Impacts of SST and SST Anomalies on Low-Frequency Oscillation in the Tropical Atmosphere

Considering the multiscale character of LFO effects of SST on LFO in the tropical atmosphere （low-frequency oscillation） in the tropical atmosphere, the are discussed by using an absolute ageostrophic, baroclinic model. Here, SST effects include sea surface heating and forcing of SST anomalies （SSTAs）. Studies of the influences of sea surface heating on LFO frequency and stability show that sea surface heating can slow the speed of waves and lower their frequency when SST is comparatively low; while higher SST leads to unstable waves and less periods of LFO. Since the impact of a SSTA on ultra-long waves is more evident than that on kilometer-scale waves, long-wave approximation is used when we continue to study the effect of SSTAs. Results indicate that SSTAs can lead to a longer period of LFO, and make waves unstable. In other words, positive （negative） SSTAs can make waves decay （grow）.     

海温对热带低频振荡系统影响的动力学研究

根据热带地区蒸发、辐合上升运动剧烈以及海温异常的特点，构造了一个斜压模式方程组，讨论了海表温度（海温加热和海温异常变化）对热带低频波动的影响。分析表明，对天气尺度波动（Lx～Ly～10^6m），采用完全非地转模式，在海温异常作用下，频率明显发生变化，并容易产生波动的不稳定：海温较低时，波稳定，并随海温的增高，频率变低，波速变慢；海温较高时，会引起波动不稳定，且周期随海温的增高而变小。对超长波系统（Lx～10^7m,L,～10^6m），可以采用半地转模式，海温作用可以激发向东传播的低频Kelvin波以及向西传播的低频Rossby波，热带超常波的波动周期随海温升高和异常增大而变长，且在海温异常作用下，波动会产生不稳定。     

2009年海洋和大气环流异常及对中国气候的影响

2009年总体来看,全国天气气候的特征为气温偏高,平均降水偏少,夏季为近10多年来降水最少的年份,区域性和持续性干旱非常显著:黄淮、华北发生了严重的秋冬季连旱,东北西南部夏秋旱严重,江南西部、华南西部和西南南部夏秋旱明显等。2009年在南海和西太平洋生成的热带气旋个数明显偏少,但是登陆的偏多,初次登陆时间偏早。分析发现,2009年赤道中东太平洋春季前处于冷水位相,4月以后进入暖水位相,6月开始了一次厄尔尼诺事件。受海洋异常强迫和海气相互作用的影响,北半球大气环流表现出的主要特征是:500 hPa西太平洋副高强度和位置变化较大;东亚冬季风偏弱,夏季风偏强;西太平洋暖池区冬春季热带对流活动偏强,夏秋季正常;亚洲中高纬度经纬向环流交替转换,其中5月纬向环流盛行,6月、10月和11月经向环流盛行。这些环流异常是影响2009年中国气候异常的主要原因。     

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.     

亚洲热带近海海温与云南夏季降水的关系

分析了1961~1999年亚洲热带近海海温与云南降水的关系。通过研究云南夏季降水对近海海温异常的响应,发现云南初夏的降水与亚洲热带近海海温有明显的负相关关系,这种降水减少海温正距平的情况在北印度洋西部和阿拉伯海表现比孟加拉湾和南海更显著,但是在盛夏相关关系不显著。同时发现云南西南部的夏季降水与前期孟加拉湾海温有显著的正相关,而与其它海域的海温相关不显著。滇东南的夏季降水只与前期南海的海温有显著的正相关。     

2008年海洋和大气环流异常及对中国气候的影响

2008年,尽管总体来看,全国天气气候的持续异常较弱,未发生大范围持续干旱和严重洪涝灾害,但依然出现了非常显著的天气气候异常特征,如全国平均年降水量比常年偏多,为近10年来降水最多的年份;夏季华南降水异常偏多,黄淮降水偏多;年平均气温偏高,但冬季气温偏低,年初南方遭遇罕见低温雨雪冰冻灾害;在南海和西太平洋生成的台风个数明显偏少,但是登陆台风偏多,初台异常偏早.分析发现,2008年赤道中东太平洋总体处在冷水位相,受海洋异常强迫和海气相互作用的影响,北半球大气环流表现出的主要特征是:500hPa西太平洋副高强度和位置变化较大;冬夏季风均偏强;冬春季西太平洋暖池区热带对流活动偏强,夏秋季则偏弱;1月份,亚洲中高纬度经向环流异常发展,2至4月份则以纬向环流为主,春季后期至秋季,经纬向环流的转换较快,环流的持续性较弱.这些环流异常是影响2008年中国气候异常的主要原因.     

赤道印度洋海温偶极子型振荡及其气候影响

对近百年观测资料的分析表明赤道印度洋海温(SST)确实存在着偶极子型振荡的变化特征,它在9～11月最强,而在1～4月最弱;年际变化(4～5年周期)和年代际变化(主要为20～25年周期)也十分清楚.这个偶极子主要有正位相型(海温西高东低)和负位相型(海温东高西低);一般正位相型的振幅强于负位相型.尽管在极个别年赤道印度洋海温偶极子似乎与太平洋ENSO无关,但总体而论,赤道印度洋海温偶极子与赤道太平洋海温偶极子(类似ENSO)有很好负相关.它们的联系主要是赤道大气纬向(Walker)环流.资料分析表明,赤道印度洋海温偶极子与亚洲南部流场、青藏高压和西太平洋副高都有明显关系,表明它对亚洲季风活动有重要影响.     

海温异常对热带内外环流相互作用影响的对比分析

运用ECMWF的风场和高度场及TBB资料,用相关方法对比分析了热带太平洋海温分布东冷西暖（1984～1985年冬季）和东暖西冷（1982～1983年冬季）两种不同背景下,热带西太平洋对流活动与中高纬环流在季内时间尺度下相互作用的特点。结果表明,不同的海温分布其对应的大尺度环流场包括Hadley和Walker环流的位置及强弱均有较大的差别。冬季热带西太平洋对流活动与热带外大气的季内相互作用过程也有明显差异。     

重庆春播期间降水特征及其与北太平洋海温的关系

运用NCEP/NCAR全球高度场再分析资料、美国NOAA全球海温资料以及重庆34个站春播期间降水资料,对重庆春播期间降水特征及其与前期秋季海温场的关系进行分析。结果表明：重庆春播期间降水与前期秋季北太平洋暖流附近（20°～40°N、165°E～140°W）的海温有显著负相关关系,而与北太平洋阿拉斯加暖流附近（40°～60°N、165°E～140°W）的海温则有显著正相关关系,即南、北海温呈现相反的相关性。当前期秋季北太平洋副热带地区海温异常偏高,中高纬度地区海温异常偏低时,后期重庆春播期间降水将异常偏多;反之,北太平洋副热带地区海温异常偏低,中高纬度地区海温异常偏高时,重庆春播期间降水将异常偏少。针对秋季北太平洋南、北海温异常的反相分布特征定义了用于诊断和预测重庆春播期间降水的判别指数,该指数代表了北太平洋海温异常南北反相的分布特征。该前期判别指数具有重要的天气气候学意义和一定的指示和预测能力。其代表的北太平洋海温异常与西太平洋区域500 hPa高度场有密切联系,其可使大气环流场产生持续性的异常,大气环流的异常特征能一直持续到春播期间,将影响重庆春播期间降水变化。     

Two Northward Jumps of the Summertime Western Pacific Subtropical High and Their Associations with the Tropical SST Anomalies

Based on the pentad mean ridgeline index of the western Pacific subtropical high (WPSH), the authors identified the two northward jumps of the WPSH from 1979 to 2008 and revealed their associations with the tropical SST anomalies. The authors show that the northward jumps, especially the second jump, exhibited remarkable interannual variability. In addition, the authors find that the two northward jumps were mutually independent and were influenced by the SST anomalies in the different regions of the tropical Pacific. The first jump was positively correlated with the SST anomalies in the tropical central Pacific from the preceding winter to June. In contrast, the second jump was positively related to ENSO in the preceding winter, but this correlation tended to weaken with the decay of ENSO and disappeared in July. Instead, a positive correlation was found in the Indian Ocean. We therefore suggest that ENSO plays an indirect role in the second jump through the capacitor effect of the Indian Ocean.     

NUMERICAL EXPERIMENTS OF THE EFFECTS OF SEA SURFACE TEMPERATURE ANOMALIES OVER THE PACIFIC ON PRECIPITATION IN 1991*

A zonal domain,primitive equation model is used in this paper to study the influences of the main sea surface temperature anomaly(SSTA) areas over the Pacific on precipitation in 1991.Some numerical experiments are made and the mechanisms of the influences are discussed.The results show that the influences of the SSTA are mainly confined within the tropical and the subtropical regions.The direct effect of the SSTA is to change the exchanges of the sensible heat and the water vapour between the air and the sea,through the consequent changes of temperature and the flow fields and the feedback process of condensation,the SSTA finally affects precipitation.     

NUMERICAL EXPERIMENTS OF THE EFFECTS OF SEA SURFACE TEMPERATURE ANOMALIES OVER THE PACIFIC ON PRECIPITATION IN 1991

A zonal domain,primitive equation model is used in this paper to study the influences of the main sea surface tem-perature anomaly(SSTA)areas over the Pacific on precipitation in 1991.Some numerical experiments are made and themechanisms of the influences are discussed.The results show that the influences of the SSTA are mainly confined withinthe tropical and the subtropical regions.The direct effect of the SSTA is to change the exchanges of the sensible heat andthe water vapour between the air and the sea,through the consequent changes of temperature and the flow fields and thefeedback process of condensation,the SSTA finally affects precipitation.     

江南北部地区梅雨期降水与海温的SVD分析

对江南北部地区梅雨期降水和海温的SVD分析结果表明，与江南北部地区梅雨期降水异常相关的海温分布型是西正东负型，关键区恰好处于相关最显著的部位。前一年10—12月为海温的关键影响时段，且与梅雨期降水有很好的正相关关系。在该海温异常型的影响之下，江南北部地区次年梅雨期降水异常表现为同位相变化特征，而长江以南的下游地区为受其影响最显著的区域。     

Interannual Variability of Autumn Precipitation over South China and its Relation to Atmospheric Circulation and SST Anomalies

The interannual variability of autumn precipitation over South China and its relationship with atmospheric circulation and SST anomalies are examined using the autumn precipitation data of 160 stations in China and the NCEP-NCAR reanalysis dataset from 1951 to 2004. Results indicate a strong interannual variability of autumn precipitation over South China and its positive correlation with the autumn western Pacific subtropical high （WPSH）. In the flood years, the WPSH ridge line lies over the south of South China and the strengthened ridge over North Asia triggers cold air to move southward. Furthermore, there exists a significantly anomalous updraft and cyclone with the northward stream strengthened at 850 hPa and a positive anomaly center of meridional moisture transport strengthening the northward warm and humid water transport over South China. These display the reverse feature in drought years. The autumn precipitation interannual variability over South China correlates positively with SST in the western Pacific and North Pacific, whereas a negative correlation occurs in the South Indian Ocean in July. The time of the strongest lag-correlation coefficients between SST and autumn precipitation over South China is about two months, implying that the SST of the three ocean areas in July might be one of the predictors for autumn precipitation interannual variability over South China. Discussion about the linkage among July SSTs in the western Pacific, the autumn WPSH and autumn precipitation over South China suggests that SST anomalies might contribute to autumn precipitation through its close relation to the autumn WPSH.     

2013年海洋和大气环流异常及对中国气候的影响

本文对2013年海洋和大气环流异常特征进行分析,讨论这些异常特征对中国气温和降水的主要影响。结果表明：2012/2013年冬季,北极涛动持续维持负位相,500 hPa位势高度场上,欧亚大陆中高纬环流呈“两槽一脊”的环流形势,乌拉尔山的高压脊持续偏强,而东亚槽也异常偏强,导致全国平均气温较常年同期偏低。季内,西伯利亚高压强度变化显著,与之相对应,我国气温季内阶段性变化大,前冬冷、后冬暖。进一步研究表明,前秋北极海冰的大幅偏少是造成东亚冬季风偏强的重要原因。2013年冬季至夏季,赤道中东太平洋海温异常偏低而海洋性大陆至西太平洋海温异常偏高,受此影响,夏季西太平洋副热带高压位置明显偏北,导致我国北方夏季多雨。与此同时,受西太平洋副热带高压下沉气流的控制,我国南方大部高温持续。2013年南海夏季风爆发偏早两候,结束偏晚4候,强度偏弱。     

Simulation of the Effects of the Preceding SST Anomalies over the Tropical Eastern Pacific on Precipitation to the South of the Yangtze River in June

Numerical experiments are performed to simulate the response of the atmospheric circulation and pre-cipitation over East China in June to the sea surface temperature（SST）anomalies over the tropical eastern Pacific（TEP）from preceding September to June by using an atmospheric general circulation model （AGCM）.We constructed composite positive/negative SST anomalies（P-SSTAs/N-SSTAs）based on the observational SST anomalies over the TEP from September 1997 to June 1998.The results show that：（1） the response of the precipitation in the Yangtze River basin and its southern area（YRBS）to El Nino with different durations varies with the maximum amplitude of the precipitation anomalies appearing when the imposed duration is from November to next June,and the minimum appearing when the SST anomalies is only imposed in June.The anomalies of the precipitation are reduced when the duration of the forcing SST anomalies over the TEP is shortened and the positive SST anomalies in the preceding autumn tend to cause significantly more rainfall in the YRBS.This is in agreement with previous diagnostic analysis results.（2）The simulated precipitation anomalies over the YRBS are always obviously positive under strong or weak positive SST anomalies over the TEP.The intensity of the precipitation anomalies increases with increasing intensity of the SST anomalies in the experiments.The simulation results are consistent with the observations during the warm SST events,suggesting reasonable modeling results.（3）When negative SST anomalies in the TEP are put into the model,the results are different from those of the diagnostic analysis of La Nina events.Negative precipitation anomalies in YRBS could be reproduced only when the negative SST anomalies are strong enough.     

层云加热对热带大气季节内振荡的影响

本文研究了层云降水加热对于激发热带大气季节内振荡(Madden-Julian oscillation,简称MJO)所起到的作用.将层云加热作用引入到非线性的CISK (Conditional Instability of Second Kind)-Kelvin波方程组,并分别利用截谱方法和四阶Runge-Kutta方法...     

Physical Mechanism of the Impacts of the Tropical Atlantic Sea Surface Temperature on the Decadal Change of the Summer North Atlantic Oscillation

In this study,physical mechanism of the impacts of the tropical Atlantic sea surface temperature(SST)on decadal change of the summer North Atlantic Oscillation(SNAO)was explored using an atmospheric general circulation model(AGCM)developed at the International Centre for Theoretical Physics(ICTP).The simulation results indicate that the decadal warming of the SST over the tropical Atlantic after the late 1970s could have significantly enhanced the convection over the region.This enhanced convection would have strengthened the local meridional circulation over the Eastern Atlantic-North Africa-Western Europe region,exciting a meridional teleconnection.This teleconnection might have brought the signal of the tropical Atlantic SST to the Extratropics,consequently activating the variability of the eastern part of the SNAO southern center,which led to an eastward shift of the SNAO southern center around the late 1970s.Such physical processes are highly consistent with the previous observations.     

中国春季降水异常及其与热带太平洋海面温度和欧亚大陆积雪的联系

利用降水观测资料, 研究了1979～2004年中国春季 (3～5月) 标准化累积降水异常的时空特征及其与前冬、 春热带太平洋海面温度和春季欧亚大陆积雪的关系。中国春季标准化累积降水量EOF第一模态最大变率位于中国东部中纬度地区, 主要反映了中国东部中纬度地区春季降水的变化特征。同时, 中国东部春季降水异常具有南、 北反相变化的特征。当长江以南大部分地区的降水偏少时, 长江以北地区的降水偏多。春季降水异常具有显著的年际变化, 但在1980年代末出现年代际转型, 即年际变化的振幅明显增大变强、 周期变长。从华北到长江流域中纬度地区的春季降水异常特征与前冬热带太平洋海面温度有密切的关系。当前冬、 春热带东太平洋海温偏暖, 西太平洋海温偏冷时, 中国东部从华北到长江流域中纬度地区的春季降水偏多, 反之亦然。虽然当春季欧亚大陆楚科奇半岛和青藏高原积雪偏多, 贝加尔湖到中国东北地区的积雪偏少时, 对应着中国东部从华北到长江流域中纬度地区的降水偏多, 但当去掉ENSO信号后, 这种关系并不显著。说明EOF第一模态所反映的中国东部从华北到长江流域中纬度地区春季降水与欧亚大陆积雪的相关关系可能是前冬热带太平洋海面温度异常的一个体现。     

春季海温对中国夏季降水影响的诊断研究和预测试验

文中利用季降水异常集合的典型相关预测模式 ,以全球春季 (3～ 5月 )海温场作为因子场 ,对中国夏季降水场进行了诊断研究 ,并对 1998,1999及 2 0 0 0年这几个典型的中国夏季降水进行了回报试验。结果表明 ,春季海温与中国夏季降水之间存在较好的关系 ,春季海温在较大程度上决定了中国夏季降水雨带及其分布类型。考虑面积因子的集合典型相关预测方案对中国夏季降水具有较强的回报能力 ,此模式不仅能诊断出降水场和海温场中一些比较典型的空间模态和时间变化规律 ,而且可以再现 1998和 2 0 0 0年中国大部分地区的旱涝灾害。揭示了全球春季海温的异常变化在中国夏季 (6～ 8月 )降水异常中的作用。