地形和非绝热加热共同强迫的流型突变

本文用低谱模式,研究了地形和非绝热加热共同强迫的准地转气流的突变。在一定的参数集合,随着外部热力强迫参数的渐变,激发出了谱系数与西风急流位置的突变。 与单纯非绝热加热强迫的情况相比,地形引入后,改变了流型多平衡态的参数范围和流型突变的参数临界点的位置,并使平衡态流型的经向度加大。由夏至冬转换期间突然建立的南支急流的形态也更为接近观测事实。     

周期性热力外强迫和地形强迫共同激发的六月和十月的流型突变

本文用二层准地转模式,经低谱途径,数值地研究了周期性热力外强迫源和地形强迫源共同作用下斜压大气的流型突变问题。在一定的参数范围,季节转换期间的流型突变清楚地显示出来了,该突变恰好发生在摸式大气的6月和10月。     

对1991年全球越赤道气流的分析和数值模拟

利用1991年国家气象中心全年分析资料,对全球各层（50～1000 hPa）越赤道气流（CEF）进行了分析。指出:主要季风区和1979年的相同,但在南美北部为弱季风区,而1979年为信风区。除南美北部外,主要信风区与1979年相同。还比较了这两类地区的特点,特别是非绝热加热分布随季节变化的特点,还用T21L5模式进行了数值模拟。结果表明:考虑地形和加热的方案最优,除个别情况外,CEF与实况很接近; 单纯加热方案次之,能定性地模拟CEF沿赤道的分布,但强度相差较大; 单纯地形方案最差。为了进行解释,还作了简单情况的理论分析。分析显示:考虑加热和地形作用,并不等于单纯地形和单纯加热的叠加,其间有非线性作用; 而且,这种非线性作用对CEF的产生是直接的、重要的; 单纯加热只有通过其对地面气压场的影响才能产生CEF。     

A STUDY ON PHYSICAL MECHANISM OF INTERANNUAL VARIATIONS OF LARGE-SCALE FLOW PATTERNS*

The thermal forcings of annual and interannual periodic variations are introduced into the barotropic vorticity equation,by using low order spectral model of the equation,more than 40 numerical experiments whose integration time is larger than 100 model years are performed in order to investigate variations of large-scale flow patterns arising from both external interannual thermal forcing and internal dynamical processes.In certain parametric range,when the frequency of the forcing term with interannual period equals to the frequency which is created by the internal dynamical processes alone,the amplitude of interannual variations of flow patterns increases obviously,and the period becomes double.In other parametric range,the amplitude of interannual variations of flow patterns shows abrupt changes and other nonlinear behavior,along with gradual changes of interannual forcing parameters.     

两层正压准平衡海洋模型的中纬度定常风场强迫解

建立了风场强迫下考虑瑞利摩擦的水平二维两层正压准平衡海洋模型,并在中纬度大尺度理想风场强迫的情况下,进行了解析求解。结果表明,在西风急流强迫下,在理想海洋的西海岸以东的上层流场上,在西风急流处会出现较强的东向流;在接近β通道侧壁处则有西向逆流出现;在近西海岸处,在上述东向流的两侧有气旋性曲率与反气旋性曲率的流动;而下层流场的强度与上层流场大致相同,但流向大体相反。由理想西风急流异常强迫出的流场异常的分布形式与以上结果类似。与实际风场异常强迫下的北太平洋上层流场异常进行比较后可知,模型得到上层海洋的结果与实际情况有相像之处。最终,该海洋模型的解趋于风场强迫特解。     

东西风廓线特征与大气运动平衡态定常波的相关关系及共振条件的研究

本文采用简化数学模型探讨了东、西风廓线特征与外源强迫下大气环流平衡态定常波结构的相关关系。文中采用实际观测资料研究了西风廓线特征与大气环流型季节特征之间的联系。研究表明,西风廓线冬、夏季节差异与中、高纬度西风槽“冬三夏四”波数差气候特征有关,且低纬强东风切变可作为赤道东风波周期振荡成因之一。冬夏西风廓线季节特征可导致大地形强迫效应、海陆加热因子影响作用的显著季节差异。研究还揭示了大气环流型优势波转换的基流特征影响效应,并导出了流场与纬向加热强迫源共振状态的西风廓线特征函数与临界曲线。     

青藏高原动力和热力作用对季节转换期全球大气环流影响的数值研究

利用ＣＣＭ１（Ｒ１５Ｌ７）－ＬＮＷＰ模式，以１９９６年３月１７日的国家气象中心客观分析资料为初始场，分别采用有、无青藏高原两种方案，数值研究了青藏高原对５月份全球大气环流季节转换的影响。试验结果表明：北半球初夏，青藏高原区域用同纬度地区的一个中空热源，其作用可以在２００ｈＰａ层形成一个２２４Ｋ的暖中心，使大气增暖７Ｋ以上。高原地形的动力和非绝热作用使得南极大陆２００ｈＰａ层大部分地区降温６Ｋ左右，最大负中心可达－８．２８Ｋ，这对于南半球由夏至冬过程中，环极涡旋的强度加深和范围扩大是有利的。高原地形作用对北半球大气环流平均槽脊的形成和维持有十分重要的影响，它加强了高原所在纬度带北侧（减弱了南侧）由南向北的正温度梯度，同时也增强了３０°Ｓ附近由北向南的正温度梯度，从而有利于季节转换过程中全球中纬西风带的整体北移和初夏亚洲季风环流的形成。同时高原地形作用在赤道及低纬地区形成的位势增加区，有利于南半球热带高压脊的北退和北半球副高增强北移。此外，它还有利于南半球极地东风带的增强和５００ｈＰａ层环极低压带的强度减弱，同时增加了罗斯海附近的极涡强度，对赤道的索马里急流的形成也有重要影响     

热力适应、过流、频散和副高II.水平非均匀加热与能量频散

利用位涡方程和热力适应原理，讨论了因非绝热加热的空间不均匀性导致的大气 动力特征的变化，进一步阐明了副热带地区的深对流凝结潜热加热的垂直非均匀性使副热带高压在中低空出现在热源区以东，在高空出现在热源区以西。在此基础上，深入研究了水平非均匀加热对大气环流的影响。结果表明加热区以北，虽然非绝热加热消失，但存在加热的水平梯度在西风环流的背景下在高低层造成深厚的负涡度强迫。因而高层热源北部边界附近的西风向南偏转进入加热区，造成加热区北部边界及其以北发生次级辐散；低层热源区的南风发生反气旋偏转，汇入加热区外的西风气流中，造成低层加热区北部边界及其以北发生次级辐合。结果该区域产生了垂直上升运动及负的涡度强迫源，对应着异常强烈的反气旋环流。该负涡度强迫源还通过能量频散，在西风带中以Rossby波的形式向中高纬传播，影响中高纬地区的异常环流型。     

热力适应、过流、频散和副高Ⅱ．水平非均匀加热与能量频散

利用位涡方程和热力适应原理，讨论了因非绝热加热的空间不均匀性导致的大气动力特征的变化，进一步阐明了副热带地区的深对流凝结潜热加热的垂直非均匀性使副热带高压中低空出现在低源区以东，在高空出现在热源区以西。在此基础上，深入研究了水平非均匀加热对大气环流的影响。结果表明加热区以北，虽然非绝热加热消失，但存在加热的水平梯度在西风环流的背景下在高低层造成深厚的负涡度强迫。因而高层热源北部边界附近的西风向南偏转进入加热区，造成加热区北部边界及其以北发生次级辐散；低层热源区的南风发生反气旋偏转，汇入加热区外的西风气流中，造成低层加热区北部边界及其以北发生次级辐合。结果该区域产生了垂直上升运动及负的涡度强迫源，对应着异常强烈的反气旋环流。该负涡强度迫源还通过能量散射，在西风带中以Rossby波的形式向中高纬传播，影响中高纬地区的异常环流型。     

Simulations of the East Asian subtropical westerly jet by LASG/IAP AGCMs

Performances of two LASG/IAP(State Key Laboratory of Numerical Modeling for Atmospheric Sci- ences and Geophysical Fluid Dynamics/Institute of Atmospheric Physics)Atmospheric General Circulation Models(AGCMs),namely GAMIL and SAMIL,in simulating the major characteristics of the East Asian subtropical westerly jet(EASWJ)in the upper troposphere are examined in this paper.The mean vertical and horizontal structures and the correspondence of the EASWJ location to the meridional temperature gradient in the upper troposphere are well simulated by two models.However,both models underestimate the EASWJ intensity in winter and summer,and are unable to simulate the bimodal distribution of the ma- jor EASWJ centers in mid-summer,relative to the observation,especially for the SAMIL model.The biases in the simulated EASWJ intensity are found to be associated with the biases of the meridional temperature gradients in the troposphere,and furthermore with the surface sensible heat flux and condensation latent heating.The models capture the major characteristics of the seasonal evolution of the diabatic heating rate averaged between 30°-45°N,and its association with the westerly jet.However,the simulated maximum diabatic heating rate in summer is located westward in comparison with the observed position,with a rela- tively strong diabatic heating intensity,especially in GAMIL.The biases in simulating the diabatic heating fields lead to the biases in simulating the temperature distribution in the upper troposphere,which may further affect the EASWJ simulations.Therefore,it is necessary to improve the simulation of the meridional temperature gradient as well as the diabatic heating field in the troposphere for the improvement of the EASWJ simulation by GAMIL and SAMIL models.     

大气非绝热加热作用的研究进展与展望

大气非绝热加热与天气系统的发生发展有密切联系,与降水等天气过程密不可分,非绝热加热在大气运动中有着至关重要的作用。对非绝热加热的研究和理解,有助于改进数值预报模式,增强数值天气预报模式的预报能力。本文系统梳理了大气非绝热加热的基本内容,近几十年非绝热加热及其作用的研究成果,主要包括非绝热加热的概念及其表征、非绝热加热的时空分布特征、非绝热加热与季风、天气系统(如西太平洋副热带高压、热带气旋、温带气旋和急流)和降水之间的关系,以及非绝热加热在数值模式中的表征,进而指出有待于进一步研究的方面。     

A study of partitioning Q vector on background conditions of a torrential rainfall over Shanghai, China on 25 August 2008

A rainfall that occurred during 0200–1400 Beijing Standard Time(BST)25 August 2008 shows the rapid development of a convective system,a short life span,and a record rate of 117.5 mm h-1for Xujiahui station since 1872.To study this torrential rainfall process,the partitioning method of Q vector is developed,in which a moist Q vector is first separated into a dry ageostrophic Q vector(DQ)and a diabatic-heating component.The dry ageostrophic Q vector is further partitioned along isothermal lines in the natural...     

LBM模式中中纬度大气对热源和涡度强迫的响应(英文)

Based on diagnostic analysis of reanalysis data for 58-year,the distribution characteristics of decadal variability in diabatic heating,transient eddy heating and transient eddy vorticity forcing related to the sea surface temperature(SST)anomalies over the North Pacific,as well as their relationship with anomalous atmospheric circulation have been investigated in this paper.A linear baroclinic model(LBM)was used to investigate atmospheric responses to idealized and realistic heat and vorticity forcing anomalies,and then to compare relative roles of different kinds of forcing in terms of geopotential height responses.The results illustrate that the responses of atmospheric height fields to the mid-latitude heating can be either baroclinic or barotropic.The response structure is sensitive to the relative horizontal location of heating with respect to the background jet flow,as well as to the vertical profile of heating.The response to the idealized deep heating over the eastern North Pacific,mimicking the observed heating anomaly,is baroclinic.The atmospheric response to the mid-latitude vorticity forcing is always barotropic,resulting in a geopotential low that is in phase with the forcing.The atmospheric responses to the realistic heat and vorticity forcing show the similar results,suggesting that diabatic heating,transient eddy heating and transient eddy vorticity forcing can all cause atmospheric anomalies and that the vorticity forcing plays a relatively more important role in maintaining the equivalent-barotropic structure of geopotential height anomalies.     

Mid-latitude atmospheric responses to heat and vorticity forcing using a linear baroclinic model

Based on diagnostic analysis of reanalysis data for 58-year, the distribution characteristics of decadal variability in diabatic heating, transient eddy heating and transient eddy vorticity forcing related to the sea surface temperature (SST) anomalies over the North Pacific, as well as their relationship with anomalous atmospheric circulation have been investigated in this paper. A linear baroclinic model(LBM) was used to investigate atmospheric responses to idealized and realistic heat and vorticity forcing anomalies, and then to compare relative roles of different kinds of forcing in terms of geopotential height responses. The results illustrate that the responses of atmospheric height fields to the mid-latitude heating can be either baroclinic or barotropic. The response structure is sensitive to the relative horizontal location of heating with respect to the background jet flow, as well as to the vertical profile of heating. The response to the idealized deep heating over the eastern North Pacific, mimicking the observed heating anomaly, is baroclinic. The atmospheric response to the mid-latitude vorticity forcing is always barotropic, resulting in a geopotential low that is in phase with the forcing. The atmospheric responses to the realistic heat and vorticity forcing show the similar results, suggesting that diabatic heating, transient eddy heating and transient eddy vorticity forcing can all cause atmospheric anomalies and that the vorticity forcing plays a relatively more important role in maintaining the equivalent-barotropic structure of geopotential height anomalies.     

大尺度流型年际变化可能机制的研究

本文将年变周期和非年变周期热力强迫项引进正压涡度方程,用方程的截谱形式实施了几十组时间长度为100年的数值积分,研究了非年变周期热力强迫和大气内部动力过程共同激发的大尺度流型的年际变化问题。在一定的参数集合,当非年变外源强迫的振荡周期与大气内部动力过程单独激发出来的振荡的周期相同时,流型年际振动的振幅明显加大,振动的周期则为倍化。在另外的参数集合,随着非年变强迫参数的渐变,流型年际变化的幅度显示出清楚的突变以及其它富有非线性特色的行为。     

Abrupt change of flow pattern in baroclinic atmosphere forced by joint effects of diabatic heating and orography

Based on the catastrophic theory, the possible causes of abrupt change in the atmospheric circulation over the Northern Hemisphere during June and October have been explored by Li and Luo (1983) and Miao and Ding (1933). However these studies are confined to the baroiropic atmosphere without consideration of orography. The purpose of this paper is to further study the physical mechanism of the abrupt change of flow pattern within the baroclinic atmosphere in the presence of orography. Results show that the abrupt change of flow pattern can be stimulated by the gradual variation of a diabaticaily heating parameter, which is similar to the observed fact about the rapid shift of position of the subtropical high center in the upper troposphere along the zonal direction during seasonal transition from the summer half year to the winter one.     

A DYNAMICAL ANALYSIS OF BASIC FACTORS OF LOW-FREQUENCY OSCILLATION IN THE TROPICAL ATMOSPHERE*

Based on dynamical characteristics of the tropical atmosphere,a mathematical model of low-frequency oscillation (LFO hereinafter) in low-latitudes has been developed.The analysis shows that the distributive features (shear of wind speed) of easterlies and westerlies in low-latitudes,the divergence and convergence of meridional and zonal flow,the vertical structure of diabatic heating and the Coriolis parameter f are the basic factors resulting in the LFO,while quasi-periodical baroclinity development or index cycle of westerly waves in middle-latitudes of the Southern Hemisphere is an external forcing to the LFO in the tropical atmosphere.The resonance on adequate condition makes LFO suddenly enhanced.     

The intraseasonal oscillations of precipitation and circulations from January to March in 2010 in East Asia

The rainfall from January to March in 2010 in East Asia is positive anomaly and the temporal evolution characteristics present the cycle of 20–40 days. In the present paper, the low-frequency circulations and its formation mechanism are analyzed. The results show that during the peak rainfall phase, the upstream of the rainfall regions is controlled by low-frequency cyclone, and the downstream is controlled by low-frequency anticyclone in the middle and low troposphere. In the upper troposphere, the westerly jet presents the oscillation characteristics between the north and the south. Both the integrated (from the surface to 100 hPa) diabatic heating and the horizontal vorticity advection contribute to the vertical velocity. In addition, the vorticity vertical advection has effects on the vertical speed, which is a self-feedback process. The latent heating in the precipitation has influences on the westerly jet in the upper troposphere. The interactions between the precipitation and the westerly jet are mainly manifested as the intraseasonal oscillations.     

非绝热加热在南亚高压建立和振荡中所起的作用

通过运用在β平面上准地转两层斜压高截断谱模式，在不同的非绝热加热和基本气流下进行计算，结果表明:1.南亚高压的建立和振荡是在外热力强迫参数取适当值的时候产生，热力强迫参数太强就可能出现混沌现象。2.当海陆热力差异减弱到某数值时，南亚高压变化就趋向于某一平衡态。3.当外界热力强迫只有经向不均匀，而无纬向不均匀加热时，不能形成南亚高压。     

一个分析大气谱模式的合理性的定性方法

利用对称运动和非对称运动的理论结果,如‘对称运动的不变性’,可以推得:如初始时刻运动是对称的,对于绝热无摩擦的谱模式,在时间积分过程中,总有 1.和反对称运动有关的谱系数等于零; 2.全球预报和半球预报在同一半球内处处相同; 3.和赤道对称的任意两个区域,其各自的运动彼此对称。 数值试验也证实了这些结果。 在有外力强迫的情形,如地形(或加热),如其分布是对称的,则在初始运动是对称的情况下,‘对称运动的不变性’仍然成立。但如果地形(或加热)分布是非对称的,则运动的对称性会减小,而变成非对称运动,并出现越赤道气流。这些也经过数值试验加以证实。 利用上述理论结果作为指导,可以用所设计的模式进行试验、分析,从而,确定模式设计是否合理,有关软件是否有误等。