Interannual variation of North China rainfall in rainy season and SSTs in the equatorial eastern Pacific

The rainfall in North China during rainy season （July and August （JA）） exhibits a strong interannual variability. In this study, the atmospheric circulation and SST anomalies associated with the interannual variation of JA North China rainfall are examined. It is found that on the interannual timescale, the JA North China rainfall is associated with significant SST anomalies in the equatorial eastern Pacific, and the North China rainfall and SST anomaly in the equatorial eastern Pacific correspond to the similar variation of the upper-level westerly jet stream over East Asia. A possible mechanism is proposed for the influence of the SST anomalies in the equatorial eastern Pacific on the North China rainfall.     

江淮流域夏季降水异常及与全球中低纬海温异常关系的诊断研究

对1951－1999年中国夏季江淮流域降水异常与海温异常关系的分析表明,前期及同期各季节三大洋海表温度异常（SSTA）与长江流域降水异常的关系是非常显著的,而对淮河流域降水异常总体上的影响较小,前期冬季SSTA的影响显著区主要有：热带印度洋、黑潮、热带中东太平洋和大西洋,各关键区海温异常对亚洲夏季风的影响特征为：当前期冬季赤道印度洋、黑潮、赤道大西洋和热带东太平洋海表温度异常升高（降低）,当年夏季印度西南季风和东亚热带辐合带减弱（加强）,副热带高压位置偏南（北）,副热带辐合带加强（减弱）,长江流域易发生洪涝（干旱）,相关显著性分析表明,前冬赤道印度洋和黑潮区的海温异常对中国夏季降水的影响更为显著。     

Signal propagations and linkages of subsurface temperature anomalies in the tropical Pacific and Indian Ocean

The propagation characteristics of signals along different zonal-time profiles are analyzed using surface and subsurface temperature anomalies over the tropical Pacific and Indian oceans. Analyses show that there are intrinsic relationships between El Nio events in the eastern equatorial Pacific and dipole events in the equatorial Indian Ocean. In the region of tropical North Pacific between the equator and 16°N, there is a circle of propagation of subsurface temperature anomalies. El Nio events only happen when the warm subsurface signals reach the eastern equatorial Pacific. Dipole events are characterized when a warm subsurface signal travels along off-equatorial Indian Ocean to the western boundary. From these analyses, we believe that subsurface temperature anomalies can be considered to be the oceanographic early signal to forecast El Nio events in Pacific Ocean and dipole events in Indian Ocean, respectively.     

Preliminary results of a new global ocean reanalysis

Using a new global ocean reanalysis of the second generation Global Ocean Data Assimilation System of the Beijing Climate Center(BCC_GODAS2.0) spanning the period 1990-2009,we firstly quantify the accuracy of BCC_GODAS2.0 in representing the temperature and salinity by comparing with OISST and SODA data.The results show that the assimilation system may effectively improve the estimations of temperature and salinity by assimilating all kinds of observations,especially in the equatorial eastern Pacific.Moreover,the root mean square errors of monthly temperature and salinity are respectively reduced by 0.53℃ and 0.28 psu,compared with the model control simulation results.Then,the applicability of this ocean reanalysis for sea surface temperature(SST) anomaly variability in the tropical Pacific is evaluated with the observational HadISST data.The NINO3 index of the new reanalysis shows a good agreement with that of HadISST,with a correlation of 93.6%.Variations in SST from BCC_GODAS2.0 are similar to those obtained from HadISST data along the equator,showing the major large zonal-scale features such as the strong magnitude of seasonal cycle.The amplitude of SST anomaly standard deviation in the equatorial eastern Pacific is also closer to observations(HadISST) than NCEP GODAS does.Besides,the first two leading empirical orthogonal function(EOF) modes of the monthly SST anomalies over the tropical Pacific region are explored.The EOF1 pattern of BCC_GODAS2.0 captures a traditional El Ni o pattern,which improves magnitudes of the positive SST anomaly in the cold tongue of the eastern Pacific.The EOF2 pattern exhibits a El Ni o Modoki pattern.Comparatively,the EOF2 pattern of BCC_GODAS2.0 extends more strongly toward the subtropics.It also overcomes the problem that negative loadings are confined in the narrow equatorial eastern Pacific.Consequently,the magnitude and spatial distribution of the leading EOF patterns of BCC_GODAS2.0 are well consistent with those of HadISST.     

Early Pleistocene formation of the asymmetric east-west pattern of upper water structure in the equatorial Pacific Ocean

Surface-and subsurface-dwelling planktonic foraminifera from the upper 43 m of Hole A at the Ocean Drilling Program (ODP) Site 807,which was recovered from the western Pacific warm pool during ODP Leg 130,were analyzed for stable oxygen and carbon isotopes.By comparing these results with data from ODP Site 851 in the eastern equatorial Pacific,this study has reconstructed the paleoceanographic changes in upper ocean waters in the equatorial Pacific since 2.5 Ma.During the period from 1.6-1.4 Ma,the oxygen isotopes of surface and subsurface waters were found to markedly change in the western and eastern equatorial Pacific,further confirming the final formation of the well-defined asymmetric east-west (E-W) pattern at that time.This feature was similar to the zonal temperature gradient (sea surface temperature is higher in the west and lower in the east) and the asymmetric upper water structure (thermocline depth is deeper in the west and shallower in the east) in the modern equatorial Pacific.The zonal gradient change of subsurface water δ18O was greater than that of surface water δ18O,indicating that the formation of the asymmetric E-W pattern in the equatorial Pacific should be much more related to the shoaled thermocline and markedly decreased subsurface water temperature in the eastern equatorial Pacific.Moreover,since ～1.6 Ma,the carbon isotopic differences between surface and subsurface waters clearly decreased in the equatorial Pacific,and their long-term eccentricity periods changed from 400 ka to ～500 ka,reflecting the reorganization of the ocean carbon reservoir.This probably resulted from the deep water reorganization in the Southern Ocean at that time and its enhanced influence on the tropical Pacific (especially subsurface water).Our study demonstrates that the tropical ocean plays an important role in global climate change.     

Northern China maximum temperature in the summer of 1743： A historical event of burning summer in a relatively warm climate background

In the context of historical climate records of China and early meteorological measurements of Beijing discovered recently in Europe, a study is undertaken on the 1743 hottest summer of north China over the last 700 a, covering Beijing, Tianjin, and the provinces of Hebei, Shanxi and Shandong, with the highest temperature reaching 44.4℃ in July 1743 in Beijing, in excess of the maximum climate record in the 20th century. Results show that the related weather/climate features of the 1743 heat wave, e.g., flood/drought distribution and Meiyu activity and the external forcings, such as solar activity and equatorial Pacific SST condition are the same as those of the 1942 and 1999 heat events. It is noted that the 1743 burning summer event occurs in a relatively warm climate background prior to the Industrial Revolution, with a lower level of CO2 release.     

The wavelet analysis of satellite sea surface temperature in the South China Sea and the Pacific Ocean

Using wavelet transform, the sea surface temperature (SST) during the period of 1982–1999 of the South China Sea and the equatorial Pacific, from datasets of NOAA/AVHRR, was analyzed. It is shown that there are 4- and 8-year interannual oscillations in the eastern equatorial Pacific and 8-year interannual oscillation in the western equatorial Pacific. In terms of attractive time-frequency localization and multi-scale properties of wavelet transform, as shown by the Morlet wavelet, it is found that an in-phase coupling oscillation occurs between the SCS and the equatorial Pacific. The SST changes of SCS will have echoed every event of EI Niño (abnormally warm) and La Niño (abnormally cold) in the equatorial Pacific. There is a positive correlation between the SCS and the western equatorial Pacific in the 8-year time-scale. Evidence is presented that the SST anomalies of the equatorial Pacific influence the SST of the SCS.     

Anomalous activity of East Asian winter monsoon and the tropical Pacific SSTA

The relationship between the anomalous East Asian winter monsoon (EAWM) activity and the tropical Pacific SST anomalies has been identified using the results of 40-year integration of the IAP CGCM1 model and 10-year observational data. In the strong EAWM year, the western and central Pacific are dominated by positive SST anomalies while the eastern Pacific is negative ones. In the weak EAWM year, the SSTA pattern is quite different and shows El Nino-like SST anomalies. The strong EAWM activity tends to create extra easterly flow to the east and extra westerly flow to the west of the warm SSTA region over the equatorial western and central Pacific, thus leading to the enhancement of convergence and convection of the flow in this region and favorable to the maintenance and development of such an SSTA pattern. On the other hand, the warm SST anomaly over the western and central Pacific, as a forcing, may lead to a specific pattern of the northern extratropical atmosphere, which is favorable to the strong EAWM activity. The tropical Pacific SSTA pattern related closely to the strong EAWM activity differs significantly from that of the La Nina year.     

冬春海温异常对东亚初夏季风环流的影响

用ＯＳＵ的两层大气环流模式进行了热带西太平洋冬春海温异常对东亚初夏（５月）季风环流影响的数值试验．结果表明：①海温的负距平引起西太平洋副热带高压脊南落和西伸，东亚热带季风环流减弱，我国西南和华南地区的降水增加；②海温的正距平引起西太平洋副热带高压明显减弱，西太平洋的赤道西风加强，我国西南和华南地区的降水减少     

Covarying modes of the Pacific SST and northern hemispheric midlatitude atmospheric circulation anomalies during winter

The interannual-to-interdecadal relationship between the Pacific sea surface temperature （SST） and the northern hemispheric midlatitude＇s atmosphere represented by the circumpolar vortex was documented with the global oceanic and atmospheric reanalysis data of recent 50 years. Two covarying modes of the Pacific SST and northern circumpolar vortex anomalies during winter were examined using the singular value decomposition and wavelet analysis techniques. One is the interannual, ENSO-related mode and the other is the interdecadal, North Pacific SST-related mode with a period of around 20 years. The two modes exhibit distinct spatial structures. For the interannual mode, the SST anomaly is characterized by a typical ENSO pattern with the principal signature in the tropical eastern Pacific and secondary one in the central North Pacific, while the atmospheric anomaly is regional, characterized by a Pacific-North American pattern. For the inter- decadal mode, large SST anomaly is located in the central North Pacific, while the atmospheric anomaly is zonally global, associated with the midlatitute＇s standing long-wave variations. When the central North Pacific is colder, the long-wave is stronger, and vice versa. Further investigations suggest that the interdecadal mode could involve an interaction between ＂two oceans and an atmosphere＂.     

Occurrence of two types of El Niño events and the subsurface ocean temperature anomalies in the equatorial Pacific

The relationships between the evolution of two types of E1 Nifio events and the subsurface ocean temperature anomaly （SOTA） in the equatorial Pacific are compared in this study. The results show that both types of E1 Nifio are negatively correlated to the SOTA in the equatorial western Pacific, but relationships are different in different phases of E1 Nifio. Furthermore, the occurrence of different types of E1 Nifio is related to different features of the equatorial thermocline, e.g. its zonal gradient, significant variation area, amplitude and duration of thermocline oscillation. The propagation of SOTA in the equator plays an important role during the evolution of both types of E1 Nifio, but shows dramatic differences in intensity, duration and phase reverse of warm SOTA. Moreover, the pathways of SOTA signal are different between these two types of E1 Nifio. The dominant pathway in the life cycle of Eastern Pacific （EP）-E1 Nifio lies on the equator and to its north, but there is no loop to the south of the equator. In contrast, the dominant pathway in Central Pacific （CP）-E1 Nifio is located on the equator and to its south, and the propagation signal of SOTA to the north of the equator is very weak. The relationships between the zonal wind anomalies and the two types of E1 Nifio are also preliminarily discussed. It is shown that EP-E1 Nifio is more likely to respond to the westerly anomalies over the equatorial central and western Pacific, while CP-E1 Nifio is more likely to respond to the westerly anomalies over the equatorial western Pacific and need the cooperation of easterly anomalies over the equa- torial eastern Pacific to certain extent.     

江淮流域梅雨期雨量的变化特征及其与太平洋海温的相关关系及年代际差异

运用相关分析和滑动相关方法,分析了江淮流域5个代表站1903-2000年梅雨期雨量的变化特征及其与太平洋海温的相关关系及年代际差异.结果表明,江淮地区梅雨期雨量在近百年来存在明显的年际和年代际变化特征.通过分析梅雨期雨量与太平洋海温的年代际相关特征发现,江淮流域梅雨期雨量与前期及同期太平洋海温关系密切,前一年冬季及梅雨期东北太平洋海温与江淮流域梅雨期雨量负相关,在热带东太平洋的Nino1 2区两者正相关显著,同年春季西太平洋部分海域海温与江淮流域梅雨期雨量正相关.从年际相关分析发现,前一年冬季太平洋海温与梅雨期雨量正相关,同年春季以及梅雨期两者相关不明显.通过分析年代际差异发现,江淮流域梅雨期雨量与前期及同期热带太平洋关键区海温的21a滑动相关存在显著的年代际差异,这种差异与海温的21a滑动平均的年代际冷暖背景关系密切,热带太平洋海温关键区前一年冬季冷海温背景下,梅雨期雨量同海温正相关显著,同年春季暖海温背景下,两者之间负相关显著,而江淮流域梅雨期雨量同中国近海海温之间(从冬季到梅雨期)维持显著的正相关,与该区海温冷暖背景的关系则并不明显.     

Role of atmospheric heat source/sink over the Qinghai-Xizang Plateau in quasi-4-year oscillation of atmosphere-land-ocean interaction

Using 1961—1995 monthly atmospheric apparent heat source/sink <Q₁> over the Qinghai-Xizang Plateau (QXP) and reanalysis data of NCEP/NCAR, and 1961—1994 monthly SST of UK/GISST2, the statistical study is undertaken on the QXP heat source/sink in relation to both atmospheric circulation in Asia and El Niño/La Niña events. It is discovered that there exists noticeable interaction in a quasi-4-year period among the <Q₁> of the QXP, low-level meridional winds east of the QXP, low-level zonal winds in the equatorial Pacific, SST in the equatorial eastern Pacific, and the circulation at mid and high latitudes north of the QXP. They have difference in phase. The cold source intensity of the QXP in winter favours a low-level meridional wind anomaly to prevail in the mainland of China and its coast east of the QXP and to last until the subsequent autumn. The wind anomaly can induce a low-level zonal wind anomaly of the tropic Pacific that finally affects an El Niño/La Niña event in the autumn and subsequent winter. The event in autumn/winter has effect on the deep trough position and cold air track of East Asia in next winter that influences the intensity of the QXP winter cold source.     

Record-breaking SST over mid-North Atlantic and extreme high temperature over the Jianghuai–Jiangnan region of China in 2013

In July 2013, the Jianghuai–Jiangnan region of China experienced a persistent extreme high temperature,and the surface air temperature(SAT) over many areas of the region set a new record, which had a profound impact on people's lives. This study explored the possible mechanism for this extreme climate phenomenon. The results show that the sea surface temperature(SST) over the midNorth Atlantic in July 2013 was the warmest observed over the past 160 years. The strong anomaly of the SST connects to the East Asian upper level westerly and western Pacific subtropical high(WPSH) via the teleconnection wave train and further contributes to the SAT variability over the Jianghuai–Jiangnan region; this connection could be one possible mechanism for the formation of the recordbreaking extreme hot event(EHE) over the Jianghuai–Jiangnan region in July 2013. In addition, for the EHE over the Jianghuai–Jiangnan region, the role of the WPSH was generally emphasised. This study found that the variability of the upper level westerly over the Jianghuai–Jiangnan region is also an important climate factor impacting the SAT of the region. In particular, the record-breaking weakness of the upper level westerly corresponded to the record-breaking SAT over the Jianghuai–Jiangnan region in July 2013. These results indicate that the role of the upper level westerly should be emphasised in addition to the WPSH, according to both the variability in the summer air temperature and the EHE over the Jianghuai–Jiangnan region.     

Interannual and interdecadal variabilities in SST anomaly over the eastern equatorial Pacific

The global sea surface temperature (SST) anomaly data from 1950 to 1996 were used to analyze spatial characters of interdecadal SST variations. A wavelet transform was made for the equatorial eastern Pacific SST anomaly time series. Results show that there are three remarkable timescale SST variations: 130-month interdecadal variation, 57-month interannual variation and 28-month quasi-2-a variation. Based on this result, an El Nino event was predicted in the early part of 1997.     

Linkage between the dominant modes in Pacific subsurface ocean temperature and the two type ENSO events

We investigate the variations of subsurface ocean temperature(SOT) based on the monthly-Simple Ocean Data Assimilation(SODA) during 1958-2007,and discuss the linkage between the variations of SOT and the eastern and central Pacific ENSO(EP and CP-ENSO) events.The wavelet analyses suggest that the variation of the EP and CP-ENSO events shows the 2-7 and the 10-15 years oscillation in the tropical sea surface temperature(SST),and coupled with a zonal dipole mode and a tripole mode in the SOT anomalous field reveled by the singular value decomposition(SVD) analysis.During the mature phase of CP-ENSO,the positive center of SOT at the subsurface layer locates in the west of dateline,which results in the increase of SOT in the Ni o4 region and causes the CP-ENSO event.Statistical analysis implies that,the eastern and central Pacific subsurface indices which are defined by the expansion coefficients of the first and third SVD mode for SOT have shown the capabilities in disguising the EP and CP-ENSO events,respectively.In addition,corresponding to the increase of the SOT amplitude on the 10-15 years time scale,we found that the frequency and intensity of CP-El Ni o events has exhibited an upward trend after the 1980s,which suggests that the CP-ENSO event has shown an enhanced impact on the global climate in the past decades.     

Occurrence of two types of El Nin?o events and the subsurface ocean temperature anomalies in the equatorial Pacific

The relationships between the evolution of two types of El Ni?o events and the subsurface ocean temperature anomaly(SOTA) in the equatorial Pacific are compared in this study. The results show that both types of El Ni?o are negatively correlated to the SOTA in the equatorial western Pacific, but relationships are different in different phases of El Ni?o. Furthermore, the occurrence of different types of El Ni?o is related to different features of the equatorial thermocline, e.g. its zonal gradient, significant variation area, amplitude and duration of thermocline oscillation. The propagation of SOTA in the equator plays an important role during the evolution of both types of El Ni?o, but shows dramatic differences in intensity, duration and phase reverse of warm SOTA. Moreover, the pathways of SOTA signal are different between these two types of El Ni?o. The dominant pathway in the life cycle of Eastern Pacific(EP)-El Ni?o lies on the equator and to its north, but there is no loop to the south of the equator. In contrast, the dominant pathway in Central Pacific(CP)-El Ni?o is located on the equator and to its south, and the propagation signal of SOTA to the north of the equator is very weak.The relationships between the zonal wind anomalies and the two types of El Ni?o are also preliminarily discussed. It is shown that EP-El Ni?o is more likely to respond to the westerly anomalies over the equatorial central and western Pacific, while CP-El Ni?o is more likely to respond to the westerly anomalies over the equatorial western Pacific and need the cooperation of easterly anomalies over the equatorial eastern Pacific to certain extent.     

Precursory SST anomalies associated with the convection over the western Pacific warm pool

The convection over the tropical western Pacific warm pool influences significantly the atmospheric circulation and climate in East Asia. Thus, the precursory signals of the convection may be used in the forecast of summer climate in China. According to the present results, the June-July-August (JJA) mean convection intensity over the warm pool is significantly related to the precursory positive and negative sea surface temperatures (SSTs) in the warm pool and in the equatorial central and eastern Pacific, respectively. It is also related to the simultaneous negative surface temperatures west to the Philippines. The analysis on the SSTs associated with the convection over the warm pool in individual month of summer shows that for the convection in June and July, there are precursory SST signals in the warm pool and the equatorial central and eastern Pacific. Therefore, this study shows that only the convection in June and July, rather than that in August, has precursory SST signals, despite the existence of the precursory signals of the JJA mean convection. Accordingly, it is implied that the interaction among the warm pool, equatorial central and eastern Pacific, and the region west to the Philippines may exhibit distinct features in the precursory period (preceding winter and spring) and in the simultaneous period.     

东北夏季降水的时间变化特征及其与太平洋海温的相关关系

利用中国降水逐日站点观测资料以及HadISST海温资料,分析了1961-2010年东北地区70个观测站夏季降水的变化特征以及太平洋海温对东北夏季降水的可能影响。结果表明：东北夏季降水近50a来呈现下降趋势,具有多阶段性,在60年代以及80-90年代存在明显的突变;在1986-1985年以及1986-2010年2个阶段,热带外太平洋与热带太平洋春季和夏季海温都存在与东北夏季降水的相关关键区,两个阶段相关性显著不同甚至相反,是1961-2010年东北夏季降水与太平洋海温总体相关性较弱的原因。东北夏季降水与太平洋海温的相关性可能与海温冷暖背景有关系：在暖的海温背景下,东北降水与热带太平洋海温呈现显著的正相关;而对于热带外太平洋,暖的海温背景下,两者为负相关,冷的海温背景下,两者为正相关,尤其表现在春季,因此太平洋春季海温异常对于东北夏季降水预测有较好的指示意义。     

黄、东海沿岸海表温度变化与厄尔尼诺的关系

利用黄、东海沿岸8个长期水文观测站多年海表温度资料,分析黄、东海沿岸海表温度的季节和年际变化特征,重点分析在1982—1983年和1997—1998年两次厄尔尼诺年期间的异常变化,以及ENSO影响黄、东海沿岸海表温度的可能机制。结果表明,在厄尔尼诺发生年,夏季风较弱,鄂霍次克海高压加强,西太平洋副高位置偏南,强度偏强,江淮流域及长江中下游降水偏多,黄、东海沿岸海表温度偏低。黄、东海沿岸海表温度受到ENSO和PDO(太平洋年代际振荡)的影响和调制,在厄尔尼诺发生的前冬半年及当年,黄、东海沿岸海表温度偏低;在厄尔尼诺发生次年,黄、东海沿岸海表温度偏高。厄尔尼诺对黄、东海沿岸海表温度变化的影响通过海洋和大气2个通道,1982—1983年海表温度异常以负异常为主,1997—1998年海表温度异常以正异常为主;ENSO期间,北赤道流减弱,黑潮流量减少,海表温度降低。海表温度受局地气温影响显著,如果ENSO期间东亚气温升高,则黄、东海沿岸海表温度偏高。