涡旋发展和移动的动力和热力问题Ⅱ:广义倾斜涡度发展

从位涡-位温（PV-θ）以及拉格朗日观点,引入广义倾斜涡度发展的概念研究绝热条件下的垂直涡度发展。广义倾斜涡度发展是一个与涡度发展的坐标无关的概念框架,该框架包括倾斜涡度发展。倾斜涡度发展研究当大气处于稳定或不稳定层结情形,空气质点沿着向上凸的陡峭等熵面下滑或沿着向下凹的陡峭等熵面上滑过程垂直涡度激烈发展。因此,倾斜涡度发展是研究强烈天气过程的涡度发展非常强的情形。此外,广义倾斜涡度发展概念澄清了涡度发展和倾斜涡度发展的区别,涡度发展和倾斜涡度发展的判别标准表明,倾斜涡度发展的要求比涡度发展的要求严格很多。在空气质点沿着向上凸的陡峭等熵面下滑或沿着向下凹的陡峭等熵面上滑过程,当在稳定大气中静力稳定度（θ_z）迅速减小或在不稳定大气中静力稳定度（θ_z）迅速增大,即静力稳定度（θ_z）趋于0时,如果C_D<0,那么垂直涡度将急速发展。应用得到的理论结果分析了2008年7月下旬的一次青藏高原低涡过程,该低涡形成于青藏高原中西部,东移滑出青藏高原然后继续东移,给四川盆地和长江中下游带来强降水。诊断表明,2008年7月22日00—06时（世界时）青藏高原低涡沿着四川盆地东北边的斜坡爬升时低涡加强发展,PV₂变化对低涡加强发展有贡献,因为此时的水平涡度（η_s）变化和斜压度（θ_s）变化都对垂直涡度发展起正贡献。而且,22日06时,330 K等熵面的倾斜涡度发展判据满足,表明倾斜涡度发展并对垂直涡度发展起重要贡献。围绕着低涡中心较强的涡度发展和倾斜涡度发展信号表明,广义倾斜涡度发展概念框架可以作为诊断天气过程的一个有用工具。     

关于亚洲夏季风爆发的动力学研究的若干近期进展

资料分析显示,与850 hPa风场相比,地面风的变化能更好地表征亚洲各季风系统的特征。基于地面风的季节性反转和降水的显著变化所构建的亚洲夏季风(ASM)爆发指数和等时线图表明:亚洲热带夏季风(TASM)在5月初首先在孟加拉湾(BOB)东南部爆发后不是向西传播,而是向东经中印半岛向东推进,于5月中到达中国南海(SCS),6月初到达热带西北太平洋。印度夏季风的表面低压系统源于近赤道阿拉伯海地区,于6月初到达印度西南部喀拉拉邦,印度夏季风随之爆发。亚洲副热带夏季风(STASM)5月初在西北太平洋日本本州东南的海区发生后向西南伸展,于6月初与南海季风降水区连接,形成东北—西南向雨带,夏季风在中国东南沿海登陆,日本的“梅雨”(Baiu)开始。6月中该雨带向北到达长江流域和韩国,江淮梅雨和韩国的“梅雨”(Changma) 开始。本文还回顾了亚洲热带夏季风爆发的动力学研究的若干近期进展。春季青藏高原和南亚海陆分布的联合强迫作用使海表温度(SST)在BOB中东部形成短暂但强盛的暖池,在高层南亚高压的抽吸作用下,常伴有季风爆发涡旋(MOV)发展,使冬季连续带状的副高脊线在孟加拉湾东部断裂,导致亚洲热带季风首先在BOB爆发。BOB东/西部有东/西风型垂直切变,利于激发/抑制对流活动,并增加/减少海洋向大气的表面感热加热,从而使得亚洲夏季风爆发的向西传播在BOB西海岸遇到屏障。季风爆发逐渐向东伸展引发南海和热带西太平洋夏季风相继爆发。季风降水释放的强大潜热使南亚高压发展西伸,纬向非对称位涡强迫显著增强;在阿拉伯半岛强烈的表面感热加热所诱发的中层阿拉伯反气旋的共同作用下,位于阿拉伯海近赤道的低压系统北移发展成为季风爆发涡旋,导致印度季风爆发。由此可见,历时约一个月的亚洲热带夏季风爆发的三个阶段(孟加拉湾、南海和印度季风爆发)是发生在特定的地理环境下受特定的动力—热力学规律驱动的接续过程。     

青藏高原化雪迟早的辐射效应对季节变化的影响

利用大气物理所九层菱形截断１５波大气环流谱模式进行数值试验，研究青藏高原化雪迟早之辐射效应对季节变化的影响。共进行了正常态（ＣＯＮ），化雪迟（ＭＳＮ），化雪早（ＬＳＮ）三个试验。高原第ｉ月积雪状况在ＣＯＮ中取ｉ月气候平均值，在ＭＳＮ中取（ｉ—１）月的气候平均状况，在ＬＳＮ中则取（ｉ＋ｌ）月的气候状况。每个试验都从１月１日气候平均状况出发，积分至１０月。通过比较各试验结果分析化雪迟早的气候效应。结果表明，高原化雪的迟早改变了进入地表的辐射通量，从而改变了地表对大气的加热，由此影响东亚地区的季节变化。化雪迟则高原上春季进入地表的辐射通量减少，导致地表的潜热通量和向外长波辐射减弱。尤其是感热通量的减弱更为严重。一般情况下，高原在冬季为大气的感热汇，３月下旬变为大气的感热源。多雪时，这一变化推迟了近１个月。与之相应，２００ｈＰａ高原上空的南亚高压建立迟，印度西南季风爆发也迟。造成夏季风降水在印度偏少，在中印度半岛和广东沿海偏多。     

DIAGNOSIS OF NWP SYSTEMATIC FORECAST ERRORS IN ZONAL MEAN CIRCULATION

It is proved in this paper that NWP systematic forecast errors in the zonal mean circulation aredue to the difference in westerly acceleration process during the forecasting period between model andreal atmospheres.Those forcing factors which evoke the zonal mean wind variation can be split into various linearterms according to the non-acceleration theorem in a primitive equation system,By applying this tech-nique to the diagnosis of the forecast produets of the T42L9 model in January 1992 and in July 1992,it is indicated that the model has the ability to forecast the zonal mean wind to a reasonable extent,but there are still some errors in several places,especially in the upper troposphere and lower strato-sphere in the mid-latitude region as well as near the surface.The results of analysis by employing thisscheme reveal the reason responsible for the systematic forecast errors of the zonal mean wind in themodel and the possible way of improving it.It is also shown that non-acceleration theorem can be used as an efficient tool to diagnose thephysical processes of NWP models.     

NUMERICAL SIMULATIONS OF EFFECTS OF LAND SURFACE PROCESSES ON CLIMATE--IMPLEMENTING OF SSiB IN IAP/LASG AGCM AND ITS PERFORMANCE*

This is an investigation of exchanges of energy and water between the atmosphere and the vegetated continents,and the impact of and mechanisms for land surface-atmosphere interactions on hydrological cycle and general circulation by implementing the Simplified Simple Biosphere(SSiB) model in a modified version of IAP/LASG global spectral general model(L9R15 AGCM).This study reveals that the SSiB model produces a better partitioning of the land surface heat and moisture fluxes and its diurnal variations,and also gives the transport of energy and water among atmosphere,vegetation and soil explicitly and realistically.Thus the coupled SSiB-AGCM runs lead to the more conspicuous improvement in the simulated circulation,precipitation,mean water vapor content and its transport.particularly in the Asian monsoon region in the real world than CTL-AGCM runs.It is also pointed out that both the implementation of land surface parameterizations and the variations in land surface into the GOALS model have greatly improved hydrological balance over continents and have a significant impact on the simulated climate.particularly over the massive continents.Improved precipitation recycling model was employed to verify the mechanisms for land surface hydrology parameterizations on hydrological cycle and precipitation climatology in AGCM.It can be argued that the recycling precipitation rate is significantly reduced,particularly in the arid and semi-arid region of the boreal summer hemisphere,coincident with remarkable reduction in evapotranspiration over the continental area.Therefore the coupled SSiB-AGCM runs reduce the bias of too much precipitation over land surface in most AGCMs,thereby bringing the simulatedprecipitation closer to observations in many continental regions of the world than CTL-AGCMruns.     

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。     

ANALYSES OF THE DYNAMIC EFFECTS ON WINTER CIRCULATION OF THE TWO MAIN MOUNTAINS IN THE NORTHERN HEMISPHERE--Ⅱ.VERTICAL PROPAGATION OF PLANETARY WAVES

A linear,hemispheric and stationary spectral model with multilayers in the vertical was employed to simulate the vertical propagation of waves triggered by mountains.Results show that,in cooperation with the East Asia zonal mean flow,Tibetan Plateau can excite a strong wavenumber 1 perturbation in the stratosphere with its ridge and trough located over the Pacific and Atlantic Oceans respectively.On the other hand,the stratospheric wavenumber 1 perturbation caused by the mechanical forcing of the Rocky Mountains in cooperation with the North America zonal mean flow is very weak.Calculations from observational data of the vertical profile of critical wavenumber for vertically propagating waves imply that the tropospheric wavenumber 1 perturbation can hardly penetrate the North America tropopause upwards,whereas it can freely propagate through the East Asia tropopause into the stratosphere.Two-dimensional E-Pcross-sections obtained from both observational data and simulated results also demonstrate that waves excited by the Rocky Mountains are refracted towards low latitudes in the troposphere during their upward propagation:whereas,in addition to the above mentioned equatorward leaning branch,the wavenumber 1 and 2 planetary waves excited by the Tibetan Plateau possess another branch which is refracted to high latitudes during upward propagation and penetrates the tropopause into the stratosphere.It is therefore concluded that the difference in the horizontal and vertical wave propagations in the two hemispheres is a result of the different dynamical forcing induced by the two main mountains in the Northern Hemisphere.     

西北地区粮食问题,潜力和发展途径

西北地区因其特定的自然条件的制约和农业基础脆弱以及投入不足的影响，人均粮食占有量一直低于全国的平均水平，是粮食调入区。本文把西北地区粮食发展划分为四个阶段，分析了粮食增产的主要途径。通过对粮食近期增长潜力和宜农荒地潜力分析，预测西北地区本世纪末粮食可能增产的幅度，并提出了达到该目标应采取的技术措施。     

大气定常波传播的运动学特征的时空变化

利用时间平均全球大气环流资料,本文计算了纬向平均位涡的南北梯度的时空分布,以及波动水平传播的临界波数n_s,和垂直传播的临界波数K_c的时空分布。由此研究全球大气定常波传播的运动学特征及其年变化。