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1.
Akira Masuda 《Journal of Oceanography》1988,44(4):189-199
A Batchelor-modon eddy is a highly specialized nonlinear vortex pair, whose potential vorticity depends linearly on the stream function viewed from the coordinates moving with the translation velocity of the eddy. To generalize it, a skewed model is developed by introducing a cubic nonlinearity in addition to the linear term. A perturbation analysis shows that the eddy region is no longer a circle but is elongated longitudinally or transversely according as the sign of the cubic term. Moreover, the eddy is slightly flattened or steepened. The cubic term increases or decreases the translation velocity, if the average radius and the amplitude are fixed. A numerical experiment on anf-plane is carried out to show that these skewed eddies retain their initial forms even after they turn a corner of the basin; they are as stable as (first-mode) standard Batchelor-modon eddies. The present skewed model gives a reasonable qualitative interpretation of deformed eddies which result from merging of two eddies or from initially Gaussian eddies near the boundary. 相似文献
2.
建立了一个描述中尺度涡的新的非线性方程,然后利用变分原理研究了孤立涡旋的Liapunov稳定性,指出反气旋和气旋涡都是稳定的。数值计算结果发现在β效应的作用下这些涡旋都向西移动而不存在向南的移动,然而在反气旋涡的上游存在一个孤立地形(例如海山)的话,孤立地形会使反气旋涡向南移动,而且移动的轨迹取决于孤立地形的位置。当两个反气旋涡同时存在并发生相互作用时,上游孤立地形使这两个反气旋涡产生弱合并并出现弱分离。而且孤立地形的位置对这两个涡的移动和旋转有重要影响。 相似文献
3.
Chunjian Sun Xidong Wang Anmin Zhang Lianxin Zhang Caixia Shao Guosong Wang 《海洋学报(英文版)》2022,41(5):27-40
The statistical characteristics and mechanisms of mesoscale eddies in the North Indian Ocean are investigated by adopting multi-sensor satellite data from 1993 to 2019. In the Arabian Sea(AS), seasonal variation of eddy characteristics is remarkable, while the intraseasonal variability caused by planetary waves is crucial in the Bay of Bengal(BOB). Seasonal variation of the eddy kinetic energy(EKE) is distinct along the west boundary of AS,especially in the Somali Current region. In the BOB, lar... 相似文献
4.
采用AVISO提供的中尺度涡最新数据集,分析了孟加拉湾1993—2016年中尺度涡的总体特征和季节变化。结果表明:研究期间在孟加拉湾共有822个气旋涡,731个反气旋涡,主要分布在湾北部(15°N以北海域)和安达曼海。涡旋生命周期以28～59 d为主,平均振幅为7. 5 cm,平均半径为119. 6 km。在纬度变化上,涡旋振幅随纬度的增加有两个峰值,分别位于6°～9°N和15°～20°N之间,而涡旋半径随纬度增加而减少。涡旋的振幅、半径在随生命周期演变过程中生长过程较慢,消散过程较快。气旋涡和反气旋涡主要是向西移动,且均以向赤道方向偏移为主。在季节变化上,孟加拉湾较长生命周期(60 d以上)的中尺度涡具有明显的季节变化,春季生成的涡旋数量最多,冬季次之,夏季最少。通过合成分析得出风应力旋度是孟加拉湾中尺度涡季节变化的主要原因,而沿岸Kelvin波激发的西传Rossby波对涡旋的产生也有一定影响。涡动能分析表明,涡动能的高值区主要位于海盆的西边界和斯里兰卡东部海域,同时,在冬季、春季海盆的西边界和夏季、秋季海盆的北部涡旋活动较多的区域对应着较大的涡动能。 相似文献
5.
《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(24):2460-2473
Eddies in the Gulf of Alaska are important sources of coastal water and associated nutrients, iron, and biota to the high-nutrient, low-chlorophyll central Gulf of Alaska. Three primary eddy formation regions along the eastern boundary of the gulf have been identified, (from south to north, Haida, Sitka, and Yakutat). In the spring of 2005, three eddies (one of each type) were sampled soon after their formation. The subsurface eddy core water in all three eddies was defined by high iron concentrations and low dissolved oxygen compared with surrounding basin water. The Sitka and Yakutat core waters also exhibited a subsurface temperature maximum (mesothermal water) coincident in depth with the iron maximum, suggesting that eddies may play a role in the formation of temperature inversions observed throughout the Gulf of Alaska. The data suggest different formation regions, with the Yakutat eddy forming in shallow shelf water with riverine input, while the Sitka and Haida eddies appear to form in deeper water. 相似文献
6.
Global observations of nonlinear mesoscale eddies 总被引：51，自引：0，他引：51
Sixteen years of sea-surface height (SSH) fields constructed by merging the measurements from two simultaneously operating altimeters are analyzed to investigate mesoscale variability in the global ocean. The prevalence of coherent mesoscale features (referred to here as “eddies”) with radius scales of O(100 km) is readily apparent in these high-resolution SSH fields. An automated procedure for identifying and tracking mesoscale features based on their SSH signatures yields 35,891 eddies with lifetimes ?16 weeks. These long-lived eddies, comprising approximately 1.15 million individual eddy observations, have an average lifetime of 32 weeks and an average propagation distance of 550 km. Their mean amplitude and a speed-based radius scale as defined by the automated procedure are 8 cm and 90 km, respectively.The tracked eddies are found to originate nearly everywhere in the World Ocean, consistent with previous conclusions that virtually all of the World Ocean is baroclinically unstable. Overall, there is a slight preference for cyclonic eddies. However, there is a preference for the eddies with long lifetimes and large propagation distances to be anticyclonic. In the southern hemisphere, the distributions of the amplitudes and rotational speeds of eddies are more skewed toward large values for cyclonic eddies than for anticyclonic eddies. As a result, eddies with amplitudes >10 cm and rotational speeds >20 cm s−1 are preferentially cyclonic in the southern hemisphere. By contrast, there is a slight preference for anticyclonic eddies for nearly all amplitudes and rotational speeds in the northern hemisphere.On average, there is no evidence of anisotropy of these eddies. Their average shape is well represented as Gaussian within the central 2/3 of the eddy, but the implied radius of maximum rotational speed is 64% smaller than the observed radius of maximum speed. In part because of this mismatch between the radii of maximum axial speed in the observations and the Gaussian approximation, a case is made that a quadratic function that is a very close approximation of the mode profile of the eddy (i.e., the most frequently occurring value at each radius) is a better representation of the composite shape of the eddies. This would imply that the relative vorticity is nearly constant within the interiors of most eddies, i.e., the fluid motion consists approximately of solid-body rotation.Perhaps the most significant conclusion of this study is that essentially all of the observed mesoscale features outside of the tropical band 20°S-20°N are nonlinear by the metric U/c, where U is the maximum circum-average geostrophic speed within the eddy interior and c is the translation speed of the eddy. A value of U/c > 1 implies that there is trapped fluid within the eddy interior. Many of the extratropical eddies are highly nonlinear, with 48% having U/c > 5 and 21% having U/c > 10. Even in the tropics, approximately 90% of the observed mesoscale features are nonlinear by this measure.Two other nondimensional parameters also indicate strong degrees of nonlinearity in the tracked eddies. The distributions of all three measures of nonlinearity are more skewed toward large values for cyclonic eddies than for anticyclonic eddies in the southern hemisphere extratropics but the opposite is found in the northern hemisphere extratropics. There is thus a preference for highly nonlinear extratropical eddies to be cyclonic in the southern hemisphere but anticyclonic in the northern hemisphere.Further evidence in support of the interpretation of the observed features as nonlinear eddies is the fact that they propagate nearly due west with small opposing meridional deflections of cyclones and anticyclones (poleward and equatorward, respectively) and with propagation speeds that are nearly equal to the long baroclinic Rossby wave phase speed. These characteristics are consistent with theoretical expectations for large, nonlinear eddies. While there is no apparent dependence of propagation speed on eddy polarity, the eddy speeds relative to the local long Rossby wave phase speeds are found to be about 20% faster in the southern hemisphere than in the northern hemisphere. The distributions of the propagation directions of cyclones and anticyclones are essentially the same, except mirrored about a central azimuth angle of about 1.5° equatorward. This small, but we believe statistically significant, equatorward rotation of the central azimuth may be evidence of the effects of ambient currents (meridional advection or the effects of vertical shear on the potential vorticity gradient vector) on the propagation directions of the eddies.While the results presented here are persuasive evidence that most of the observed westward-propagating SSH variability consists of isolated nonlinear mesoscale eddies, it is shown that the eddy propagation speeds are about 25% slower than the westward propagation speeds of features in the SSH field that have scales larger than those of the tracked eddies. This scale dependence of the propagation speed may be evidence for the existence of dispersion and the presence of features that obey linear Rossby wave dynamics and have larger scales and faster propagation speeds than the nonlinear eddies. The amplitudes of these larger-scale signals are evidently smaller than those of the mesoscale eddy field since they are not easily isolated from the energetic nonlinear eddies. 相似文献
7.
《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(4):487-509
In recent years, large anticyclonic eddies have been observed quasi-annually in the region seaward of Kodiak Island, Alaska. In situ sampling in 3 of these eddies was undertaken in 2002, 2003, and 2004. Satellite altimetry data showed that these 3 eddies had 3 different formation regions but their translation pathways were similar near Kodiak Island. Eddies in this region can persist for several years, moving southwestward along the Alaskan Peninsula to the Aleutian Archipelago. Water properties in the cores of the 2003 and 2004 eddies were significantly different from each other, probably because the 2003 eddy formed on the shelf near Yakutat while the 2004 eddy formed farther out in the basin in the northern Gulf of Alaska. Calculation of heat, salinity, and nutrient anomalies associated with the eddies showed that, in their subsurface core waters, the eddies carry excess heat, salt, nitrate and silicic acid seaward from the eddy formation regions. 相似文献
8.
This study produced a statistical analysis of multicore eddy structures based on 23 years' altimetry data in global oceans. Multicore structures were identified using a threshold-free closed-contour algorithm of sea surface height, which was improved for this study in respect of certain technical details. Meanwhile a more accurate definition of eddy boundary was used to estimate eddy scale. Generally, multicore structures, which have two or more closed eddies of the same polarity within their boundaries, represent an important transitional stage in their lives during which the component eddies might experience splitting or merging. In comparison with global eddies, the lifetimes and propagation distances of multicore eddies were found to be much smaller because of their inherent structural instability. However, at the same latitude, the spatial scale of multicore eddies was found larger than that of single-core eddies, i.e., the eddy area could be at least twice as large. Multicore eddies were found to exhibit some features similar to global eddies. For example, multicore eddies tend to occur in the Antarctic Circumpolar Current, some western boundary currents, and mid-latitude regions around 25°N/S, the majority(70%) of eddies propagate westward while only 30% propagate eastward, and large-amplitude eddies are restricted mainly to reasonably confined regions of highly unstable currents. 相似文献
9.
The continental slope in the northern South China Sea(SCS) is rich in mesoscale eddies which play an important role in transport and retention of nutrients and biota. In this study, we investigate the statistical properties of eddy distributions and propagation in a period of 24 years between 1993 and 2016 by using the altimeter data. A total of 147 eddies are found in the continental slope region(CSR), including 70 cyclonic eddies(CEs) and 77 anticyclonic eddies(ACEs). For those eddies that appear in the CSR, the surrounding areas of Dongsha Islands(DS) and southwest of Taiwan(SWT) are considered as the primary sources, where eddies generated contribute more than 60% of the total. According to the spatial distribution of eddy relative vorticity, eddies are weakening as propagating westward. Although both CEs and ACEs roughly propagate along the slope isobaths, there are discrepancies between CEs and ACEs. The ACEs move slightly faster in the zonal direction, while the CEs tend to cross the isobaths with large bottom depth change. The ACEs generally move further into the basin areas after leaving the CSR while CEs remain around the CSR. The eddy propagation on the continental slope is likely to be associated with mean flow at a certain degree because the eddy trajectories have notable seasonal signals that are consistent with the seasonal cycle of geostrophic current. The results indicate that the eddy translation speed is statistically consistent with geostrophic velocity in both magnitude and direction. 相似文献
10.
The formation of the South China Sea (SCS) deep basin warm-core and cool-core eddies was studied numerically using the Princeton
Ocean Model (POM) with 20 km horizontal resolution and 23 sigma levels conforming to a realistic bottom topography. Numerical
integration was divided into pre-experimental and experimental stages. During the pre-experimental stage, we integrated the
POM model for three years from zero velocity and April temperature and salinity climatological fields with climatological
monthly mean wind stresses, restoring type surface salt and heat fluxes, and observational oceanic inflow/outflow at the open
boundaries. During the experimental stage, we integrated the POM model for another 16 months under three different conditions:
one control and two sensitivity runs (no-wind and no lateral transport). We take the fields of the last 12 months for analysis.
The simulation under control run agrees well with earlier observational studies on the South China Sea surface thermal variabilities.
In addition, the sensitivity study further confirms that the wind effect is the key factor for generation of the SCS deep
basin warm/cool eddy and that the lateral boundary forcing is the major factor for the formation of the strong western boundary
currents, especially along the southeast Chinese coast during both summer and winter monsoon seasons. 相似文献
11.
Eiji Watanabe Michio J. Kishi Akio Ishida Maki Noguchi Aita 《Journal of Oceanography》2012,68(5):703-718
The response of phytoplankton to the Beaufort shelf-break eddies in the western Arctic Ocean is examined using the eddy-resolving coupled sea ice–ocean model including a lower-trophic marine ecosystem formulation. The regional model driven by the reanalysis 2003 atmospheric forcing from March to November captures the major spatial and temporal features of phytoplankton bloom following summertime sea ice retreat in the shallow Chukchi shelf and Barrow Canyon. The shelf-break warm eddies spawned north of the Barrow Canyon initially transport the Chukchi shelf water with high primary productivity toward the Canada Basin interior. In the eddy-developing period, the anti-cyclonic rotational flow along the outer edge of each eddy moving offshore occasionally traps the shelf water. The primary production inside the warm eddies is maintained by internal dynamics in the eddy-maturity period. In particular, the surface central area of an anti-cyclonic eddy acquires adequate light, nutrient, and warm environment for photosynthetic activity partly attributed to turbulent mixing with underlying nutrient-rich water. The simulated biogeochemical properties with the dominance of small-size phytoplankton inside the warm eddies are consistent with the observational findings in the western Arctic Ocean. It is also suggested that the light limitation before autumn sea ice freezing shuts down the primary production in the shelf-break eddies in spite of nutrient recovery. These results indicate that the time lag between the phytoplankton bloom in the shelf region following the summertime sea ice retreat and the eddy generation along the Beaufort shelf break is an important index to determine biological regimes in the Canada Basin. 相似文献
12.
The eddy formation determined as an anticyclonic spin-off eddy of the Gulf Stream is analysed from the CTD data of surveys made in the Gulf Stream region. The differences in its structure and conditions of formation from cyclonic eddies of this type observed previously are examined. Barotropic instability of the Gulf Stream's main jet is considered as a possible reason for such unstable disturbances existing at the south boundary of the Gulf Stream.Translated by M. M. Trufanov. 相似文献
13.
J. G. Bruce 《Geo-Marine Letters》1995,15(3-4):185-194
A considerable amount of the Amazon River water that is discharged into the equatorial Atlantic is then advected northward along the shelf by the strong North Brazil Current (NBC). Being relatively fresh, this water remains in the near-surface layer and can serve as an excellent tracer for the complex and variable flow of the offshore mesoscale eddies. Both surface salinity observations and CZCS (Coastal Zone Color Scanner) imagery can be mapped to estimate the circulation patterns of the eddies. Presented here are two sets of XBT (expendable bathythermograph) sections that give the thermal structure of eddies off the Demerara Rise (6–9°N). They were occupied nearly contemporaneously with CZCS imagery obtained during October 1980 and November 1981. Several studies have shown from ship drift data, from CZCS observations, and from Geosat altimetry that, particularly during late summer and fall, the NBC is found to retroflect offshore to the east, supplying the North Equatorial Counter Current (NECC) and is associated with eddies along the coast. Good agreement is shown between the CZCS and a NAVOCEANO AXBT (airborne bathythermograph) survey during this period as well as observations of surface phytoplankton and geopotential anomaly from an earlier 1964 survey. Estimates of volume transport within the eddy structure indicate that at times the offshore retroflection during spring as well as autumn can amount to 10 × 106 m3 s–1. The pronounced eddy variability off South America is shown by comparing a number of past hydrographic surveys. These suggest that considerable spatial variability can occur as can seasonal changes in volume transport of the NBC and the associated eddy circulation. 相似文献
14.
Seven-year(2005–2011) Synthetic Aperture Radar(SAR) images are applied to study oceanic eddies in the East China Sea. It is found that most of these eddies detected from the SAR images are less than 10 km, which are submesoscale eddies. Seasonal differences are evident in the distribution of eddies, with the highest and the lowest number of eddies noted in summer and winter, respectively. Since slick streaks in SAR images look dark, an eddy identified due to the slicks is referred to as "black eddy". As a result of wave-current interactions in the zones of current shear, it can be seen that an eddy exhibits a bright curve, the eddy is called "white eddy". During the seven years, 95 black eddies and 50 white eddies are identified in the study area. Black eddies are found in the whole study area while white eddies are mainly distributed in the vicinity of the Kuroshio Current. This study suggests that the distribution of the white eddy is denser around the Kuroshio because of the strong shear in the Kuroshio region. In terms of the eddy sizes, white eddies are generally smaller than black eddies. 相似文献
15.
《African Journal of Marine Science》2013,35(3):343-350
This paper describes the westward movement of a cyclonic eddy across the Mozambique Channel and the subsequent south-westward propagation of the eddy along the east coast of South Africa and its interaction with the shelf. A hydrographic survey on 13 September 2006 off Nine-mile Reef (NMR), Sodwana Bay, showed a well-developed Agulhas Current along the continental shelf inshore of a cyclonic eddy flanked by two anti-cyclonic eddies, further offshore. A satellite-tracked drifter and complementary altimetry data confirmed the dimensions of the eddy and tracked its movement towards the coast. Shelf-edge upwelling was measured at NMR by an underwater temperature recorder (UTR) when the cyclonic eddy first came into contact with the shelf and again when the cyclonic eddy interacted with the leading edge of the anti-cyclonic eddy moving onto the shelf. Further shelf–eddy interactions off Aliwal Shoal, south of Durban, and consequent upwelling were similarly caused by the same cyclonic eddy as it progressed south-westward along the east coast. Analysis of UTR data between 2004 and 2006 indicated that between two and five cyclonic eddies impact the shelf off NMR per year. 相似文献
16.
Wenjin Sun Yu Liu Gengxin Chen Wei Tan Xiayan Lin Yuping Guan Changming Dong 《海洋学报(英文版)》2021,40(10):17-29
In general, a mesoscale cyclonic (anticyclonic) eddy has a colder (warmer) core, and it is considered as a cold (warm) eddy. However, recently research found that there are a number of “abnormal” mesoscale cyclonic (anticyclonic) eddies associated with warm (cold) cores in the South China Sea (SCS). These “abnormal” eddies pose a challenge to previous works on eddy detection, characteristic analysis, eddy-induced heat and salt transports, and even on mesoscale eddy dynamics. Based on a 9-year (2000–2008) numerical modelling data, the cyclonic warm-core eddies (CWEs) and anticyclonic cold-core eddies (ACEs) in the SCS are analyzed. This study found that the highest incidence area of the “abnormal” eddies is the northwest of Luzon Strait. In terms of the eddy snapshot counting method, 8 620 CWEs and 9 879 ACEs are detected, accounting for 14.6% and 15.8% of the total eddy number, respectively. The size of the “abnormal” eddies is usually smaller than that of the “normal” eddies, with the radius only around 50 km. In the generation time aspect, they usually appear within the 0.1–0.3 interval in the normalized eddy lifespan. The survival time of CWEs (ACEs) occupies 16.3% (17.1%) of the total eddy lifespan. Based on two case studies, the intrusion of Kuroshio warm water is considered as a key mechanism for the generation of these “abnormal” eddies near the northeastern SCS. 相似文献
17.
两个西边界流延伸体区域中尺度涡统计特征分析 总被引：3，自引：2，他引：1
黑潮和湾流是世界大洋中最典型的两支西边界流，黑潮延伸体（Kuroshio Extention，KE）和湾流延伸体（Gulf Stream Extention，GSE）区域中尺度涡活动十分活跃。本文综合利用卫星高度计资料和Argo浮标资料，对KE和GSE区域中尺度涡的表层特征及其对温盐影响进行了统计研究和对比分析。结果表明:黑潮和湾流主轴附近为涡旋频率的高值区，主轴南北两侧分别以气旋涡和反气旋涡数量占多，主轴附近的涡旋强度明显大于其他区域；两个区域的涡旋以西向移动为主，气旋涡和反气旋涡都具有向南（赤道）偏离的趋势；两个区域的涡旋数量都以夏、秋季较多，涡旋强度都在春、夏季较大，且GSE区域涡旋强度明显大于KE区域；气旋涡（反气旋涡）引起内部明显的温度负（正）异常，KE区域气旋涡（反气旋涡）内部呈"负-正"（"正-负"）上下层相反的盐度异常分布，GSE区域气旋涡（反气旋涡）在各层呈现较为一致的盐度负（正）异常；两个区域中尺度涡对温盐场的平均影响深度可达1 000×104 Pa以上。 相似文献
18.
The HNLC waters of the Gulf of Alaska normally receive too little iron for primary productivity to draw down silicate and nitrate in surface waters, even in spring and summer. Our observations of chlorophyll sensed by SeaWiFS north of 54°N in pelagic waters (>500 m depth) of the gulf found that, on average, more than half of all surface chlorophyll was inside the 4 cm contours of anticyclonic mesoscale eddies (the ratio approaches 80% in spring months), yet these contours enclosed only 10% of the total surface area of pelagic waters in the gulf. Therefore, eddies dominate the chlorophyll and phytoplankton distribution in surface pelagic waters. We outline several eddy processes that enhance primary productivity. Eddies near the continental margin entrain nutrient - (and Fe) - rich and chlorophyll-rich coastal waters into their outer rings, advecting these waters into the basin interior to directly increase phytoplankton populations there. In addition, eddies carry excess nutrients and iron in their core waters into pelagic regions as they propagate away from the continental margin. As these anticyclonic eddies decay, their depressed isopycnals relax upward, injecting nutrients up toward the surface layer. We propose that this transport brings iron and macro-nutrients toward the surface mixed layer, where they are available for wind-forced mixing to bring them to surface. These mesoscale eddies decay slowly, but steadily, perhaps providing a relatively regular upward supply of macro-nutrients and iron toward euphotic layers. They might behave as isolated oases of enhanced marine productivity in an otherwise iron-poor basin. We note that much of this productivity might be near or just below the base of the surface mixed layer, and therefore poorly sampled by colour-sensing satellites. It is possible, then, that eddies enrich phytoplankton populations to a greater extent than noted from satellite surface observations only. 相似文献
19.
Rhines效应是指Rossby波和大湍流（中尺度涡）相互作用,将涡动能量以波的形式传播出去,从而使中尺度涡发生形变,最终消亡的一种动力学机制。本文通过比较海洋里涡特征速度和Rossby长波波速的方法,研究了一种广义的Rhines效应对高度计观测的海洋中尺度涡空间分布特征的影响。结果显示,广义Rhines效应比只考虑行星涡度梯度的传统形式对中尺度涡的分布具有更显著的影响。大部分中尺度涡分布在涡特征速度（Ue）大于由广义Beta值计算的Rossby长波波速（Ucg）的区域。这些涡可以由动能反向串级过程获取能量,成长为振幅和空间尺度较大的涡。热带海域以外的“涡旋沙漠”区域,中尺度涡的数量稀少,强度很弱,大都分布于Uecg的海域。广义Rhines效应可能是这些海域中尺度涡难以成长的动力学机制。 相似文献
20.
Mesoscale eddies off Peru in altimeter records: Identification algorithms and eddy spatio-temporal patterns 总被引：18，自引：1，他引：17
Relatively little is known about coherent vortices in the eastern South-Pacific along the Peruvian coast, even with regard to basic facts about their frequency of occurrence, longevity and structure. This study addresses these issues with nearly 15 years of relatively high-resolution satellite altimetry measurements.We first compare two distinct automated methods for eddy identification. The objective validation protocol shows that the rarely-used geometrical or “winding-angle method”, based on the curvature of the streamline functions, is more accurate than the commonly-used “Okubo–Weiss algorithm”, which defines a vortex as a simple connected region with values of Okubo–Weiss parameter weaker than a given threshold.We then investigate vortices off Peru using more than 20,000 mesoscale eddies identified by the winding-angle method. Coherent eddies, characterized by a high ratio of vorticity to deformation rate, are typically formed along the coast and propagate westward at 3–6 cm s−1. The vortices have a mean radius of 80 km, increasing northward, and are most frequently observed off of Chimbote (9°S) and south of San Juan (15°S). The mean eddy lifetime is about 1 month, but if eddies survive at least 2 months, the probability for surviving an additional week (or month) is constant at 90% (or 67%). Anticyclonic eddies tend to propagate northwestward whereas cyclonic vortices migrate southwestward. In general, cyclones and anticyclones are similar, except for eddies surviving at least 6 months. In this case, after a similar 3–4 months of radius and amplitude growth, amplitudes (or sizes) decay particularly rapidly for anticyclonic (or cyclonic) eddies. In terms of intensity, cyclonic eddies show a rapid decay during the first 3 months before arriving at a quasi-constant value, whereas anticyclones exhibit steady decline. Finally, eddy temporal variations were examined at seasonal and interannual scales in the “coastal” region favorable to the formation of energetic mesoscale structures. On seasonal scales, eddy activity is maximal in fall and minimum in spring. At interannual scales, the eddy activity index was maximal during the strong El Niño of 1997–1998 but another strong maximum of eddy activity also occurred late in 2004. These temporal variations are probably associated with the intensification of the upwelling thermal front and with the passage of coastal-trapped waves which generate baroclinic instabilities. Further investigation of the mechanisms involved on the eddy genesis is needed. 相似文献