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1.
Using the operational model(B model)of Beijing Meteorological Center,we do some of numerical experi-ments of crossing and rounding mountains in all velocity adjustment scheme,and study dynamic effect ofQinghai-Xizang Plateau and Rocky Mountains on lee cyclones.The results show that due to air flow roundthe Qinghai-Xizang Plateau,divergence is distributed in the shape of confluence which matches cyclogenesisarea and cyclonic track in East Asia.In the downstream of the Qinghai-Xizang Plateau,convergence inthe upper troposphere restrains cyclone development in the east of China mainland.In North America,air flow primarily crosses over Rocky Mountains.Air is adiabatically cooled when it flows upward in thewest flank of Rocky Mountains,while air is warmed when it flows downward in the lee side.The fact isimportant for the lee cyclogenesis and the lee frontogenesis of Rocky Mountains.Air flow crossing over RockyMountains is also the main cause for forming dryline in the mid-west of United States. 相似文献
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本文利用北京气象中心的业务预报模式(B模式),采用全风速调整方案,进行了绕流、爬坡等各种数值试验,研究青藏高原和落基山对气旋的动力影响。结果表明,气流绕青藏高原而行,产生的散度场与东亚的气旋生成区和路径匹配;在青藏高原主体下游,高层辐合,抑制了我国大陆东部的气旋发展。在北美,落基山对大气的动力影响以爬坡为主,由于气流在迎风坡上升,空气绝热冷却,在背风面大规模下沉增温,对流层低层形成暖脊,这对背风锋生和背风气旋的发生发展有着直接的影响;另外爬坡作用也是美国中西部干线形成的主要原因。 相似文献
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ANALYSES OF THE DYNAMIC EFFECTS ON WINTER CIRCULATION OF THE TWO MAIN MOUNTAINS IN THE NORTHERN HEMISPHERE——Ⅰ.RELATIONSHIP AMONG GENERAL CIRCULATION,TELECONNECTION AND STATIONARY WAVES 
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下载免费PDF全文 The distribution of troughs and ridges of geopotential height,the teleconnection patterns and the propagation pat-terns of stationary waves are the main features of the January mean geopotential height field at 500hPa.Data analysesand numerical experiments indicate that these three characteristics are associated to one another and closely related tothe mechanical forcing of the Rocky Mountains and Tibetan Plateau.There exists a prominent negative correlation inthe intensity variation between the American trough and the Asian trough at high and middle latitudes.Such negativecorrelation,in connection with the interannual variation of the intensity of the jets in front of the two troughs,leads tothe existence of similar teleconnection patterns in North America and East Asia.On the other hand,the different propa-gation behaviour of quasi-stationary waves downstream of the two main mountains results in a fundamental differencein the distribution of correlation chains in North America and East Asia. 相似文献
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ANALYSES OF THE DYNAMIC EFFECTS ON WINTER CIRCULATION OF THE TWO MAIN MOUNTAINS IN THE NORTHERN HEMISPHERE--Ⅰ.RELATIONSHIP AMONG GENERAL CIRCULATION, TELECONNECTION AND STATIONARY WAVES 下载免费PDF全文
下载免费PDF全文 The distribution of troughs and ridges of geopotential height,the teleconnection patterns and the propagation patterns of stationary waves are the main features of the January mean geopotential height field at 500hPa.Data analyses and numerical experiments indicate that these three characteristics are associated to one another and closely related to the mechanical forcing of the Rocky Mountains and Tibetan Plateau.There exists a prominent negative correlation in the intensity variation between the American trough and the Asian trough at high and middle latitudes.Such negative correlation,in connection with the interannual variation of the intensity of the jets in front of the two troughs,leads to the existence of similar teleconnection patterns in North America and East Asia.On the other hand,the different propagation behaviour of quasi-stationary waves downstream of the two main mountains results in a fundamental difference in the distribution of correlation chains in North America and East Asia. 相似文献
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Summary Due to its complex orography, a lee trough can occur along leeward coasts of Tasmania. Of particular interest to meteorologists
and others, is the lee trough that can form along eastern parts of Tasmania. This effect is often observed under broad westerly
flow due mainly to a topographic barrier, which lies to the west of the area of interest.
The lee trough seems to be most pronounced when the troposphere is stable with an inversion just above the highest parts of
the western and central highlands, known as the Western Mountains and Central Plateau, respectively. Blocking of the low-level
airflow, coupled with the formation of a windward ridge of high pressure may also contribute to the formation of the lee trough.
From time to time, mesoscale thermal lows and pronounced standing wave activity has also been observed to form over parts
of the state co-incident with the lee trough. These can further complicate the overall wind pattern over parts of the Tasmania.
This study attempts to investigate and verify some aspects of this lee trough by the utilization of a very high resolution
numerical weather prediction model, known as HIRES (HIghRESolution).
Received October 18, 2001 Revised December 16, 2001 相似文献
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From a statistical study of the atmospheric circulation types over the Northern Hemisphere it is found that the zonal type circulation predominates in East Asia. From a three-layer primitive equation model in σ-coordinate, the orographic effect on a westerly current over the Northern Hemisphere is studied. A distinguished deepening trough is observed in the lee-side slope of the Rocky Mountains. But a pronounced trough is over the East Asia coast far from the Tibetan Plateau. In a case of 48 h numerical forecast, it is found that the effect of the Tibetan Plateau tends to build up a rather zonal type circulation, which is con-sistent with the observations. These may be partly explained by the topographic effect of the north slope of the Tibetan Plateau in a simple geostrophic theory. 相似文献
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ANALYSES OF THE DYNAMIC EFFECTS ON WINTER CIRCULATION OF THE TWO MAIN MOUNTAINS IN THE NORTHERN HEMISPHERE——Ⅱ.VERTICAL PROPAGATION OF PLANETARY WAVES 下载免费PDF全文
下载免费PDF全文 A linear,hemispheric and stationary spectral model with multilayers in the vertical was employed to simulate thevertical propagation of waves triggered by mountains.Results show that,in cooperation with the East Asia zonal meanflow,Tibetan Plateau can excite a strong wavenumber 1 perturbation in the stratosphere with its ridge and trough lo-cated over the Pacific and Atlantic Oceans respectively.On the other hand,the stratospheric wavenumber 1 perturbationcaused by the mechanical forcing of the Rocky Mountains in cooperation with the North America zonal mean flow isvery weak.Calculations from observational data of the vertical profile of critical wavenumber for vertically propagatingwaves imply that the tropospheric wavenumber 1 perturbation can hardly penetrate the North America tropopause up-wards,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 theRocky Mountains are refracted towards low latitudes in the troposphere during their upward propagation:whereas,inaddition to the above mentioned equatorward leaning branch,the wavenumber 1 and 2 planetary waves excited by theTibetan Plateau possess another branch which is refracted to high latitudes during upward propagation and penetratesthe tropopause into the stratosphere.It is therefore concluded that the difference in the horizontal and vertical wavepropagations in the two hemispheres is a result of the different dynamical forcing induced by the two main mountains inthe Northern Hemisphere. 相似文献
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本文利用耦合气候模式研究了“有/无”青藏高原和落基山脉对厄尔尼诺—南方涛动（ENSO）的影响,并从温度变率方程的角度详细分析了ENSO变化的成因,结果表明:移除青藏高原或落基山脉均会造成ENSO变率增强;ENSO变率在无青藏高原试验中增强的幅度比在无落基山脉试验中更大。ENSO变率在地形敏感性试验中的变化与热带太平洋平均气候态的改变密切相关。移除青藏高原后热带太平洋信风减弱,大气对流中心东移,混合层变浅,温跃层变平,呈现出El Ni?o型海温分布,这些平均态的变化使海表风应力敏感性,Ekman抽吸敏感性以及温跃层敏感性幅度增强,最终导致ENSO振幅增大60%。然而,在移除落基山脉的情景下,热带太平洋信风变化更加复杂,大气对流中心稍有东移,混合层加深,温跃层变平,呈现出类La Ni?a型海温分布。这些变化增强了风应力敏感性和温跃层敏感性,最终导致ENSO振幅仅增大15%左右。本文研究表明,在地质时间尺度上青藏高原和落基山脉的抬升均抑制了ENSO变率。 相似文献
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ANALYSES OF THE DYNAMIC EFFECTS ON WINTER CIRCULATION OF THE TWO MAIN MOUNTAINS IN THE NORTHERN HEMISPHERE--Ⅱ.VERTICAL PROPAGATION OF PLANETARY WAVES 下载免费PDF全文
下载免费PDF全文 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. 相似文献
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本文主要讨论地形对天气系统的影响,研究了斜压大气中地形背风气旋的问题。用小参数法简化基本运动方程,利用青藏高原和落基山脉的实际地形,采用FFT的数值方法,考虑了不同地形、风切变、大气层结等诸因素对地形扰动的影响。结果表明:青藏高原和落基山脉东侧的地形扰动与统计结果较一致;层结对地形扰动的影响较敏感。 相似文献
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线性、定常、多层半球谱模式模拟结果表明,在东亚纬向气流下,青藏高原能在平流层激发出强大的1波扰动,脊槽分别位于太平洋和大西洋上空。在北美纬向气流下,落基山在平流层激发的1波很弱。观测资料计算指出,对流层行星1波很难通过北美对流层顶上传,但却能自由穿过东亚高纬度地区的对流层顶向平流层传播。北美地形所激发的波动在上传过程中均折向低纬传播。青藏高原所激发的行星1波和2波在上传过程中有分支:折向低纬的一支主要局限在对流层中;折向高纬的一支进入平流层。模拟和分析证明,这些差异是北半球两大地形不同的动力作用的结果。 相似文献
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本文利用正压原始方程,对48°S——48°N间的给定的平直副热带西风和东风切变带进行了西风爬越西藏高原为主、西风绕过西藏高原和无西藏高原存在的三种不同情况的数值试验。这些试验表明,由于西藏高原与落基山等大地形的存在,不但能造成副热带高压带的断裂,并且能形成四个副热带高压单体。在北半球,这四个单体具有相当稳定的位置,一个在西太平洋,一个在中太平洋,一个在大西洋,一个在北非。这些试验还表明,当西风以爬越西藏高原为主时,对南半球澳大利亚高压的存在与稳定有一定的作用。西风绕过西藏高原流动时有利于西太平洋高压向西伸展。 相似文献
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利用兰州和民勤两站干年(1995年)、湿年(1994年)的5~6月08:00和20:00气象观测资料,采用Scorer背风波参数等方法对兰州小高压的形成、发展机制进行动力和热力学诊断分析。分析表明,兰州存在明显的背风波效应和下沉逆温;民勤有较强的逆温层特征,逆温频数多且强度大,辐射和扰动逆温较明显,它们的背风波和逆温层特征影响着兰州小高压的形成、尺度和位置。兰州小高压是青藏高原大地形和大气环流共同作用的一种边界层现象,与青藏高原北部较强的逆温和背风波效应有着重要的关系,运用中尺度天气学方法得出兰州小高压的预报流程,以建立其诊断和预报的概念模型。 相似文献
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Climate change in mountains: a review of elevation-dependent warming and its possible causes 总被引：5，自引：1，他引：4
Available observations suggest that some mountain regions are experiencing seasonal warming rates that are greater than the global land average. There is also evidence from observational and modeling studies for an elevation-dependent climate response within some mountain regions. Our understanding of climate change in mountains, however, remains challenging owing to inadequacies in observations and models. In fact, it is still uncertain whether mountainous regions generally are warming at a different rate than the rest of the global land surface, or whether elevation-based sensitivities in warming rates are prevalent within mountains. We review studies of four high mountain regions – the Swiss Alps, the Colorado Rocky Mountains, the Tibetan Plateau/Himalayas, and the Tropical Andes – to examine questions related to the sensitivity of climate change to surface elevation. We explore processes that could lead to enhanced warming within mountain regions and possible mechanisms that can produce altitudinal gradients in warming rates on different time scales. A conclusive understanding of these responses will continue to elude us in the absence of a more comprehensive network of climate monitoring in mountains. 相似文献
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利用1979—2016年1月逐日0.125°×0.125° ERA-Interim再分析资料及冻雨观测资料,通过个例合成等方法,探讨了中国南方准静止锋和冬季大范围冻雨的关系。结果表明:（1）中国南方大范围冻雨受昆明和华南准静止锋共同影响呈东西带状分布;（2）青藏高原东侧逆温之强,范围之广以及水汽之充沛的主要原因,一是冷空气常堆积在横断山脉以东和南岭山脉以北等中国广大的南方地区,其形成机制主要为冷平流和绝热冷却,地势较高地带非绝热冷却也较明显;二是700和850 hPa暖平流形成的暖层也十分宽广;三是850 hPa源自中国南海和西太平洋的湿平流输送;（3）500 hPa东亚大槽、700 hPa南支槽、850 hPa反气旋和地面蒙古冷高压为青藏高原东侧对流层低层极地大陆性气团与热带海洋性气团和热带大陆性气团交绥创造了必要的环流条件;（4）东亚冷空气爆发从青藏高原东侧南下,迫使近地面暖湿气团抬升形成华南准静止锋。同时,受青藏高原东部地形的阻挡产生冷空气堆积。当冷空气堆积到一定厚度向西爬上低纬高原时,又与南支西风相遇形成昆明准静止锋。由昆明和华南准静止锋形成的复杂锋面结构,伴随宽广而强烈的逆温有利于中国南方大范围冻雨的产生。 相似文献
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Huang Ronghui 《大气科学进展》1985,2(1):81-92
In this paper, a quasi-geostrophic, 34-level spherical coordinate model with Rayleigh friction, New-tonian cooling and the horizontal eddy thermal diffusivity is used to simulate the three-dimensional teleconnection in the summer circulation over the Northern Hemisphere.The computed results show that the change of the heat source over the Tibetan Plateau may cause the change of the atmospheric circulation over the middle and high latitudes in the Northern Hemisphere. When the heat source over the Tibetan Plateau is enhanced, it may cause the Tibetan high to enhance over South Asia and cause the change of the atmospheric circulation over East Asia and North America, i. e. Northeast China and North Japan will be controlled by a trough, which brings about a cold summer in this area. In the same way, an anticyclone will be enhanced over the Okhotsk sea. Moreover, another trough will be formed over Alaska, while another ridge will develop to the northeast of North America. Besides, the Pacific subtropical high will be weakened. These results are in good agreement with those obtained from the observed data. 相似文献
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Summary Climatological studies show that the Altai-Sayan lee side is one of the major cyclogenesis areas in the Northern Hemisphere. In case of the Altai-Sayan lee cyclogenesis, the surface cyclone is generated when a primary cyclone is swept north of the mountains. In the mid-troposphere, a trough develops and finally turns into a cutoff low within 48 h. The main synoptic features are similar to those of Alpine cyclogenesis. Numerical simulations are performed to assess the effect of different representation of orography on the Altai-Sayan cyclogenesis. Two experiments are performed, a step-mountain (ETA) and an envelope orography (SGM) experiment. The ETA experiment produced the cyclogenesis in a way similar to that in the analysis both at the surface and at mid-troposphere. The SGM experiment failed in the simulation of the upper cutoff low. The difference in predicted pressure between the ETA and the SGM experiment shows a dipolar structure suggesting that the blocking effect of the mountains is essential in the development of the Altai-Sayan lee cyclogenesis.With 7 Figures 相似文献