全球海温异常作用下的低层大气环流和降水异常的数值模拟

通过在ＩＡＰＡＧＣＭ中加进太平洋和印度洋海温异常的数值模拟，证实了实况月平均８５０ｈＰａ上的异常环流特征：ＥｌＮｉｎｏ海温位相时低纬太平洋低层大气出现异常的西风气流以及在东南亚沿海出现向赤道的异常气流；而在ＬａＮｉｎａ位相时，低纬太平洋低层大气出现异常的东风气流和在东南亚沿海出现离赤道的异常气流。若在模式中仅引入太平洋的海温异常或在模式中去掉地形以后，模拟的低纬低层异常气流与上述结果有所不同。用该模式还模拟出了与观测相符的低纬地区降水的异常     

Effects of Sea Surface Temperature Anomalies off the East Coast of Japan on Development of the Okhotsk High

The study examined effects of sea surface temperature anomalies (SSTAs) off the east coast of Japan on the blocking high over the Okhotsk Sea in June by diagnostic analysis and numerical simulation. Firstly, based on 500-hPa geopotential height fields, the Okhotsk high index (OKHI) for June from 1951 to 2000 is calculated and analyzed. The result indicates that the OKHI has obvious inter-annual and inter-decadal variations, and there are 9 yr of high OKHI and 8 yr of low OKHI in 50 yr. Secondly, by using the OKHI, the relationship between the Okhotsk high and the 500-hPa geopotential height anomaly is investigated. The results indicate that the "+-+" pattern of geopotential height anomaly crossing Eurasia in the mid-high latitudes and the "+-" pattern of geopotential height anomaly from high to low latitudes over East Asia are in favor of the formation and maintenance of the Okhotsk high. The relationship between the OKHI and the SSTA over the North Pacific is investigated in early summer by using correlation and composite analysis. We found that when the blocking circulation over the Okhotsk Sea occurs, there is an obvious negative SSTA off the east coast of Japan in early summer. We simulated the effects of the negative SSTA of east coast of Japan on the atmospheric circulation anomaly over East Asia through the control and sensitivity experiments using NCAR CAM3 model in order to confirm our analysis results. The simulation shows that the negative SSTA off the east coast of Japan results in the significant positive 40 gpm 500-hPa geopotential height anomaly over the Okhotsk Sea and the negative anomalies off the east coast of Japan which might contribute to the formation and development of the Okhotsk high in June.     

西北太平洋冷海温对东亚初夏大气环流影响的数值研究

利用改进的NCAR CCM3气候模式, 研究了1992年西北太平洋持续冷海温对东亚初夏季节大气环流的影响。西北太平洋冷海温不利于初夏东亚南支西风急流季节性北移, 引起亚洲东部沿海低槽明显加深, 东亚大槽平均高度场降低了4.66 dagpm, 从而也不利于西太平洋副热带高压的西伸加强。西北太平洋冷海温还不利于我国大陆初夏温度场回升, 特别是引起我国东北地区近地面温度下降2~5 ℃, 是影响东北冷夏现象的重要原因之一。模拟结果表明, 1992年初夏江淮入梅期较常年偏晚, 降水异常偏少, 与紧邻东亚大陆的西北太平洋持续冷海温有关。     

SYNERGISTIC EFFECTS ON ATMOSPHERIC ANOMALY OF THE TROPICAL INDIAN AND PACIFIC OCEANS IN NORTHERN WINTER*

In terms of observational analysis and numerical simulations,study is performed of the synergistic effects of the tropical Indian Ocean and Pacific SSTA on the atmosphere in northern winter.It turns out that the SSTA features show in-phase variation for the Indian Ocean and the central/eastern Pacific at low latitudes and anti-phase change compared with that in the neighborhood of the western Pacific "warming pool".When negative SSTA in the western Pacific and positive SSTA in the central/eastern Pacific and the Indian Ocean are available,the 500 hPa height anomaly exhibits a wave train of a positive-negative-positive anomaly following a great-circle path emanating from the subtropical western Pacific via the NW portion to North America,with enhanced westerly jet over midlatitude East Asia and the NW Pacific,and v.v.The comparison to the results from the numerical modeling of the tropical western Pacific SSTA reveals the importance of the synergistic effects of the oceans on atmospheric circulations.     

热带西太平洋海温异常对东北亚阻塞形势影响的数值模拟

本文利用ＩＡＰ－ＡＧＣＭ模拟研究了实测海温异常和热带西太平洋假想海温异常对夏季东亚地区环流异常的影响,并与观测结果进行了比较,籍此间接地研究了海温异常对东北亚阻塞形势的影响。首先,利用１９８０年实测海温异常,分三种试验（全球海温异常试验、热带海温异常试验、热带外海温异常试验）模拟了该年７月和８月的大气环流异常,指出海温异常是致使东北亚阻塞形势得以形成和维持的一个重要原因,同时也表明在对东亚大气环流异常型的影响方面,热带海温异常比热带经温异常更为重要。此外,我们还模拟研究了热带西太平洋的假想海温异常对东亚大气环流异常的影响,表明了热带西太平浃海温负异常对东北亚阻塞形势形成和维持有着重要作用     

1999年东亚夏季风异常活动的物理机制研究

文中从海-气相互作用的角度探讨了1999年东亚夏季风及与其相联系的雨带异常活动的物理机制。结果表明,由于1998年春季至1999年南海-热带西太平洋出现了近20 a最强的异常暧海温,该地强异常海-气相互作用的维持使得这种局地的热力强迫成为1999年东亚夏季风和降水异常的最主要外强迫机制,并使得1999年的季风活动和降水分布有别于一般的统计情形。从1998年秋到1999年,由于热带大气对南海-西太平洋暧海温所诱发的局地强加热的响应,热带西太平洋地区所出现的Gill模态的异常环流分布从冬季一直发展到夏季,并因此在海洋和大气之间形成了局地的强烈正反馈,不仅使得异常环流得以持续发展,而且也使得暖海温得以维持,成为影响1999年环流异常的最强前期信号。随着从冬到夏的季节演变,大气基本态对上述持续性异常环流的影响导致了冬、夏异常环流呈现出不同的纬向非对称,诱发了盛夏期间东亚到北美沿岸的遥相关波列。在东亚沿岸异常气旋性环流的影响下,大尺度异常东风在东亚沿岸的维持形成了极不利于季风西风在南海北部转向的条件,导致了季风在中国东部北进的异常偏弱和低纬西风转向位置的异常偏东。     

LOW FREQUENCY OSCILLATION IN EAST ASIA DURING THE 1991 EXCESSIVELY HEAVY RAIN OVER THE CHANGJIANG-HUAIHE RIVER BASIN

The activity of low frequency oscillation (LFO) widely exists in East Asia during the period of1991 excessively heavy rain over the Changjiang-Huaihe River Basin (Jianghuai).Both the rainfallamount of Jianghuai and the atmosphere from subtropical area to mid-high latitudes have thedominant period of 10—20 d,while the atmospheres in tropical area and high latitudes have thedominant period of 30—60 d.Compared with normal Meiyu season,the anomaly of the 1991 Meiyu process may be reflectedin the following two low frequency synoptic events:(a) The Meiyu process onsets extremely early(in the second dekad of May,which is nearly one month earlier than in normal Meiyu) and isimmediately followed by the first episode of heavy rain.(b) In the first dekad of July,there occursthe heaviest episode of rainfall of the whole Meiyu season,and it is even the heaviest rainfall forthe recent 30 years in China.For these two periods,corresponding to the adjustment of large-scalesituation from“double blocking high”to“bipolar blocking high”,the propagation direction of LFOin East Asia has a distinct seasonal variation,from eastward/northward propagation (passingthrough Jianghuai) during the first episode to westward/southward propagation during the thirdepisode.Oscillations of different frequency bands are superposed in phase.The LFO activity of thecold and warm/moist airs over Jianghuai can be strengthened through those LFO propagationprocesses in East Asia,although they may have different directions in three episodes.Particularly,the eastward (westward) propagation in low latitudes makes the southwest (southeast) airflowtransport intensively the low frequency warm/moist air to the south of Jianghuai from the IndianOcean (tropical West Pacific Ocean) in the first (third) episode.Such warm/moist airs meet andinteract with the cold air which vigorously invades Jianghuai persistently,and finally three episodesof heavy rain occur in mode of LFO.     

NUMERICAL SIMULATION OF THE IMPACT OF LATENT HEAT FLUX ANOMALY IN THE TROPICAL WESTERN PACIFIC ON PRECIPITATION OVER SOUTH CHINA IN JUNES

Based on composite analysis and numerical simulations using a regional climate model （RegCM3）, this paper analyzed the impact of the LHF anomaly in the tropical western Pacific on the precipitation over the south of China in June. The results are as follows. （1） Correlation analysis shows that the SC precipitation in June is negatively correlated with the LHF of the tropical western Pacific in May and June, especially in May. The SC precipitation in June appears to negatively correlate with low-level relative vorticity in the abnormal area of LHF in the tropical western Pacific. （2） The LHF anomaly in the tropical western Pacific is a vital factor affecting the flood and drought of SC in June. A conceptual model goes like this： When the LHF in the tropical western Pacific is abnormally increased （decreased）, an anomalous cyclone （anticyclone） circulation is formed at the low-level troposphere to its northwest. As a result, an anomalous northeast （southwest） air flow affects the south of China, being disadvantageous （advantageous） to the transportation of water vapor to the region. Meanwhile, there is an anomalous anticyclone （cyclone） at the low-level troposphere and an anomalous cyclone （anticyclone） circulation at the high-level troposphere in the region, which is advantageous for downdraft （updraft） there. Therefore a virtual circulation forms updraft （downdraft） in the anomalous area of LHF and downdraft （updraft） in the south of China, which finally leads to the drought （flood） in the region.     

Increased summer electric power demand in Beijing driven by preceding spring tropical North Atlantic warming

本文利用北京市电力负荷资料,北京市站点观测温度资料,CN05.1温度资料,ERA5大气再分析资料及ERSST v3b海表温度资料,发现3-4月副热带北大西洋海温异常和北京市夏季电力呈很好的正相关关系,并揭示了副热带北大西洋海温异常影响北京市夏季电力的可能物理机制.春季副热带北大西洋海温异常偏暖,热带中太平洋出现东风异常...     

冬夏季环流隔季相关的数值试验

利用海气耦合和大气气候模式研究东亚冬季风异常对夏季环流的影响, 结果表明, 东亚冬季风异常对于后期环流及海洋状态异常都起了很大的作用.一般情况下, 强的冬季风与后期弱的东亚夏季风和较强的南海季风相对应.与强(弱)冬季风异常相关的风应力的改变可以使热带太平洋海温从冬季至夏季呈现La Nina (El Nio)型异常分布.试验得到的由冬季风异常所产生的海洋及夏季环流的变化与实况是相当接近的.在异常的冬季风偏北风分量强迫下, 西太平洋上形成的偏差气旋环流在夏季已不存在, 这时东亚夏季风反而增强.而冬季赤道西风分量所产生的影响, 则在西太平洋上形成显著的偏差气旋环流, 使东亚副热带夏季风减弱, 南海夏季风加强.对于东亚大气环流而言, 与强弱冬季风对应的热带海洋海温异常强迫下, 不仅是冬季, 后期春季和夏季环流的特征都能得到很好的模拟.但是从分区看, 西太平洋暖池区的海温异常比东太平洋更为重要.单纯的热带中东太平洋的海温异常对东亚大气环流的影响主要表现在冬季, 对后期的影响并不十分清楚.整个热带海洋的异常型分布(不论是El Nio还是La Nia)型, 对冬夏季风的影响是重要的, 而单纯的某个地区的海温异常都比它的整体影响要小.从试验结果看, 海温在大尺度冬夏季环流的隔季相关中起了十分重要的作用.     

北太平洋冬季海-气耦合的主模态及其与瞬变扰动异常的联系

利用45年的ECMWF 再分析资料,使用SVD方法研究了冬季北太平洋地区表层海温(SST)异常与大气环流异常间的主要耦合模态,探讨了大尺度海-气耦合型与天气尺度瞬变扰动的相互关系.分析结果表明,中纬度北太平洋地区冬季存在两种主要的海-气耦合型,第1种耦合型反映了与ENSO紧密相关的中纬度北太平洋冬季海温异常分布型以及大气的PNA型,第2种耦合型SST 异常集中在东亚沿海以及中纬度北太平洋海流区,相应的大气场则为暖(冷)SSTA上空东西向带状区域内位势高度偏高(低),明显独立于ENSO型.进一步的合成分析表明,在第1种耦合型SST正(负)异常年里,冬季阿留申低压主体位置偏西南(东北),从东北亚到北美西海岸的西北-东南向带状区域内是低层大气温度正(负)异常区和高层西风负(正)异常区,西风负(正)异常中心位于西风急流出口处的北太平洋中东部,而西风急流主体区的风速变化很小.在第2种耦合型东亚沿海至中纬度北太平洋海流区SST偏暖(冷)时,阿留申低压整体偏弱(强),SST暖(冷)异常上空的大气温度偏暖(冷),高层西风急流区西风偏弱(强).两种耦合型均显示出在北太平洋中纬度地区大气和海洋的异常相关中心有很好的空间对应性.在两种耦合型下,中纬度北太平洋冬季的大气斜压性也发生截然不同的改变,引起中纬度天气尺度瞬变扰动活动异常.瞬变扰动异常的动力强迫作用对北太平洋西风异常的形成存在正反馈作用,而其热力作用则试图破坏与两种海-气耦合模态相关的大气温度异常型.     

春季热带大西洋北部海温异常与我国盛夏降水异常的联系

利用Hadley中心的海表温度资料、全国160站降水资料以及NCEP-DOE AMIP-Ⅱ再分析等资料,运用多种统计分析方法,分析了春季（3—5月）热带大西洋北部海温异常变化特征及其对我国盛夏（7、8月）降水异常的影响。结果表明:春季热带大西洋北部模态是热带大西洋海温异常REOF分解的第一模态,方差贡献率为34.5%。热带大西洋北部海温异常年际变率具有明显的季节差异,其中春季最为显著。春季热带大西洋北部海温异常与我国盛夏华中地区降水异常有显著的正相关关系。进一步分析表明,春季热带大西洋北部的海温正异常可以激发出Rossby波,在热带大西洋西北部和热带东太平洋北部产生异常的气旋式环流,引起上述区域的对流层低层（上层）大气出现异常辐合（辐散）,并通过热带大西洋北部地区和太平洋之间的垂直环流异常,在中太平洋地区对流层低层大气出现异常辐散,有利于西北太平洋地区产生异常反气旋式环流,异常反气旋西北侧的西南气流有利于水汽输送至我国华中地区,使该地区降水偏多。且这种影响可以通过热带大西洋北部海温异常的持续性,从春季一直持续到盛夏。      

东亚季风指数及其与大尺度热力环流年际变化关系

将东西向海平面气压差与低纬度高、低层纬向风切变相结合 ,定义了东亚季风指数 ,该季风指数较好地反映了东亚冬、夏季风变化。其中 ,夏季风指数年际异常对西太平洋副热带高压南北位置变化和长江中下游旱涝具有较强的反映能力。分析表明 :东亚夏季风年际变化与印度洋 -西太平洋上空反 Walker环流及夏季越赤道南北半球间的季风环流呈显著正相关关系。在强、弱异常东亚夏季风年份 ,异常的 Walker环流在西太平洋上的辐合 (辐散 )中心在垂直方向不重合 ,高层 ( 2 0 0 h Pa)速度势与东亚夏季风显著相关区域位于西北太平洋上 ,该异常环流的高层的辐合 (辐散 )通过改变低层空气质量而影响夏季 50 0 h Pa西北太平洋副热带高压。采用 SVD分析进一步发现 :与海温耦合的异常 Walker环流在西太平洋上空的上升支表现出南北半球关于赤道非对称结构 ,亚澳季风区受该异常 Walker环流控制。因而 ,东亚季风与热带海气相互作用可直接通过这种纬向非对称的 Walker环流发生联系。     

热带和热带外海表温度异常与低空环流特征比较

利用旋转主分量方法（ＲＰＣ），在对西太平洋和印度洋１９８０年１月至１９８８年９月共１０５个月的月平均海表温度（ＳＳＴ）进行分析的基础上，提取热带模及高纬模两种ＳＳＴ异常（ＳＳＴＡ）分布。再通过分析同期８５０ｈＰａ，各气象要素在该两模上的投影，比较低层大气与不同纬度上ＳＳＴＡ相联系的异常特征。结果表明，无论是热带还是热带外地区，暖性ＳＳＴＡ上空均有正的水汽异常及平均流场对月平均水汽输送的异常辐合。两地区ＳＳＴＡ上空８５０ｈＰａ月平均异常的最重要差异表现在流场、高度场及温度场上。热带正ＳＳＴＡ上方８５０ｈＰａ位势高度及温度均为负距平，流场呈Ｇｉｌｌ型的气旋式异常环流。热带外正ＳＳＴＡ上方８５０ｈＰａ高度及温度均为正距平，流场则呈反气旋式异常环流。分析表明，高纬度的这种异常特征主要是由于中高纬度大气的地转性和斜压性较强所致。     

Primary reasoning behind the double ITCZ phenomenon in a coupled ocean-atmosphere general circulation model

This paper investigates the processes behind the double ITCZ phenomenon, a common problem in Coupled ocean-atmosphere General Circulation Models (CGCMs), using a CGCM-FGCM-0 (Flexible General Circulation Model, version 0). The double ITCZ mode develops rapidly during the first two years of the integration and becomes a perennial phenomenon afterwards in the model. By way of Singular ValueDecomposition (SVD) for SST, sea surface pressure, and sea surface wind, some air-sea interactions are analyzed. These interactions prompt the anomalous signals that appear at the beginning of the coupling to develop rapidly. There are two possible reasons, proved by sensitivity experiments: (1) the overestimatedeast-west gradient of SST in the equatorial Pacific in the ocean spin-up process, and (2) the underestimatedamount of low-level stratus over the Peruvian coast in CCM3 (the Community Climate Model, VersionThree). The overestimated east-west gradient of SST brings the anomalous equatorial easterly. The anomalous easterly, affected by the Coriolis force in the Southern Hemisphere, turns into an anomalouswesterly in a broad area south of the equator and is enhanced by atmospheric anomalous circulationdue to the underestimated amount of low-level stratus over the Peruvian coast simulated by CCM3. Theanomalous westerly leads to anomalous warm advection that makes the SST warm in the southeast Pacific.The double ITCZ phenomenon in the CGCM is a result of a series of nonlocal and nonlinear adjustmentprocesses in the coupled system, which can be traced to the uncoupled models, oceanic component, andatmospheric component. The zonal gradient of the equatorial SST is too large in the ocean componentand the amount of low-level stratus over the Peruvian coast is too low in the atmosphere component.     

亚洲夏季风环流结构与热带印度洋偶极型海温异常

使用T42L28大气环流模式就夏季风时期大气对印度洋海温偶极子型异常的响应进行了数值试验研究,结果表明,印度洋偶极子型海温异常可以引起感热和潜热加热异常并进而形成异常辐合辐散,导致热带印度洋及其邻近地区夏季降水异常。同时此热带扰动可激发或造成中纬度异常波列。通过改变季风区温度场分布,偶极子型海温强迫可以影响大气的正／斜压环流结构和斜压性强弱。强的纬向风垂直切变趋向于靠近海洋异常偏暖的地区。不论是正偶极子型强迫或负偶极子型强迫,西太平洋暖池和东亚地区的大气环流均出现异常并激发出中纬度的异常波列,但异常类型并未显著反相。     

A NUMERICAL EXPERIMENT STUDY ON THE FORMING MECHANISMS OF LOW-LATITUDE CIRCULATION CELLS AND PRECIPITATION DURING AN EAST ASIAN COLD SURGE

The forming mechanisms of low-latitude circulation cells and precipitation during an East Asian cold surge have been studied by using a five-layer primitive equation model.Numerical experiments show that in mid-high latitudes,the propagation of the East Asian winter monsoon is nearly a dry process;in low-latitudes,the effects of cumulus convection intensify the northeast monsoon and northeast trade wind;however,they also prevent the intertropical convergence zone(ITCZ) from further southward invasion,and strengthen the meridional and zonal cells over East Asia. Numerical results also indicate that the winter monsoon precipitation in Indonesia and Northern Australia can exist independently.Both the South China Sea(SCS) cold surge and the West Pacific northeast cross-equatorial trade wind are of importance for the formation of the Northern Australia summer monsoon and its precipitation.Numerical results show that the development of cumulus convection,triggered by the SCS cold surge,is a crucial factor in forming the heavy monsoon precipitation and low-level stationary disturbances in Indonesia and Borneo.The tropical topography and northeast trade wind disturbances only affect the intensity of precipitation there.     

Interdecadal variability of winter precipitation in Southeast China

Interdecadal variability of observed winter precipitation in Southeast China (1961–2010) is characterized by the first empirical orthogonal function of the three-monthly Standardized Precipitation Index (SPI) subjected to a 9-year running mean. For interdecadal time scales the dominating spatial modes represent monopole features involving the Arctic Oscillation (AO) and the sea surface temperature (SST) anomalies. Dynamic composite analysis (based on NCEP/NCAR reanalyzes) reveals the following results: (1) Interdecadal SPI-variations show a trend from a dryer state in the 1970s via an increase during the 1980s towards stabilization on wetter conditions commencing with the 1990s. (2) Increasing wetness in Southeast China is attributed to an abnormal anticyclone over south Japan, with northward transport of warm and humid air from the tropical Pacific to South China. (3) In mid-to-high latitudes the weakened southward flow of polar airmasses induces low-level warming over Eurasia due to stronger AO by warmer zonal temperature advection. This indicates that AO is attributed to the Southeast China precipitation increase influenced by circulation anomalies over the mid-to-high latitudes. (4) The abnormal moisture transport along the southwestern boundary of the abnormal anticyclone over south Japan is related to anomalous south-easterlies modulated by the SST anomalies over Western Pacific Ocean; a positive (negative) SST anomaly will strengthen (weaken) warm and humid air transport, leading to abundant (reduced) precipitation in Southeast China. That is both AO and SST anomalies determine the nonlinear trend observed in winter precipitation over Southeast China.     

FORMATION MECHANISM AND PROPAGATION CHARACTERISTICS OF THE EQUATORIAL THERMALLY-FORCED SHORT-TERM CLIMATIC OSCILLATION DURING THE NORTHERN SUMMER

In this study, in order to investigate the global climatic oscillations forced by sea surface temperature (SST) anomalies over equatorial central-eastern Pacific, two numerical schemes with different SST distri-butions (normal and anomalous cases) are tested by using a nine-layer global spectral model. Experiment results show that (i) in northern summer, a wave train that is similar to the teleconnection pattern suggested by Nitta (1987) and Huang (1987) in the Northern Hemisphere and another one in the Southern Hemisphere are reproduced; (ii) simulated results suggest that the response of atmosphere in middle-high latitudes of both hemispheres to an anomalous heating source is more sensitive in tropical western Pacific than in equatorial central-eastern Pacific; and (iii) in northern summer, the formation of low-frequency oscillations on monthly (seasonal) time scale results from energy dispersion as well as interactions between eddies and zonal flow; and between eddies.     

1991～1994年El Niño的异常特征的诊断研究

1991～1994年热带中东太平洋海温持续4a多出现正距平。Niño3指数一直为正值。在此正距平背景下,产生了两次振荡和3次ElNiño暖期。在此期间赤道东太平洋海温在±5°纬度范围内发生了两次负距平的变化,形成了一个狭窄的温度梯度很大的“冷核”,而赤道外的中纬度海洋则持续维持两个正海温距平。这一时期海表温度资料EOF分析的结果进一步表明,第一特征向量的空间分布实际上反映了上述冷核特征。1991～1994年的ENSO事件主要是低频分量发生了较大异常,赤道低层纬向风和高层西风在前期减弱(1991-01-1992-05),后期加强(1992-06-1994-011).无论是海温还是风场的低频分量都表现出一次ENSO循环的特征。因此作者认为,虽然Niño3指数等在这4a多期间均为正值,但是大气和海洋耦合系统的低频变化部分只发生了一次完整的ENSO循环过程。1991年至1992年上半年对应于ElNiño暖位相,1992年下半年至1994年底对应于LaNina冷位相。但是这个冷位相没有能够得到充分发展,只出现两次极狭窄的冷核。冷位相的明显“夭折”,而代之以出现两次较弱的增暖,可能与季节内尺度的大气强迫与低频变化部分的相互作用有关。