection

A comparison is made between the magnitudes of observed large-scale weather waves over the tropical Pacific and the magnitudes of the corresponding waves, predicted by wave-CISK theories, which are driven by the observed amount of latent heating (i.e., precipitation). The theoretical wave fields of meridional velocity, vorticity, and temperature rate are shown to exceed the observed quantities by an order of magnitude. An attempt is made to simulate the observed balance between the diabatic heating and adiabatic cooling within the context of the inviscid theories. For a broad class of heating profiles, geometries and basic states, it is found that this compensation without temperature change cannot be satisfactorily modelled, regardless of the vertical shape of the heating, when the vertical wavelength of the disturbance exceeds about 6 km.Scale analysis demonstrates that an important dynamical term has been neglected in the inviscid models, viz., the vertical transport of horizontal momentum by cumulus clouds. When this process is included in the wave model, velocities, relative vorticity, and the time rate of temperature change are all comparable to the observed values. The general behavior of a system where both forcing and cumulus “friction” are proportional to each other has not been previously examined. We find the behavior of such a system to have several novel features. For example, we find that for a wide range of precipitation amplitudes (from 1/4 to 4 times the precipitation amplitudes of waves in the western Pacific) we get essentially constant amplitudes for wind. The implications of this and other features for various aspects of tropical wave modelling are discussed.     

对流和加热对重力惯性波的激发

用线性模型讨论了对流和加热对重力惯性波的激发，分别讨论了初始垂直速度扰动和初始位温扰动及大气内部加热在静态层结大气中激发的重力惯性波，及重力惯性波过程引起的大气温压场的变化。得到的结果可以帮助理解中小尺度系统的发生发展、对流过程与环境大气的相互作用。     

青藏高原东北边坡复杂地形重力波的数值模拟

基于2007年7月青海祁连站的野外加密探空资料,结合高分辨率的三维边界层模式,模拟研究了青藏高原东北边坡复杂地形条件下,边界层对流引起的干动力过程对该地区地形重力波产生及传播的影响机理。结果表明:在不同的背景场强迫下,高原东北边坡复杂地形上空对流和重力波的空间结构存在较大差异。当背景风向与山体垂直时,随着风速增加,山脊背风坡混合层顶附近大气不稳定能量加强,激发了下游区域较强的重力波信号,此时对流线组织性增强、重力波波列较长,高水汽含量的空气被波峰传输到较高的高度,为对流云发展提供了有利条件;当背景风向与山脊走向平行时,山顶上空对流发展旺盛,山脊背风坡混合层顶大气状态较稳定,激发的地形重力波信号较弱且波列较短,整个混合层顶附近水汽较少,对流云形成条件减弱;当背景大气浮力频率减小时,整个区域上空对流发展更加旺盛但组织性减弱,背风坡下游重力波向上传输的距离减小,信号不显著,混合层顶附近水汽分布均匀且变化幅度较小,有利于层状云发展。     

NUMERICAL EXPERIMENTS OF THE INFLUENCE OF DIABATIC HEATING ON TROPICAL CYCLONE ASYMMETRIC STRUCTURE

Using the barotropic volticity equation that contains forcing from diabatic heating with appropriate parameterization. a number of numerical experiments are conducted for the tropical cyclone that is initially symmetric The result shows that the diabatic heating has important effects on the asymmetric structure in addition to the roll of the β term and nonlinear advection term in its formation. It again confirms the conclusion that the diabatic heating is a possible mechanism responsible for such structures in the tropical cyclone.     

非绝热加热对热带气旋非对称结构影响的数值试验

利用含非绝热加热强迫的正压涡度方程。将非绝热加热作适当的参数化处理。对初始对称 热带气旋作了一系列数值试验,结果表明：不仅β项、平流项在热带气旋非对称结构的形成中有重要作用,而且非绝热加热对热带气旋的非对称结构亦有重要影响,从而验证了非绝热加热是热带气旋非对称结构形成的一种可能机制的结论。     

等熵面和湿等熵面倾斜发展的诊断分析

利用等压坐标系中的热力学方程和水汽方程推导出可以诊断分析等熵面（等位温面）和湿等熵面（等相当位温面） 倾斜变化的倾角方程。等熵面倾角的局地变化由倾角平流输送项、风速切变项和非绝热加热项共同决定,而影响湿等熵面倾角局地变化的强迫项除倾角平流输送项、风速切变项和非绝热加热项之外,还包括垂直热量通量切变项。NCEP/NCAR实时分析资料的分析结果表明,大气斜压性、相对垂直涡度与等熵面和湿等熵面的倾角密切相关,它们的正高值区互相重叠;垂直风速切变项,特别是垂直速度的经向切变项是影响等熵面倾斜发展的主要强迫项,而纬向和经向风速的垂直切变项对湿等熵面倾角演变的贡献最大。     

Numerical simulations of a large-amplitude mesoscale gravity wave event

Summary Numerical simulations with the NCAR/PSU Mesoscale Model 5 (MM5) were performed to study a large-amplitude gravity wave event that occurred on 4 January 1994 along the East Coast of the United States. Results from the MM5 control simulation using a 12-km mesh resolution compared well with the synoptic and mesoscale observational analysis. The simulated gravity waves displayed timing, location, wavelength, and propagation speed similar to those observed in a synoptic-scale environment described by the Uccellini and Koch (1987) conceptual model. Additional features existing upstream of the wave generation region not contained within their conceptual model were a warm occlusion and tropopause fold prior to and during the gravity wave generation. Wave ducting criteria were nearly satisfied along the path of the gravity waves.Several sensitivity tests were performed. In a simulation in which the Appalachian Mountains were removed, the model still produced similar cyclone development and mesoscale gravity waves. Thus topography was not directly responsible for the gravity wave genesis. Also, three different fake dry sensitivity tests were performed with the latent heating related to changes of water substance turned off in the model at different stages of the simulation. The results from these simulations suggest that diabatic heating played an important role in both jet/cyclone development and in gravity wave amplification and maintenance, though not wave generation. The simulation with grid resolution increased to 4km, which included fully explicit microphysics produced gravity wave characteristics similar to those in the control simulation, though the higher resolution resolved much shorter waves (though unverifiable) closely associated with convection. This 4-km sensitivity experiment with no cumulus parameterization also confirmed that the dominant gravity wave was not an artifact of the particular cumulus parameterization scheme used for the control simulation. The reliability of the simulated gravity waves is further confirmed with another sensitivity experiment initialized 20 hours before the observed wave generation in which qualitatively-similar gravity waves were produced.Received August 28, 2000; revised May 2002; accepted October 8, 2002 Published online: April 10, 2003