印度洋dipole事件的年际变化与ENSO事件的联系

通过对nino3指数和DMI序列的分析,发现两种物理现象都有4 a左右的主要周期,而且印度洋偶极子事件还存在有2 a左右的振荡周期,而厄尔尼诺事件在2 a时间尺度上周期性不明显;对nino3指数和DMI进行年际时间尺度滤波,结果表明,在年际时间尺度上,两者的相关性比未滤波时有了一定的提高;对年际滤波之后的偶极子事件和ELNINO事件的相关分析可以发现,ELNINO对于印度洋偶极子事件的影响要大于IOD对于太平洋ENSO事件,显示了两者物理现象的影响不对称。     

夏冬季热带太平洋、印度洋海表温度年际异常的年代际变化

用Nino3指数、印度洋单极指数、偶极子指数描述热带太平洋、印度洋海表温度(SST)的年际异常，季节分析表明：冬季Nino3区与热带印度洋海表温度距平(SSTA)相互关系表现为单极，且1976年以后两者的相互关系减弱，其可能原因：一是冬季是ENSO(厄尔尼诺)事件的盛期；二是冬季西太平洋暖水区东移，造成两洋的垂直纬向环流耦合减弱。夏季两者相互关系表现为偶极，1976年以后两者的相互关系加强，其可能原因，一是夏季是偶极子盛期，ENSO事件的发展期；二是夏季西太平洋暖水区虽然东移，但暖水区位置偏北，且东南印度洋的上升支强度增大，造成两洋的．纬向环流耦合更强烈。     

夏冬季热带太平洋、印度洋海表温度年际异常的年代际变化

用Nino 3指数、印度洋单极指数、偶极子指数描述热带太平洋、印度洋海表温度 (SST)的年际异常 ,季节分析表明 :冬季Nino3区与热带印度洋海表温度距平 (SSTA)相互关系表现为单极 ,且 1976年以后两者的相互关系减弱 ,其可能原因 :一是冬季是ENSO(厄尔尼诺 )事件的盛期 ;二是冬季西太平洋暖水区东移 ,造成两洋的垂直纬向环流耦合减弱。夏季两者相互关系表现为偶极 ,1976年以后两者的相互关系加强 ,其可能原因 ,一是夏季是偶极子盛期 ,ENSO事件的发展期 ;二是夏季西太平洋暖水区虽然东移 ,但暖水区位置偏北 ,且东南印度洋的上升支强度增大 ,造成两洋的纬向环流耦合更强烈     

中国黄土高原汛期降水异常特征

分析黄土高原汛期降水40a的变化，结果表明黄土高原汛期降水异常有3个敏感区，各敏感区异常降水存在明显的阶段，存在3—5a、8a左右的年际振荡和16—20左右的年代际振荡，3—5a的周期最明显；极端降水主要集中在20世纪60年代，90年代猛然减少。     

近50 a ENSO时频特征及其与南海台风的相关性

【目的】分析表征ENSO事件的特征值和南海台风活动的多时间尺度结构特征及其相关关系。【方法】采用日本气象厅东京台风中心(JMA)1967-2016年西北太平洋TC最佳路径数据集,统计分析了近50 a来南海台风活动月频数。同时又采用Morlet小波变换、交叉小波变换、小波相干等方法,分析了近50 a来ENSO事件时频变化特征及其与南海台风相关性。【结果与结论】ENSO循环具有2-6 a的主周期;7-10月南海台风活动最为频繁,其频数时间序列存在准2 a尺度周期;ENSO指数与南海台风活动频数的相关表现在多个时间尺度上。1970-1978年、1995-2000年,ONI指数和南海台风活动频数在2-6 a周期尺度上具有较好的相关关系,并且南海台风活动频数变化先于ONI指数半个周期。1980-1985年间,在1.5-3 a的周期尺度上SOI指数和南海台风活动频数具有较好的相关关系,且两序列同步变化。     

高原季风对500hPa中纬度西风带活动的影响

利用1948--2008年NCEP／NCAR逐月再分析资料和1958—2007年中国560站夏季降水资料,设计了一个区域西风指数,探讨了高原夏季风和500百帕中纬度西风带活动的时间一频率多层次年际、年代际时间尺度变化特征以及对我国夏季降水的影响。结果表明：高原夏季风对区域西风带活动具有显著的影响,近61年来,两者总体变化趋势相反,前者增强后者减弱。除了都具有1—2年、27—28年和线性趋势变化的共同周期外,还呈现出各自的周期变化,并且均发生过一次年代际气候跃变现象,前者发生在20世纪70年代中期,后者发生在80年代中期,高原夏季风由偏弱转为偏强,区域西风由偏强转入偏弱,在跃变前后两者各种周期的时间尺度和强度存在明显的不同。如果排除1—2年周期的不确定性,预计接下来高原夏季风将直接进入偏弱期,区域西风指数可能在3—4年后才转入偏强期,并且高原夏季风会比区域西风指数提前发生突变,对区域西风指数具有一定的指示意义。高原夏季风不仅自身对我国夏季降水产生重要的作用,同时,它通过影响中纬度西风带的活动,间接地影响着我国的夏季降水。     

海南琼海暴雨频次的诊断及预测研究

利用MHAT小波变换分析和灰色拓扑预测方法对海南琼海1953—2007年55年的暴雨频次的变化特征进行分析，结果表明，暴雨频次分别存在2a、6a、8a的准周期变化，8a准周期在20世纪70年代初期和80年代初期的信号最强，但1990年代后，暴雨频次较降水量出现了更多的小尺度周期波动扰动，表明极端降水事件有频繁出现的趋势。暴雨频次的季节变化主要体现在夏秋两季的暴雨多发季节，夏季主要存在2a、6a、12—13a、18a左右的准周期，秋季主要存在2—3a、8—9a、12a、17—18a左右的准周期，并且在各个季节表现出多时间尺度交替的复杂结构变化的非周期性特征，能在一定程度上解释暴雨频次较为异常的状况。琼海大暴雨和特大暴雨主要发生在秋季原因，可能与西行热带气旋和南下弱冷空气共同影响海南岛，同时配合偏东回流的环流背景有很大关系。文中基于小波分析和灰色预测方法的研究结果，提供了琼海地区暴雨预报和防灾减灾的一定科学依据。     

北半球环状模变化特征及其对中国冬季气温的影响

平流层异常对于对流层的影响研究,尤其是与中国天气气候的关系已成为近年来的研究热点。首先利用1951~2010年逐月NAM指数(NAMI)序列,采用小波方法分析了北半球环状模的时间变化特征。结果表明,近60年来,尤其是自1970年以来,北半球环状模NAM指数一直呈现持续增长趋势,并存在15a的年代际振荡周期,在1970s前8a的年际振荡明显。进一步挑出9个NAM指数强值年和8个NAM指数弱值年,结合中国160台站的气温资料和NCEP/NCAR再分析资料,探讨NAM指数变化对中国冬季气温的影响。结果发现,在NAM指数强值年,相对于NAM指数弱值年,中国北方、东部地区尤其在东北南部和华北地区气温偏高,西南的大部分地区气温偏低;NAM指数与中国东北冬季气温呈明显的正相关,同期相关性最好。     

基于Argo海洋观测资料分析2005~2015年全球比容海平面变化的时空特征

利用3家机构（JAMSTEC、SIO、IPRC）发布的Argo海洋温度和盐度数据分析2005~2015年全球SSL在不同时间和空间尺度上的变化特征。结果表明，全球平均SSL（即由海水密度变化引起的）上升速率为1.08±0.38 mm/a；年际信号对SSL变化速率的估算结果存在显著影响，近期（2011~2015年）Argo数据的估算结果（2.16±0.50 mm/a）显著大于早期（2005~2010年）的结果（0.66±0.64 mm/a）。当前Argo产品用于全球平均SSL变化趋势的分析结果较为一致，差异为3家机构所得结果平均值的10%左右；而小尺度上(20°宽纬度带)的计算结果差异很大，能达到平均值的80%。对全球SSL的空间特征的分析结果也显示，3家机构产品估算的海平面比容变化周年振幅和线性速率在更小的尺度(±5°)上存在不可忽视的差异。     

大空间GPS网共模误差剔除研究

利用叠加滤波、PCA、KLE 3种方法对欧洲区域平均基线长度为2 000 km的大空间GPS网12个IGS站9 a（2006-01~2014-12）的观测数据进行处理，分析对比3种方法剔除共模误差的效果。结果显示，3种方法剔除百分比分别为25.87%、41.48%、35.72%，滤波后坐标精度明显提高；对于较大的GPS观测网，相对于叠加滤波，PCA和KLE法效果更好，可以显示不同站点的空间特征。     

Indian Ocean Dipole response to global warming: A multi-member study with CCSM4

Based on a coupled ocean-atmosphere model, the response of the Indian Ocean Dipole (IOD) mode to global warming is investigated with a six member ensemble of simulations for the period 1850–2100. The model can simulate the IOD features realistically, including the east-west dipole pattern and the phase locking in boreal autumn. The ensemble analysis suppresses internal variability and isolates the radiative forced response. In response to increasing greenhouse gases, a weakening of the Walker circulation leads to the easterly wind anomalies in the equatorial Indian Ocean and the shoaling thermocline in the eastern equatorial Indian Ocean (EEIO), and sea surface temperature and precipitation changes show an IOD-like pattern in the equatorial Indian Ocean. Although the thermocline feedback intensifies with shoaling, the interannual variability of the IOD mode surprisingly weakens under global warming. The zonal wind feedback of IOD is found to weaken as well, due to decreased precipitation in the EEIO. Therefore, the atmospheric feedback decreases much more than the oceanic feedback increases, causing the decreased IOD variance in this model.     

Southern Meridional Atmospheric Circulation Associated with IOD

Using the monthly wind and sea surface temperature （SST） data, southern meridional atmospheric circulation cells associated with the Indian Ocean Dipole Mode （IOD） events in the Indian Ocean are for the first time described and examineS. The divergent wind and pressure vertical velocity are employed for the identification of atmospheric circulation cells. During the four different phases of the positive IOD events, the anomalous meridional Hadley circulation over the western Indian Ocean shows that the air rises in the tropics, flows poleward in the upper troposphere, sinks in the subtropics, and returns back to the tropics in the lower troposphere. The anomalous Hadley circulation over the eastern Indian Ocean is opposite to that over the western Indian Ocean. During positive IOD events, the meridional Hadley circulation over the eastern Indian Ocean is weakened while it is strengthened over the western Indian Ocean. Correlation analysis between the IOD index and the indices of the Hadley cells also proves that, the atmospheric circulation patterns are evident in every IOD event over the period of record.     

Climate variability and predictability associated with the Indo-Pacific Oceanic Channel Dynamics in the CCSM4 Coupled System Model

An experiment using the Community Climate System Model (CCSM4), a participant of the Coupled Model Intercomparison Project phase-5 (CMIP5), is analyzed to assess the skills of this model in simulating and predicting the climate variabilities associated with the oceanic channel dynamics across the Indo-Pacific Oceans. The results of these analyses suggest that the model is able to reproduce the observed lag correlation between the oceanic anomalies in the southeastern tropical Indian Ocean and those in the cold tongue in the eastern equatorial Pacific Ocean at a time lag of 1 year. This success may be largely attributed to the successful simulation of the interannual variations of the Indonesian Throughflow, which carries the anomalies of the Indian Ocean Dipole (IOD) into the western equatorial Pacific Ocean to produce subsurface temperature anomalies, which in turn propagate to the eastern equatorial Pacific to generate ENSO. This connection is termed the “oceanic channel dynamics” and is shown to be consistent with the observational analyses. However, the model simulates a weaker connection between the IOD and the interannual variability of the Indonesian Throughflow transport than found in the observations. In addition, the model overestimates the westerly wind anomalies in the western-central equatorial Pacific in the year following the IOD, which forces unrealistic upwelling Rossby waves in the western equatorial Pacific and downwelling Kelvin waves in the east. This assessment suggests that the CCSM4 coupled climate system has underestimated the oceanic channel dynamics and overestimated the atmospheric bridge processes.     

Southern high latitude climate anomalies associated with the Indian Ocean dipole mode

1 INTRODUCTION In southern high latitudes, recent observations have shown a standing mode of ACW (Antarctic Circumpolar Wave) with eastward propagation across the Southern Ocean of the Antarctic in co- varying SST (sea surface temperature) and SLP (sea le…     

Variations in the eastern Indian Ocean warm pool and its relation to the dipole in the tropical Indian Ocean

Based on the monthly average SST and 850 hPa monthly average wind data,the seasonal,interannual and long-term variations in the eastern Indian Ocean warm pool(EIWP) and its relationship to the Indian Ocean Dipole(IOD),and its response to the wind over the Indian Ocean are analyzed in this study.The results show that the distribution range,boundary and area of the EIWP exhibited obviously seasonal and interannual variations associated with the ENSO cycles.Further analysis suggests that the EIWP had obvious l...     

Relationships of interannual variability between the equatorial pacific and tropical Indian Ocean in 17 CMIP5 models

Seventeen coupled general circulation models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) are employed to assess the relationships of interannual variations of sea surface temperature (SST) between the tropical Pacific (TP) and tropical Indian Ocean (TIO). The eastern/central equatorial Pacific features the strongest SST interannual variability in the models except for the model CSIRO-Mk3-6-0, and the simulated maximum and minimum are produced by models GFDL-ESM2M and GISS-E2-H respectively. However, It remains a challenge for these models to simulate the correct climate mean SST with the warm pool-cold tongue structure in the equatorial Pacific. Almost all models reproduce El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole mode (IOD) and Indian Ocean Basin-wide mode (IOB) together with their seasonal phase lock features being simulated; but the relationship between the ENSO and IOD is different for different models. Consistent with the observation, an Indian Ocean basin-wide warming (cooling) takes place over the tropical Indian Ocean in the spring following an El Niño (La Niña) in almost all the models. In some models (e.g., GFDL-ESM2G and MIROC5), positive ENSO and IOB events are stronger than the negative events as shown in the observation. However, this asymmetry is reversed in some other models (e.g., HadGEM2-CC and HadGEM2-ES).     

Sediment Delivery across Multiple Spatio-temporal Scales in an Agriculture Watershed of the Chinese Loess Plateau

There is a consensus that sediment delivery ratio in the Chinese Loess Plateau is close to 1at the inter-annual timescale. However, little information is available about the sediment delivery at finer timescales. We evaluated the sediment delivery from plots to watersheds at the event or intra-annual, annual, and inter-annual timescales within the Wudinghe river basin, a 30,261 km2 basin in the Loess Plateau. We calculated the ratio of sediment output to sediment input and presented the temporal change of the channel morphology to determine whether sediment deposition occurs.Although a single flood event frequently has a sediment yield exceeding 10,000 t km-2, sediment deposition rarely occurs except during some small runoff events(sediment yield 5000 t km-2) or dry years(sediment yield 10,000 t km-2) when moving from slopes up to the main channels of the Wudinghe River. This observation suggests a sediment delivery ratio close to 1 even at the event or intra-annual and the annual timescales, but not necessarily at the interannual timescale. Such a high sediment delivery ratio can be related to hyper-concentrated flows, which have very strong sediment transport capacity even at low flow strength. Because hyper-concentrated flows are well-developed in the whole Loess Plateau, a sediment delivery ratio close to 1 below the interannual timescale possibly remains true for other rivers in the Loess Plateau.     

Research on the Interannual Variability of the Great Whirl and the Related Mechanisms

Based on AVISO(archiving, validation and interpretation of satellite data in oceanography) data from 1993 to 2010, Quik SCAT(Quick Scatterometer) data from 2000 to 2008, and Argo data from 2003 to 2008, the interannual variability of the Great Whirl(GW) and related mechanisms are studied. It shows that the origin and termination times of the GW, as well as its location and intensity, have significant interannual variability. The GW appeared earliest(latest) in 2004(2008) and vanished earliest(latest) in 2006(2001), with the shortest(longest) duration in 2008(2001). Its center was most southward(northward) in 2007(1995), while the minimum(maximum) amplitude and area occurred in 2003 and 2002(1997 and 2007), respectively. The GW was weaker and disappeared earlier with its location tending to be in the southwest in 2003, while in 2005 it was stronger, vanished later and tended to be in northeast. The abnormal years were often not the same among different characters of the GW, and were not all coincident with ENSO(El Ni?o-Southern Oscillation) or IOD(Indian Ocean Dipole) events, indicating the very complex nature of GW variations. Mechanism investigations shows that the interannual variability of intraseasonal wind stress curl in GW region results in that of the GW. The generation of the GW is coincident with the arrival of Rossby waves at the Somali coast in spring; the intensity of the GW is also influenced by Rossby waves. The termination of the GW corresponds well to the second one of the top two peaks in the baroclinic energy conversion rate in GW region, and the intensity and the position of the GW are also closely related to the top two baroclinic energy conversion rates.     

Variability of subduction rates of the subtropical North Pacific mode waters

The climatology subduction rate for the entire Pacific is known, but the mechanism of interannual to decadal variation remains unclear. In this study, we calculated the annual subduction rates of three types of North Pacific subtropical mode waters using a general circulation model (LICOM1.0) for the period of 1958-2001. The model experiments focused on interannual variations of ocean dynamical processes under daily wind forcings and seasonal heat fluxes. The mode water formation region was defined by a potential vorticity minimum at outcrop locations. The model results show that two subduction rate maxima (>100 m/a) were located in the Subtropical Mode Water (STMW) and the Central Mode Water (CMW) formation regions. These regions are consistent with a climatologically calculated value. The subduction rate in the Eastern Subtropical Mode Water (ESTMW) formation region was smaller at about 75 m/a. The subduction rate shows clear interannual and decadal variations associated with oceanic dynamic variabilities. The average subduction rate of the STMW was much smaller during the period of 1981-1990 compared with other periods, while that of the CMW had a negative anomaly before 1975 and a positive anomaly after 1978. The variability agreed with Ekman and geostrophic advections and mixed layer depths. The interannual variability of the subduction rate for the ESTMW was smallest during 1970-1990, as a result of a weak wind stress curl. This paper explores how interannual signals from the atmosphere are stored in different parts of the ocean, and thus may contribute to a better understanding of feedback mechanisms for the Pacific Decadal Oscillation (PDO) event.