The Singular Value Decomposition Analysis Between

利用奇异值分解法(SVD)分析了云南21个站各月降水距平与北太平洋海温的相关关系,得到了奇异向量,对贡献最大的前2个奇异向量进行分析,结果表明∶①平均意义上,秋冬季海温与云南各月降水存在显著的相关关系;②秋冬季热带东太平洋海温对翌年春末盛夏云南中部地区的降水有显著的影响;③秋冬季的热带中东太平洋海温与前一年春末和盛夏降水也存在明显的相关关系.     

云南地区降水与太平洋海温的奇异值分解分析

利用奇异值分解法（ＳＶＤ）分析了云南２１个站各月降水距平与北太平洋海温的相关关系,得到了奇异向量,对贡献原前２个奇异向量进行分析,结果表明：①平均意义上,秋 季海温与云南各月降水存在显著的相关关系;②秋冬季热带东太平洋海温对型年春末盛夏云南中部地区的降水有显著的影响。③秋冬季的热带中东太平洋海温与前一年春末和盛夏降水也存在明显的相关关系。     

云南降水场与太平洋海温场典型相关分析

 利用典型相关理论分析云南省5月份降水场与头年5月至当年4月各月太平洋热带海温距平场之间的关系,得出一些有意义的结果.并通过1994～1995年的预报,效果较理想.     

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.     

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。     

RCP8.5情景下长江中下游降水变化预估不确定性

利用第五次耦合模式比较计划(CMIP5)的历史模拟以及典型浓度路径(RCP8.5)高排放情景下的实验资料,对全球变暖下长江中下游夏季的降水变化进行了预估.结果表明,多模式平均预估的全球变暖下长江中下游降水变化增加幅度较小.一方面全球变暖导致水汽含量增加,有利于长江中下游降水增加;另一方面,全球变暖下夏季风环流减弱,不利于长江中下游降水增加.两者共同作用下,多模式平均预估的长江中下游未来夏季降水变化不明显.这一预估结果存在很大的模式间不确定性.分析表明,模式对降水变化预估的不确定性主要来源于大尺度夏季风环流变化预估的不确定性,而气候变暖所致的水汽增加对降水变化不确定性的影响较小.对这种不确定性来源的进一步研究表明,长江中下游降水及东亚夏季风环流变化均与北大西洋和西北太平洋海温增暖幅度相关,北大西洋海温影响更显著.这说明,在全球强增暖背景下北大西洋和西北太平洋海温增暖对长江中下游降水变化预估有很大的影响,如果能降低两个区域海温变化预估的不确定性,长江中下游降水预估结果将更为可靠.     

热带海温对纵向岭谷区5月降水年际变化的影响研究

 利用主成分分析和典型相关分析方法,研究了纵向岭谷区76个站点5月份降水场与其前期(12~4月)和同期(5月份)热带海温距平场之间的相关关系.其中,资料选用了1961~2001年共41 a的数据资料.研究结果表明,纵向岭谷区5月降水与热带海温距平场以同期相关为最好,而前期热带海温距平场除12月、3月和4月外,其它月份即1月、2月均有很好的相关.通过对热带海温距平场及降水场典型特征向量的分布作分析,太平洋暖池区热带海温与纵向岭谷区5月降水有正相关关系,赤道东太平洋海温与纵向岭谷区5月降水有负相关关系.当太平洋Walker环流增强时,纵向岭谷区5月降水增多;当Walker环流减弱时,纵向岭谷区5月降水减少.     

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。     

基于CAM3T42的云南5月降水的可预报性试验研究

取逐月地表温度作外强迫,用NCAR CAM3T42模式积分50a,获得1951～2000年的模式大气环流资料,截取40a的5月500hPa高度场与云南124个测站5月降水资料建立的基于CAM3T42公共预报因子集具有很好的一致性,可以用来讨论云南5月降水的可预报性.CAM3T42的5月500hPa高度场影响云南5月雨量的关键区主要分布在地中海、印度次大陆、西太平洋暖池、东北太平洋、北美等区域以及南印度洋、南太平洋和南大西洋等区域.应用公共预报因子集建立的云南124个测站5月雨量预报试验表明有113个复相关系数通过0.05的显著性检验,占总测站数的91%左右.利用10a样本作为独立预报检验表明复相关系数的量值与非独立样本检验的相比略有减小.试验结果和独立样本检验结果表明:5月CAMT42的500hPa高度场的变化与云南124测站5月降水间具有良好且稳定的关系,CAMT42对云南5月降水具有一定的预报能力.     

ENSO事件对云南短期气侯影响的研究

利用云南1951～1997年逐月降水和气温资料和全于1951～1997年月平均海温资料,统计了云南降水和气温对赤道东太平洋海表温度变化的响应,结果表明：云南降水和气温与赤道东太平洋海温的异常有着密切的关系。     

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.     

The responses of East Asian Summer monsoon to the North Atlantic Meridional Overturning Circulation in an enhanced freshwater input simulation

We investigated the response of the East Asian Summer Monsoon （EASM） to a weakened Atlantic Meridional Overturning Circulation （AMOC） and its mechanism in an enhanced freshwater input experiment （FW） by using a fully-coupled climate model. The response was a weakened EASM and the mechanisms can be explained as follows. The simulated weakened AMOC resulted in a drop in sea surface temperature （SST） in the North Atlantic （NA） and, correspondingly, an anomalous high sea level pressure （SLP） over the North American regions, which in turn increased the northeast surface winds across the equator in the eastern tropical Pacific （ETP）. The anomalous northeast winds then induced further upwelling in the ETP and stronger air/sea heat exchange, therefore leading to an anomalous cooling of the eastern tropical sea surface. As a result, the climatologic Hadley Circulation （HC） was weakened due to an anomalous stronger sinking of air in the ETP north of the equator, whereas the Walker Circulation （WC） in the western tropical Pacific （WTP） north of the equator was strengthened with an eastward-shifted upwelling branch. This feature was in agreement with the anomalous convergent winds in the WTP, and led to a weakened EASM and less East Asian summer precipitation （EASP）. Furthermore, comparison with previous freshwater experiments indicates that the strength of EASP could be influenced by the magnitude of the added freshwater.     

Significant relationship between spring AO and the summer rainfall along the Yangtze River

The influence of spring AO on the summer rainfall along the Yangtze River is investigated. The long-term rainfall observations are filtered to remove the low-frequency variations longer than 10 years. The inter-annual components show a high correlation to AO in the last hundred years. The strongest correlation appears for May AO and summer rainfall with a value of -0.39, significant above the 99% confidence level. Associated with one standard deviation stronger May AO index, the rainfall over the Yangtze River to the southern Japan decreases by about 3%-9%, while, at the same time increases by about 3%-6% in the northern China and far-eastern Russia. The coherent changes in rainfall are significantly related to the East Asian summer jet stream in the upper troposphere. When there is stronger AO in spring, the jet stream tends to move polarward in summer, and leads the rainfall-belt to move northward too. That gives rise to a drier condition in the Yangtze River valley, wetter anomalies in northern China. This signal would be helpful for the summer rainfall prediction in China.     

A dipole mode in the tropical Indian Ocean

For the tropical Pacific and Atlantic oceans, internal modes of variability that lead to climatic oscillations have been recognized, but in the Indian Ocean region a similar ocean-atmosphere interaction causing interannual climate variability has not yet been found. Here we report an analysis of observational data over the past 40 years, showing a dipole mode in the Indian Ocean: a pattern of internal variability with anomalously low sea surface temperatures off Sumatra and high sea surface temperatures in the western Indian Ocean, with accompanying wind and precipitation anomalies. The spatio-temporal links between sea surface temperatures and winds reveal a strong coupling through the precipitation field and ocean dynamics. This air-sea interaction process is unique and inherent in the Indian Ocean, and is shown to be independent of the El Ni?o/Southern Oscillation. The discovery of this dipole mode that accounts for about 12% of the sea surface temperature variability in the Indian Ocean--and, in its active years, also causes severe rainfall in eastern Africa and droughts in Indonesia--brightens the prospects for a long-term forecast of rainfall anomalies in the affected countries.     

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.     

Advancing decadal-scale climate prediction in the North Atlantic sector

The climate of the North Atlantic region exhibits fluctuations on decadal timescales that have large societal consequences. Prominent examples include hurricane activity in the Atlantic, and surface-temperature and rainfall variations over North America, Europe and northern Africa. Although these multidecadal variations are potentially predictable if the current state of the ocean is known, the lack of subsurface ocean observations that constrain this state has been a limiting factor for realizing the full skill potential of such predictions. Here we apply a simple approach-that uses only sea surface temperature (SST) observations-to partly overcome this difficulty and perform retrospective decadal predictions with a climate model. Skill is improved significantly relative to predictions made with incomplete knowledge of the ocean state, particularly in the North Atlantic and tropical Pacific oceans. Thus these results point towards the possibility of routine decadal climate predictions. Using this method, and by considering both internal natural climate variations and projected future anthropogenic forcing, we make the following forecast: over the next decade, the current Atlantic meridional overturning circulation will weaken to its long-term mean; moreover, North Atlantic SST and European and North American surface temperatures will cool slightly, whereas tropical Pacific SST will remain almost unchanged. Our results suggest that global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.     

云南5月强降水天气与亚洲季风变化的关系

 利用相关分析和EOF方法,研究了云南5月大雨、暴雨日数与亚洲季风这一大尺度气候环流背景变化的关系.研究结果表明,云南5月强降水天气与南亚季风强度指数相关较好,其中同期5月,相关系数为0.493,前期4月,相关系数为0.447,均超过了99%的显著性水平;其次是前期1月,相关系数为0.312,通过了95%的显著性检验.而云南5月强降水天气仅与前期4月南海季风强度指数相关较好,相关系数为0.415,通过了98%的显著性检验,与其他月份相关不显著.同时11a滑动相关系数也清楚地反映了南亚季风对云南5月强降水天气的影响大于南海季风.另外,利用EOF方法,获得了云南5月大雨、暴雨日数3种主要的空间分布型:全省一致型(除昭通市)、西部和东部、南部相反型以及东部和西部、南部相反型.第1类型与亚洲季风强度指数关系较为密切,特别是与南亚季风;第2类型主要与南海季风相关较好,第3类型受亚洲季风强度的影响不大.     

Response of the East Asian climate system to water and heat changes of global frozen soil using NCAR CAM model

Under the condition of land-atmosphere heat and water conservation, a set of sensitive numerical experiments are set up to investigate the response of the East Asian climate system to global frozen soil change. This is done by introducing the supercooled soil water process into the Community Land Model (CLM3.0), which has been coupled to the National Center of Atmospheric Research Community Atmosphere Model (CAM3.1). Results show that:(1) The ratio between soil ice and soil water in CLM3.0 is clearly changed by the supercooled soil water process. Ground surface temperature and soil temperature are also affected. (2) The Eurasian (including East Asian) climate system is sensitive to changes of heat and water in frozen soil regions. In January, the Aleutian low sea level pressure circulation is strengthened, Ural blocking high at 500 hPa weakened, and East Asian trough weakened. In July, sea level pressure over the Aleutian Islands region is significantly reduced; there are negative anomalies of 500 hPa geopotential height over the East Asian mainland, and positive anomalies over the East Asian ocean. (3) In January, the southerly component of the 850 hPa wind field over East Asia increases, indicating a weakened winter monsoon. In July, cyclonic anomalies appear on the East Asian mainland while there are anticyclonic anomalies over the ocean, reflective of a strengthened east coast summer monsoon. (4) Summer rainfall in East Asia changed significantly, including substantial precipitation increase on the southern Qinghai-Tibet Plateau, central Yangtze River Basin, and northeast China. Summer rainfall significantly decreased in south China and Hainan Island, but slightly decreased in central and north China. Further analysis showed considerable upper air motion along ~30°N latitude, with substantial descent of air at its north and south sides. Warm and humid air from the Northeast Pacific converged with cold air from northern land areas, representing the main cause of the precipitation anomalies.