对称不稳定理论

本文从四个方面概述了对称不稳定理论的主要研究成果,其中包括:无粘性干大气的对称不稳定问题;粘性大气的对称不稳定问题;湿大气的对称不稳定问题;非线性对称不稳定的研究。     

实际大气中对称不稳定的存在及特征：—对称不稳定理论的应用现状分析

文章从多个方面分析了对称不稳定在实际大气中的存在和特征，总结了不对称不稳定理论在锋面降水带、雪暴、雷暴、飑线和爆发性气旋等领域中的应用现状，并且指出对称不稳定分析中的不确定性和以后的发展方向。     

暴雨中尺度系统不稳定理论的数值试验

针对已有的不稳定理论研究，提出把不稳定问题由求解特征值问题转化为求解初值问题，在考虑扰动气压和水汽作用的基础上建立一个二维线性化的非静力模式，以真实反映不稳定扰动特征。     

对称不稳定理论及其应用问题(二)非线性理论

文章对对称不稳定理论及其应用的现状进行了全面的评述。主要讨论非线性理论，这包括非线性对称不稳定的一般研究方法（能量积分法，奇异摄动法，气块质点法，分岔和突变理论，数值试验），二维定常非线性对称环流的稳定性等问题。最后讨论了线性理论和非线性理论在实际应用方面的差异。     

线性与非线性对称不稳定的数值试验

设计了一个准二维非静力数值模式，用该模式研究了对称不稳定的发展和演变特征。线性和非线性对称不稳定的数值试验结果表明。线性和非线性对称环流的演变特征及其结构有很大差异。在基本状态是对称不稳定的情况下，线性对称不稳定在其发展过程中始终维持着向冷区倾斜的对称环流；而非线性对称不稳定在其发展初期与线性情况相同，当扰动增长到一定程度时非线性平流项的作用不可忽略，原来对称的环流则被破坏。     

一次罕见的山东暴雪天气的对称不稳定分析

采用对称不稳定判据，对发生在2001年1月6－7日的一次罕见的山东暴雪天气过程进行了分析，结果表明：暴雪产生在对称不稳定大气中，低空急流促使对流层低层暖湿气流辐合上升，触发对称不稳定能量释放，产生暴雪天气。江淮气旋和暴雪区有向对称不稳定区移动的趋势。     

近四百年北半球气温变化的分析:EMD方法的应用

利用一个二维非弹性非静力的数值模式，讨论了初始扰动的尺度对于对称不稳定发展的影响。结果表明：虽然对称不稳定是β-中尺度的不稳定，但其不一定必须由β-中尺度的扰动来激发；由不同水平尺度的扰动所激发的倾斜环流有不同的特点；对称不稳定倾斜环流可能存在最小临界尺度；对称不稳定的发展存在最优扰动水平尺度，而扰动的垂直尺度对于对称不稳定的发展影响不大。     

对流对称不稳定的发展演变和环流特征

利用1999年6月一次典型梅雨锋暴雨过程和敏感性试验的数值模拟结果分析了对流对称不稳定的发展演变和环流特征.结果表明：条件对称不稳定是大气稳定状态和条件不稳定状态之间的中间纽带,大气由稳定向不稳定或者由不稳定向稳定的演变均通过条件对称不稳定来实现;对流对称不稳定环流的形成与不稳定层的配置有关,当低层为条件不稳定而高层叠加深厚的条件对称不稳定时,对流对称不稳定环流低层出现垂直上升气流,高层出现范围较广的倾斜上升气流,对称不稳定能量释放产生中尺度云带.当低层和高层出现条件不稳定,中间呈条件对称不稳定或弱稳定度层结时,从低层到高层出现较深厚的垂直上升气流,湿重力不稳定能量的释放导致了云带的形成.     

低纬大气的对称不稳定

本文从低纬大气对称扰动的控制方程组出发,导出了低纬大气对称不稳定的产生条件,并与中高纬大气的对称不稳定特征进行了比较和分析讨论。      

Ertel位涡和非线性对称不稳定性问题

本文应用Lagrange质点理论对大气中对称运动方程进行了简化,在此基础上进一步利用分岔和突变理论分析了环境地转风为非线性分布的情况下,Ertel位涡在非线性对称不稳定中的作用,并得到了一些有意义的结果。     

CISK理论中的若干问题

在本文中,对Charney与Eliassen等人所提出的CISK理论所包含的低层风速不随高度变化的假定作了分析与改进,并讨论了它对结果的影响。     

青藏高原热状况对南亚高压活动的影响

本文分析了青藏高原下垫面与高原上空热状况变化的异同及其二者与南亚高压的关系。指出青藏高原下垫面热状况与高原上空热状况年际变化的一致性及月际变化的差异——青藏高原下垫面从2月就开始大幅度增温,而高原上空5月才开始突发性增温。高原下垫面降温幅度最大的月份出现在11月,高原上空则出现在10月。分析还指出,青藏高原下垫面热状况与南亚高压南北振荡,青藏高原上空热状况与南亚高压东西振荡有密切关系。并且前期青藏高原上空热状况较高原下垫面热状况对南亚高压的预报更具有指示意义。     

SOME ASPECTS ON CISK THEORY

A great deal of work has been done to perfect the theory first proposed by Charney and Eliassen.In this paper.we reexamine the theory and find out that the observational evidence does not support their assumption that the wind velocity in the lower layet does not change with height.An improved assumption based on the observation is proposed and its influence on the results of CISK theory such as stability and catastrophic feature is discussed.     

ANALYSIS ON EFFECT OF SOUTH ASIA HIGH ON MID-SUMMER EXTREME DROUGHT AND FLOOD IN SICHUAN-CHONGQING REGION

NCEP/NCAR data are utilized to analyze an extreme flood year （1998） and an extreme dry year （2006） in the Sichuan-Chongqing region （SCR） and the results are as follows. The positive divergence of South Asia High （SAH） is stronger in the flood year; the position of the ridge line of SAH is southward compared with the annual average; Western Pacific Subtropical High （WPSH） extends westward and its ridge line is southward. In the drought year, the positive divergence of SAH is weaker, its ridge line is northward, and the position of WPSH is also northward. As shown in the dynamics, in drought （flood） years, negative （positive） vorticity advection in the upper atmosphere can cause the atmosphere to ascend （descend）, and anomalous circulation of SAH displays divergence （convergence）, and anomalous circulation of the lower atmosphere shows convergence （divergence）. Thermal structure of the atmosphere shows that there is warm （cold） temperature advection in the lower atmosphere, and the vertical distribution of diabetic heating causes SAH＇s local circulation to display convergence （divergence） and affects vertical motion of the lower atmosphere circulation eventually. To some extent, the two extreme years in the SCR is closely related to the vertical motion of atmosphere circulation and the variation of such vertical motion is caused by differences of interactions between SAH and lower atmosphere circulations.     

STUDY ON THE GENESIS OF ASYMMETRICAL DISTRIBUTION CHARACTERISTICS OF PRECIPITATION ASSOCIATED WITH THE TYPHOON HAITANG (2005) FROM THE VIEW OF ATMOSPHERIC FACTOR

The distribution of precipitation field from the typhoon Haitang (2005) during its landing on Fujian province shows obvious asymmetric feature. Based on the NCEP/NCAR FNL (Final Analysis) data, this study reveals the contributions of atmospheric factor to the asymmetrical distribution characteristics of precipitation associated with the typhoon, through the analysis of water vapor condition, vertical ascending motion condition, the calculation of the dry Q vector and its decomposition, and adiabatic heating in the air column of 1000hPa -600hPa (lower atmosphere) and 500hPa-100hPa (upper atmosphere). The results are as follows: (1) In the lower atmosphere, the humidity on both sides of typhoon path can be equivalent, while it is more wet on the right side than left in the upper atmosphere, which obviously presents asymmetric distribution characteristics. (2) Both range and intensity of the vertical motion on the right side are wider and stronger than counterparts on the left side no matter in the lower or upper atmosphere. (3) In the upper atmosphere, forcing role of atmosphere in vertical upward motion on the right side of typhoon path is the same as that on the left, while it is significantly different in the lower atmosphere, which is significantly broader in scope and stronger in the intensity, along with obvious asymmetric distribution characteristics. In addition, the further analysis of the Q vector decomposition indicates that the forcing effect of mesoscale weather systems on vertical upward motion is stronger than that of large scale weather systems in the lower atmosphere. (4) The adiabatic heating always exists on both lower and upper atmosphere, and the range and intensity of the adiabatic heating forcing showed asymmetric distribution on both lower and upper atmosphere. (5) In a summary, the upper atmosphere humidity conditions, the forcing role of lower atmosphere in vertical upward motion, especially, to mesoscale weather system, and adiabatic heating in the lower atmosphere, all show similar asymmetric distribution characteristics to that of precipitation field from the typhoon Haitang (2005), that is to say, the atmospheric factors as mentioned above are all contributed to genesis of the asymmetric distribution characteristics of precipitation.     

THE RELATIONSHIP BETWEEN HORIZONTAL VORTICITY INDUCED BY VERTICAL SHEAR AND VERTICAL MOTION DURING A SQUALL LINE PROCESS

The horizontal vorticity equation used in this study was obtained using the equations of motion in the pressure coordinate system without considering friction, to reveal its relationship with vertical shear. By diagnostically analyzing each term in the horizontal vorticity equation during a squall line process that occurred on 19 June 2010, we found that the non-thermal wind term had a negative contribution to the local change of upward movement in the low-level atmosphere, and that its impact changed gradually from negative to positive with altitude, which could influence upward movement in the mid- and upper-level atmosphere greatly. The contribution of upward vertical transport to vertical movement was the largest in the low-level atmosphere, but had negative contribution to the upper-level atmosphere. These features were most evident in the development stage of the squall line. Based on analysis of convection cells along a squall line, we found that in the process of cell development diabatic heating caused the subsidence of constant potential temperature surface and non- geostrophic motion, which then triggered strong convergence of horizontal acceleration in the mid-level atmosphere and divergence of horizontal acceleration in the upper-level atmosphere. These changes of horizontal wind field could cause a counterclockwise increment of the horizontal vorticity around the warm cell, which then generated an increase of upward movement. This was the main reason why the non-thermal wind term had the largest contribution to the strengthening of upward movement in the mid- and upper-level atmosphere. The vertical transport of large value of horizontal vorticity was the key to trigger convection in this squall line process.     

北半跨冬半年大西洋地区海气相互作用及其遥相关

本文分析表明,冬半年大西洋海温场及其海气的相关场都具有明显的WA型遥相关结构,且主要是海温相对较高频率变化的贡献。海气系统的这种遥相关结构是互相维持的,它们具有准一年的振荡周期。WA型的振荡变化对中高纬以及热带地区的环流和大气有着重要的影响。     

大气准双周振荡的研究进展

大气准双周振荡(Quasi-Biweekly Oscillation,QBWO)主要是指时间尺度为10~20 d的振荡,它是大气中重要的低频系统之一,是在研究季风天气及其相联系的季风系统时被发现的。QBWO对大范围的长期天气变化及异常有着重要影响,且具有全球性和多季性。本文较系统总结了近年来QBWO的研究成果,主要对其结构、活动特征,以及它对天气气候的影响及其激发维持机制等进行了综述。在此基础上,对今后的一些研究重点进行了展望。     

洱海盆地一次冬季大风演变特征及其机制模拟分析

利用WRF模式耦合Noah陆面模式和CLM湖泊模式,对2015年1月23日大理地区洱海盆地的大风天气进行模拟,对大风的发展期、强盛期和减弱期的三维动力热力结构特征进行分析,并得出了洱海盆地大风形成机制:在洱海盆地大风发展期,高空以西风为主,盆地中部上空1km高度处出现局地小气旋,地面以偏东风为主,高空偏西气流翻越苍山形成波动扰动,在背风坡侧形成空腔区和二次涡,低层形成了波不稳定区域,波不稳定区域发生波破碎,波破碎区域湍流运动活跃,把上层的能量往下传播。大风强盛期,盆地南北侧高空为两支西风气流控制,中部变为弱的辐散场,造成高空扰动,苍山东侧近地面浅薄逆温层消失,低空逆温层之上温度廓线几乎垂直上升,大气层结处于不稳定状态,有利于高空动量向下输送。大风减弱期,高空西风减弱,扰动消失,湍流动能耗散,地面风速逐渐减小。