亚欧阻塞高压的变化特征及其与重庆夏季降水的联系

使用国家气候中心(NCC)沿用的北半球阻塞高压监测公式,利用NCEP/NCAR逐日500hPa环流场再分析资料,计算出1961-2011年逐日阻高指数,分析了北半球阻塞高压出现的关键地区阻高指数的年际和年代际变化特征及其与重庆夏季降水的联系.结果表明,三个关键区阻高的季节分布以鄂霍次克海阻高在冬季和夏季出现的频率最高,而春季和秋季则是乌拉尔山阻高活动频繁的季节,贝加尔湖地区阻高活动不及前两个区域活跃.从变化趋势来看,乌拉尔山阻高和鄂霍次克海阻高有增强的趋势,贝加尔湖阻高有减弱的趋势.各关键区的阻高日数都存在2~5年的显著性周期特点.三个关键区对重庆夏季降水的影响各有其特点,贝加尔湖和鄂霍次克海的阻塞形势对重庆夏季降水的影响较大,鄂霍次克海阻高日数对重庆夏季降水的影响比其强度对重庆夏季降水的影响关系更加显著,夏季鄂霍次克海阻高日数偏多(少),重庆夏季降水偏多(少).     

Relationship between El Ni(n)o and sea surface temperature variation in coastal region of Yellow Sea and East China Sea

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.     

宁夏冬季气温变化与大气环流异常的关系

利用1961~2015年冬季(12月到次年2月)宁夏20个气象站月平均气温资料,NCEP/NCAR发布的500 h Pa位势高度场和海平面气压场,200 h Pa、850 h Pa风场月平均再分析资料,运用线性倾向估计、M-K法及合成分析等方法,在研究宁夏冬季平均气温的年际变化及年代际变化特征的基础上,分突变前后的冷、暖期时段进一步分析大气环流场不同影响因子与宁夏冬季气温异常的关系,揭示宁夏冬季气温异常的成因。结果表明:(1)宁夏冬季平均气温由冷变暖的趋势非常显著,在1985年之前为冷期,1985年以后为暖期;冬季平均气温年代际变化在20世纪增暖趋势显著,21世纪后上升趋势趋于平缓。(2)不仅500 h Pa位势高度场的乌拉尔山高压脊和西太平洋副高是影响宁夏冬季气温异常的主要系统,海平面气压场的西伯利亚高压也是影响宁夏冬季气温异常的关键系统;高低空的偏北气流和偏南暖湿气流异常流场也对宁夏冬季气温变化造成一定影响。     

近47年来长江中下游气温异常的特征

利用1951年1月～1997年11月中国160站月平均气温资料分析了长江中下游气温异常的特征及其与全国气温异常的关系.结果表明：和全国一样,长江中下游冬、夏气温在近46年存在明显的变化趋势：冬季趋于变暖,夏季相反.冬、夏季气温异常年的合成分析指出,冬季偏冷(暖)时,全国大部地区也偏冷(暖),且从春季开始持续偏冷(暖)到冬季,因此,前期气温与冬季气温有较好的对应关系;该地区凉、热夏年,全国气温异常也具有不同的时空分布特征.     

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。     

近63年中国东部冬季气温异常的时空分布特征

利用中国东部地区115站1951-2013年冬季气温以及美国国家大气科学研究中心和环境预报中心再分析资料,采用经验正交展开和旋转经验正交展开方法,分析中国东部地区近63 a冬季气温变化特征,并基于气候划分的区域分析了其与大气环流异常的关系.结果表明中国东部冬季气温变化在总体一致型的基础上还存在东北一西南反向变化的类型.近63 a冬季气温在1984年前后发生了显著变化,东部冬季气温突变略早于全国,近30 a来中国东部冬季气温明显偏高.中国东部地区冬季气温异常可以分为华南-东南区、东北区、华中区和河套区。西伯利亚高压、东亚大槽和西风急流与中国东部地区冬季气温变化有着显著的相关关系.     

1961—2014年云南冬季寒潮活动规律及其与大气环流异常的关系

利用云南122个气象站1961—2015年逐日最低气温和平均气温资料,分析了云南冬季寒潮的活动规律以及大气环流异常特征.结果表明:①1961—2014年(近50 a)云南冬季寒潮频次(强度)呈减少(减弱)趋势,1984年为寒潮频次(强度)由多(强)转少(弱)的一个转折点.云南冬季寒潮存在8 a左右的显著性变化周期;②云南冬季寒潮与气温、降水存在较好的协同变化.当冬季寒潮频次偏多(少)时,云南气温偏低(高),降水量偏多(少);③云南冬季寒潮频次年际变异与大气环流异常密切相关.在海平面气压场,冬季北极涛动为正(负)位相、西伯利亚高压偏强(弱)以及东亚冬季风偏强(弱)时,云南冬季寒潮频次偏多(少).在500 hPa高度场,当极涡偏强(弱)、贝加尔湖高压脊偏强(弱)、东亚大槽和南支槽偏强(弱)时,有利于云南冬季寒潮频次偏多(少);④副热带对流层上层的急流变化是影响云南寒潮频次变化的一个重要因子,其可能通过影响冷涌向南爆发的频次进而影响云南寒潮的发生频次.     

北冰洋海平面变化的观测和研究现状

回顾北冰洋海平面观测和研究现状,总结了北冰洋海平面变化特征和变化机制。北冰洋海平面季节变化受海冰生消、蒸发降水和陆地径流季节变化的影响,由比容变化主导;年际到年代际海平面变化受北极涛动影响显著,可用风场异常导致的淡水分布来解释。盐比容变化是深水洋盆海平面变化的主导因素,由之引起的质量变化控制陆架海域和北冰洋平均的海平面变化。近期波弗特环流区域海平面上升极快,与波弗特高压持续增强及淡水积聚有关。气候变暖会导致北冰洋海平面持续上升。海冰快速减退和格陵兰岛冰川融化对北冰洋海平面变化的影响有待深入研究。数据的短缺和观测的不确定性目前仍然制约北冰洋海平面变化的研究工作,高分辨率数值模拟有望成为未来研究的重要工具。     

大气环流年代际变化对东亚北部冬季气温异常的影响

 利用NCEP资料1949～1999年间的地表气温(SAT)进行经验正交函数分解(EOF).得到的前2个模态均表明,20世纪70年代中期以后,东亚北部地区冬季气温增暖明显,发生了显著的年代际变化.这种气温的异常变化主要受到东亚冬季风的直接影响.近20多年来,北极涛动维持在正位相并持续增强,其对东亚冬季风的影响也越来越显著,东亚冬季风持续减弱,使得东亚北部地区冬季气温增暖.通过对SAT和SLP进行奇异值分解(SVD),结果表明北极涛动的持续增强可能是东亚北部地区冬季增暖的重要原因之一.     

近51年贵州南部冬季气温气候特征及其变化规律

利用贵州南部12个站51年气温观测资料,研究这个地区冬季气温的长期变化,其中包括用线性趋势分析了冬季气温的变化趋势和特征,以及利用小波周期分析方法研究了冬季气温的周期变化.结果表明:51年来,贵州南部冬季平均气温、12月气温、2月气温、平均最低气温、极端最低气温均呈现升温的趋势,其中2月增温趋势达到0.46℃/10 a,平均最低气温达到0.23℃/10 a,两者升温显著;1月气温呈现下降的趋势,趋势率为-0.13℃/10 a,平均最高气温和极端最高气温呈现弱的降温趋势.贵州南部冬季气温和冬季各月气温存在年际振荡和年代际振荡.     

Arctic sea ice bordering on the North Atlantic and interannual climate variations

Variations of winter Arctic sea ice bordering on the North Atlantic are closely related to climate variations in the same region. When winter North Atlantic Oscillation (NAO) index is positive (negative) anomaly phase, Icelandic Low is obviously deepened and shifts northwards (southwards). Simultaneously, the Subtropical High over the North Atlantic is also intensified, and moves northwards (southwards). Those anomalies strengthen (weaken) westerly between Icelandic Low and the Subtropical High, and further result in positive (negative) sea surface temperature (SST) anomalies in the mid-latitude of the North Atlantic, and increase (decrease) the warm water transportation from the mid-latitude to the Barents Sea, which causes positive (negative) mixed-layer water temperature anomalies in the south part of the Barents Sea. Moreover, the distribution of anomaly air temperature clearly demonstrates warming (cooling) in northern Europe and the subarctic regions (including the Barents Sea) and cooling (warming) in Baffin Bay/Davis Strait. Both of distributions of SST and air temperature anomalies directly result in sea ice decrease (increase) in the Barents/Kara Seas, and sea ice increase (decrease) in Baffin Bay/Davis Strait. :     

Effects of autumn-winter Arctic sea ice on winter Siberian High

The intensity of the winter Siberian High has significantly negative correlations with Arctic sea ice concentration anomalies from the previous autumn to winter seasons in the Eastern Arctic Ocean and Siberian marginal seas. Our results indicate that autumn-winter Arctic sea ice concentration and concurrent sea surface temperature anomalies are responsible for the winter Siberian High and surface air temperature anomalies over the mid-high latitudes of Eurasia and East Asia. Numerical experiments also support this conclusion, and consistently show that the low sea ice concentration causes negative surface air temperature anomalies over the mid-high latitudes of Eurasia. A mechanism is proposed to explain the association between autumn-winter sea ice concentration and winter Siberian High. Our results also show that September sea ice concentration provides a potential precursor for winter Siberian High that cannot be predicted using only tropical sea surface temperatures. In the last two decades (1990–2009), a strengthening trend of winter Siberian High along with a decline trend in surface air temperature in the mid-high latitudes of the Asian Continent have favored the recent frequent cold winters over East Asia. The reason for these short-term trends in winter Siberian High and surface air temperature are discussed.     

The East Asian winter monsoon: re-amplification in the mid-2000s

Based on several reanalysis and observational datasets,this study demonstrates that the East Asian winter monsoon(EAWM)recovered from its weak epoch and reamplified in the mid-2000s.Accordingly,East Asia has experienced more cold winters and significant negative surface air temperature anomalies during the recent strong EAWM epoch spanning the period 2004–2012.The associated cooling was mainly located over inland northern East Asia with a west–east orientation.The cooling generally coincided with negative winter temperature trends in eastern Eurasia in the last two decades,possibly contributing to the observed regional cooling trend when the global mean temperature is still trending up.Enhanced wintertime blocking activity around the Ural mountain region and diminished Arctic sea ice concentration in the previous September are suggested to be the responsible internal atmospheric process and external driver for the recent re-amplification of the EAWM,respectively.     

Relationship between Hadley circulation and sea ice extent in the Bering Sea

The linkage between Hadley circulation （HC） and sea ice extent in the Bering Sea during March-April is investigated through an analysis of observed data in this research. It is found that HC is negatively correlated to the sea ice extent in the Bering Sea, namely, strong （weak） HC is corresponding to less （more） sea ice in the Bering Sea. The present study also addresses the large-scale atmospheric general circulation changes underlying the relationship between HC and sea ice in the Bering Sea. It follows that a positive phase of HC corresponds to westward located Aleutian low, anomalous southerlies over the eastern North Pacific and higher temperature in the Bering Sea, providing unfavorable atmospheric and thermal conditions for the sea ice forming, and thus sea ice extent in the Bering Sea is decreased, and vice versa. In addition, it is further identified that East Asian-North Pacific-North America teleconnection may play an important role in linking HC and changes of atmospheric circulations as well as sea ice in the Bering Sea.     

Reduction of the East Asian winter monsoon interannual variability after the mid-1980s and possible cause

The East Asian winter monsoon (EAWM) consists of subsystems such as the Siberian high, Aleutian low, East Asian trough, low-level northerly wind and high-level East Asian jet stream. It is revealed that the interannual variation of the EAWM-related atmospheric circulation has exhibited an obvious weakening since the mid-1980s. During 1956-1980, significant negative correlations between the EAWM and sea surface temperature are observed in the oceans along the east coast of East Asia, accompanied by significant positive correlations in the western Warm Pool. However, the significant interannual relationship in the previous period is found to have been disrupted during 1986-2010. Further analysis reveals that the Arctic Oscillation after the mid-1980s tends to suppress the interannual variability of the EAWM. In addition, it was found that the large-scale warming after the mid-1980s is favorable to reduce the land-sea thermal contrast variability on both the interdecadal and interannual time scales.     

The leading correlation of the winter Aleutian Low with surface air temperature during the subsequent summer over the Arctic and its possible mechanism

The variations of surface air temperature(SAT)over the Arctic are closely related to global climate change.Based on reanalysis datasets and a newly defined Aleutian Low intensity index,we found a good correlation between intensity of winter Aleutian Low and the SAT over the Arctic during the subsequent summer.Explanations were given using correlation analysis,composite analysis,and singular value decomposition methods.When intensity of winter Aleutian Low was weaker,sea surface temperature appeared higher in the North Pacific in the subsequent spring and summer,resulting in mean meridional circulation anomalies and 500 hPa geopotential height anomalies in spring and summer.Anomalous upward motion in mid-latitudes and downward motion in high latitudes(Ferrel cell weakening)transported the warmer air to the north from lower layer to the upper layer followed by increases in the SAT over the Arctic.Anomalous downward motion over about 75°N also caused consequent adiabatic warming and contributed to inhibit the heat transportation from surface to upper layer.Negative 500 hPa geopotential height anomalies existed in mid-latitudes and positive anomalies existed in high latitudes.The pattern(low-in-south and high-in-north)benefited from increasing the inflow volume flux of the Bering Strait,which also made the SAT over the Arctic increase.The results of this study reveal the process that the summer SAT over the Arctic was modulated by interannual variability of intensity of winter Aleutian Low.     

Spring surface cooling trend along the East Asian coast after the late 1990s

This paper presents the surface cooling trend observed in spring along East Asia coast after the late 1990s, in contrast to the global warming trend. This surface cooling trend is comprehensible as it agrees well with the cooling of sea surface temperature (SST) in the northwestern Pacific and the weakening of 300 hPa East Asian jet (EAJ) during spring. Moreover, this cooling phenomenon has been shown to be related to the rapid decline of Arctic sea ice cover (SIC) in previous autumns. The Arctic SIC signals in previous autumns can continue in spring and act as enhanced moisture sources that support the increased snow cover in Siberia during spring. The increased Siberian snow cover possibly favors the southward invasion of cold air masses via strong radiative cooling and large-scale descending motion, which may contribute indirectly to the reduction of temperature in East Asia. In addition, three climate models that can reproduce well the East Asian spring surface cooling observed in the past predicted uncertainty in the spring temperature projection in the next decade.     

Interdecadal variations of the East Asian winter surface air temperature and possible causes

Using the NCEP/NCAR and JRA-25 monthly analysis data from 1979 to 2011, this paper analyzes the interdecadal variations of winter (Dec.–Feb.) mean surface air temperature (SAT) over East Asia by means of the empirical orthogonal function (EOF) analysis method. Two dominant modes were extracted, with the leading mode basically depicting a sign consistent SAT variation and the second mode describing a meridional dipole structure between the northern and southern parts of East Asia. These two modes can explain more than 60% of the variance. The leading mode is closely related to the intensity of Siberian high and the East Asian winter monsoon. The second mode exhibits a notable interdecadal shift in the late 1990s, with a turning point around 1996/1997. Winter SAT in the northern (southern) part of East Asia tends to be cooler (warmer) since the late 1990. Winter sea level pressure (SLP) differences between 1997–2011 and 1979–1996 show negative (positive) anomalies over southern (northern) Eurasia. At 500-hPa, an anomalous blocking high occurs over northern Eurasia, while a cyclone anomaly appears over northern East Asia. In addition, the upper-level East Asian jet stream tends to shift northward and become stronger after the late 1990. Indeed, the interdecadal shift of winter SAT over East Asia is dynamical consistent with changes of the large-scale atmospheric circulation in the late 1990s. The result indicates that previous autumn sea surface temperature (SST) in the North Atlantic Ocean, the Northern Indian Ocean and the western North Pacific Ocean, as well as sea ice concentration (SIC) in the northern Eurasia marginal seas and the Beaufort Sea also experienced obvious changes in the late 1990s. In particular, the interdecadal shifts of both SST in the North Atlantic Ocean and SIC in the Arctic Ocean and its marginal seas are well coherent with that of the winter SAT over East Asia. The results indicate that the interdecadal shift of East Asian winter SAT may be related to changes in the North Atlantic SST and the Arctic SIC in the late 1990s.     

采用地球物理学指示对加拿大哈得逊海湾进行长期预测

对加拿大哈得逊海湾存在的地球物理学指示或“记忆”的若干系统进行了检测,用以探讨该地区不同时间长度的预测。文章对三个案例进行了研究．首先对哈得逊海湾海平面的水文学惯量的二个不同状况作了阐述;其次,成功的证实了海面浮冰与海水耦合的热力学惯量可用以预测哈得逊海峡海冰的形成与消失;最后,对低温惯量是导致哈得逊海湾西南部的永久冻结带的可能性进行了讨论．