混合坐标模式HYCOM模拟COADS强迫下的南海平均环流

采用混合坐标模式(HYCOM)模拟南海环流,同时利用海表温度卫星资料和吕宋海峡Sb-ADCP观测海流数据来评估模式结果.地形敏感性实验表明,吕宋海峡地形数据对模拟黑潮入侵方式影响较大,在地形误差较大的情况下,模拟的黑潮可能以反气旋流套方式入侵.和Pathfinder海表温度卫星资料比较,模式输出的月平均温度在海盆区域误差较小.ERA-15资料强迫所模拟的吕宋海峡上层环流和Sb-ADCP观测一致,而COADS结果低估了吕宋海峡的体积输送.     

潮汐对吕宋海峡附近海域环流结构的影响

为了考察潮汐混合效应对吕宋海峡附近海域环流场的影响,本文使用ROMS区域海洋模式,通过无潮实验与有潮实验的对比分析指出,潮汐混合作用可以影响121°E断面上的水交换和120d平均的纬向流速分布;在模拟时段内加入潮汐后,模拟结果中台湾岛西南的反气旋涡强度大幅减弱,贴近黑潮东侧的涡旋强度明显强于无潮实验,证明潮汐作用可以引起吕宋海峡海洋环流场较大的改变,特别对黑潮以"跨隙"路径通过吕宋海峡有贡献。     

理想台风驱动的涡旋对吕宋海峡黑潮影响的数值研究*

吕宋海峡以东即北太平洋热带地区常年存在着大量的涡旋,这些涡旋在向西运动的过程中遇到吕宋海峡黑潮后是否会穿越黑潮进入南海值得研究。文章用数值模式来模拟吕宋海峡的黑潮以及吕宋海峡以东的众多涡旋,结果表明没有一个涡旋可以穿越吕宋海峡进入南海。在此基础上引入了一个理想台风风场,通过风应力旋度的形式驱动出强劲的气旋式和反气旋式涡旋,这两个涡旋分别添加在源区黑潮附近,也是在源区黑潮流量最小的8月。以往研究表明,黑潮流量小而涡旋强劲的时候涡旋容易穿越吕宋海峡进入南海,但由何种原因产生的涡旋可以穿越吕宋海峡难以确定;而文章的数值计算结果表明,即使在黑潮较弱的夏季8月,由风应力旋度产生的中尺度涡,无论是气旋式还是反气旋式,都受到了吕宋海峡的阻挡而难以穿越。     

涡分辨率海洋模式及其海气耦合模式中吕宋海峡处的黑潮入侵

比较了准全球涡分辨率海洋模式（简记为LICOMH）及其海气耦合模式（简记为LICOMHC）中的黑潮入侵南海与观测中黑潮入侵的差异。我们发现在单独海洋模式中黑潮入侵与观测相比过强，而在其海气耦合模式中这一差异得到了改善。冬季的吕宋海峡输送（LST）在LICOMH中为-8.8×10⁶ m³s^-1，而在LICOMHC中则下降到-6.0×10⁶ m³s^-1 。进一步的研究表明是大尺度风场，局地风应力和吕宋海峡以东中尺度涡旋的共同作用导致了黑潮入侵在两个模式中的不同。LICOMH中吕宋岛东北部相对较强的气旋导致了较弱的黑潮输送及吕宋海峡处较强的黑潮入侵。以上三者共同作用造成的LST差异大约是2.0×10⁶ m³s^-1，与两个模式间的LST差异大小基本相当。进一步对LICOMH与LICOMHC中的EKE收支进行分析表明，LICOMH中更强的EKE输送及斜压转换项导致了黑潮以东存在更强的气旋，而海表风场对两个模式中的涡旋差异贡献极小。     

台湾以东中尺度涡对黑潮入侵东海路径的影响

利用AVISO数据集的卫星高度计资料,分析了中国台湾以东中尺度涡的时空特征,通过具体的中尺度涡实例探讨了其对台湾以东黑潮路径的影响。研究表明气旋式中尺度涡在春夏季节的数目要少于反气旋式中尺度涡,在秋冬季节气旋式涡旋个数则多于反气旋涡;并且台东以东区域涡旋传播存在多种路径,涡旋的存在对台湾东北部黑潮入侵东海的路径具有重大影响,特别是2004年夏季台湾以东区域存在多个涡旋,相应的吕宋海峡黑潮主轴向东偏移明显,台湾东北黑潮入侵东海的路径发生了显著变化。     

利用Argos浮标资料对黑潮入侵南海问题的分析

通过对Argos浮标资料的分析,针对黑潮能否在吕宋海峡入侵南海的问题进行了研究,结果表明:黑潮由吕宋海峡入侵南海主要发生在秋、冬两季,春、夏季基本上不发生。而入侵主要是以流的形式传入,秋季少量的入侵水会有分支沿台湾海峡北上,冬季黑潮自吕宋海峡入侵南海后向西进入南海腹部。并对其季节变化原因作了初步讨论,该区域风应力和黑潮流量的季节性变化可能是重要原因。     

吕宋海峡水交换季节和年际变化特征的数值模拟研究

利用ROMS(Regional Ocean Modeling System)建立了一套覆盖西北太平洋的涡尺度分辨率环流模型,并对吕宋海峡附近的环流进行了模拟研究。结果表明,吕宋海峡120.75°E断面净流量季节变化显著,全年均为西向输运,6月份达到最小,为0.40×106 m3/s,然后逐渐增大,在12月份达到最大,为6.14×106 m3/s,全年平均流量为3.04×106 m3/s。在500 m以浅,秋、冬季都有明显的黑潮流套存在,并伴有黑潮分支入侵南海,而春、夏季黑潮南海分支减弱或消失,黑潮入侵不明显。在500 m以深,冬、春季,吕宋海峡以东有非常明显的南向流存在,流速约10 cm/s,而到了夏、秋季该南向流出现明显的减弱,黑潮与南海的水交换主要通过吕宋海峡以北的吕宋海沟进行。在垂向结构上,120.75°E断面浅层呈多流核结构,并且流核的位置和强弱受黑潮的季节性变化影响显著,深层流的季节变化不大。在年际尺度方面,吕宋海峡年际体积输运量异常与Niño3.4滞后6个月相关系数达到41.6%,吕宋海峡水交换与ENSO现象有较为显著的正相关关系,并存在2~3 a和准8 a周期的年际变化。     

热带气旋过境期间黑潮流轴变化的初步分析

利用卫星高度计资料分析了热带气旋"艾碧"(Abe,9315)、"贝姬"(Becky,9316)、"莫拉克"(Morakot,0309)和"茉莉"(Melor,0319)对吕宋海峡及其附近海域黑潮流轴的影响。研究表明:1)吕宋海峡附近海域黑潮流轴容易受到热带气旋的影响而发生一定的变化。2)在热带气旋的作用下,黑潮流轴因中尺度涡的变异而变化;当吕宋海峡东侧的暖涡西移时,将使黑潮的流轴向西弯曲,有利于黑潮在该处的入侵。     

基于海洋模式数据的吕宋海峡输运量和菲律宾黑潮流量关系的分析

利用全球涡分辨率海洋环流模式OFES的60年(1950—2009)输出资料,用流速资料计算了吕宋岛东侧18°N断面黑潮上游流量(Kuroshio Transport,KT)和120.5°E断面吕宋海峡输运量(Luzon Strait Transport,LST)。研究表明,KT和LST存在四种情况,即:(1)KT大LST小、(2)KT大LST大、(3)KT小LST小和(4)KT小LST大,分别占其总数的34%、11%、13%、42%。合成分析证实:一般情况下,KT大对应黑潮跨越吕宋海峡流态,此时LST较小;KT小时,地转β效应迫使黑潮向西入侵吕宋海峡,此时LST大。然而,吕宋岛东侧和台湾东南沿岸的涡旋常削弱黑潮在吕宋海峡处流量,造成KT大时黑潮亦入侵吕宋海峡,从而出现KT大LST大的情形;太平洋一侧的异常高海表高度诱发吕宋海峡处强地转流,造成KT虽小而黑潮在吕宋海峡处仍是跨越流态,因而LST小。结果表明,LST不仅受KT影响,亦受局地涡旋和海表高度的重要控制。     

吕宋海峡流场季节变化的数值模拟

基于海洋模式HYCOM(Hybrid Coordinate Ocean Model),利用大小区嵌套技术,分别对全球海洋和西北太平洋进行了网格嵌套数值模拟,研究了吕宋海峡海域环流场的季节性变化。考虑全球海洋环流影响的西北太平洋模式,成功地刻画了黑潮的流结构及季节变化。吕宋海峡海洋环流流场在不同深度处差异较大,存在着明显的季节变化。黑潮入侵南海主要发生在500m深度以上,冬季最明显,夏秋两季不明显。在500m层常年存在一支南海暖流流入西北太平洋,在800m层南海暖流消失。一年四季黑潮主要通过吕宋海峡的南部和中部进入南海。1 000m层流场表明,黑潮主要通过吕宋海峡的中部入侵南海。在800~1 000m处主要是黑潮水流入南海。     

Seasonal characteristics of the near-surface circulation in the northern South China Sea obtained from satellite-tracked drifters

The surface circulation of northern South China Sea (hereafter SCS) for the period 1987–2005 was studied using the data of more than 500 satellite-tracked drifters and wind data from QuikSCAT. The mean flow directions in the northern SCS except the Luzon Strait (hereafter LS) during the periods October~March was southwestward, and April~September northeastward. A strong northwestward intrusion of the Kuroshio through the LS appears during the October~March period of northeasterly wind, but the intrusion became weak between April and September. When the strong intrusion occurred, the eddy kinetic energy (EKE) in the LS was 388 cm²/s² which was almost 2 times higher than that during the weak-intrusion season. The volume transport of the Kuroshio in the east of the Philippines shows an inverse relationship to that of the LS. There is a six-month phase shift between the two seasonal phenomena. The volume transport in the east of the Philippines shows its peak sis-month earlier faster than that of the LS. The strong Kuroshio intrusion is found to be also related to the seasonal variation of the wind stress curl generated by the northeasterly wind. The negative wind stress curl in the northern part of LS induces an anticyclonic flow, while the positive wind stress curl in the southern part of LS induces a cyclonic flow. The northwestward Kuroshio intrusion in the northern part of LS happened with larger negative wind stress curl, while the westward intrusion along 20.5°N in the center of the LS occurred with weaker negative wind stress curl.     

Features of eddy kinetic energy and variations of upper circulation in the South China Sea

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     

Seasonal variation of eddy kinetic energy in the South China Sea

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 ...     

南海环流的一个约化模式

利用约化数值模式研究了黑潮在巴士海峡的流况及受其影响的南海海盆区的环流,结果为:定常的黑潮入流在巴士海峡不易出现显著的环状流动结构,但在海峡西侧诱生一气旋涡,该涡旋达到一定强度时,β因子和侧边界作用使其向西南移动,因此,模式给出的南海环流呈准半年周期的气旋涡现象。动力分析表明,气旋涡因非线性平流作用将黑潮西侧的气旋性切变涡度向南海北部输送所致。模式同时计算了入流方向和流轴位置呈周期性变化时,巴士海峡和南海的流动结构。     

Statistical characteristics and mechanisms of mesoscale eddies in the North Indian Ocean

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...     

Satellite altimeter observations of nonlinear Rossby eddy–Kuroshio interaction at the Luzon Strait

Satellite altimeter sea level data from 1993 to 2008 are used to analyze the interaction of nonlinear Rossby eddies with the Kuroshio at the Luzon Strait (LS). The sea level anomaly data show that the west Pacific (WP) is a source of nonlinear Rossby eddies, and the South China Sea (SCS) is a sink. The LS serves as a gateway between the two. The scale analysis indicates that eddies with a radius larger than 150 km are strong enough to significantly alter the Kuroshio and are able to modify the local circulation pattern. Statistical analysis indicates that the probability for eddies to penetrate through the Kuroshio may reach at least 60%. A case study of an anticyclonic mesoscale eddy passing through the LS in June–July 2004 indicates that the Kuroshio behaves as an unsteady flow with its stream path frequently modified, in a way of cutting off, meandering and branching during its interaction with the eddy. We therefore suggest that nonlinear Rossby eddies may play a significant role in modification of the local circulation system near the LS and in exchanges of the mass, momentum and energy between the WP and the SCS.     

南黄海涡动能及其谱特征的季节性变化

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。     

中国近海及其附近海域若干涡旋研究综述 Ⅰ.南海和台湾以东海域

综述了南海和台湾以东海域若干气旋型和反气旋型涡旋研究.在南海存在着许多活跃的中尺度涡,我们分别对南海中、南部海域和南海北部海域中尺度涡作了评述.在南海北部海域,目前最感兴趣的问题为:南海水与西菲律宾海通过吕宋海峡的交换的物理过程,以及黑潮是否以反气旋流套形式进入南海.这些问题目前尚不清楚,尤其是这些问题的机理.这些问题必须通过今后深入和细致的、长时间的海流和水文观测,以及长时间卫星遥感观测资料的论证才能逐渐认识清楚.台湾以东海域,黑潮两侧经常出现中尺度涡,而且变化较大而复杂.文中着重讨论兰屿冷涡和台湾东北的气旋式冷涡.     

Variations of eddy kinetic energy in the South China Sea

Fifteen years of merged altimetric data were used to acquire the seasonal to interanual variations of eddy kinetic energy (EKE) in the South China Sea (SCS). The results show that climatological mean EKE in the SCS ranges from 50 cm²/s² to 1,400 cm²/s², with high values in the regions southeast of Vietnam and southwest of Taiwan Island. The amplitude of the annual harmonic of the EKE is characterized by high values to the southeast of Vietnam where the maximum exceeds 800 cm²/s². The EKE in the northern SCS reaches its maximum in August-February, while it peaks in September–December in the southern SCS. Besides the seasonal variation, the EKE also shows strong interannual variation, which has a negative (positive) anomaly in boreal winter during El Niño (La Niña) events. The interannual variation of local wind stress curl associated with El Niño-Southern Oscillation events may be the cause of the interannual variation of the EKE in the SCS.