EMPIRICAL ORTHOGONAL MODES IN THE WESTERN PACIFIC

The method of empirical orthogonal modes has been widely used since the 1970's in physical oceanography to study and rebuild vertical structures of ocean dynamic factors. Because of the dominance of the low modes, the dynamic profile data can be largely reduced.Up to now, all expressions of empirical orthogonal modes are numerical. In this study, an analytic expression for empirical orthogonal ocean modes is constructed for convenient use whereby any numerical expressions can be repeated.The features of the normal modes decomposed from the buoyance frequency profiles obtained in October of 1986,1987 and 1988 by the R/V Science 1 in the western Pacific are quantitatively examined in this study.     

PN断面东海黑潮的地转经验模态分析

基于东海PN断面近50年的历史水文数据,本文中作者应用一种斜压流函数空间投影的方法分析冲绳海槽北部黑潮水团的季节性和年代际变异.诊断生成的地转经验模态(GEM)显示黑潮中层水的盐度在夏季相对较低,春季达到最高.通过比较1987年之后CTD数据生成的GEM场与1987年之前BOttle数据生成的GEM场,得以证实黑潮的年代际变化特征,即黑潮表层水近20年来温度升高而盐度减小,同时发现黑潮热带水具有盐度增加而中层水具有盐度减小的趋势.     

热带太平洋海洋环流与暖池的结构特征、变异机理和气候效应

热带西太平洋暖池是引发强烈的大气对流、驱动Walker环流和Hadley环流系统的主要热源之一,对全球、尤其是东亚气候有重要影响。针对我国在提升气候预测水平方面的重大和迫切需求,国家重点基础研究发展计划项目"热带太平洋海洋环流与暖池的结构特征、变异机理和气候效应"于2011年7月正式立项。项目拟解决的关键科学问题包括:①调控暖池形成和变异的海洋环流多尺度相互作用过程;②海洋动力过程在暖池热盐结构变异中的作用及其机理;③暖池变异对不同类型El Nio影响机理的异同和对东亚季风变异的调制机理。围绕上述关键科学问题,项目将以暖池变异为中心,关注影响和控制暖池结构与变异的关键海洋过程,以及暖池海气相互作用影响ENSO循环、东亚季风年际变异的过程和机理,重点组织开展以下3个方面有针对性的调查研究:①热带太平洋环流和暖池的结构和变异特征;②热带太平洋环流与暖池相互作用的关键过程和机理;③暖池变异的海洋—大气耦合过程及其气候效应。在此基础上,项目将力争阐明暖池影响东亚季风和我国气候变异的过程、机理与敏感区,改进模式的混合参数化方案,提出有效提高ENSO预报技巧的同化方案,为我国短期气候预测能力的提高提供科学支撑。     

RESPONSE OF THE EQUATORIAL WESTERN PACIFIC THERMOHALINE STRUCTURE TO WIND VARIATION

During the Global Weather Experiment oceanographic measurements were recorded during winter and summer in the western Pacific region 5°S-5°N,160°E-175°E. The variations of the upper ocean temperature and salinity fields were produced by the large seasonal and spatial wind fluctuations. The vertical temperature structure of the thermocline at the equator, the meridional slope of the thermocline south of the equator, and the northward penetration of high salinity water were related to the direction and intensity of the zonal wind-stress.     

Interannual variations of North Equatorial Current transport in the Pacific Ocean during two types of El Niño

Interannual variations of Pacific North Equatorial Current (NEC) transport during eastern-Pacific El Niños (EP-El Niños) and central-Pacific El Niños (CP-El Niños) are investigated by composite analysis with European Centre for Medium-Range Weather Forecast Ocean Analysis/Reanalysis System 3. During EP-El Niño, NEC transport shows significant positive anomalies from the developing to decay phases, with the largest anomalies around the mature phase. During CP-El Niño, however, the NEC transport only shows positive anomalies before the mature phase, with much weaker anomalies than those during EP-El Niño. The NEC transport variations are strongly associated with variations of the tropical gyre and wind forcing in the tropical North Pacific. During EP-El Niño, strong westerly wind anomalies and positive wind stress curl anomalies in the tropical North Pacific induce local upward Ekman pumping and westward-propagating upwelling Rossby waves in the ocean, lowering the sea surface height and generating a cyclonic gyre anomaly in the western tropical Pacific. During CP-El Niño, however, strength of the wind and associated Ekman pumping velocity are very weak. Negative sea surface height and cyclonic flow anomalies are slightly north of those during EP El Niño.     

西太平洋暖池的跃变及其气候效应

用SST（COADS，NCEP）资料研究热带西太平洋暖池的年代际变化和跃变特征，讨论其气候效应。结果表明：西太平洋暖池有显著的10-20年周期的年人际变化和40-50年周期的气候跃变：一百多年来西太平洋暖池发生了4次大跃变，在1910年代中期和1950年代中期，西太平洋暖池由异常发展转为异常减弱，1930年代初和1980年代初，西太平洋暖池由异常减弱转为异常发展：西太平洋暖池在1980年代初的跃变，具明显的效应，跃变后热带中东太平洋海温显著升高，大范围海域升温超过0.5℃，夏季西太平洋副高加强西伸，脊线偏南，我国汛期降水呈南方偏多、北方偏少的分布趋势，与跃变前基本相反。研究结果还表明：在西太平洋暖池异常发展期，El Nino事件出现多且强于La Nina事件，而在西太平洋暖池异常减弱期，La Nina事件出现多且强于El Nino事件。     

PRELIMINARY STUDY ON THE FORMATION MECHANISM OF COUNTER WESTERN BOUNDARY UNDERCURRENTS BELOW THE THERMOCLINE——A CONCEPTUAL MODEL

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Interannual variability of transport and bifurcation of the North Equatorial Current in the tropical North Pacific Ocean

The relationship of the interannual variability of the transport and bifurcation latitude of the North Equatorial Current (NEC) to the El Ni o-Southern Oscillation (ENSO) is investigated. This is done through composite analysis of sea surface height (SSH) observed by satellite altimeter during October 1992-July 2009, and correspondingly derived sea surface geostrophic currents. During El Nio/La Ni a years, the SSH in the tropical North Pacific Ocean falls/rises, with maximum changes in the region 0-15°N, 130°E-160°E. The decrease/increase in SSH induces a cyclonic/anticyclonic anomaly in the western tropical gyre. The cyclonic/anticyclonic anomaly in the gyre results in an increase/decrease of NEC transport, and a northward/southward shift of the NEC bifurcation latitude near the Philippine coast. The variations are mainly in response to anomalous wind forcing in the west-central tropical North Pacific Ocean, related to ENSO events.     

Surface circulation patterns observed by drifters in the Yellow Sea in summer of 2001, 2002 and 2003

In summer of 2001, 2002 and 2003, ten, six and seventeen satellite-tracked surface drifters with drogues centered at 15 and 4 m were deployed, respectively, in the southern Yellow Sea (YS). 23 drifters of them transmitted useful data of at least 30 days. The wind-driven component of the drift was removed from the original drift velocity of drifters. The wind data used are from NCEP (National Center for Environmental Prediction), USA.Trajectories and drift velocities of the 23 drifters depicted the upper circulation structure in the southern YS. There exists an anti-cyclonic eddy with a mean speed and radius of 0.063 m/s and 50km in the central southern YS, whose center lingered within 35.3-36.0°N / 123.5-124.0°E. Showed by 6 drifters, a basin-scale elliptic cyclonic gyre with a mean speed of 0.114 m/s, long and short radius of 250 and 200 km surrounds the anti-cyclonic eddy. In the southwestern part of the southern YS has obvious frontal eddy activities within about 100 km with a mean speed about 0.076