The characteristics of the forced stationary planetary wave propagations in summer Northern Hemisphere

The three-dimensional propagations of the forced stationary planetary waves in a realistic summer current, in which the vertical and horizontal wind shears are included, are discussed by using the refractive index squared of waves in a spherical coordinate system.The results show that there is no polar wave guide in stationary planetary wave propagations in summer. Thus, stationary planetary waves cannot propagate into the stratosphere. However, there are a wave guide pointing from the subtropics toward middle and high latitudes in the troposphere and another wave guide pointing from the lower troposphere at middle latitudes toward the upper troposphere near 30°oN in the forced stationary planetary wave propagations.A linearized, steady-state, quasi-geostrophic 34-level spherical coordinate model with Rayleigh friction and Newtonian cooling, horizontal kinematic thermal diffusivity is used to simulate the wave guides of three-dimensional propagations of stationary planetary waves in summer.     

Interdecadal Variability of the East Asian Summer Monsoon and Associated Atmospheric Circulations

Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research （NCEP/NCAR） reanalysis data from 1950-1999, interdecadal variability of the East Asian Summer Monsoon （EASM） and its associated atmospheric circulations are investigated. The EASM exhibits a distinct interdecadal variation, with stronger （weaker） summer monsoon maintained from 1950-1964 （1976-1997）. In the former case, there is an enhanced Walker cell in the eastern Pacific and an anti-Walker cell in the western Pacific. The associated ascending motion resides in the central Pacific, which flows eastward and westward in the upper troposphere, descending in the eastern and western ends of the Pacific basin. At the same time, an anomalous East Asian Hadley Cell （EAHC） is found to connect the low-latitude and mid-latitude systems in East Asia, which strengthens the EASM. The descending branch of the EAHC lies in the west part of the anti-Walker cell, flowing northward in the lower troposphere and then ascending at the south of Lake Baikal （40°-50°N, 95°- 115°E） before returning to low latitudes in the upper troposphere, thus strengthening the EASM. The relationship between the EASM and SST in the eastern tropical Pacific is also discussed. A possible mechanism is proposed to link interdecadal variation of the EASM with the eastern tropical Pacific SST. A warmer sea surface temperature anomaly （SSTA） therein induces anomalous ascending motion in the eastern Pacific, resulting in a weaker Walker cell, and at the same time inducing an anomalous Walker cell in the western Pacific and an enhanced EAHC, leading to a weaker EASM. Furthermore, the interdecadal variation of summer precipitation over North China is found to be the south of Lake Baikal through enhancing and reducing strongly regulated by the velocity potential over the regional vertical motions.     

东亚夏季风降水年代际变异模态及其与太平洋年代际振荡的关系

利用全球陆地月平均降水资料、英国气象局哈德莱中心的月平均海表温度距平(SSTA)资料及NCEP/NCAR再分析大气环流资料,探讨东亚夏季风降水年代际变率及其与太平洋年代际振荡(PDO)的联系。研究指出:东亚夏季风降水年代际变异模态以及PDO均在1976年前后呈现显著的年代际转折,并且东亚夏季风降水与PDO在年代际尺度上具有较好的相关关系。PDO能够在对流层低层激发出与年代际东亚夏季风环流较为相似的大气环流异常特征,表明东亚夏季风环流的年代际变化可能受大气外强迫因子PDO在对流层低层的外源强迫作用影响,最终导致东亚夏季风降水发生年代际变化。     

The effects of land-surface characteristics on the East Asian summer monsoon

 The Community Climate Model version 2 (CCM2) of the National Center for Atmospheric Research (NCAR) was used to investigate the effects of the land-surface characteristics on the East Asian summer monsoon. Four numerical experiments were performed in this study. They include the control run, the biosphere–atmosphere transfer scheme (BATS) run, the heavy snow run, and the light snow run. The results show that CCM2 can reasonably simulate many characteristics of the East Asian summer monsoon, such as the 850-hPa southwesterlies, 200-hPa easterlies, high precipitation rate, two monsoon subsystems, the low-level subtropical high, and the upper level South Asian anticyclone. Nevertheless, the model still exhibits some systematic errors, including oversimulation of the temperature over the Eurasian continent, which in turn intensifies the monsoon circulations. In the BATS run, the model can significantly relieve the temperature bias over the continent in spring and early summer. However, the effect of BATS decreases in the summer due to excessive incoming solar radiation. The Eurasian continent is still occupied by an oversimulated thermal low in summer. In the heavy snow case, the high albedo of snow and larger soil moisture suppress the warming rate of the surface and atmosphere in the early summer and hence the cooler troposphere results in a weaker monsoon circulation. Moreover, anomalous cyclonic flows are found in the leeside of Tibetan Plateau (i.e. the southwest vortex in China) in the heavy snow case. This may shed a light on the precipitation anomalies (floods) over Yangtze River Valley (Central China) and eastern Asia due to intensified baroclinic disturbances. Received: 8 September 1999 / Accepted: 5 June 2000     

2005年夏季的主要天气及其环流分析

简要讨论了2005年夏季的主要天气过程和形势。2005年夏季全国大部分地区降雨量接近常年同期或偏多,特别是新疆地区降雨异常偏多,华南地区出现严重洪涝,而长江流域出现了空梅。造成6月华南地区强降雨的影响天气系统为切变线和地面静止锋,主要为从东北和西北来的冷空气与暖湿气流交汇于华南地区而形成。2005年与1994、1998年环流的对比表明,1998年西南季风强度比1994、2005年都要弱,但2005年梅雨期东阻位置在贝加尔湖东侧,比1998年的鄂霍次克阻高偏西,中纬度地区多小槽活动,贝加尔湖地区没有长波槽建立,中高层西风急流带偏北大约10个纬度,低层西南风急流也偏北,有利于北方降水的发生。2005年夏季登陆我国的台风偏多,强度较强,这是又一特点。华北地区的暴雨过程多与登陆或西太平洋上活动的台风有关;东北地区多低涡活动。与2004年对比,2005年华北地区的高温日数偏多,而且出现持续闷热天气,江南部分地区的高温天数也偏多。     

冬季亚洲—太平洋涛动年际变率与东亚气候异常

利用1948—2011年NCEP/NCAR月平均再分析资料和1951—2010年我国160站降水量资料,研究了冬季亚洲—太平洋区域的大气遥相关及其与东亚冬季风和降水的关系。结果表明:冬季在亚洲—西太平洋与中、东太平洋中低纬度对流层上层扰动温度之间存在类似于夏季的亚洲—太平洋涛动 (APO) 现象,即当东亚中低纬度对流层中、上层偏暖时,中东太平洋中低纬度对流层中上层温度偏冷,反之亦然。冬季APO可以反映冬季亚洲—太平洋东西向热力差异强度变化,与夏季相比,冬季APO遥相关在亚洲的中心位置略偏南、偏东,且冬季APO与大气环流关系与夏季也有所不同;当冬季APO指数偏高时,对流层上层东亚大槽位置偏西,而东亚热带地区的高压向北伸展,导致我国南方对流层为深厚的异常反气旋系统所控制,此时南方地区对流层低层盛行异常的偏东北气流,并伴随水汽辐散和异常下沉运动,南方降水偏少;冬季APO指数与ENSO有紧密联系。     

青藏高原大地形高度变化对东亚地区定常扰动能源转换的影响

利用CAM3（Community Atmosphere Model version 3）模式和ERA-Interim再分析数据研究了对流层中青藏高原大地形对东亚地区定常扰动能量源的影响。在冬季对流层中东亚地区的定常扰动的能量源地主要有两个,分别是高原北部的东亚地区和高原下游的西太平洋地区。高原高度增加时,对流层整层东亚地区斜压发展随高原高度增高而减弱,西太平洋地区斜压发展增强。定常扰动的正压发展与斜压发展的位置相似,但是明显的要比定常扰动的斜压发展弱。随着高原高度升高,在对流层中高原北部的东亚地区正压发展先减弱后增强,而在高原下游的西太平洋地区随高原高度增高正压发展一直增强。在冬季对流层中定常扰动的总能量发展与定常扰动的斜压发展一致,这样的发展趋势说明了冬季东亚地区和西太平洋地区定常扰动在对流层中的能量发展主要是斜压性引起的。     

积云参数化方案对热带降水年循环模态模拟的影响

本文利用中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室( LASG)发展的大气环流模式(SAMIL),采用Zhang-McFarlane (ZM)和Tiedtke (TDK)两种积云对流参数化方案,讨论了积云对流参数化方案对热带降水年循环模态模拟的影响.结果表明,两种积云对流参数化方案均能合理再现...     

北半球准定常行星波气候平均态的资料分析和数值模拟

利用NCEP/NCAR再分析资料和大气环流模式(CCSR/NIES AGCM Ver 5.6),对北半球准定常行星波的气候平均态分布进行分析和模拟.再分析资料分析的结果表明:北半球冬季,准定常行星波沿两支波导向上传播,其中一支在对流层上层转向中低纬度传播,另外一支折向高纬度,通过极地波导上传到平流层.其中,1波和2波可以上传到平流层,因而其振幅分布除在中低纬的对流层上层出现一个次大值外,在高纬度平流层中上层会出现一个最大值,3波则主要限制在对流层,其振幅分布除在副热带对流层上层出现一个次大值外,最大值出现在中纬度对流层上层.北半球夏季,整个平流层为东风环流,极地波导不存在,行星波不能上传到平流层,在对流层活动也较弱,1波、2波、3波的传播情况大致相似,表现为在对流层上层由中纬度向赤道地区的传播.相应的振幅分布是,对1波和2波而言,最大值出现在中低纬对流层顶附近,同时在中高纬对流层上层出现一个次大值,而3波的振幅分布正好相反,最大值出现在中高纬对流层上层,次大值则在中低纬对流层顶附近.利用大气环流模式进行的数值模拟表明,模式可以比较好地模拟冬夏季准定常行星波的传播路径,但模拟的北半球冬季沿极地波导向平流层的传播明显偏弱,其结果是对1波、2波而言,高纬度平流层中上层的振幅最大值明显小于再分析资料的数值.文中还讨论了数值模拟与资料分析中行星波的差异可能对大气环流模拟的影响.     

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。      

云南夏季降水量在21世纪初的突变减少及原因分析

利用1960—2013年云南125个台站观测资料和美国环境预报中心/国家大气研究中心再分析资料,以及1960—2013年美国国家海洋和大气管理局(NOAA)提供的逐月平均全球海表温度资料,分析了云南地区降水量变化的特征以及与之相关联的大气环流背景场。分析结果表明:云南降水量在2002年发生了一次显著减少的突变,而这次突变主要是由于夏季降水的明显减少而形成的。进一步的分析揭示了该地区夏季降水减少主要与印度洋热带赤道地区低层东风加强和高空西风加强有关,亚洲地区中高纬度温度的升高也对该地区夏季降水量显著减少有重要作用。     

Interannual variability of total ozone and its relation with the Asia Pacific Wave

Analysis of the NCEP/NCAR reanalysis wind data shows the presence of a stationary Rossby wave in the lower stratosphere during May. This wave is seen prominently below 70 hPa level, confined between 10°N and 50°N latitudes and has a zonal wave number of 6 or 7. It is an extension into the stratosphere of the Asia Pacific Wave (APW) of the troposphere documented by Joseph and Srinivasan (1999) . As in the troposphere, in the lower stratosphere this wave shows a phase shift of 20° longitude between deficient and excess Indian summer monsoon rainfall (ISMR) years. This wave has maximum amplitude at about 200 hPa. The amplitude of the wave decreases both above and below 200 hPa level. The large-amplitude portion of this wave is thus situated in the break region between the tropical and extratropical tropopauses around 30°N latitude. It is suggested that this large-amplitude APW exchanges the tropical and extratropical airmasses through the tropopause break, making the APW signature seen in the satellite monitored total ozone (TOMS data). APW is found to exist in the following monsoon season (June to September) with the same phase as in May and its signature is also seen in that season in total ozone.     

Fluctuations of Tropical Easterly Jet during contrasting monsoons over India: A GCM study

Summary  The fluctuations of intensity of the Tropical Easterly Jet (TEJ) and its association with the Indian summer monsoon rainfall have been examined using the diagnostics from NCEP/NCAR (National Centre for Environmental Prediction/National Centre for Atmospheric Research) reanalyses project for the period 1986 to 1994. The intensity of TEJ is found to be well correlated with India summer monsoon rainfall. The TEJ is weaker/stronger during the El Ni?o/La Ni?a year of 1987/1988 and is associated with deficient (excess) summer monsoon rainfall over India. A numerical study was carried out for the same period using the Centre for Ocean-Land-Atmosphere studies General Circulation Model (COLA GCM, T30L18) with observed Sea-Surface Temperature (SST). The GCM simulates the TEJ with reasonable accuracy. The strong interannual variability of TEJ during the El Ni?o/La Ni?a years of 1987/1988 are well simulated in the GCM. Like observations, the intensity of the TEJ is positively correlated with the summer monsoon rainfall over India in the model simulation. The intensity of Tibetan anticyclone and diabatic heating over the Tibetan Plateau diminished during the El Ni?o-year of 1987. The divergence centre in the upper troposphere associated with Asian monsoon becomes weaker and shifts eastward during the weak monsoon season of 1987. However, the opposite happens for the strong monsoon season of 1988. Also the middle and upper tropospheric meridional temperature gradient between the Tibetan High and Indian Ocean region decreased (increased) during the weak(strong) monsoon season of 1987 (1988). Received May 27, 1999/Revised March 20, 2000     

副热带东太平洋低云对LASG耦合环流模式FGCM-0中"双ITCZ"的影响

与其他耦合环流模式一样,LASG耦合模式FGCM-0也存在虚假的“双ITCZ”。为了认识FGCM-0中“双ITCZ”,首先研究了FGCM-0的大气分量模式,剧INCAR(美国国家大气研究中心)的公用气候模式CCM3对秘鲁和加利福尼亚沿岸低云以及低层大气整体稳定度的模拟能力。发现：尽管CCM3模拟的低层大气整体稳定度与利用NCEP(美国国家环境预报中心)再分析资料分析的结果较一致,但模拟的低云量比ISCCP(国际卫星云气候计划)观测值显偏少。利用ISCCP低云量与由NCEP再分析温度场分析的低层整体稳定度之间的回归关系,修改了CCM3中低云参数化方案,并用于敏感性试验,以研究副热带东太平洋低云对FGCM-0中“双ITCZ”的影响。结果发现,修改的方案能显增强对低云量的模拟,秘鲁沿岸冷海域低云量增加能显减弱赤道以南热带东太平洋海表面温度(SST)的暖偏差,但同时也将使赤道冷舌增强、向西伸展更远;加利福尼亚沿岸低云量增加可以有效减弱赤道以北ITCZ区SST暖偏差。为了检验秘鲁沿岸SST与低云间的正反馈,又实施了一个控制秘鲁沿岸SST的敏感性试验,结果表明：控制秘鲁沿岸SST抑制其增暖,对自东南太平洋向西北至中、西赤道太平洋广大区域产生的影响,与增加秘鲁沿岸低云量产生的影响相似。     

全球大气／热带太平洋耦合距平模式中由ENSO增暖引起的全球大气环流异常

本文利用全球大气／热带太平洋耦合距平模式模拟了一次类似于实际的ENSO增暖过程，并对由ENSO增暖引起的海洋和全球大气环流异常的主要特征进行了分析，指出:耦合模式中的ENSO增暖在热带地区主要伴随着赤道中西太平洋Walker环流的减弱、中东太平洋气压降低以及表层辐合上升运动的增强；夏季和冬季低纬环流异常具有明显的差异性，夏季主要表现为印度夏季风环流的显著减弱和东亚季风的增强，而冬季则主要表现为赤道所有纬向环流圈均减弱；温带大气环流异常冬夏季也具有明显不同特征，夏季温带大气异常主要限于东半球，且发源于亚洲季风区，和赤道中东太平洋海温异常似无直接联系，但冬季温带大气异常则主要是发源于海温异常区的波列响应，反映了海温异常直接热力强迫的结果。另外，本文对耦合模式中的温带大气环流异常产生的可能机制也进行了讨论。     

空间非均匀加热对副热带高压形成和变异的影响──Ⅲ:凝结潜热加热与南亚高压及西太平洋副高

通过理论分析和数值模拟,研究了降水所致凝结潜热影响副热带高压带断裂的物理机制。基于全型垂直涡度方程的尺度分析指出,强的对流凝结加热的垂直梯度的变化,导致副热带地区对流层高层和中低层的高低压分布呈现出反位相。数值试验证实凝结潜热是决定东半球夏季副热带高压位置和强度的关键因素：东亚季风降雨所致凝结潜热加热使高层南亚高压位于加热中心西侧,中层西太平洋副热带高压位于加热中心东侧。通过定常波的传播,副热带地区的凝结潜热加热对中高纬天气的形成和维持有一定影响。     

东亚夏季风与澳洲冬季风强弱互补变化联系及其异常环流特征

利用NCEP/NCAR再分析资料、Hadley中心海温资料及CMAP降水资料等,通过亚澳季风联合指数挑选异常年份,对东亚夏季风和澳洲冬季风强度反相变化特征进行研究。结果表明,当东亚夏季风偏强、澳洲冬季风偏弱时,南北半球中低纬地区都出现了复杂的异常环流系统。在热带地区对流层低层,西北太平洋为异常反气旋式环流系统所控制,与南太平洋赤道辐合带的异常反气旋环流在赤道地区发生耦合,形成赤道异常东风,而在南北印度洋上则存在两个异常气旋式环流系统。在这两对异常环流之间的海洋性大陆地区,出现赤道以南为反气旋环流而赤道以北为气旋式环流。在东亚季风区,东南沿海的东侧海洋上存在反气旋异常,中国东南地区受异常反气旋西南侧的东南风影响。此外,澳洲北部受异常西风影响。这就形成了东亚夏季风偏强、澳洲冬季风偏弱的情形,从而东亚夏季风和澳洲冬季风活动出现了强弱互补的变化特征。当东亚夏季风偏弱、澳洲冬季风偏强时,南北半球的环流特征则出现与上述相反的环流特征。总体而言,当东亚夏季风偏强、澳洲冬季风偏弱时,东亚—澳洲季风区在南北半球呈现出不同的气候异常分布特征,即北半球降水北少南多、气温北高南低,南半球降水西多东少、气温西高东低。     

论大气环流的季节划分与季节突变 Ⅲ.气候平均情况

该文第Ⅰ部分定义了大气环流的季节划分和季节突变,第Ⅱ部分按此对个别年份的情况作了具体计算,第Ⅲ部分则利用NCEP/NCAR 1978～1997年气候平均资料做了实际计算,其结果与第Ⅱ部分大体一致,但更鲜明且更有代表性(是气候平均而非个别年份).主要结果有:(1)在对流层中下层,亚洲冬季风环流的建立始于欧亚大陆高纬西风带,夏季风环流的建立始于太平洋副高(副热带季风),以及由于马斯克林高压和澳大利亚冷高等几个大气活动中心的建立或加强(热带季风).(2)各季节的建立始于平流层,之后是对流层低层的极区和热带个别区域,并由上述层及地区分别向上、下层和中纬度地区发展,最终导致整个半球季节环流场的建立.(3)季节突变最强在平流层,分别位于两半球的热带到副热带以及高纬到极地,其中从冬到夏的突变明显强于从夏到冬的突变,而对流层的季节突变较平流层偏弱,主要位于热带到副热带的中上层.     

东亚-北太平洋偶极型气压场及其与东亚季风年际变化的关系

利用美国NCEP/NCAR的月平均再分析资料,研究东亚-太平洋地区地面气压的耦合模态与东亚副热带季风异常的关系,结果表明:在亚洲大陆和北半球太平洋之间气压场的偶极子模态主要反映了东亚地区东西向气压梯度的异常.从20世纪60年代到70年代中期,东亚-太平洋的这种偶极子表现为蒙古地区气压偏低和太平洋地区气压偏高的特征,而从20世纪70年代后期到90年代,则表现为蒙古地区气压偏高和太平洋地区气压偏低的特征.在偶极子指数值较高的年份,冬季(或夏季)蒙古高压(或蒙古低压)和太平洋阿留申低压(或太平洋副热带高压)较强     

NUMERICAL SIMULATIONS ON INFLUENCES OF VARIATION OF SEA ICE THICKNESS AND EXTENT ON ATMOSPHERIC CIRCULATION*

By using a 2-layer AGCM designed by Institute of Atmospheric Physics,Chinese Academy of Sciences.this paper investigates influences of thickness and extent variations in Arctic sea ice on the atmosphere circulation,particularly on climate variations in East Asia.The simulation results have indicated that sea ice thickness variation in the Arctic exhibits significant influences on simulation results,particularly on East Asian monsoon.A nearly reasonable distribution of sea ice thickness in the model leads directly to stronger winter and summer monsoon over East Asia.and improves the model's simulation results for Siberia high and Icelandic low in winter.On the other hand,sea ice thickness variation can excite a teleconnection wave train across Asian Continent,and in low latitudes,the wave propagates from the western Pacific across the equator to the eastern Pacific.In addition,the variation of sea ice thickness also influences summer convective activitiesover the low latitudes including South China Sea and around the Philippines.Effects of winter sea ice extents in the Barents Sea on atmospheric circulation in the following spring and summer are also significant.The simulation result shows that when winter sea ice extent in the target region is larger (smaller) than normal.(1)in the following spring (averaged from April to June).positive (negative) SLP anomalies occupy the northern central Pacific.which leads directly to weakened (deepened)Aleutian low.and further favors the light (heavy) sea ice condition in the Bering Sea:(2)in the following summer,thermal depression in Asian Continent is deepened (weakened).and the subtropical high in the northwestern Pacific shifts northward(southward) from its normal position and to be strengthened (weakened).