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1.
Monthly mesoscale eddy kinetic energy (EKE) per unit mass has been computed for four years, 1993-1996, from TOPEX altimeter data in the Indian Ocean. It ranges from 50 cm2/s2 to 2,700 cm2/s2 (about 4,000 cm2/s2 near the Somali region in a few months). In the Arabian Sea and the Bay of Bengal, regions of high energies associated with various current systems under the influence of monsoonal winds have been delineated. Monthly variation of EKE near the Somali region has been studied. In this region the maximum EKE per unit mass has been observed during August every year, with variations in magnitude from year to year. The mesoscale eddy kinetic energy computed from TOPEX altimeter-derived SSH during 1993-1996 is highest near the Somali region during the SW monsoon, due to formation of mesoscale eddies and also because of upwelling. In the Bay of Bengal, high eddy kinetic energy is seen toward the western side during nonmonsoonal months due to the western boundary current. In the South Indian Ocean, it is high at a few places in some of the months. A large part of the Indian Ocean exhibits low eddy kinetic energy (less than 300 cm2/s2) year-round. 相似文献
2.
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
3.
文章主要使用全球简单海洋资料同化分析系统(Simple Ocean Data Assimilation, SODA)产出的海洋再分析数据产品和美国国家环境预报中心(National Centers for Environmental Prediction, NCEP)发布的风场资料, 通过能量学方法分析了2000—2015年夏季至秋季(6—11月)孟加拉湾涡-流相互作用特征在不同印度洋偶极子(Indian Ocean Dipole, IOD)事件发生年的表现。结果表明, 在IOD负位相年更强的西南季风背景下, 涡动能和涡势能的量值均较大, 海洋不稳定过程更多地将平均流场的能量输向涡旋场, IOD正位相年反之。另外, 研究发现孟加拉湾湾口区的涡动能在个别年份会发展出一种与气候态存在显著异常的空间分布, 即在个别年份湾口中央海域异常出现涡动能极大值。通过对出现该异常现象最显著的2010年进行个例分析, 发现当年的孟加拉湾海表风场发展出一个气旋式环流异常, 显著地改变了海洋上层环流形态, 极大地影响了平均流场与涡旋场之间的相互作用。进一步对维持涡动能平衡的各做功项进行诊断后发现, 湾口异常海域涡动能年际变化的主要影响因素为海洋内部的压强做功, 其次是正压不稳定过程和平流的做功, 海表风应力做功项贡献较小。 相似文献
4.
基于一套涡分辨模式数据,本文利用一种新的泛函工具—多尺度子空间变换—将孟加拉湾（BOB）海域的环流系统分解到背景流（>96 d）、中尺度（24～96 d）和高频尺度（<24 d）3个子空间,并用正则传输理论探讨了3个尺度子空间之间内在的非线性相互作用。结果表明,BOB西北部边界和斯里兰卡岛东部是BOB海域多尺度相互作用最显著的区域,中部则较弱。前两个区域的背景流大多正压、斜压不稳定,动能和有效位能正则传输主要表现为正向级串;后者则以逆尺度动能级串为主。具体来说,在BOB西北部与斯里兰卡东部,中尺度涡动能（EKE）主要来源于正压能量路径（即背景流动能向EKE传输）,其次来源于斜压能量路径（即背景流有效位能向中尺度有效位能传输,并进一步转换为EKE）。通过这两个能量路径得到的EKE向更高频的扰动传输能量,起到了耗散中尺度涡的作用。不同于此二者,BOB中部海域的EKE和高频尺度动能主要通过斜压路径获得,随后通过逆尺度级串将动能返还给背景流。苏门答腊岛的西北部也是中尺度和高频尺度扰动较强的海域,正压能量路径和斜压能量路径均是该海域扰动能的来源,但以斜压能量路径为主。 相似文献
5.
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. 相似文献
6.
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. 相似文献
7.
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
8.
TOPEX altimeter data of 1993 have been analyzed to study the following three types of oceanographic phenomena in the Indian Ocean: (1) sea level variability of the Indian Ocean (20=S to 25=N. 40=E to 100=E): (2) sea surface height signals of the Somali eddy; and (3) sea surface slope variations of the equatorial Indian Ocean (EIO) spanning 5=S to 5=N and 45=E to 95=E. Root‐mean‐square sea level variability revealed the presence of Rossby waves in the southern Indian Ocean. Fast Fourier technique analysis of a few passes near the Somali region is used to study the formation and dissipation of an anticyclonic eddy. 相似文献
9.
Features of eddy kinetic energy and variations of upper circulation in the South China Sea 总被引：8，自引：3，他引：8
The features of eddy kinetic energy (EKE) and the variations of upper circulation in theSouth China Sea (SCS) are discussed in this paper using geostrophic currents estimated from Maps of Sea Level Anomalies of the TOPEX/Poseidon altimetry data. A high EKE center is identified in the southeast of Vietnam coast with the highest energy level 1 400 cm2 ·s~(-2) in both summer and autumn. This high EKE center is caused by the instability of the current axis leaving the coast of Vietnam in summer and the transition of seasonal circulation patterns in autumn. There exists another high EKE region in the northeastern SCS, southwest to Taiwan Island in winter. This high EKE region is generated from the eddy activities caused by the Kuroshio intrusion and accumulates more than one third of the annual EKE, which confirms that the eddies are most active in winter. The transition of upper circulation patterns is also evidenced by the directions of the major axises of velocity variance ellipses between 10°and 14.5°N 相似文献
10.
《Ocean Modelling》2008,20(3):223-239
A turbulence closure for the effect of mesoscale eddies in non-eddy-resolving ocean models is proposed. The closure consists of a prognostic equation for the eddy kinetic energy (EKE) that is integrated as an additional model equation, and a diagnostic relation for an eddy length scale (L), which is given by the minimum of Rhines scale and Rossby radius. Combining EKE and L using a standard mixing length assumption gives a diffusivity (K), corresponding to the thickness diffusivity in the [Gent, P.R., McWilliams, J.C. 1990. Isopycnal mixing in ocean circulation models. J. Phys. Oceanogr. 20, 150–155] parameterisation. Assuming downgradient mixing of potential vorticity with identical diffusivity shows how K is related to horizontal and vertical mixing processes in the horizontal momentum equation, and also enables us to parameterise the source of EKE related to eddy momentum fluxes.The mesoscale eddy closure is evaluated using synthetic data from two different eddy-resolving models covering the North Atlantic Ocean and the Southern Ocean, respectively. The diagnosis shows that the mixing length assumption together with the definition of eddy length scales is valid within certain limitations. Furthermore, implementation of the closure in non-eddy-resolving models of the North Atlantic and the Southern Ocean shows consistently that the closure has skill at reproducing the results of the eddy-resolving model versions in terms of EKE and K. 相似文献
11.
有效重力势能作为重力势能中活跃的部分，能够参与海洋能量循环。本文计算和评估了CMIP5中9个模式的全球大洋2 000 m以上积分的有效重力势能和200～500 m深度范围内的中尺度有效重力势能，并与由BOA_Argo观测数据计算的结果进行比较。分析表明，就全球大洋2 000 m以上积分的有效重力势能而言，多数模式的计算结果均大于由Argo观测数据计算的结果。通过比较有效重力势能的空间分布特征，发现在强动力活跃区（特别是黑潮、湾流、南极绕极流区），模式与观测相差较大，其差别主要来源于观测与模式中扰动密度的差异。此外，在黑潮和南大洋区域，涡动能和有效重力势能具有较高的时间相关性，而在北大西洋湾流区域，两者的相关性较低；功率谱分析显示中尺度有效重力势能与涡动能都存在显著的半年和年变化周期。 相似文献
12.
Based on the latest oceanic surface drifter dataset from the global drifter program during 2000–2019, this study investigated the global variation of relative frequency shift(RFS), near-inertial energy(NIE) and inverse excess bandwidth(IEB) of near-inertial motions, and analyzed their relations with oceanic mesoscale dynamics, relative vorticity and strain. Compared with previous works, we have some new findings in this study:(1) the RFS was high with negative values in some regions in which we found a significant blue shift of the RFS in the equatorward of 30°N(S) and from 50°N to 60°N in the Pacific, and a red shift in the western boundary currents and their extension regions, the North Atlantic and the Antarctic Circumpolar Current regions;(2) more peak values of the NIE were found in global regions like the South Indian Ocean, the Luzon Strait and some areas of the South Ocean;(3) the global distribution of the IEB were characterized by clear zonal bands and affected by vorticity and wind field;(4)the RFS was elevated as the absolute value of the gradient of vorticity increased, the IEB did not depend on the gradient of vorticity, and the eddy kinetic energy(EKE) weakened with the decrease of the absolute value of RFS;(5) the NIE decreased with increasing absolute value of the relative vorticity and the gradient of vorticity, but it increased with increasing strain and EKE when EKE was larger than 0.003 2 m~2/s~2. 相似文献
13.
Vinu Valsala 《Journal of Oceanography》2009,65(6):803-816
The spreading pathways of the Somali and Arabian coastal upwelled waters in the northern Indian Ocean are identified from
an ocean re-analysis data set of a single year using numerical passive tracers in a transport model. The Somali and Arabian
coastal upwelled waters are found to have entirely different spreading pathways in the northern Indian ocean. The former circulates
anticyclonically, is mixed vertically, and is advected to the eastern Indian Ocean along the north equatorial region; while
the later intrudes into the northern Arabian Sea, circulates anticyclonically and is advected to the south in the central
Arabian Sea and then to the eastern Indian Ocean. The seasonal surface mixing by strong monsoon winds and sheared currents
due to dominant eddies of the Somali region are found responsible for mixing 25% of Somali upwelled water with the subsurface
and affecting the resultant pathways. The effect of mixing is, however, found negligible in the case of Arabian coastal upwelled
water pathways. The seasonal reversal of circulation and eddy dominance during the southwest monsoon cause the Somali upwelled
water to spread over the northern Indian Ocean faster than the simultaneously upwelled Arabian coastal water. 相似文献
14.
The statistical characteristics and vertical thermohaline properties of mesoscale eddies in the Bay of Bengal are studied from the view of satellite altimetry data and Argo profiles. Eddy propagation preferences in different lifetimes, eddy evolution process, and geographical distribution of eddy kinetic properties are analyzed in this area. Eddies exist principally in the western Bay of Bengal, and most of them propagate westward. There is a clear southward(equatorward) preference for eddies with long lifetimes, especially for cyclones. Moreover, the eddies in different areas of the bay show different north-southward preferences. Evolution of eddy kinetic properties with lifetime shows that eddies have the significant three-stage feature: the growth period in the former one-fifth lifetime, the stable period in the middle two-fifth to four-fifth lifetime, and the dying period in the last one-fifth lifetime. Large-amplitude and high-intensity eddies occur only in the relatively confined regions of highly unstable currents, such as the East Indian Coastal Current and eastern Sri Lanka. Based on Argo profile data and climatology data, the eddy synthesis method was used to construct three-dimensional temperature and salt structures of eddies in this area. The mean temperature anomaly is negative/positive to the cyclonic/anticyclonic eddies in the upper 300×10~4 Pa, and below this depth, the anomaly becomes weak. The salinity structures of positive anomalies inside cyclonic eddies and negative anomalies inside anticyclonic eddies in the Bay of Bengal are not consistent with other regions. Due to the special characteristics of the water mass in the bay, especially under the control of the low-salinity Bay of Bengal water at the surface and the Indian equatorial water in the deep ocean, the salinity of seawater shows a monotonic increase with depth. For regional varieties of temperature and salinity structures, as the eddies move westward, the temperature anomaly induced by the eddies increases, the effecting depth of the eddies deepens, and the salinity structures are more affected by inflows. In the north-south direction, the salinity structures of the eddies are associated with the local water masses, which comprise lowsalinity water in the northern bay due to the inflow of freshwater from rivers and salty water in the southern bay due to the invasion of Arabian Sea high-salinity water from the north Indian Ocean. 相似文献
15.
The North Indian Ocean exhibits profound impact of variation in lower tropospheric winds. In the present study climatological monthly winds are used to force a nonlinear reduced gravity model of the North Indian Ocean to simulate climatological surface circulation and sea level anomaly for all 12 months of the year. The sea level anomalies agree reasonably well with satellite altimeter derived sea level anomalies. The model successfully simulates the varying eddy structure and current pattern of the North Indian Ocean. Finally, the kinetic energy variation in the North Indian Ocean with special reference to equatorial region and the boundaries is analyzed in detail. 相似文献
16.
The North Indian Ocean exhibits profound impact of variation in lower tropospheric winds. In the present study climatological monthly winds are used to force a nonlinear reduced gravity model of the North Indian Ocean to simulate climatological surface circulation and sea level anomaly for all 12 months of the year. The sea level anomalies agree reasonably well with satellite altimeter derived sea level anomalies. The model successfully simulates the varying eddy structure and current pattern of the North Indian Ocean. Finally, the kinetic energy variation in the North Indian Ocean with special reference to equatorial region and the boundaries is analyzed in detail. 相似文献
17.
Seasonal variation of eddy kinetic energy in the South China Sea 总被引：4，自引：0，他引：4
Mesoscale eddy activity and its modulation mechanism in the South China Sea (SCS) are investigated with newly reprocessed satellite altimetry observations and hydrographic data.The eddy kinetic energy ... 相似文献
18.
南大洋太平洋扇区中尺度涡旋的统计特性及其变化 总被引：1，自引：0，他引：1
中尺度涡旋在南大洋海洋动力学中具有重要地位,其对气候变化的响应表现也引起了海洋学家与气候学家的广泛关注。本文利用涡动动能与涡旋自动探测技术两种方法对南大洋太平洋扇区的涡旋特性及其变化进行了分析。与前人结果相一致的是,高值的涡动动能主要集中在南极极锋海区,并且自西向东逐渐减弱。在过去的20年里,涡动动能在太平洋扇区的显著增强也集中在中西部海域,这里也是南极绕极流斜压性较强的海域。涡旋统计特性揭示了涡动动能的空间分布及其年际变化主要归因于涡旋振幅与旋转速度,而并非涡旋个数或者涡旋半径。这些结果进一步确认了对应于南半球环状模正位相的绕极西风异常改变了南大洋的涡旋特性,从而表现出涡旋活跃性增强。 相似文献
19.
A statistical analysis of mesoscale eddies in the Bay of Bengal from 22–year altimetry data 总被引：4，自引：1，他引：3
本文使用一种基于SLA数据的涡旋识别方法,通过22年的AVISO高度计测高数据对孟加拉湾的中尺度涡特征进行了研究。本文主要分析了孟加拉湾涡旋的地理分布、涡旋极性、涡旋生命周期和传播距离、涡旋产生和消失位置、涡旋传播方向和移动轨迹、涡旋运动特征、涡旋属性的演化以及涡旋活动的季节和年际变化等特性。涡旋主要分布在孟加拉湾西部海域,并且大部分涡旋向西移动。涡旋极性分布显示气旋涡更经常出现在湾的西北部和南部,而反气旋涡主要出现在湾的东部。在22年间,共追踪探测到生命周期超过30天的气旋涡565个、反气旋涡389个;对所有生命周期和传播距离而言都是气旋涡数量居多。所有观测到的涡旋的运动属性分析显示气旋涡的涡旋平均振幅大于反气旋涡;对平均半径和平均移动速度而言,气旋涡和反气旋涡相差不大。而且,涡旋属性演化显示生命周期超过90天的涡旋具有明显的双阶段演化特征,包括一个前50天的涡旋成长阶段和一个50天之后的涡旋消亡阶段。针对涡旋活动的季节变化,气旋涡在春季居多而反气旋涡在夏季较多;长生命周期的涡旋季节分布显示在孟加拉湾涡旋活动具有明显的季节分布特征。涡旋数量的年际变化与EKE变化有一个明显的负相关。 相似文献
20.
南黄海涡动能及其谱特征的季节性变化 总被引：1，自引：0，他引：1
为进一步了解南黄海涡动能的季节变化特点,本文利用气候态月平均数据分析了南黄海涡动场的季节变化规律,并通过计算动能通量谱探讨了相关的变化机制。结果显示,南黄海涡动能在季节变化尺度上存在双峰结构,9月和1月各存在一个峰值,9月峰值较大,1月峰值较小。而且,上半年南黄海存在的涡主要为经向伸长,下半年主要为纬向伸长。动能通量谱的计算结果显示,9月存在的涡动能峰值主要是斜压不稳定过程直接作用的结果,而1月的峰值主要与涡涡相互作用相关。本文从一个新的角度(涡动能)对南黄海进行了探究,有利于加深人们对该海域海水动力机制的认识。 相似文献