Seasonality of the Interaction between Convection over the Western Pacific and General Circulation in the Northern Hemisphere

The seasonality of the interaction between convection over the western Pacific and general circulation in the Northern Hemisphere (NH) is analyzed in the present paper with singular value decomposition (SVD) and empirical orthogonal function (EOF) analysis approaches, based on 500 hPa monthly mean geopotential height data and high-cloud amount data. The analyses demonstrate that coupled dominant patterns in the interaction between the convection over the western Pacific and the general circulation in NH are different in various seasons. In spring, the convection over the western Pacific is closely related with the western Atlantic (WA) and North Pacific (NP) like patterns of the general circulation in NH, and some associations between the WA and NP like pat?terns and the El Ni?o / Southern Oscillation (ENSO) cycle are also existed. The Pacific Japan (PJ) pattern is the dom?inant pattern in the interaction between the interannual variabilities of the convection over the western Pacific and the general circulation in NH summer. The WA like pattern and 3-4 year period oscillation are also relatively obvious for the summer case. In autumn, the convection over the western Pacific is closely linked with the Eurasian (EU) like pattern and the Atlantic oscillation in the general circulation in NH, it is suggested that in autumn the vitiation of convective activity over the western Pacific is largely affected by the general circulation anomaly (cold air from high latitudes) through EU like teleconnection pattern. Abrupt change happened by the end of 1980’s in the autumn interaction. The strong interaction between the western Pacific (WP) and EU like patterns in the general circulation in NH and the convection over the western Pacific and a linear trend of increasing of this interaction are also suggested in winter. It is also demonstrated that the interaction in summer and winter is stronger than in the transition seasons (spring and autumn).     

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.     

THE CONTRASTS BETWEEN STRONG AND WEAK MJO ACTIVITY OVER THE EQUATORIAL WESTERN PACIFIC IN WINTER

This paper investigates the contrasts between strong and weak Madden-Julian Oscillation (MJO) activity over the equatorial western Pacific during winter using the NCEP reanalysis data. It is shown that the MJO over the equatorial western Pacific in winter shows significant interannual and interdecadal variabilities. During the winters with strong MJO activity, an anomalous cyclonic circulation lies east of the Philippines, strong anomalous easterlies control the equatorial eastern Pacific, and anomalous westerlies extend from the Indian Ocean to the western Pacific in the lower troposphere, which strengthens the convergence and convection over the equatorial western Pacific. The moisture convergence in the lower troposphere is also enhanced over the western Pacific, which is favorable to the activity of MJO. Eastward propagation is a significant feature of the MJO, though there is some westward propagation. The space-time spectral power and center period of the MJO are higher during strong MJO activity winters. The anomalous activity of MJO is closely related to the sea surface temperature (SST) and East Asian winter monsoon (EAWM). During strong MJO activity winters, there are positive/negative anomalies at high/low latitudes in both sea level pressure and 500 hPa geopotential height, and the temperature is lower over the central part of the Chinese mainland, which indicates a strong EAWM. China experiences more rainfall between the Yellow and Yangtze Rivers, but less rainfall south of the Yangtze River. The SSTA is negative near the Taiwan Island due to the impact of strong EAWM and shows a La Ni?a pattern anomaly over the eastern Pacific. During the weak MJO activity winters, the situation is reversed.     

Association between Tropical Convection and Boreal Wintertime Extratropical Circulation in 1982／83 and 1988／89

Boreal wintertime extratropical circulation is studied in relation to the tropical convection during the 1982/83 El Nino and 1988/89 La Nina. The anomaly structure of 1982/83 and 1988/89 over the extratropics reveals remarkably different features as the longitudinal tropical forcing region changes. The Rossby wave source (Positive) shows the largest maximum over East Asia in both years due to the persistent heating from the western Pacific warm pool area. However, the sink term shows contrasting features over the subtropics and extratropics between the two years. In the El Nino year, enhanced tropical convection over the eastern Pacific produces the Rossby wave sink at 10?N and shifted eastward over the North Pacific, while in the La Nina year, the sink area is shifted westward over the North Pacific. The contrasting features between the two events in mean-eddy interaction appears especially over the downstream area of the East Asian Jet. The extension (retraction) of the meanflow eastward (westward) to     

Interdecadal Variability in Large and Small Warm Pools in Western Pacific and Their Association with Rainfall Anomalies简

This study investigated interdecadal variability of June–October（JJASO） the large and small warm pools in western Pacific and their association with rainfall anomalies using station and reanalysis data from 1958 to 2008.The results indicated that the large and small warm pools in western Pacific showed an interdecadal shift around 1986.The large warm pool years over western Pacific were found after 1986,whereas the small warm pool years were often seen throughout the periods before 1986.The analysis results also showed that there were obvious interdecadal variability in JJASO rainfall in Southeast China and warm pool in western Pacific.During 1958–1985（small warm pool years）,the decrease in rainfall was associated with tropospheric moisture divergence and sinking motion over Southeast China and warm pool in western Pacific.However,during 1986–2008（large warm pool years）,the increase in rainfall was associated with tropospheric moisture convergence and ascending motion.Further analysis showed that large warm pool contributed to the increase in surface latent heat fluxes over warm pool in the western Pacific.Thus,there was an increase in the amount of water vapor over Southeast China and warm pool in western Pacific,which contributed to increased rainfall in these regions.     

Interdecadal Variability in Large and Small Warm Pools in Western Pacific and Their Association with Rainfall Anomalies

This study investigated interdecadal variability of June–October(JJASO) the large and small warm pools in western Pacific and their association with rainfall anomalies using station and reanalysis data from 1958 to 2008.The results indicated that the large and small warm pools in western Pacific showed an interdecadal shift around 1986.The large warm pool years over western Pacific were found after 1986,whereas the small warm pool years were often seen throughout the periods before 1986.The analysis results also showed that there were obvious interdecadal variability in JJASO rainfall in Southeast China and warm pool in western Pacific.During 1958–1985(small warm pool years),the decrease in rainfall was associated with tropospheric moisture divergence and sinking motion over Southeast China and warm pool in western Pacific.However,during 1986–2008(large warm pool years),the increase in rainfall was associated with tropospheric moisture convergence and ascending motion.Further analysis showed that large warm pool contributed to the increase in surface latent heat fluxes over warm pool in the western Pacific.Thus,there was an increase in the amount of water vapor over Southeast China and warm pool in western Pacific,which contributed to increased rainfall in these regions.     

A DIAGNOSTIC STUDY OF THE TELECONNECTION ASSOCIATED WITH THE WARM POOL OF THE WESTERN PACIFIC AND ASIAN MONSOON DURING EL NINO AND NON-EL NINO YEARS

Based on the monthly mean OLR, geopotential height and wind data from the NCEP/NCAR reanalyzed data sets for 1982-1996, the atmospheric teleconnection associated with the warm pool of the tropical western Pacific and Asian monsoon region during E1 Nino and non-El Niño years are studied diagnostically in this paper. It is found that, the teleconnection pattern caused by the activity of the Asian summer monsoon (ASM) emanates from the Asian monsoon region to the tropical eastern Pacific via the Aleutians in summer of the El Niño years. In the non-El Niño years, however, the ASM-related teleconnection pattern stretches northward and westward from the Asian monsoon region, exerting its influences mainly on the circulation over middle and high latitude rather than that over the tropical eastern Pacific. Evidences also show that the anomalous convection over the tropical western Pacific warm pool leads to the East Asia/Pacific(EAP) teleconnection pattern during the non-El Niño years. It is interesting to note that the teleconnection in the 500 height field associated with the warm pool convection disappears in the El Niño years. The differences of the teleconnection pattern between the El Niño years and the non-El Niño years suggest that the activities of the ASM and the convection over the warm pool of the tropical western Pacific, the most energetic weather events in boreal summer, are intertwined and interactive with other global-scale circulation in different ways under different climate backgrounds.     

The Summer Snow Cover Anomaly over the Tibetan Plateau and Its Association with Simultaneous Precipitation over the Mei-yu–Baiu region

The summer snow anomalies over the Tibetan Plateau （TP） and their effects on climate variability are often overlooked,possibly due to the fact that some datasets cannot properly capture summer snow cover over high terrain.The satellite-derived Equal-Area Scalable Earth grid （EASE-grid） dataset shows that snow still exists in summer in the western part and along the southem flank of the TP.Analysis demonstrates that the summer snow cover area proportion （SCAP） over the TP has a significant positive correlation with simultaneous precipitation over the mei-yu-baiu （MB） region on the interannual time scale.The close relationship between the summer SCAP and summer precipitation over the MB region could not be simply considered as a simultaneous response to the Silk Road pattern and the SST anomalies in the tropical Indian Ocean and tropical central-eastern Pacific.The SCAP anomaly has an independent effect and may directly modulate the land surface heating and,consequently,vertical motion over the western TP,and concurrently induce anomalous vertical motion over the North Indian Ocean via a meridional vertical circulation.Through a zonal vertical circulation over the tropics and a Kelvin wave-type response,anomalous vertical motion over the North Indian Ocean may result in an anomalous high over the western North Pacific and modulate the convective activity in the western Pacific warm pool,which stimulates the East Asia-Pacific （EAP） pattern and eventually affects summer precipitation over the MB region.     

INTERANNUAL VARIATION IN HEAT CONTENT OF THE WESTERN PACIFIC WARM POOL AND ITS EFFECT ON EASTERN ASIAN CLIMATE ANOMALIES

Using the 1980-2010 winter GODAS oceanic assimilations, study is conducted of the winter heat content (HC) established in the subsurface layer (5 to 366 m in depth) over the western Pacific warm pool (WP), followed by investigating the HC spatiotemporal characteristics, persistence and the impacts on the climate anomalies of neighboring regions. Results are as follows: 1) the pattern of integral consistency is uncovered by the leading EOF1 (PC1) mode of HC interannual variability, the year-to-year fluctuation of the time coefficients being well indicative of the interannual anomaly of the WP winter subsurface-layer thermal regime. The HC variation is bound up with ENSO, keeping pronounced autocorrelation during the following two seasons and more, with the persistence being more stable in comparison to SSTA in the equatorial middle eastern Pacific; 2) the winter HC anomalies produce lasting effect on the WP thermal state in the following spring and summer and corresponding changes in the warm water volume lead to the meridional transport and vertical exchange of warm water, which exerts greater impacts upon the sea surface temperature/heat flux over the warm pool per se and neighboring regions, especially in the Philippine Sea during the posterior spring and summer; 3) the increase in the winter HC corresponds to the spring OLR decrease and richer precipitation over the waters east to the Philippine Sea and the resultant convective heating anomalies are responsible for the rise of geopotential isobaric surfaces over tropical and subtropical western North Pacific, thereby producing effect on the western Pacific subtropical high (anomaly). Subsequently, the sea-surface heat flux exchange is intensified in the warm pool, a robust anomalous cyclone shows up at lower levels, air-sea interactions are enhanced and abnormal convective heating occurs, together making the winter HC anomalies even more closely associated with the variation in the summer subtropical high. As a result, the WP winter HC can be used as an effective predictor of the variation in spring/summer western Pacific subtropical high and the strength of summer monsoon over the northwestern Pacific.     

THE EFFECT OF EQUATORIAL CENTRAL PACIFIC SSTAS ON THE INTERANNUAL VARIATION OF PRECIPITATION OVER SOUTHWEST CHINA DURING SPRING

The interannual variations of rainfall over southwest China (SWC) during spring and its relationship with sea surface temperature anomalies (SSTAs) in the Pacific are analyzed, based on monthly mean precipitation data from 26 stations in SWC between 1961 and 2010, NCEP/NCAR re-analysis data, and Hadley global SST data. Sensitivity tests are conducted to assess the response of precipitation in SWC to SSTAs over two key oceanic domains, using the global atmospheric circulation model ECHAM5. The interannual variation of rainfall over SWC in spring is very significant. There are strong negative (positive) correlation coefficients between the anomalous precipitation over SWC and SSTAs over the equatorial central Pacific (the mid-latitude Pacific) during spring. Numerical simulations show that local rainfall in the northwest of the equatorial central Pacific is suppressed, and a subtropical anticyclone circulation anomaly is produced, while a cyclonic circulation anomaly in the mid-latitude western Pacific occurs, when the equatorial Pacific SSTAs are in a cold phase in spring. Anomalous northerly winds appear in the northeastern part of SWC in the lower troposphere. Precipitation increases over the Maritime Continent of the western equatorial Pacific, while a cyclonic circulation anomaly appears in the northwest of the western equatorial Pacific. A trough over the Bay of Bengal enhances the southerly flow in the south of SWC. The trough also enhances the transport of moisture to SWC. The warm moisture intersects with anomalous cold air over the northeast of SWC, and so precipitation increases during spring. On the interannual time scale, the impacts of the mid-latitude Pacific SSTAs on rainfall in SWC during spring are not significant, because the mid-latitude Pacific SSTAs are affected by the equatorial central Pacific SSTAs; that is, the mid-latitude Pacific SSTAs are a feedback to the circulation anomaly caused by the equatorial central Pacific SSTAs.     

夏季对流和环流10-25天季内变化-5西太平洋暖池热力状况的关系

主要讨论了西太平洋暖池热力状况年际变化相联系的10－25天季内振荡的特征。在西太平洋暖池处于“暖”夏季和“冷”夏季两种状态时，10－25天季内振荡呈现出明显差异，在所讨论的亚洲－太平洋大部分区域，“暖”夏季时对流活动的10－25天季内变化和“冷”夏季时对流活动的10－25天季内变化表现出显的反相关关系，表明对流活动的年际变化与季内变化的相互作用。当西太平洋暖池上空对流活动的10－25天季内振荡处于最强和最弱阶段时，低层大气表现为Gill型环流响应，即气旋式（反气旋式）环流出现在最强（最弱）对流活动的西北，这种对流和环流关系在西太平洋暖池出于“暖”夏季和“冷”夏季两种状态时均成立。而当西太平洋暖池上空对流活动的10－25天季内振荡处于除此以外其他阶段时，就看不到Gill型环流响应。     

热带大气季节内振荡对西南地区东部夏季降水的影响及其可能机制

利用1979~2013年6~8月的西南地区东部20个台站日降水量资料、逐日MJO(Madden-Julian Oscillation)指数、全球OLR(Outgoing Longwave Radiation)逐日格点资料以及NCEP/NCAR再分析日资料,采用合成分析和线性回归等方法,对夏季MJO不同位相活动影响西南地区东部夏季降水的原因及其可能机制进行了初步分析。研究表明,MJO与西南地区东部夏季降水之间存在着显著的关系,当MJO处于第4(第6)位相时,由于西太平洋副高位置偏南(偏北)、向西南地区东部的水汽输送偏多(偏少),在异常上升(下沉)气流影响下,西南地区东部夏季降水偏多(偏少)。MJO影响西南地区东部夏季降水的可能原因是:当MJO处于第4位相时,赤道东印度洋地区上空大气释放凝结潜热,其激发东北向传播的异常波动,进而影响东亚环流,使得西南地区东部出现夏季降水偏多的环流形势,西南地区东部夏季降水增多;但在第6位相时,西太平洋地区上空对流释放的凝结潜热,其激发PJ(太平洋-日本)型Rossby波列,出现不利于西南地区东部夏季降水的环流形势,西南地区东部夏季降水偏少。     

全球变化背景下北半球冬季MJO传播的年代际变化

利用1979~2013年实时多要素MJO（Madden-Julian Oscillation）监测（RMM）指数,美国NOAA逐日长波辐射资料和NCEP/NCAR再分析资料等,分析了全球变化背景下北半球冬季MJO传播的年代际变化特征。从全球平均气温快速增暖期（1985~1997）到变暖趋缓期（2000~2012）,MJO 2~4位相频次减少,5~7位相频次增多,即MJO对流活跃区在热带印度洋地区停留时间缩短、传播速度加快,而在热带西太平洋停留时间加长、传播明显减缓。进一步分析发现,以上MJO的年代际变化特征与全球变化年代际波动有关。当太平洋年代际涛动（PDO）处于负位相时,全球变暖趋缓,热带东印度洋—西太平洋海温异常偏暖,使其上空对流加强,垂直上升运动加强,对流层低层辐合,大气中的水汽含量增多,该区域的湿静力能（MSE）为正异常。当MJO对流活跃区位于热带印度洋地区时,MJO异常环流对季节平均MSE的输送在强对流中心东侧为正、西侧为负,有利于东侧MSE扰动增加,使得MJO对流扰动东移加快;而当MJO对流活跃区在热带西太平洋地区,MJO异常环流对平均MSE的输送形成东负西正的形势,东侧MSE扰动减小,不利于MJO快速东传。因此,全球变化背景下PDO引起的大气中水汽含量及MSE的变化可能是MJO传播年代际变化的重要原因。     

西太平洋暖池对西北太平洋季风槽和台风活动影响过程及其机理的最近研究进展

本文回顾和综述了近年来关于西太平洋暖池对西北太平洋热带气旋和台风（TCs）活动影响过程及其机理的研究进展。文中首先简单回顾了近年来关于西太平洋暖池热状态和菲律宾周围对流活动变化特征及其对与TCs活动有关的南海夏季风爆发和西太平洋副热带高压的季节内、年际变异的影响过程和机理的研究;然后,本文系统地回顾了近年来关于西太平洋暖池热状态通过西北太平洋季风槽影响TCs活动年际和年代际变化的影响过程及其机理的研究。此外,文中还指出了关于西太平洋暖池对西北太平洋上空季风槽和TCs活动变异的热力和动力作用需进一步深入研究的科学问题。     

Anomalies in the tropics associated with the heavy rainfall in east asia during the summer of 1998

1.IntroductionInthesummerof1998,theYangtzeRiverbasin,includingNenjiangRiverValleyinNortheastChinasufferedaseverelarge--scalefloodonlynexttothatinthesummerof1954inthiscentury.Thefloodcausedapproximatelythedeathof3000individualsandthedirecteconomicdamageof250billionRMByuans(Yan,1998).Thisextremedisasterpromptedaseriesofimmediatestudiesonit(e.g.,Iluangetal.,1998;Taoetal.,1998).TheevolutionoftheEastAsiansupsmermonsoonshowsagreatvariabilityfromyeartoOThisstudywassupportedbytheNationalNatura…     

Impacts of the MJO on Winter Rainfall and Circulation in China

Impacts of the MJO on winter rainfall and circulation in China are investigated using a real-time multivariate MJO index.Composite results using the daily rainfall anomalies and "rainy day" anomalies according to eight different MJO phases show that the MJO has considerable influence on winter rainfall in China. Rainfall anomalies show systematic and substantial changes(enhanced/suppressed) in the Yangtze River Basin and South China with the eastward propagation of the MJO convective center from the Indian Ocean to the western Pacific.When the MJO is in phase 2 and 3(MJO convective center is located over the Indian Ocean),rainfall probability is significantly enhanced.While in phase 6 and 7(MJO convective center is over the western Pacific),rainfall probability is significantly reduced. MJO in winter influences the rainfall in China mainly through modulating the circulation in the subtropics and mid-high latitudes.For the subtropics,MJO influences the northward moisture transport coming from the Bay of Bengal and the South China Sea by modulating the southern trough of the Bay of Bengal and the western Pacific subtropical high.For the mid-high latitudes,the propagation of the low frequency perturbations associated with the eastward-propagating MJO convection modulate the circulation in the mid-high latitudes,e.g.the East Asian winter monsoon and the low trough over central Asia.     

POSSIBLE IMPACTS OF MADDEN-JULIAN OSCILLATION ON THE SEVERE RAIN-SNOW WEATHER IN CHINA DURING NOVEMBER 2009

Possible relationships between MJO and the severe rain-snow weather in Eastern China during November of 2009 are analyzed and results show that a strong MJO process is one of the strong impact factors.MJO is very active over the Indian Ocean in November 2009.Especially,it maintains 9 days in MJO phase 3,just corresponding to the two strongest rain-snow processes.Composites of MJO events show that when the MJO convective center is located over the Indian Ocean,the probability of rainfall is significantly increased and the temperature is lower than normal in eastern China,which is consistent with the situation in November of 2009.Atmospheric circulation anomalies of mid-and higher-latitudes can be influenced by the tropical MJO convection forcing and this influence could be realized by teleconnection.When the MJO is over the Indian Ocean,it is favorable for the maintenance of a circulation pattern of two ridges versus one trough at mid-and higher-latitudes.Meanwhile,the western Pacific subtropical high is stronger and more westward than normal,and a significant convective belt appears over eastern East Asia.All these circulation anomalies shown in the composite result also appeared in the observations in November 2009,which indicates the general features of relationships between the MJO and the circulation anomalies over the extratropics.Besides the zonal circulation anomalies,the MJO convection can also lead to meridional circulation anomalies.When the MJO convection is located over the Indian Ocean,the western Pacific is dominated by anomalous descending motion,and the eastern East Asia is controlled by strong convergence and ascending motion.Therefore,an anomalous meridional circulation is formed between the tropics and middle latitudes,enhancing the northward transportation of low-level moisture.It is potentially helpful to understanding and even forecasting such kind of rain-snow weather anomalies as that in November 2009 using MJO.     

Delayed Impacts of the E1 Nino Episodes in the Central Pacific on the Summertime Climate Anomalies of Eastern China in 2003 and 2007

In the summers of 2003 and 2007, eastern China suffered similar climate disasters with severe flooding in the Huaihe River valley and heat waves in the southern Yangtze River delta and South China. Using SST data and outgoing longwave radiation (OLR) data from NOAA along with reanalysis data from NCEP/NCAR, the 2002/03 and 2006/07 El Ni(n)o episodes in the central Pacific and their delayed impacts on the following early summertime climate anomalies of eastern China were analyzed. The possible physical progresses behaved as follows: Both of the moderate E1 Ni(n)o episodes matured in the central equatorial Pacific during the early winter. The zonal wind anomalies near the sea surface of the west-central equatorial Pacific excited equatorial Kelvin waves propagating eastward and affected the evolution of the E1 Ni(n)o episodes. From spring to early summer, the concurring anomalous easterly winds in the central equatorial Pacific and the end of upwelling Kelvin waves propagating eastward in the western equatorial Pacific, favored the equatorial warm water both of the SST and the subsurface temperature in the western Pacific. These conditions favored the warm state of the western equatorial Pacific in the early summer for both cases of 2003 and 2007. Due to the active convection in the western equatorial Pacific in the early summer and the weak warm SST anomalies in the tropical western Pacific from spring to early summer, the convective activities in the western Pacific warm pool showed the pattern in which the anomalous strong convection only appeared over the southern regions of the tropical western Pacific warm pool, which effects the meridional shift of the western Pacific subtropical high in the summer. The physical progress of the delayed impacts of the E1 Nifio episodes in the central equatorial Pacific and their decaying evolution on the climate anomalies in eastern China were interpreted through the key role of special pattern for the heat convection in the tropical western Pacific warm pool and the response of the western North Pacific anomalous anticyclone.