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.     

Interdecadal shift in the western North Pacific Summer SST anomaly in the late 1980s

An interdecadal shift in summer (June―August) sea surface temperature (SST) variations during the period of 1968―2002 was identified in the late 1980s, which is characterized by a phase alternating from negative to positive phases of the leading mode of the empirical orthogonal function (EOF) analysis of the summer monthly mean SST in the Pacific domain 100°―180°E and 0°―40°N, accounting for 30.5% of the total variance. During the period of 1968―1987, the leading mode with a mean negative phase state (mean standard deviation = ?0.586) controlled SST variability in the western North Pacific. Correspondingly, negative SST anomalies occupied the western North Pacific south of Japan and Chinese marginal seas. During the period of 1988―2002, the leading mode shifted to its strong positive polarity (mean standard deviation = 0.781), thus positive SST anomalies appeared in the western North Pacific. Accompanied by the interdecadal shift in summer mean SST, summer mean rainfall increased in southern and southeastern China during the late period, particularly in southeastern China where increase in summer mean rainfall exceeded 40 mm, at the 0.05 significance level.     

Regional relationship between the Jiang-Huai Meiyu and the equatorial surface-subsurface temperature anomalies

The Jiang-Huai Meiyu rainy season can be distinguished into the Jiangnan Meiyu spell and the Huaihe Meiyu spell. The Jiangnan Meiyu spell appears on the last ten days in June and the Huaihe Meiyu spell lasts from early July to middle July. An inter-decadal transition was observed in 1998 respectively from the anomalies of Jiangnan Meiyu rainfall, the sea surface temperature (SST), and the subsurface tem- perature in the equatorial Pacific. Since the beginning of the 21^_st century, opposite trends and biennial oscillations of the Meiyu rainfall are observed in the Jiangnan and Huaihe basins. Before the strong La Niña of 1999―2000, the positive SST anomalies usually occurred in the eastern equatorial Pacific. Since the beginning of the 21^_st century, a precursory warming signal of SST anomaly comes from the subsurface temperature which is centrally exposed near the dateline in the central equatorial Pacific. The above-normal Meiyu rainfall in 2003, 2005 and 2007 over the Huaihe basin followed the prior winter- spring positive SST anomaly near the dateline. A relationship shows that the more Jiangnan (Huaihe) Meiyu follows the winter-spring warm water in the eastern (central) equatorial Pacific.     

中国西南秋季旱涝的诊断分析

为了分析中国西南秋季旱涝情况,利用西南地区东部1961~2012年的降水资料和区域旱涝指数对该地区秋季旱涝等级进行了评定,并运用NCEP/NCAR再分析资料与英国气象局海温资料对典型旱涝年的成因进行了探讨。结果表明,西南地区东部降水呈显著减少趋势,并在1990年左右发生了突变。旱年秋季,低层在南中国海附近为显著的气旋性环流异常,西南地区上空存在显著的下沉运动,涝年则相反。进一步分析发现,当西太平洋海温偏高时,可以激发罗斯贝波环流异常,对应在南中国海附近存在异常的气旋性环流,临近的西南地区东部处于异常的下沉气流控制,容易发生干旱,涝年则相反。此外,热带西太平洋海温于20世纪80年代中后期发生了由冷转暖的突变,这与随后西南地区东部秋季降水的突变密切相关。     

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.     

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     

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。     

副热带太平洋海温异常对赤道海洋的影响

利用完全耦合的气候模式进行敏感性试验, 定量研究副热带太平洋不同经度带的海表面温度异常(SSTA)对赤道太平洋的影响。研究发现, 赤道表层和温跃层海温对副热带太平洋(20°?30°N)西部、中部和东部SSTA的热力响应是相当的。 研究中强调大气?海洋耦合在副热带SSTA影响赤道温跃层过程中的决定性作用, 并提出一种间接的、较“海洋通道”机制更为快速的机制: 副热带SSTA引发局地大气的气旋性响应, 继而引起局地海洋内区的上升流和其面向赤道一侧海洋内区的下沉流, 该下沉流造成的局部温跃层暖异常向着赤道传播, 导致赤道温跃层增暖。     

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＂.     

Linkage between the Asian-Pacific Oscillation and the sea surface temperature in the North Pacific

The linkage between the Asian-Pacific Oscillation (APO) and the sea surface temperature (SST) in the North Pacific during the summertime (June-August) is preliminarily investigated through an analysis of observed data.It is found that APO is significantly and positively correlated to the North Pacific SST,with the correlation coefficient being 0.58 on the interannual timescale during the period 1954-2003,which suggests that a strong (weak) APO corresponds to high (low) SST in the North Pacific.Their in-phas...     

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.     

Linear relationship between the interdecadal and interannual variabilities of North China rainfall in rainy season

Interdecadai and interannuai timescales are dominant in the North China rainfall in rainy season (July and August). On the interdecadai timescale, the North China rainfall exhibited an abrupt decrease at the end of 1970s. In this study, we examined the effect of this abrupt rainfall decrease on the association between rainfall and circulation on the interannuai timescale, and found that the interdecadal variation does not change the physical mechanism responsible for the interannuai variation of North China rainfall.There is a linear relationship between the interdecadai and interannuai variabilities of North China rainfall in rainy season.     

The spring soil moisture and the summer rainfall in eastern China

The relation between the soil moisture in spring and the rainfall in summer in eastern China is investi- gated. Results show that the summer rainfall in eastern China is closely related to the spring soil moisture in the area from North China to the lower reaches of Yangtze River (NCYR). When spring soil moisture anomalies over NCYR are positive, the summer precipitation exhibits positive anomalies in Northeast China and the lower reaches of Yangtze River, and negative anomalies in southern China and North China. The higher soil moisture over NCYR cools land surface and reduces the land-sea tem- perature gradient, which weakens East Asian summer monsoon. The western Pacific Subtropical High (WPSH) is located to the south and shifts westward, resulting in more rainfall in the lower reaches of Yangtze River and less in southern China and North China.     

Interannual atmospheric variability forced by the deep equatorial Atlantic Ocean

Climate variability in the tropical Atlantic Ocean is determined by large-scale ocean-atmosphere interactions, which particularly affect deep atmospheric convection over the ocean and surrounding continents. Apart from influences from the Pacific El Ni?o/Southern Oscillation and the North Atlantic Oscillation, the tropical Atlantic variability is thought to be dominated by two distinct ocean-atmosphere coupled modes of variability that are characterized by meridional and zonal sea-surface-temperature gradients and are mainly active on decadal and interannual timescales, respectively. Here we report evidence that the intrinsic ocean dynamics of the deep equatorial Atlantic can also affect sea surface temperature, wind and rainfall in the tropical Atlantic region and constitutes a 4.5-yr climate cycle. Specifically, vertically alternating deep zonal jets of short vertical wavelength with a period of about 4.5?yr and amplitudes of more than 10?cm?s(-1) are observed, in the deep Atlantic, to propagate their energy upwards, towards the surface. They are linked, at the sea surface, to equatorial zonal current anomalies and eastern Atlantic temperature anomalies that have amplitudes of about 6?cm?s(-1) and 0.4?°C, respectively, and are associated with distinct wind and rainfall patterns. Although deep jets are also observed in the Pacific and Indian oceans, only the Atlantic deep jets seem to oscillate on interannual timescales. Our knowledge of the persistence and regularity of these jets is limited by the availability of high-quality data. Despite this caveat, the oscillatory behaviour can still be used to improve predictions of sea surface temperature in the tropical Atlantic. Deep-jet generation and upward energy transmission through the Equatorial Undercurrent warrant further theoretical study.     

Asian-Pacific Oscillation index and variation of East Asian summer monsoon over the past millennium

To study the long-term variation of the East Asian summer monsoon （EASM）, the Asian-Pacific Oscillation index （IAPO）, representing a zonal thermal contrast between Asia and the North Pacific, is reconstructed over the past millennium. During the Little Ice Age （LIA）, the variability of the reconstructed IAPO is closely linked to dry-wet anomalies in eastern China on the centennial scale. This correlation pattern is consistent with the observation during the current period, which suggests that the reconstructed IAPO may generally represent the centennial-scale variation of the EASM and rainfall anomalies over eastern China during the LIA.     

Indian Ocean temperature dipole and SSTA in the equatorial Pacific Ocean

The observed sea surface temperature (SST) data of recent 100 years are analyzed and the existence of the Indian Ocean temperature dipole in the equatorial region is exposed further. It is very clear that the amplitude of the positive phase (higher SST in the west and lower SST in the east than normal) is larger than that of the negative phase (higher SST in the east and lower SST in the west). The dipole is stronger in September-November and weaker in January-April than in other months and it also appears obviously inter-annual and inter-decadal variations. Although the Indian Ocean dipole in the individual year seems to be independent of ENSO in the equatorial Pacific Ocean, in general, the Indian Ocean dipole has obviously negative correlation with the Pacific Ocean dipole (similar to the inverse phase of ENSO mode). The atmospheric zonal (Walker) circulation over the equator is fundamental to relate the two dipoles to each other.     

Differences between dynamics factors for interannual and decadal variations of rainfall over the Yangtze River valley during flood seasons

The prediction of rainfall in the Yangtze River valley, especially, during flood seasons is the main means for scientists in China working on and the understanding of rainfall-associated processes is a crucial component of this effort. It can be derived f…     

Monsoonal oscillation revealed by the upper-troposphere water vapor band brightness temperature

The measurements of brightness temperature (BT) from the upper-troposphere water vapor channel 12 of the National Oceanic and Atmospheric Administration polar satellites from 1979 through 1995 are used to analyze the interannual variations of the global monsoon strength. Results show that in the interannual time-sclae the BT variability in the equatorial eastern Pacific (EEP) is out of phase with the BT variabilities in other four regions, i. e. South Asia, tropical south American, two subtropical areas in the South and North Pacific. The BT interannual variation mode may be called monsoonal oscillation (MO). The MO is the result of the atmospheric circulation anomaly in the troposphere.     

太平洋海表面温度季节内振荡特征

为了研究太平洋海表面温度季节内振荡的特征,利用NOAA(national oceanic and atmospheric ad-ministration)周平均SST资料,采用谐波方法重构了太平洋海表面温度季节内振荡信号,针对不同海域,用小波分析等方法,揭示了SST季节内振荡的空间、频谱、季节性和传播特征.结果表明:海表面温度季节内振荡在黑潮区、黑潮续流区和赤道东太平洋较活跃,在赤道东西太平洋有相对重要的地位;在北太平洋谱特征均为单峰结构,在赤道东西太平洋呈双峰结构.不同海域海表面温度季节内振荡的活跃期分别为:北太平洋夏秋季,赤道东太平洋春和秋季,热带西太平洋活跃期较分散;在北太平洋以缓慢东传为主,在赤道东太平洋以西传为主,在热带西太平洋无明显传播.     

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。