云南5月雨量与热带海温异常及亚洲季风变化的关系

利用相关分析和合成分析方法 ,研究了云南 5月雨量与热带海温、热带对流活动及亚洲季风等大尺度气候环流背景变化的关系。指出云南 5月雨量与北印度洋季风气流区赤道东太平洋地区的对流活动有明显的相关 ,揭示了云南 5月多雨年和少雨年赤道东太平洋和印度洋地区的海温距平、2 0 0hPa纬向风和 850hPa矢量风场的不同分布特征。这种前后期海温、对流活动和高低层风场的变化具有很好的持续性 ,对预测云南 5月雨量的变化有一定的指示指义。还计算了南亚地区 4～ 6月的季风指数 ,分析了云南 5月雨量与初夏南亚季风指数变化的关系。结果表明 ,南亚季风指数高 ,云南 5月雨量偏多 ;南亚季风指数低 ,云南 5月雨量偏少。同时 ,研究还表明南亚季风指数在季风爆发前期和季风爆发时段的变化有很好的一致性。

我国秋季降水的年际变化及与热带太平洋海温异常分布的关系

利用我国160个站点58年(1951～2008年)的降水资料、NCEP/NCAR再分析环流资料和Hadley海表温度资料,对我国秋季降水年际变化的特征和可能成因进行了分析。结果显示,秋季降水前两模态分别反映长江流域及以南地区和长江以北的江淮、黄淮、华北、四川盆地北部至河套等地降水的变化,两降水模态的变化都以年际尺度为主,年代际变化特征不明显。就环流形势而言,第一模态的年际变化主要与西太平洋副热带高压的强度及相应的对流层低层菲律宾群岛附近的异常气旋/反气旋联系紧密,第二模态的年际变化则可能受到副热带高压的南北位置和相应的日本岛附近的异常气旋/反气旋的影响。同时,两模态及相应的异常环流还分别与热带东印度洋和热带西太平洋附近的异常垂直运动关系密切,热带地区的异常垂直运动可能通过经圈方向的异常环流影响到东亚地区。此外,两降水模态不仅与热带地区的异常环流关系密切,而且与热带海温异常也存在紧密的联系。与两模态相关联的热带太平洋海温异常显示出不同的分布特征,当热带东太平洋偏暖/冷,西太平洋偏冷/暖时,长江以南地区降水偏多/少。而当热带东太平洋和中太平洋一致偏暖/冷时,长江以北地区降水易偏少/多。两降水模态与热带海温及热带地区异常环流之间的密切关系显示热带太平洋海温异常的不同分布可能通过激发不同的热带地区异常垂直环流形势而对降水产生影响。

热带太平洋和印度洋海温异常对东亚冬季风影响的一个物理机制

本文利用NCEP/NCAR提供的大气环流资料和海表温度异常资料,在分析热带太平洋和印度洋海温异常与冬季大气环流之间关系的基础上提出了一个综合反映热带太平洋和印度洋海温异常的综合指数。分析表明,冬季太平洋和印度洋海温异常指数的值越大(小),东亚冬季风指数的值越大(小),东亚地区将出现异常的南(北)风的响应,东亚冬季风将越弱(强)。应用加热强迫影响热带环流的简单模式研究了热带太平洋印度洋异常海温对东亚冬季风影响的物理机制。结果表明,当冬季热带太平洋和印度洋海温异常指数处于正(负)位相时,西太平洋区域强迫出异常南(北)风。这是使得东亚冬季风偏弱(强)的重要原因之一。冬季热带太平洋和印度洋海温异常对东亚冬季风影响最为显著的关键区是赤道西太平洋。

南半球对流层大气对热带太平洋—印度洋海温异常综合模的响应及其机制解释

利用NOAA SST及NCEP/NCAR再分析资料,研究了热带太平洋—印度洋海温异常综合模和南半球对流层大气之间的遥相关模态并对其进行了机制解释。首先通过相关和合成分析,给出了遥相关的空间模态,结果表明：北半球秋、冬季,在南半球对流层大气存在和热带太平洋—印度洋海温异常综合模密切联系的遥相关作用中心,该中心的分布构成一列明显的从赤道中太平洋出发,最终到达非洲中南部及赤道印度洋的Rossby波列,将赤道太平洋、印度洋与南半球中高纬度大气连接起来,起到了类似＂大气桥＂的作用。而单纯IOD和单纯EN-SO均难以在南半球对流层激发出遥相关波列,进一步证实了两者共同作用的影响。其次,利用行星波能量传播理论对两者之间的遥相关进行了机制分析,发现纬向波数为1~3的大气行星波的能量传播是热带太平洋—印度洋海温异常综合模与南半球对流层大气之间遥相关的一种可能的联系方式。

热带印-太海温与海河流域夏季降水的联合模态及降水预测应用

利用1961—2020年中国站点观测降水资料和英国Hadley中心海表面温度资料,针对海河流域夏季降水预测困难的问题,通过多变量经验正交分解(MVEOF)方法的正、反向应用,分析了热带印度洋-太平洋前期海温变化与海河流域夏季降水异常年际变化的联合模态特征,据此建立了海河流域夏季降水的客观统计预测模型并检验预测效果.结果表明:(1)前期ENSO事件和热带印度洋(TIO)海温季节演变与海河流域夏季降水异常分布型关系密切.若前冬El Niño事件达到鼎盛,春季开始衰减,并引起TIO海盆尺度滞后增暖,则当年夏季海河流域降水一致性偏多,偏多中心在流域北部;若前秋El Niño向La Niña事件转变,随后TIO暖海温转冷,则夏季海河流域降水易出现西部偏多、东部偏少型分布;此外,如果前期出现太平洋经向模态(冷舌模态)的海温异常分布时,夏季流域降水异常为西北多、东南少(南多北少).(2)根据联合模态统计关系建立的预测模型,对2013—2020年海河流域夏季降水有较好的预测能力.与实况相比,模型对全域降水异常预测的时间相关系数为0.86、趋势预测准确率为87.50%,对站点的趋势预测准确率为51.35%~70.27%,对旱涝程度预测的平均偏差仅为45.92%,但对降水异常空间分布的预测技巧整体较低.本文阐明了前期热带印-太海温与海河流域夏季降水异常的统计关系,并建立了海河流域夏季降水的客观统计预测模型,为我国华北地区短期气候预测提供了一种新的有效参考.

2008年1月乌拉尔阻塞高压异常活动的分析研究

不少研究已经表明,乌拉尔阻塞高压的持续活动对2008年1月中国南方雨雪冰冻灾害的发生有重要作用。本文针对2008年1月乌拉尔阻塞高压的异常,利用NCEP再分析逐日环流资料、哈德莱中心的海温资料等,从对流层北极涛动(AO)、平流层极涡(PV)以及海温异常等几方面,对2008年1月乌拉尔阻塞高压异常产生的原因进行了分析研究。结果显示,虽然从以往多年情况来看,前期AO及平流层极涡的异常很可能会导致其后乌拉尔阻塞高压发生异常,然而就2008年1月的情况而言,2007～2008年冬季对流层AO和平流层极涡的异常都不能成为异常乌拉尔阻塞高压产生和偏强的原因,因为它们的关系与多年存在的长期关系相反。进一步的分析研究则显示,2007年12月和2008年1月赤道太平洋的LaNin～a事件也对乌拉尔阻塞高压的活动没有明显影响;而北大西洋海温正异常,尤其是北大西洋副热带海温正异常的存在,是2008年1月乌拉尔阻塞高压持续的重要外强迫因素。

西太平洋副热带高压的准两年振荡及其与热带海温和大气环流异常的关系

东亚季风区在年际尺度上存在显著的准两年振荡（TBO）周期, 对我国气候异常有着重要影响. 本文基于一套能够客观描述西太平洋副热带高压系统的重建指数, 重点分析了东亚季风系统中的关键成员之一——西太平洋副热带高压（以下简称副高）的TBO特征及其与低纬地区海温与大气环流异常的关系. 研究表明： （1） TBO作为副高一个重要的年际分量, 在20世纪70年代末期表现出显著的转折特征, 近30年副高TBO的变率比前30年显著增大, 具有年代际尺度的变化. （2） 副高TBO与几个关键海区SSTa的时滞关系比副高原始序列更为显著, 相关持续时间更长; 其中西伸脊点对ENSO响应要早于副高强度, 分别在滞后3~5个月和5~6个月时相关系数达到最大. （3） 在一次完整的副高TBO循环过程中, 冬季赤道中东太平洋的类似El Ni？o型总是和弱东亚冬季风耦合出现, 对应副高TBO处于显著增强期; 而冬季的类似La Ni？a型则总是和强东亚冬季风耦合出现, 副高TBO则处于显著减弱期. （4） 在副高TBO循环中, 热带海洋和大气环流呈现不对称的异常分布, 副高TBO振荡在中东太平洋地区类似El Ni？o型发展期较类似La Ni？a型发展期更为显著, 因此当热带海洋处于类似El Ni？o型发展时, 在短期气候预测中需要更加关注TBO年际分量的信号.

两广地区前、后汛期降水异常反位相现象及可能机理

利用1961-2018年中国地面气象台站2400站中广东省和广西壮族自治区(两广地区)134站逐日降水资料、英国Hadley中心逐月海表温度资料、NCEP/NCAR逐月再分析资料,筛选了两广地区前汛期降水正(负)异常、后汛期降水负(正)异常的年份,即前、后汛期降水异常反位相年份。结果表明,近60 a来,两广地区前、后汛期降水反位相现象与热带西太平洋海温异常存在密切联系。前汛期期间,当热带西太平洋海温为负异常时,大气对该冷源的Rossby波响应引起西北太平洋反气旋环流异常,且水汽由热带西太平洋向两广地区输送并辐合,同时两广地区为水汽的湿平流区域、风场异常辐合区域,其上空受异常上升运动控制,这样的环流配置有利于两广前汛期期间降水正异常。热带西太平洋海温负异常可持续至后汛期期间,大气的Rossby波响应所致的西太平洋反气旋较前汛期偏西北,两广地区为水汽异常辐散区域,同时水汽干平流且风场异常辐散,受异常下沉运动控制,不利于两广地区降水的产生。反之亦然。

热带太平洋-印度洋海温异常综合模及其影响

已有研究表明,由于大气瓦克环流和印度尼西亚灌穿流的影响,太平洋和印度洋的海温异常既有紧密关系、又有各自的一些特点,单独考虑太平洋的ENSO模并不能完全说明海温异常对气候的影响.本文从统一综合考虑太平洋和印度洋海温异常(SSTA)的形势及特征出发,提出了太平洋-印度洋海温异常综合模概念;并进一步比较研究了各个异常模态的不同特征,以及它们对中国气候和印度夏季降水的不同影响.为进一步确认资料分析结果,还用大气环流模式进行了数值模拟试验.其结果清楚地表明,必须考虑和研究太平洋-印度洋海温异常综合模及其影响,从而为短期气候预测提供更好科学依据.

热带大西洋对东亚气候的影响

运用Hadley中心资料,对1980—2015年间热带大西洋平均海温进行EOF分析。通过对其第一模态空间分布和时间系数图的分析,运用NCEP/NCAR再分析资料做出对应正相关年与负相关年的东亚地区500 hPa位势高度场距平与800 hPa年平均环流场图。通过2个高度正/负相关年环流场差值分析,研究热带大西洋地区海温异常与东亚地区上空环流场之间的关系。结果表明,热带大西洋海温异常对东亚大气环流影响存在一定因素,热带大西洋海温异常可能对东亚地区部分气旋移动产生影响,具体表现为热带大西洋海温变化影响着东亚区域季风推进。

我国西南地区秋季降水年际变化的空间差异及其成因

使用1980~2010年全国站点降水资料、ERA-Interim再分析环流资料、哈德莱海表温度资料,运用聚类分析和旋转经验正交函数分解,对西南地区的秋季降水按照其年际变化规律进行分区,进而分析影响各区域降水变化的物理过程和机理。结果表明：西南地区被分为东、西两个区域。西南东、西区域秋季降水的年际变化、显著周期、旱涝异常年份、相关的环流系统都有明显差异。西南东部秋季降水主要与热带海温异常有关,受低纬度环流影响。当赤道东太平洋为暖海温异常,热带印度洋为西正东负的偶极子型海温异常时,分别激发出西北太平洋反气旋和孟加拉反气旋,共同向西南东部输送水汽,造成西南东部降水偏多。西南西部降水在秋季三个月份与不同的环流形势对应：9月降水由中南半岛反气旋输送的暖湿气流决定;10月降水受高原以东反气旋环流和孟加拉湾低槽共同影响;11月降水主要受中高纬环流异常的影响,与斯堪的纳维亚遥相关存在显著负相关。

中国西南秋季旱涝的诊断分析

摘要：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。

Enhanced correlation between ENSO and western North Pacific monsoon during boreal summer around the 1990s

The correlation between summertime Nino3.4 index and western North Pacific(WNP)summer monsoon index has strikingly enhanced since the early 1990 s,with nonsignificant correlation before the early1990 s but significant correlation afterward.This observed interdecadal change around the 1990 s may be associated with more frequent occurrences of central Pacific(CP)El Nino and the interdecadal changes in ENSO-associated SST anomalies.During the post-1990 s period(the pre-1990 s period),highly noticeable tropical Atlantic(Indian)Ocean SST anomalies tend to co-occur with the summertime Nino3.4 SST anomalies.The concurrent tropical Atlantic(Indian)Ocean SST anomalies could constructively reinforce(destructively mitigate)the WNP monsoon circulation anomalies induced by the summertime Nino3.4 SST,thus boosting(muting)the correlation between summertime Nino3.4 SST and WNP monsoon.In addition,the faster decaying pace of preceding-winter El Nino after the 1990 s,which may have been mainly induced by the influences from the spring tropical North Atlantic SST anomalies,could also have contributed to the enhanced correlation between the summertime Nino3.4 index and WNP monsoon.These results suggest that the enhanced influences from the tropical Atlantic SST may have triggered the intensified correlation between summertime ENSO and WNP monsoon since the early 1990 s.

Interannual Variability of the Hadley Circulation Associated with Tropical Pacific SST Anomaly

The seasonal and interannual variability of zonal mean Hadley circulation are analyzed, and the important effects of sea surface temperature(SST), especially the tropical Pacific SST, on the meridional circulation are discussed. Following results are obtained: 1) the Hadley circulation presents a single clockwise(anticlockwise) cross-equator circulation in the Northern(Southern) Hemisphere winter,while it is a double-ring-shaped circulation quasi-symmetric about the equator in spring and autumn. The annual mean state just indicates the residual of the Hadley cell in winter and summer. 2) The first mode of interannual anomalies shows a single cell crossing the equator like the climatology in winter and summer but with narrower width. The second mode shows a double ring-shaped cell quasi-symmetric about the equator which is similar to the Hadley cell in spring or autumn. 3) Vertical motion of the Hadley circulation is driven by sea surface temperature(SST) through latent and sensible heat in the tropics, and the interannual anomalies are mainly driven by the SST anomaly(SSTa) in the tropical Pacific. 4) The meridional gradient of SSTa is well consistent with the lower meridional wind of Hadley circulation in the interannual part. For the spatial distribution, the meridional gradient of SSTa in the Pacific plays a major role for the first two modes while the effects of the Indian Ocean and the Atlantic Ocean can be ignored.

Traditional El Nio and El Ni o Modoki Revisited:Is El Nio Modoki Linearly Independent of Traditional El Nio?

The present study revisited the first two leading modes of tropical Pacific sea surface temperature anomalies （SSTA） during the period of 1979-2008. It is suggested that the so-called El Nino Modoki, which is captured by the second mode, exists objectively and exhibits obvious differences from traditional El Nifio, which is captured by the first mode, in terms of its spatial characteristics. Furthermore, the authors found that El Nino Modoki is linearly independent of traditional El Nino; hence, it cannot be described as part of the traditional El Nino evolution, and vice versa.

Relationship Between North Pacific SST Anomalies and the Atmospheric Circulation Anomalies in January 2008

Based on the NCEP (National Centers for Environmental Prediction) data,the relationship between the Sea Surface Temperature Anomalies (SSTAs) in the North Pacific and the atmospheric circulation anomalies in January 2008 is analyzed in this study.The SSTA mode most correlated with the Geopotential Height anomalies (GHAs) in January 2008 in the North Pacific exhibited a basin-wide horseshoe pattern with a warm center in November 2007.This persistent SSTA pattern would induce positive GHAs in the Aleutian Low area and East Asia and the northward extension of the West Pacific Subtropical High in January 2008 by maximum diabatic heating in the atmosphere over the Kuroshio Oyashio Extension (KOE) area,leading to the occurence of the circumpolar trough-ridge wave train anomaly in January 2008.

Variations of SST and Thermocline Depth in the Tropical Indian Ocean During Indian Ocean Dipole Events

Interannual variations in the surface and subsurface tropical Indian Ocean were studied using HadlSST and SODA datasets. Wind and heat flux datasets were used to discuss the mechanisms for these variations. Our results indicate that the surface and subsurface variations of the tropical Indian Ocean during Indian Ocean Dipole （IOD） events are significantly different. A prominent characteristic of the eastern pole is the SSTA rebound after a cooling process, which does not take place at the subsurface layer. In the western pole, the surface anomalies last longer than the subsurface anomalies. The subsurface anomalies are strongly correlated with ENSO, while the relationship between the surface anomalies and ENSO is much weaker. And the subsurface anomalies of the two poles are negatively correlated while they are positively correlated at the surface layer. The wind and surface heat flux analysis suggests that the thermocline depth variations are mainly determined by wind stress fields, while the heat flux effect is important on SST.

ENSO cycle and climate anomaly in China

The inter-annual variability of the tropical Pacific Subsurface Ocean Temperature Anomaly （SOTA） and the associated anomalous atmospheric circulation over the Asian North Pacific during the E1 Nifio-Southern Oscillation （ENSO） were investigated using National Centers for Environmental Prediction/ National Center for Atmospheric Research （NCEP/NCAR） atmospheric reanalysis data and simple ocean data simulation （SODA）. The relationship between the ENSO and the climate of China was revealed. The main results indicated the following： 1） there are two ENSO modes acting on the subsurface tropical Pacific. The first mode is related to the mature phase of ENSO, which mainly appears during winter. The second mode is associated with a transition stage of the ENSO developing or decaying, which mainly occurs during summer; 2） during the mature phase of E1Nifio, the meridionality of the atmosphere in the mid-high latitude increases, the Aleutian low and high pressure ridge over Lake Baikal strengthens, northerly winds prevail in northern China, and precipitation in northern China decreases significantly. The ridge of the Ural High strengthens during the decaying phase of E1 Nifio, as atmospheric circulation is sustained during winter, and the northerly wind anomaly appears in northern China during summer. Due to the ascending branch of the Walker circulation over the western Pacific, the western Pacific Subtropical High becomes weaker, and south-southeasterly winds prevail over southern China. As a result, less rainfall occurs over northern China and more rainfall over the Changjiang River basin and the southwestern and eastern region of Inner Mongolia. The flood disaster that occurred south of Changjiang River can be attributed to this. The La Nifm event causes an opposite, but weaker effect; 3） the ENSO cycle can influence climate anomalies within China via zonal and meridional heat transport. This is known as the ＂atmospheric-bridge＂, where the energy anomaly within the tropical Pacific transfers to the mid-high latitude in the northern Pacific through Hadley cells and Rossby waves, and to the western Pacific-eastern Indian Ocean through Walker circulation. This research also discusses the special air-sea boundary processes during the ENSO events in the tropical Pacific, and indicates that the influence of the subsurface water of the tropical Pacific on the atmospheric circulation may be realized through the sea surface temperature anomalies of the mixed water, which contact the atmosphere and transfer the anomalous heat and moisture to the atmosphere directly. Moreover, the reason for the heavy flood within the Changjiang River during the summer of 1998 is reviewed in this paper.

INTERANNUAL VARIATIONS OF ATMOSPHERIC HEAT SOURCES AND MOISTURE SINKS OVER THE EQUATORIAL PACIFIC AND THEIR RELATIONS TO THE SST ANOMALIES

The interannual variations of atmospheric heat sources and moisture sinks over the Equatorial Pacific and their relations with the SST anomalies are studied using ECMWF reanalysis data from 1979 to 1993. It is found by singular value decomposition (SVD) analysis that the region in the tropical Pacific with high positive correlation between the vertically integrated heat source <Q1> anomaly and the SST anomaly, and between the vertically integrated moisture sink <Q2> anomaly and the SST anomaly, is mainly located in a long and narrow belt to the east of 170 °E between 5 °S and 5 °N. The analysis of the vertical structure of atmospheric heat sources and moisture sinks shows that the interannual variations of Q1, Q2 and SST in the equatorial central and eastern Pacific are strongly and positively correlated in the whole troposphere except the bottom (962.5 hPa) and the top (85 hPa) layers. However, in the western Pacific, the interannual variations of Q1 below 850 hPa is negatively related to the SST. The correlation coefficient at the level 962.5 hPa reaches even –0.59. In other layers the positive correlation between the interannual variations of Q1, Q2 and the SST are weak in the western Pacific.

Sea surface temperature anomaly in the tropical North Atlantic during El Nino decaying years

Based on reanalysis data from 1979 to 2016,this study focuses on the sea surface temperature(SST)anomaly of the tropical North Atlantic(TNA)in El Nino decaying years.The TNA SST exhibits a clear warm trend during this period.The composite result for 10 El Nino events shows that the TNA SST anomaly reaches its maximum in spring after the peak of an El Nino event and persists until summer.In general,the anomaly is associated with three factors-namely,El Nino,the North Atlantic Oscillation(NAO),and a long-term trend,leading to an increase in local SST up to 0.4℃,0.3℃,and 0.35℃,respectively.A comparison between 1983 and 2005 indicates that the TNA SST in spring is affected by El Niño,as well as the local SST in the preceding winter,which may involve a long-term trend signal.In addition,the lead-lag correlation shows that the NAO leads the TNA SST by 2-3 months.By comparing two years with an opposite phase of the NAO in winter(i.e.,1992 and 2010),the authors further demonstrate that the NAO is another important factor in regulating the TNA SST anomaly.A negative phase of the NAO in winter will reinforce the El Nino forcing substantially,and vise versa.In other words,the TNA SST anomaly in the decaying years is more evident if the NAO is negative with El Nino.Therefore,the combined effects of El Nino and the NAO must be considered in order to fully understand the TNA SST variability along with a long-term trend.