北太平洋风场变化对东亚陆架海SST的影响

太平洋内部的气候变化与东亚陆架海海洋环境变化密切相关.本文利用OAflux资料、NCEP再分析资料,分析北太平洋内部风场的时空变化特征,将其距平场序列与东亚陆架海SSTA序列进行相关性分析,找出对东亚陆架海SST影响显著的风场关键区.结果表明:东亚陆架海SST距平序列与PDO指数同期相关系数接近于0,说明北太平洋内部异常信号只能通过斜压Rossby波调整影响东亚陆架海SST,不存在正压调整过程;北太平洋风场“关键区A、B”对东亚陆架海SST的变化影响最显著,且1958-2010年,2个风场“关键区”风速异常增强,分别被风应力旋度偶极子、异常负风应力旋度场控制,异常信号从中东太平洋传递到东亚陆架海,导致该海区SST明显升高,尤其是黑潮海域;“关键区A、B”风场异常信号分别超前东亚陆架海SST变化4a (7a)、4a时呈显著正相关,该时间基本与斜压Rossby波从大洋中东部传递到西部或副热带环流对风场变化通过斜压Rossby波进行调整所需的时间一致.     

台湾以东黑潮流量的年际变化特征

利用长时间序列的石垣和基隆两个验潮站的海平面高度记录(18年)计算了台湾以东的黑潮流量,并结合风应力资料(SODA),探讨了台湾以东黑潮流量的年际变化及其和风应力旋度的关系。台湾以东黑潮流量的峰值出现在1980—1981、1982—1983、1986、1988及1991年。低值出现在1984、1990、1993—1995年。小波分析结果显示,台湾以东黑潮流量具有2—5年的显著周期(峰值在2年和5年);台湾以东北太平洋区域风应力旋度具有2—7年的显著周期(峰值在3年和6年)。在1980—1991年间,黑潮大弯曲频繁发生,台湾以东黑潮流量偏大,与台湾以东太平洋区域风应力旋度间的关系较好;而在1991—1995年间,没有黑潮大弯曲发生,台湾以东黑潮流量偏低,与台湾以东太平洋区域风应力旋度间的关系较差。     

孟加拉湾局地动力过程的季节变化研究

利用观测资料和理论模型,研究了孟加拉湾海表面高度的季节循环.结果表明,局地风应力旋度驱动的斜压Rossby波是孟加拉湾海表高度季节循环的主要控制因子,而孟加拉湾海底地形分布也影响了海表面高度的季节循环.受风应力旋度驱动的斜压Rossby波在短时间内就可以穿越孟加拉湾海盆,使得海洋温跃层在短时间内完成了对Rossby波的响应,保证了上层海洋满足准静止的Sverdrup平衡.在夏季(冬季)西南(东北)季风驱动下,上层海洋分别在孟加拉湾北部和南部形成气旋(反气旋)式和反气旋(气旋)式环流.     

Rossby波模型对西北太平洋海表面高度年际变异的可预测性研究

根据海洋Rossby波的西传特性, 使用一阶斜压Rossby波模型对北太平洋海表面高度的年际变异进行了回报和预测研究。回报结果表明, Rossby 波模型能够较好地模拟北太平洋海表面高度的年际变异。尤其是黑潮延伸区的下游, 模拟结果与卫星观测的相关系数达到0.8以上。预测结果表明, Rossby 波模型在两个纬向分布的海域有显著的预报能力, 分别位于高纬度中部和副热带环流西部。前者可提前5—6年, 后者可提前2—4年。此外, 重点开展了Rossby波模型在西北太平洋的预报能力研究。结果表明, Rossby波模型对中国的边缘海有着很好的预测能力, 包括南海北部、台湾以东和东海黑潮海域, 分别在提前32、40和52个月时能取得最佳的预测效果。     

基于IPCC预测结果的北太平洋海表面温度变化分析

利用IPCC-AR4气候模式诊断与比较计划(PCMDI)20C3M试验和A1B情景试验模拟数据,研究了在温室气体排放情景下,北太平洋海表面温度的变化及其对太平洋风应力旋度变化的响应。结果表明,温室气体中等排放A1B情景与20C3M情景相比,北太平洋年平均海表面温度表现为一致增温的趋势,且最大的增温中心位于黑潮及其延伸体区。与20C3M试验相比,CO2增加情景下北太平洋中部东风加强,增加向北的Ekman输送,使得北太平洋内区增温。风应力旋度零线也向北略有移动,导致黑潮延伸体向北移动并得到加强,从而引起延伸体区较强增温。风应力旋度零线的纬度附近产生的Rossby波,向西传播到黑潮延伸体区,进一步加强黑潮延伸体区的温度异常。海洋对北太平洋风应力场变化的局地响应及延迟响应,使黑潮延伸体海域海表面增温远大于周围海区。     

黑潮延伸体区海平面异常和中尺度涡的时空特征分析

利用1993-2010年间的卫星高度计资料,用EOF方法及小波分析研究了黑潮延伸体区域的海平面异常和中尺度涡的时空变化特征.研究结果表明:海平面EOF第一模态是季节模态,与该海域风应力旋度第一模态类似,相关系数达0.65.EOF第二模态主要反映了黑潮南部次级环流的变化情况,显著性周期是8-10年.通过相关分析发现黑潮延伸体南部次级环流的年代际变化与PDO有关,同时它又与风应力旋度第二模态有关;该海域的海面高度受到北太平洋东部SSH信号西传的影响,信号的传播需要大约3-4年时间.EOF第三模态是黑潮弯曲模态.日本南部的气旋涡和反气旋涡可以表征黑潮弯曲的形成,而且弯曲强度和涡的持续时间、强度和位置有关.     

太平洋海平面变化特征及影响因素分析

采用经验模态分解法对太平洋沿岸验潮站的月平均海平面资料进行处理,结合T/P高度计资料、Church(2004)重构SSH资料、Ishii(2005)月均海温资料,研究太平洋海平面年际、年代际变化以及资料长度内海平面变化趋势。太平洋沿岸海平面总体呈上升趋势,平均上升速率为1.4 mm/a,趋势项分布有明显的区域性和纬度特征。ENSO对太平洋地区海平面年际变化有显著影响,海平面年际变化与Nino3指数在西(东)太平洋为负(正)相关,海平面年际变化与Nino3指数的相关性在热带太平洋最大,并随着纬度升高相关性减弱,且不同地区年际变化有滞后ENSO时间不等的最大相关。海平面年际变化与PDO指数在西(东)太平洋为负(正)相关,海平面与PDO的相关性分布有区域性和随时间演变特征。年代际变化对目前使用卫星高度计资料分析海平面长期趋势项的预测有直接影响,可能完全掩盖海平面长期变化趋势。     

基于观测数据的2003?2014年北冰洋海平面时空特征

本文对比了3个不同机构提供的北冰洋月均高度计数据,发现英国极地观测与建模中心和丹麦科技大学空间中心两套数据比较一致且空间覆盖率高,适用于北冰洋海平面变化研究,而前者在数据分辨率、平滑性和与验潮站的符合程度方面均更优。对高度计和验潮站数据的分析表明,北冰洋海平面的气候态特征表现为加拿大海盆的高值和欧亚海盆的低值之间形成鲜明对比;海平面的变化以季节变化和北极涛动引起的低频变化为主,加拿大海盆的季节和年际振幅均较大,俄罗斯沿岸海平面季节变化显著。2003?2014年,北冰洋平均海平面呈上升趋势,其中加拿大海盆海平面上升最快,而俄罗斯沿岸海平面有微弱下降趋势。加拿大海盆和俄罗斯沿岸由于海冰变化显著,不同高度计产品以及高度计与验潮站数据之间差别较大,使用时需慎重。     

福建近海海平面变化研究

利用福建沿海几个主要验潮站数据与法国空间局(CNES)AVISO多卫星融合资料分析了福建近海及其周边海域海平面的时、空变化特征及主要模态,并简要分析福建近海海平面变化趋势.得到如下结论:近54a(1960~2013年)福建沿海相对海平面上升约2 mm/a,福建沿海海平面变化存在显著的季节变化和2~3a及6~8a的年际变化特征,这与ENSO和长周期天文分潮的变化周期较为吻合;对比同期卫星高度计资料和潮位站资料(1993~2012年)发现,卫星高度计与潮位站分析结果基本一致;卫星高度计和潮位站分析结果表明,福建沿海区域海平面近20a平均线性变化趋势约为4 mm/a.     

2011年西北太平洋海平面异常及其与拉尼娜和负印度洋偶极子的联系

西北太平洋海平面异常模态在纯拉尼娜事件与拉尼娜和负印度洋偶极子（IOD）事件同时发生时表现出完全不同的形态。在纯拉尼娜事件期间，西北太平洋海平面呈现显著的正异常；而2010/2011拉尼娜事件期间西北太平洋海平面明显降低，呈显著的负异常，其与印度洋负IOD事件密切相关。研究结果表明，负IOD事件能在热带西太平洋驱动显著的西风异常，由此减弱了拉尼娜峰值期间西北太平洋海平面正异常。同时，在负IOD峰值期的9月，在日经线附近存在显著的风应力旋度正异常，激发负的海平面异常以Rossby波的形式向西传播，并在第二年6月抵达菲律宾以东海域，维持并加强该海域海平面负异常，进而对北赤道流分叉点位置及输运产生重要的影响。     

Interannual variations in the Hawaiian Lee Countercurrent

The Hawaiian Lee Countercurrent (HLCC) is an eastward surface current flowing against the broad westward flow of the North Pacific subtropical circulation. Analyses of satellite altimeter data over 16 years revealed that the HLCC is characterized by strong interannual variations. The strength and meridional location of the HLCC axis varied significantly year by year. The eastward velocity of the HLCC was higher when the location of the axis was stable. Mechanisms for the interannual variations were explored by analyses of the altimeter data and results from a simple baroclinic model. The interannual variations in the strength of the HLCC did not correlate with those of the wind stress curl (WSC) dipole formed on the leeward side of the Hawaii Islands, although the WSC dipole has been recognized as the generation mechanism of the HLCC. Meridional gradients of the sea surface height anomaly (SSHA) across the HLCC generated by baroclinic Rossby waves propagating westward from the east of the Hawaii Islands were suggested as a possible mechanism for the interannual variations in the HLCC. The spatial patterns in the observed SSHAs were reproduced by a linear baroclinic Rossby wave model forced by wind fields from a numerical weather prediction model. Further analysis of the wind data suggested that positive and negative anomalies of WSC associated with changes in the trade winds in the area east of the Hawaii Islands are a major forcing for generating SSHAs that lead to the HLCC variations with a time lag of about 1 year.     

Calculation of Interannual Variations of Sea Level in the Subtropical North Pacific

The interannual variations of sea level at Chichi-jima and five other islands in the subtropical North Pacific are calculated for 1961–95 with a model of Rossby waves excited by wind. The Rossby-wave forcing is significant east of 140°E. Strong forcing of upwelling (downwelling) Rossby wave occurs during El Niño (La Niña) and warm (cold) water anomaly in the eastern equatorial Pacific. The first and second baroclinic modes of Rossby wave are more strongly generated than the barotropic mode in the study area. A higher vertical mode of Rossby wave propagates more slowly and is more decayed by eddy dissipation. The best coefficient of vertical eddy dissipation is determined by comparing the calculated sea level with observation. The variation in sea level at Chichi-jima is successfully calculated, in particular for the long-term change of the mean level between before and after 1986 with a rise in 1986 as well as the variations with periods of two to four years after 1980. It is concluded that variations of sea level at Chichi-jima are produced by wind-forced Rossby waves, the first baroclinic wave primarily and the barotropic wave secondly. The calculation for other islands is less successful. Degree of the success in calculation almost corresponds to a spatial difference in quantity of wind data, and seems to be determined by quality of wind data.     

An Amplification Mechanism of Intraseasonal Long Rossby Wave in Subtropical Ocean

The satellite altimeter data reveal that intraseasonal long Rossby wave is amplified in the western part of subtropical ocean. Based on a two and half layer ocean model we infer that the intraseasonal long Rossby wave may be amplified by the baroclinic instability. According to the baroclinic instability criterion derived from the two and half layer model, we calculate the baroclinic instability area of the Subtropical North Pacific Ocean based on Levitus98 data. The baroclinic instability area is well in accord with the amplification area of the intraseasonal long Rossby wave, and this also proves that the baroclinic instability is the main amplification mechanism of the intraseasonal long Rossby wave in the subtropical ocean. The consistency between the baroclinic instability area and potential vorticity (PV) pool is further proved in this paper, therefore, we have confidence that the intraseasonal long Rossby wave is amplified in the PV pool. Due to the relatively large ocean basin and weak ventilation, the PV pool is much larger in the North Pacific Ocean than in the North Atlantic Ocean, and this is the reason for the difference of wave amplification areas of these two Oceans.     

Wind-driven interannual variability over the northeast Pacific Ocean

Interannual variability of the sea surface height (SSH) over the northeast Pacific Ocean is hindcast with a reduced-gravity, quasi-geostrophic model that includes linear damping. The model is forced with monthly Ekman pumping fields derived from the NCEP reanalysis wind stresses. The numerical solution is compared with SSH observations derived from satellite altimeter data and gridded at a lateral resolution of 1 degree. Provided that the reduced gravity parameter is chosen appropriately, the results demonstrate that the model has significant hindcast skill over interior regions of the basin, away from continental boundaries. A damping time scale of 2 to 3 years is close to optimal, although the hindcast skill is not strongly dependent on this parameter.A simplification of the quasi-geostrophic model is considered in which Rossby waves are eliminated, yielding a Markov model driven by local Ekman pumping. The results approximately reproduce the hindcast skill of the more complete quasi-geostrophic model and indicate that the interannual SSH variability is dominated by the local response to wind forcing. There is a close correspondence the two leading empirical orthogonal modes of the local model and those of the observed SSH anomalies. The latter account for over half of the variance of the interannual signal over the region.     

副热带一热带太平洋密跃层水量交换年际变化的模拟研究

利用一个全球海洋环流模式在3组风应力资料的强迫下模拟分析了副热带太平洋向热带太平洋密跃层水量输送的年际变化特征及其和风应力的关系,并设计数值试验,研究了密跃层水量输送的变化机制.结果表明,副热带太平洋向赤道太平洋的密跃层水量输送具有显著的年际变化.在年际时间尺度上,南北太平洋西边界密跃层水量输送都起着补偿内部路径输送的...     

ENSO-induced interannual variability in the southeastern South China Sea

In this study, El Niño Southern Oscillation (ENSO)-induced interannual variability in the South China Sea (SCS) is documented using outputs from an eddy-resolving data-assimilating model. It is suggested that during an El Niño (La Niña) event, off-equatorial upwelling (downwelling) Rossby waves induced by Pacific equatorial wind anomalies impinge on the Philippine Islands and excite upwelling (downwelling) coastal Kelvin waves that propagate northward along the west coast of the Philippines after entering the SCS through the Mindoro Strait. The coastal Kelvin waves may then induce negative (positive) sea level anomalies in the southeastern SCS and larger (smaller) volume transport through the Mindoro and Luzon Straits during an El Niño (La Niña) event.     

大洋Rossby波动纬向传播速度的分布特征

利用1992年10月22日-2001年7月17日扣除年循环的T／P和ERS-1／-2的卫星融合高度计资料，应用二维Radon变换方法，对太平洋和大西洋的洋盆东部、西部的大洋Rossby波的纬向传播速度进行了分析与对比，并将二者分别与经典线性理论值比较，得出洋盆西部的Rossby波普遍比洋盆东部传播要快；中纬度海域大洋Rossby波的传播速度观测值与理论值的比率小于前人结果；并且在热带及副热带海域，大洋Rossby波的传播速度的观测值要低于理论值的结论。     

Sea Surface Height Variability in the Indian Ocean from TOPEX/POSEIDON Altimetry and Model Simulations

Sea Surface Height (SSH) variability in the Indian Ocean during 1993-1995 is studied using TOPEX/POSEIDON (T/P) altimetry data. Strong interannual variability is seen in the surface circulation of the western Arabian Sea, especially in the Somali eddy structure. During the Southwest (SW) monsoon, a weak monsoon year is characterized by a single eddy system off Somalia, a strong or normal monsoon year by several energetic eddies. The Laccadive High (LH) and Laccadive Low (LL) systems off southwest India are observed in the altimetric SSH record. The variability of the East India Coastal Current (EICC), the western boundary current in the Bay of Bengal, is also detected. Evidence is found for the propagation of Kelvin and Rossby waves across the northern Indian Ocean; these are examined in the context of energy transfer to the western boundary currents, and associated eddies. A simple wind-driven isopycnal model having three active layers is implemented to simulate the seasonal changes of surface and subsurface circulation in the North Indian Ocean and to examine the response to different wind forcing. The wind forcing is derived from the ERS-1 scatterometer wind stress for the same period as the T/P altimeter data, enabling the model response in different (active/weak) monsoon conditions to be tested. The model output is derived in 10-day snapshots to match the time period of the T/P altimeter cycles. Complex Principal Component Analysis (CPCA) is applied to both altimetric and model SSH data. This confirms that long Rossby waves are excited by the remotely forced Kelvin waves off the southwest coast of India and contribute substantially to the variability of the seasonal circulation in the Arabian Sea.