Interdecadal Modulation of AMO on the Winter North Pacific Oscillation-Following Winter ENSO Relationship

It is known that the wintertime North Pacific Oscillation (NPO) is an important extratropical forcing for the occurrence of an El Ni?o?Southern Oscillation (ENSO) event in the subsequent winter via the “seasonal footprinting mechanism” (SFM). This study reveals that the Atlantic Multidecadal Oscillation (AMO) can notably modulate the relationship between the winter NPO and the following winter ENSO. During the negative AMO phase, the winter NPO has significant impacts on the following winter ENSO via the SFM. In contrast, the influence of the winter NPO on ENSO is not robust at all during the positive AMO phase. Winter NPO-generated westerly wind anomalies over the equatorial western Pacific during the following spring are much stronger during negative than positive AMO phases. It is suggested that the AMO impacts the winter NPO-induced equatorial westerly winds over the western Pacific via modulating the precipitation climatology over the tropical central Pacific and via modulating the connection of the winter NPO with spring sea surface temperature in the tropical North Atlantic.     

太平洋年代际涛动与云南夏季气温的年代际变化

云南夏季气温具有年代际变化特征,近年来一系列的云南夏季气温异常偏高事件是年代际变化的体现.其中云南夏季气温在准50年年代际变率上与春季太平洋年代际涛动(PDO)指数具有较好的正相关关系,夏季西太平洋副热带高压西伸脊点位置与前两者在年代际上都具有较好的负相关关系.分析认为,可能是由于当春季PDO进入暖(冷)位相阶段时,中东太平洋海温距平持续偏高(低),夏季西太平洋副热带高压位置偏西(东),导致云南夏季不(容)易出现云雨天气,从而进入了气温偏高(低)的年代际时期的关系.春季PDO的变化是夏季云南气温年际变化的重要背景.     

Interdecadal variability of the ENSO teleconnection to the wintertime North Pacific

The El Niño/Southern Oscillation (ENSO) strongly influences the large-scale atmospheric circulation over the extratropical North Pacific during boreal winter, which has an important impact on North American winter climate. This study analyses the interdecadal variability of the ENSO teleconnection to the wintertime extratropical North Pacific, over the period 1900–2010, using a range of observationally derived datasets and an ensemble of atmospheric model simulations. The observed teleconnection strength is found to vary substantially over the 20th century. Specifically, 31-year periods in the early-century (1912–1942), mid-century (1946–1976) and the late-century (1980–2010) are identified in the observations when the ENSO teleconnection to the North Pacific circulation are found to be particularly strong, weak and strong respectively. The ENSO teleconnection to the North Pacific in the atmospheric model ensemble is weak in the mid-century period and substantially stronger in the late-century, closely following the variability in the observed ENSO-North Pacific teleconnection. In the early-century, however, the atmospheric model also exhibits a weak teleconnection to the North Pacific, unlike in observations. In a subset of the model realisations that exhibit similar ENSO-North Pacific teleconnection as in observations during the early-century period there are large differences in extratropical circulation but not in equatorial Pacific precipitation anomalies, in contrast to the late-century period. This suggests that the high correlation in the early century period is largely due to internal extratropical variability. The important implications of these results for seasonal predictability and the assessment of seasonal forecasting systems are discussed.

     

北大西洋涛动指数的比较及其年代际变率

首先对各种北大西洋涛动（NAO）指数的定义进行了比较。发现冬季和夏季NAO的涛动中心有显著的差异,所以分别进行定义,定义时的中心由EOF分析及相关分析确定,新的定义能解释更多的海平面气压方差。在此基础上建立了1873年以来的冬、夏NAO指数序列。近百年来的NAO指数最突出的年代际变化是,夏季在1910～1920年期间的突变性质的增强,以及冬季近20多年来的持续加强。最后还对NAO年代际变化产生的可能原因进行了分析。     

南极海冰涛动与ENSO的关系

对近30年南极海冰密集度资料的EOF和SVD分析,发现南极地区在罗斯海外围和别林斯高晋海的海冰密集度场存在着“翘翘板”的变化特征,并与ENSO有密切联系。由此定义两个海冰关键区的差值为南极海冰涛动指数（ASOI）,ASOI超前SOI和Nino3指数2个月时,其正、负相关系数达到最大,并通过α=0.001的信度检验。ASOI高、低指数阶段对应的南半球海平面气温、气压场和风场的合成分析表明,海冰关键区的异常变化可能引起温度、气压、风场的响应而影响南太平洋的洋流,进而对ENSO的发生、发展产生影响。     

华北地区春季降水与ENSO的关系

根据1961—2010年华北地区53个气象站降水资料、NOAA海温资料及NCEP/NCAR再分析资料,采用相关分析和合成分析等统计方法,研究了华北地区春季降水与ENSO的关系。结果表明,华北地区春季降水偏少年份出现的频次高于偏多年份,强度强于偏多年份的,并且呈现出阶段性偏多和偏少特征,尤其是在20世纪70年代呈现出比较突出的偏少特征,一直延续到80年代中期。华北春季降水和前冬Nino3区海温存在显著的正相关关系(相关系数达0.42):当前冬Nino3区海温负异常时,华北春季降水偏少;而正异常时,华北春季降水偏多。因此,前冬海温异常对华北春季降水有较好的指示意义。大气对前冬海温的异常有明显的响应:Nino3区海温正异常可导致次年春季热带和西北太平洋副热带地区的500 h Pa高度场升高(即西太平洋副热带高压偏强、偏西、偏北),东亚大槽偏弱、偏东,巴尔喀什湖至贝加尔湖的高度场降低(即该地区经常有低槽维持),亚洲至西太平洋地区盛行纬向环流;而前冬Nino3区海温负异常则相反。     

中国东部夏季降水型的年代际变化及其与北太平洋海温的关系

采用中国160站降水资料、NOAA ERSST海温资料以及ERA－40大气再分析资料, 分析了中国东部夏季降水型的年代际变化特征及其与北太平洋海温的可能联系。结果表明: 中国东部夏季降水型在近50年中经历了两次年代际变化, 第1次发生在20世纪70年代中后期, 北太平洋中纬度地区冬季海温由正距平向负距平转变, 太平洋年代际振荡(PDO, Pacific decadal oscillation) 由负位相向正位相转变, 通过影响东亚夏季风环流, 使东亚夏季风减弱, 中国东部夏季降水从北到南呈现出“＋－＋” 转变为“－＋－”的三极分布形态, 这次年代际变化体现了同一模态正负位相的转变; 第2次发生在20世纪80年代末90年代初, 北太平洋海温转变为日本以南西北太平洋的正距平分布, 同时菲律宾群岛附近海温偏暖, 西太平洋副热带高压偏南偏西, 使得中国东部夏季降水由北至南转变成“－＋”的偶极分布形态, 这次年代际变化体现了一种模态向另一种模态的转变。     

太平洋年代际振荡、大西洋年代际振荡和全球变暖对北美地区降水的相对贡献

本文研究了1934～2018年期间太平洋年代际振荡（Interdecadal Pacific Oscillation,IPO）、大西洋年代际振荡（Atlantic Multidecadal Oscillation,AMO）以及全球变暖（Global Warming,GW）对北美地区陆地降水年代际变化的相对贡献。首先通过对冬（12至次年2月）、夏季（6～8月）北美地区的陆地降水与中低纬地区的海表面温度进行奇异值分解分析,得到对北美陆地冬季降水相对贡献较大的主要海温模态为IPO（42.33%）和AMO（23.21%）,夏季则为AMO（32.66%）和IPO（21.60%）。其次利用线性回归模型,分析三种信号分别对北美冬、夏季陆地降水的相对贡献及对北美陆地不同区域降水的相对重要性,结果表明AMO对夏季北美陆地降水变化的贡献最大,IPO次之,冬季则相反,GW对冬夏季北美陆地降水都有一定的贡献。夏季期间阿拉斯加地区AMO的贡献最大,约占65.8%,加拿大地区GW的贡献最大,约占44.5%,美国本土及墨西哥地区三者贡献基本一致;冬季期间阿拉斯加和加拿大地区GW的贡献最大,分别为62.3%和44.7%,美国本土和墨西哥地区IPO的贡献最大,分别为47.9%和71.5%。进一步利用信息流方法,验证了IPO、AMO、GW对降水的敏感性区域。最后运用全球大气环流模式ECHAM 4.6进一步确定了太平洋和大西洋海温异常对北美地区陆地降水变化的影响途径,结果表明印度洋海表面温度异常在AMO和IPO对北美陆地降水变化的作用中至关重要。     

ENSO与西北太平洋强TC相关关系年代际变化研究

利用美国联合台风警报中心(Joint Typhoon Warning Center,JTWC),中国气象局(China Meteorological Administration,CMA)上海台风所,日本气象厅(Japan Meteorological Agency,JMA)的台风最佳路径资料以及美国NCAR/NCEP再分析资料等,深入研究厄尔尼诺—南方涛动(El Ni1o-Southern Oscillation,ENSO)与西北太平洋强热带气旋(Tropical Cyclone,TC),即1 min最大风速大于等于114 kn相关关系的变化。结果表明,ENSO与热带西北太平洋(Western North Pacific,WNP)强TC频数之间的相关关系存在明显年代际变化。在1960—1971年期间(前一阶段),强TC年频数与Ni1o3. 4(11月—次年1月平均)相关性较弱;而在1983—2014年期间(后一阶段)两者的相关性则为强的正相关。并且强TC的年频数、生命史以及生成位置在后一阶段El Ni1o和La Ni1a年之间的差异相比前一阶段都有明显的增大。进一步分析发现:热带太平洋海温异常(Sea Surface Temperature Anomaly,SSTA)的西移是造成后一阶段Ni1o3. 4指数与强TC年频数相关性提高的关键因素。在后一阶段的El Ni1o(La Ni1a)年,SSTA的西移使得WNP东南象限的相对湿度明显增加(减少),从而有利于(不利于) TC在此象限生成。又因为位于东南象限的TC比较容易发展成强TC,因此导致后一阶段的El Ni1o(La Ni1a)年有更多(更少)的强TC在西北太平洋的东南象限生成。     

东太平洋暖池及经向风异常在ENSO事件发生、发展过程中的作用

利用1982～1999期间LDEO海表温度资料和NCEP/NCAR再分析风场资料,分析东太平洋暖池及经向风异常与ENSO事件的可能关系。结果表明,东太平洋暖池气候平均海表温度存在明显的季节变化特征,且与El Niño事件春季发生、夏季发展、秋季达到成熟及冬季衰亡的成长过程非常相似。经向风异常及其散度与ENSO事件密切相关。综合考虑,提出了东太平洋暖池及经向风异常（北风距平及经向风距平散度辐合）对ENSO事件发生、发展作用的概念模型:北风距平爆发通过产生北风吹洋流的作用,将东太平洋暖池暖水由北向南输送至赤道附近,从而有利于Ni?o3区海表温度上升;几乎与此同时,东太平洋暖池赤道上经向风距平散度辐合不仅能导致暖水在赤道附近堆积,而且辐合的风场对赤道附近的冷上升流有抑制作用,从而有利于Niño3区海表温度的增加,上述增温因素的叠加作用有（不）利于El Niño（La Niña）事件的发生、发展。进一步分析表明,东太平洋暖池及经向风异常仅对El Niño（La Niña）事件发生、发展起促进（抑制）作用而不起决定作用。将东太平洋暖池、经向风异常与西太平洋暖池、西风距平结合起来一并考虑,完善了El Niño事件发生、发展机制。最后,初步分析1980、1990年代El Niño事件特性差异的可能原因。     

Interdecadal Change of the Northward Jump Time of the Western Pacific Subtropical High in Association with the Pacific Decadal Oscillation

In this paper, the northward jump time of the western Pacific subtropical high(WPSH) is defined and analyzed on the interdecadal timescale. The results show that under global warming, significant interdecadal changes have occurred in the time of the WPSH northward jumps. From 1951 to 2012, the time of the first northward jump of WPSH has changed from "continuously early" to "continuously late", with the transition occurring in 1980. The time of the second northward jump of WPSH shows a similar change, with the transition occurring in 1978. In this study, we offer a new perspective by using the time of the northward jump of WPSH to explain the eastern China summer rainfall pattern change from "north-abundant-southbelow-average" to "south-abundant-north-below-average" at the end of the 1970 s. The interdecadal change in the time of the northward jump of WPSH corresponds not only with the summer rainfall pattern, but also with the Pacific decadal oscillation(PDO). The WPSH northward jump time corresponding to the cold(warm) phase of the PDO is early(late). Although the PDO and the El Nino–Southern Oscillation(ENSO)both greatly influence the time of the two northward jumps of WPSH, the PDO’s effect is noticed before the ENSO’s by approximately 1–2 months. After excluding the ENSO influence, we derive composite vertical atmospheric circulation for different phases of the PDO. The results show that during the cold(warm)phase of the PDO, the atmospheric circulations at 200, 500, and 850 h Pa all contribute to an earlier(later)northward jump of the WPSH.     

Interdecadal Change of the Relationship Between the Tropical Indian Ocean Dipole Mode and the Summer Climate Anomaly in China

The interdecadal change of the relationship between the tropical Indian Ocean dipole(IOD) mode and the summer climate anomaly in China is investigated by using monthly precipitation and temperature records at 210 stations in China and the NCEP/NCAR reanalysis data for 1957-2005.The results indicate that along with the interdecadal shift in the large-scale general circulation around the late 1970s,the relationship between the IOD mode and the summer climate anomaly in some regions of China has significantly changed.Before the late 1970s,a developing IOD event is associated with an enhanced East Asian summer monsoon,which tends to decrease summer precipitation and increase summer temperature in South China;while after the late 1970s,it is associated with a weakened East Asian summer monsoon,which tends to increase(decrease) precipitation and decrease(increase) temperature in the south(north) of the Yangtze River.During the next summer,following a positive IOD event,precipitation is increased in most of China before the late 1970s,while it is decreased(increased) south(north) of the Yangtze River after the late 1970s.There is no significant correlation between the IOD and surface air temperature anomaly in most of China in the next summer before the late 1970s;however,the IOD tends to increase the next summer temperature south of the Yellow River after the late 1970s.     

华北汛期降水月内时间尺度周期振荡的年代际变化分析

利用中国740站逐日降水资料和NCEP/NCAR逐日再分析资料,使用小波分析等方法,对华北汛期降水的月内时间尺度周期振荡的年代际变化及其原因进行了分析.结果表明:由于西太平洋副热带高压和华北夏季风的月内时间尺度周期振荡存在显著的年代际变化,使得华北汛期降水在两个不同阶段,存在着显著不同的月内时间尺度的周期振荡.在华北汛...     

北太平洋海温变化的年代际模及其演变特征

用近百年的海温(SST)资料,分析研究了北太平洋海温的年代际变化特征及其基本形势(模态).结果表明,它主要存在准7～10年周期和准25～35年周期两类年代际变化;这两类年代际变化又都有类似的形势(模态),但却与所谓"类ENSO模"明显不同.同时,两个年代际模都有呈西北一东南向振荡和沿海盆作顺时针旋转的共存活动(演变)特征.     

Development Processes of the Tropical Pacific Meridional Mode

Mechanisms for the spatio-temporal development of the Tropical Pacific Meridional Mode(TPMM) are investigated using a coupled ocean-atmosphere model and observations.In both observations and the model,this meridional mode displays decadal variations and is most pronounced in spring and early summer.The model simulation suggests that once SST anomalies in the subtropical northeastern Pacific are initiated,say by northeasterly trade wind variability,perturbations evolve into a merdional dipole in 2-3 months.A...     

Asymmetry of Salinity Variability in the Tropical Pacific during Interdecadal Pacific Oscillation Phases

It has been recognized that salinity variability in the tropical Pacific is closely related to the Interdecadal Pacific Oscillation(IPO). Here, we use model simulations from 1900 to 2017 to illustrate obvious asymmetries of salinity variability in the tropical Pacific during positive and negative IPO phases. The amplitude of salinity variability in the tropical Pacific during positive IPO phases is larger than that during negative IPO phases, with a more westward shift of a large Sea Surface Sal...     

北太平洋的年代际振荡与全球变暖

通过回顾和总结前人工作,特别是有关北太平洋年代际振荡的研究,针对近50年来北太平洋中纬度海温变冷的现象进行了分析与讨论。从全球气候变化的角度,总结了影响北太平洋中纬度海温变冷现象的几种可能机制,推测了全球气温变暖可能会对北太平洋的直接或间接影响,归纳指出了研究该问题的复杂性与目前面临的困难。