北太平洋冬季SST、风场及环流对淡水强迫的响应

通过海气耦合模式CCSM3(The Community Climate System Model version 3),研究在北大西洋高纬度淡水强迫下,北太平洋冬季的海表温度SST、风场及流场的响应及其区域性差异。结果表明:淡水的注入使北太平洋整体变冷,但有部分区域异常增暖;在太平洋东部赤道两侧,SST的变化出现北负南正的偶极子型分布。阿留申低压北移的同时中纬度西风减弱,热带附近东北信风增强。黑潮和南赤道流减弱,北太平洋副热带逆流和北赤道流增强,日本海被南向流控制。风场及流场的改变共同导致了北太平洋SST异常出现复杂的空间差异:北太平洋中高纬度SST的降温主要由大气过程决定,海洋动力过程主要影响黑潮、日本海及副热带逆流区域的SST,太平洋热带地区SST异常由大气与海洋共同主导。     

Oceanic Rossby waves induced by the meridional shift of the ITCZ in association with ENSO events

This study investigated the eastern Pacific Intertropical Convergence Zone (ITCZ) as an atmospheric forcing to the ocean by using various observed and reanalysis data sets over 29 years. Climatologically, a zonal band of positive wind stress curl (WSC) with a 10° meridional width was exhibited along the ITCZ. A southward shift of the positive WSC band during the El Niño phase induced a negative (positive) WSC anomaly along the northern (southern) portion of the ITCZ, and vice versa during the La Niña phase. This meridional dipole accounted for more than 25 % of interannual variances of the WSC anomalies (WSCAs), based on analysis of the period 1993–2008. The negative (positive) WSCA in the northern portion of the ITCZ during the El Niño (La Niña) phase was collocated with a positive (negative) sea surface height anomaly (SSHA) that propagated westward as a Rossby wave all the way to the western North Pacific. This finding indicates that this off-equatorial Rossby wave is induced by the WSCA around the ITCZ. Our analysis of a 1.5-layer reduced gravity model revealed that the Rossby waves are mostly explained by wind stress forcing, rather than by reflection of an equatorial Kelvin wave on the eastern coastal boundary. The off-equatorial Rossby wave had the same SSHA polarity as the equatorial Kelvin wave, and generation of a phase-preserving Rossby wave without the Kelvin wave reflection was explained by meridional movement of the ITCZ. Thus, the ITCZ acts as an atmospheric bridge that connects the equatorial and off-equatorial oceanic waves.     

2019年11月西北太平洋热带气旋生成频数异常偏多的成因分析

基于1979-2019年NCEP-DOE再分析资料、中国气象局发布的热带气旋(TC)最佳路径数据集和HadISST全球海温资料等,研究了2019年11月西北太平洋TC生成频数异常偏多的可能原因.结果表明:2019年11月西太平洋副热带高压(WPSH)强度偏强、脊线偏北,其南侧偏东气流与越赤道气流交汇形成的西北太平洋热带...     

Spatial and temporal structure of Tropical Pacific interannual variability in 20th century coupled simulations

Tropical Pacific interannual variability is examined in nine state-of-the-art coupled climate models, and compared with observations and ocean analyses data sets, the primary focus being on the spatial structure and spectral characteristics of El Niño-Southern Oscillation (ENSO). The spatial patterns of interannual sea surface temperature (SST) anomalies from the coupled models are characterized by maximum variations displaced from the coast of South America, and generally extending too far west with respect to observations. Thermocline variability is characterized by dominant modes that are qualitatively similar in all the models, and consistent with the “recharge oscillator” paradigm for ENSO. The meridional scale of the thermocline depth anomalies is generally narrower than observed, a result that can be related to the pattern of zonal wind stress perturbations in the central-western equatorial Pacific. The wind stress response to eastern equatorial Pacific SST anomalies in the models is narrower and displaced further west than observed. The meridional scale of the wind stress can affect the amount of warm water involved in the recharge/discharge of the equatorial thermocline, while the longitudinal location of the wind stress anomalies can influence the advection of the mean zonal temperature gradient by the anomalous zonal currents, a process that may favor the growth and longer duration of ENSO events when the wind stress perturbations are displaced eastwards. Thus, both discrepancies of the wind stress anomaly patterns in the coupled models with respect to observations (narrow meridional extent, and westward displacement along the equator) may be responsible for the ENSO timescale being shorter in the models than in observations. The examination of the leading advective processes in the SST tendency equation indicates that vertical advection of temperature anomalies tends to favor ENSO growth in all the CGCMs, but at a smaller rate than in observations. In some models it can also promote a phase transition. Longer periods tend to be associated with thermocline and advective feedbacks that are in phase with the SST anomalies, while advective tendencies that lead the SST anomalies by a quarter cycle favor ENSO transitions, thus leading to a shorter period.     

气侯平均风场作用下热带太平洋主流系和赤道行星波研究

将两层约化重力原始流体动力方程耦合气候月平均风场,数值计算流场基本能够正确反映热带太平洋上层主流系和温跃层的空间分布和季节变化．在气候平均条件下,东太平洋125°W附近经向风应力可激发出高阶混合Rossby重力波．海洋高阶赤道Kelvin波流速模态可从西太平洋边界传播到东太平洋边界,而高阶赤道Kelvin波温跃层模态从西太平洋边界东传后,在中太平洋受到高阶混合Rossby重力波诱发的西传温跃层扰动的阻挡．     

北太平洋海温分布与7月副高的遥相关分析

选取1952-2005年共54 a北太平洋月平均海表温度(SST)资料,奇异值分解结果表明,6月日界线附近西风漂流区的SST包含了北太平洋SST场的主要信息,西风漂流区与赤道冷水区的SST存在遥相关振荡,并且在6月振幅达全年最高值,11月其振幅出现次高值。分析结果表明,6月西风漂流区的SST可视为来年7月西太平洋副高强弱变化的信号:6月西风漂流区的SST偏低,则来年7月西太平洋副高偏强;反之,来年7月西太平洋副高偏弱。     

Changes of equatorial wind fields in the Western Pacific and El Nino

The relationship between SST in the Eastern Pacific and equatorial wind fields in the Western Pacific is analysed by using COADS.It is pointed out that in the year before El Nino , the continuative easterly anomalies and the meridional anomalies blowing from the Equator to both sides in the Equatorial Western Pacific cause the sea level in the Western Pacific to rise higher than in the Eastern Pacific and the sea level at the Equator to drop lower than on both sides of it. In the El Nino year, the westerly anomalies and the meridional anomalies blowing from both sides to the Equator bring warm water to build up around the Equator. At such times Kelvin waves are generated and they play an important role in raising SST in the Eastern Pacific. It is also emphatically pointed out that in the El Nino year the two maxima of the equatorial westerly anomalies, the two cross-equatorial air flows from the Northern Hemisphere to the Southern one and the two maxima of the near-equatorial tropical cyclones in the Eq     

中国科学院气候系统模式模拟的ENSO循环

On the basis of more than 200-year control run, the performance of the climate system model of Chinese Academy of Sciences(CAS-ESM-C) in simulating the El Ni?o-Southern Oscillation(ENSO) cycle is evaluated, including the onset, development and decay of the ENSO. It is shown that, the model can reasonably simulate the annual cycle and interannual variability of sea surface temperature(SST) in the tropical Pacific, as well as the seasonal phase-locking of the ENSO. The model also captures two prerequisites for the El Ni?o onset, i.e., a westerly anomaly and a warm SST anomaly in the equatorial western Pacific. Owing to too strong forcing from an extratropical meridional wind, however, the westerly anomaly in this region is largely overestimated. Moreover, the simulated thermocline is much shallower with a weaker slope. As a result, the warm SST anomaly from the western Pacific propagates eastward more quickly, leading to a faster development of an El Ni?o. During the decay stage, owing to a stronger El Ni?o in the model, the secondary Gill-type response of the tropical atmosphere to the eastern Pacific warming is much stronger, thereby resulting in a persistent easterly anomaly in the western Pacific. Meanwhile, a cold anomaly in the warm pool appears as a result of a lifted thermocline via Ekman pumping. Finally, an El Ni?o decays into a La Ni?a through their interactions. In addition, the shorter period and larger amplitude of the ENSO in the model can be attributed to a shallower thermocline in the equatorial Pacific, which speeds up the zonal redistribution of a heat content in the upper ocean.     

Relation between sea surface temperature anomaly in the Atlantic and summer precipitation over the Northeast China

1 IwrRoDUcrIowln recen l00 years. mateorolQgi8ts have paid mu0h aneation to impact of ocean onlong-range weather process. Because fram view POillt of space and tAne scale condition,ocean is one of very important phySical factor for the evolotion of thespheric circulation.The scientific research cooperation grOup (l979) first found that SST in the equatorialeastern Pacific reversely correlates with summer tempendre aver Nowheast China. Pan etal (1981) discussed re1atfon between heating of…     

热带三大洋海表温度和云水关系的初探

热带太平洋、大西洋和热带印度洋是全球海洋-大气相互作用最显著的海域。为了探讨热带三大洋局地海洋-大气相互作用中的某些特征,利用新的卫星遥感资料对热带三大洋的云水和海表温度(SST)异常变化进行了统计相关分析。研究发现:在赤道太平洋和赤道大西洋云水和SST二者在超前或滞后5周内都呈现明显的正相关关系,表明3个赤道海域云水和SST之间具有明显的相互作用正反馈机制;在热带西印度洋SST异常超前CLW异常一周时,正相关系数最大,SST的变化导致云水的变化;而在以较冷海水为下垫面的赤道外东北太平洋,东南太平洋以及赤道外的南大西洋海域,二者呈明显的负相关关系,云水的变化会引起SST的变化。位于菲律宾以东的热带西北太平洋区,云水量的变化引起SST的变化;而赤道东印度洋暖池区即存在云水量的增加(减少)引起SST降低(升高)的现象,也存在SST降低(升高)引起云水量的减少(增加)的现象。以上结果将为进一步理解海洋-大气相互作用,在数值模式中正确设计海洋-大气边界层参数化方案提供参考。     

北半球热带中太平洋与印度洋海表温度梯度对夏季西北太平洋热带气旋生成频数变化的影响

基于1951—2018年哈德里中心海温资料、美国气象环境预报中心和美国国家大气研究中心再分析资料和第四代欧洲中心汉堡模式, 针对1994年、2018年等西北太平洋热带气旋(TC)生成异常多的年份, 研究了引起TC增加的海表温度异常(SSTA)模态及其影响机制。结果表明, 北半球热带中太平洋增暖与印度洋变冷是夏季西北太平洋TC生成频数增加的主要原因, 北大西洋负三极型式SSTA促使TC生成的进一步增加。热带中太平洋增暖与印度洋冷却在菲律宾以东激发出西风异常和气旋性环流异常。北大西洋负三极型式SSTA在我国南海、菲律宾至东南沿岸激发出气旋性环流异常。前者在西北太平洋中部, 后者在南海产生有利于TC生成的局地环境。1994年和2018年夏季热带中太平洋出现暖SSTA、印度洋为冷SSTA、北大西洋呈现负三极型式SSTA, 西北太平洋TC生成频数极端增多。近30年来, 当出现热带中太平洋增暖和印度洋冷却时, 北大西洋表现出比1989年以前更强的负三极型式SSTA, 使西北太平洋TC生成频数和北半球热带印度洋-太平洋SSTA梯度的线性相关更显著。     

Analysis of the global relationship of biennial variation of sea surface temperature and air-sea heat flux using satellite data

We investigated the phase difference and the cross correlation coefficient between the band-pass filtered biennial variations of sea surface temperature (SST) and air-sea heat flux estimated by the monthly mean 2°×2° satellite data of Advanced Very High Resolution Radiometer (AVHRR) and Special Sensor Microwave/Imager (SSM/I) from July 1987 to June 1991. Judging from the phase difference, it can be determined whether the biennial variation of SST is controlled by local thermal air-sea interaction or oceanic processes of horizontal transport. When the local air-sea heat flux controls the biennial variation of SST, the phase of SST advances /2 (6 months) against that of the air-sea heat flux. In contrast, when the biennial variation of SST is controlled by the oceanic process, the phase difference between the SST and the air-sea heat flux becomes 0 or (12 months). In this case, two types of the phase differences are determined, depending on which variability of SST and air-sea heat flux is larger. The close thermal air-sea interaction is noticeable in the tropics and in the western boundary current region. The phase difference of /2 appears mainly in the north Pacific, the southeast Indian Ocean, and the western tropical Pacific; zero in the eastern tropical Pacific and the northeast and equatorial Atlantic; and that of in the central equatorial Pacific and north of the intertropical convergence zone (ITCZ) of the Atlantic. Phase differences of 0, , or /2 are possible in the western boundary current regions. This fact indicates that each current plays a different role to the biennial variation of SST. It is inferred that SST anomalies in the tropics are mutually correlated, and the process in which marked SST anomalies in the tropics are transferred to the remote area was probed. In the equatorial Pacific, the SST anomaly is transferred by the long planetary wave. On the other hand, it is found from the phase relationship and the horizontal correlation of SST that the SST anomaly in the central and western equatorial Pacific is connected through atmospheric mediation. It is suggested that the biennial variation of SST in the eastern Indian Ocean is affected by heat transport due to the Indonesian throughflow from the western tropical Pacific. It is found that the mentioned pattern of the interannual variation of SST in the tropical Atlantic as a dipole is not tenable.     

SST年循环对El Niño事件局地海气过程的影响

利用Hadley中心逐月海表温度、欧洲中心ERA-40的10 m风场及CMAP降水资料探讨了年循环对热带太平洋El Niño海气相互作用过程的影响。尽管El Niño对应的海表温度异常主要出现在赤道东太平洋,经向上呈南北对称分布,然而其对应的大气响应在El Niño年衰减阶段却有着强的向南移动特征。在El Niño发展年的11月之前,强的西风和降水异常主要出现在赤道中太平洋;在12月份之后,赤道上的西风和降水异常迅速南移至5°S,随后西风一直维持在该位置直至衰亡。同时,西太平洋负降水和反气旋异常向北移动。这种SST异常与其大气响应的经向移动不一致,主要是由热带中太平洋气候态SST的季节性南移导致的。由于对流与海温之间存在非线性关系,即当总SST超过一定的阈值,对流降水才会迅速增强;因此相应的对流响应也随着总海温的南移而南移,风场响应也同时南移。此外,南半球增强的对流会通过经向环流进一步抑制北半球的降水,从而使西太平洋负降水和反气旋异常增强并北移。通过分析有/无年循环的两组数值试验结果验证了上述结论,即有年循环的试验较真实地模拟出了观测中异常西风南移和西北太平洋反气旋异常的出现;无年循环试验尽管能模拟出El Niño年赤道中太平洋的西风异常,但其却没有南北向的移动,西北太平洋的反气旋也没有出现。因此,热带中太平洋气候态暖海温的季节循环对El Niño事件大气响应有着至关重要的作用。     

太平洋表层海温的年代际变化

众所周知，ENSO(El Nino/ Southern Oscillation)是发生在热带太平洋的年际时间尺度上最强的气候信号，与 El Nino (La Nina)相应的正(负)海温距平(SSTA)主要分布于赤道中东太平洋地区(Rasmusson et al.，1982)。相对于热带太平洋的年际ENSO现象，人们注意到北太平洋海平面气压(SLP)存在更长周期的年代际变化(Trenberth et al.，1994)，有人认为这与北太平洋的表层温度(SST)变化有关(Latif et al.，1994)，也有人认为与热带SST的异常关系更为密切(Jacobs et al.，1994)。20世纪80年代后的ENSO事件和20世纪60，70年代有明显的差别(Wang，1995)，20世纪90年后El Nino发生频数增加，并且在1997和1998年出现了20世纪最强的一次Nino事件(McPhaden，1999)。 因此，不论是作为大气年代际变化可能的一个驱动因子，还是作为年际ENSO的背景场，从整体上了解太平洋SST的年代际时间尺度上的时、空变化特征都是十分重要的。     

Decadal variability of the shallow Pacific meridional overturning circulation: Relation to tropical sea surface temperatures in observations and climate change models

In this study, we use existing observational datasets to evaluate 20th century climate simulations of the tropical Pacific. The emphasis of our work is decadal variability of the shallow meridional overturning circulation, which links the tropical and subtropical Pacific Ocean. In observations, this circulation is characterized by equatorward geostrophic volume transport convergence in the interior ocean pycnocline across 9°N and 9°S. Historical hydrographic data indicate that there has been a decreasing trend in this convergence over the period 1953–2001 of about 11 Sverdrup (1 Sv = 10⁶ m³ s⁻¹), with maximum decade-to-decade variations of 7–11 Sv. The transport time series is highly anti-correlated with sea surface temperature (SST) anomalies in the central and eastern tropical Pacific, implying that variations in meridional overturning circulation are directly linked to decadal variability and trends in tropical SST. These relationships are explored in 18 model simulations of 20th century climate from 14 state-of-the-art coupled climate models. Significant correlation exists between meridional volume transport convergence and tropical SST in the majority of the models over the last half century. However, the magnitude of transport variability on decadal time scales in the models is underestimated while at the same time modeled SST variations are more sensitive to that transport variability than in the observations. The effects of the meridional overturning circulation on SST trends in most the models is less clear. Most models show no trend in meridional transport convergence and underestimate the trend in eastern tropical Pacific SST. The eddy permitting MIROCH model is the only model that reasonably reproduces the observed trends in transport convergence, tropical Pacific SST, and SST gradient along the equator over the last half century. If the observed trends and those simulated in the MIROCH model are ultimately related to greenhouse gas forcing, these results suggest that the Bjerknes feedback, by affecting pycnocline transport convergences, may enhance warming that arises from anthropogenic forcing in the eastern tropical Pacific.     

Atmospheric forcing of the eastern tropical Pacific: A review

The increase in marine, land surface, atmospheric and satellite data during recent decades has led to an improved understanding of the air–sea interaction processes in the eastern tropical Pacific. This is also thanks to extensive diagnoses from conceptual and coupled ocean–atmosphere numerical models. In this paper, mean fields of atmospheric variables, such as incoming solar radiation, sea level pressure, winds, wind stress curl, precipitation, evaporation, and surface energy fluxes, are derived from global atmospheric data sets in order to examine the dominant features of the low level atmospheric circulations of the region. The seasonal march of the atmospheric circulations is presented to depict the role of radiative forcing on atmospheric perturbations, especially those dominating the atmosphere at low levels.In the tropics, the trade winds constitute an important north–south energy and moisture exchange mechanism (as part of the low level branch of the Hadley circulation), that determines to a large extent the precipitation distribution in the region, i.e., that associated with the Inter-Tropical Convergence Zone (ITCZ). Monsoonal circulations also play an important role in determining the warm season precipitation distribution over the eastern tropical Pacific through a large variety of air–sea–land interaction mechanisms. Westward traveling waves, tropical cyclones, low latitude cold air intrusions, and other synoptic and mesoscale perturbations associated with the ITCZ are also important elements that modulate the annual rainfall cycle. The low-level jets of the Gulf of California, the Intra-Americas Sea (Gulf of Mexico and Caribbean Sea) and Chocó, Colombia are prominent features of the eastern tropical Pacific low-level circulations related to sub-regional and regional scale precipitation patterns. Observations show that the Intra-Americas Low-Level Jet intensity varies with El Niño/Southern Oscillation (ENSO) phases, however its origin and role in the westward propagation and development of disturbances that may hit the eastern tropical Pacific, such as easterly waves and tropical cyclones, are still unclear. Changes in the intensity of the trade winds in the Caribbean Sea and the Gulf of Mexico (associated with eastern tropical Pacific wind jets) exert an important control on precipitation by means of wind–topography interactions. Gaps in the mountains of southern Mexico and Central America allow strong wind jets to pass over the continent imprinting a unique signal in sea surface temperatures and ocean dynamics of the eastern tropical Pacific.The warm pools of the Americas constitute an important source of moisture for the North American Monsoon System. The northeastern tropical Pacific is a region of intense cyclogenetic activity, just west of the coast of Mesoamerica. Over the oceanic regions, large-scale properties of key variables such as precipitation, moisture, surface energy fluxes and wind stress curl are still uncertain, which inhibits a more comprehensive view of the region and stresses the importance of regional field experiments. Progress has been substantial in the understanding of the ocean and atmospheric dynamics of the eastern tropical Pacific, however, recent observational evidence such as that of a shallow meridional circulation cell in that region, in contrast to the classic concept of the Hadley-type deep meridional circulation, suggests that more in situ observations to validate theories are still necessary.This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific Ocean.     

印度洋海温异常对西北太平洋台风的影响及机制研究

基于近40 a NCEP/NCAR再分析月平均高度场、风场、涡度场、垂直速度场以及NOAA重构的海面温度(sea surface temperature,SST)资料和美国联合台风预警中心(Joint Typhoon Warning Center,JTWC)热带气旋最佳路径资料,利用合成分析方法,研究了前期春季及同期夏季印度洋海面温度同夏季西北太平洋台风活动的关系。结果表明:1)前期春季印度洋海温异常(sea surface temperature anomaly,SSTA)尤其是关键区位于赤道偏北印度洋和西南印度洋地区对西北太平洋台风活动具有显著的影响,春季印度洋海温异常偏暖年,后期夏季,110°～180°E的经向垂直环流表现为异常下沉气流,对应风场的低层低频风辐散、高层辐合的形势,这种环流形势使得低层水汽无法向上输送,对流层中层水汽异常偏少,纬向风垂直切变偏大,从而夏季西北太平洋台风频数偏少、强度偏弱,而异常偏冷年份则正好相反。2)春季印度洋异常暖年,西北太平洋副热带高压加强、西伸;而春季印度洋异常冷年,后期夏季西北太平洋副热带高压减弱、东退,这可能是引起夏季西北太平洋台风变化的另一原因。     

The circulation of the eastern tropical Pacific: A review

During the 1950s and 1960s, an extensive field study and interpretive effort was made by researchers, primarily at the Scripps Institution of Oceanography, to sample and understand the physical oceanography of the eastern tropical Pacific. That work was inspired by the valuable fisheries of the region, the recent discovery of the equatorial undercurrent, and the growing realization of the importance of the El Niño phenomenon. Here we review what was learned in that effort, and integrate those findings with work published since then as well as additional diagnoses based on modern data sets.Unlike the central Pacific, where the winds are nearly zonal and the ocean properties and circulation are nearly independent of longitude, the eastern tropical Pacific is distinguished by wind forcing that is strongly influenced by the topography of the American continent. Its circulation is characterized by short zonal scales, permanent eddies and significant off-equatorial upwelling. Notably, the Costa Rica Dome and a thermocline bowl to its northwest are due to winds blowing through gaps in the Central American cordillera, which imprint their signatures on the ocean through linear Sverdrup dynamics. Strong annual modulation of the gap winds and the meridional oscillation of the Intertropical Convergence Zone generates a Rossby wave, superimposed on the direct forcing, that results in a southwestward-propagating annual thermocline signal accounting for major features of observed thermocline depth variations, including that of the Costa Rica Dome, the Tehuantepec bowl, and the ridge–trough system of the North Equatorial Countercurrent (NECC). Interannual variability of sea surface temperature (SST) and altimetric sea surface height signals suggests that the strengthening of the NECC observed in the central Pacific during El Niño events continues all the way to the coast, warming SST (by zonal advection) in a wider meridional band than the equatorially trapped thermocline anomalies, and pumping equatorial water poleward along the coast.The South Equatorial Current originates as a combination of equatorial upwelling, mixing and advection from the NECC, and Peru coastal upwelling, but its sources and their variability remain unresolved. Similarly, while much of the Equatorial Undercurrent flows southeast into the Peru Undercurrent and supplies the coastal upwelling, a quantitative assessment is lacking. We are still unable to put together the eastern interconnections among the long zonal currents of the central Pacific.     

Can the mean structure of the tropical pycnocline affect ENSO period in coupled climate models?

The dynamical link between mean state biases and dominant timescales of interannual variability is examined using the output from two state-of-the-art coupled model simulations, results from an ocean-only simulation forced with observed surface fields, and various observational data sets. The focus of this study is the relative role of the mean upper ocean density structure vs. anomalous wind forcing in controlling the spectral characteristics of tropical Pacific interannual variability. It is shown that an extensive South Pacific Convergence Zone (SPCZ) creates a potential vorticity (PV) barrier in the Southern Hemisphere similar to the one associated with the Intertropical Convergence Zone (ITCZ) in the Northern Hemisphere in both climate models. The PV barrier in the Southern Hemisphere strongly constrains the mean equatorward flow in the ocean model pycnocline, creating a “choke point” for the mean flow around 10°S. It is then examined whether the PV barrier can also limit the anomalous flow associated with mass recharge/discharge to/from the equatorial thermocline at interannual timescales. If the anomalous flow were impeded by the mean PV structure the meridional extent of the area involved in the mass recharge/discharge process would be narrower, leading to a shorter adjustment (and ENSO) timescale. Comparison of the two climate models, both of which have similarly erroneous PV structures in the southern tropical Pacific, but different interannual timescales, shows that the meridional extent of the anomalous meridional transport is primarily controlled by the latitudinal location of the wind stress curl anomalies, while the mean state bias in the Southern Hemisphere does not seem to have any significant influence.     

Seasonal cycle of phosphate in the open ocean

The seasonal cycle of phosphate in the world ocean is described using all historical data (over 170,000 profiles) held at the U.S. National Oceanographic Data Center and World Data Center-A for Oceanography. Generally, phosphate concentrations are depressed in the season of highest primary production, in conformance with phosphate's role as a major nutrient. Mean phosphate concentration in the North Pacific are twice those in the North Atlantic. The largest seasonal differences occur in the sub-polar North Atlantic and Pacific, where changes in concentration are as large as a factor of two. Temperate and equatorial regions exhibit less seasonal variability. High latitudes, upwelling areas, and river mouths exhibit a notable seasonal signal in phosphate. Enrichment of phosphate from the Amazon and Orinoco rivers appears to dominate the seasonal signal in the tropical Atlantic. In fact, the extent of the rivers’ effects extend so far north into the North Atlantic gyre that it obscures the normal pattern of summer depletion occurring elsewhere in the basin. The seasonal signal in the tropical Pacific Ocean is a function of seasonal variability in the winds, which affect the strength of coastal upwelling.