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1.
A high-resolution ocean general circulation model （OGCM） is used to investigate the Kuroshio path variations south of Japan. The model reproduces many important features of the Kuroshio system including its interannual bimodal variability south of Japan. A decreasing trend of the spatial averaged relative vorticity is detected when the Kuroshio takes the non-large meander （NLM） path, and during the transition period from the NLM to the large meander （LM）, a sudden release of velocity shear corresponds well to the weakening of the Shikoku recirculation gyre （SRG）, which plays a key role in modulating the Kuroshio path variations. Analysis of eddy energetics indicates that baroclinic instability is mainly responsible for the formation of the LM. In addition, further analysis shows that the strength of the SRG could be largely influenced by the baroclinic Rossby wave adjustment process, forced by the wind stress curl anomalies in the North Pacific basin, based on the model investigation. It is suggested that the cyclonic disturbances might account for the weakening of the SRG, and act as a remote trigger for the baroclinic instability of the Kuroshio south of Japan. 相似文献
2.
Hiroyuki Tsujino Shiro Nishikawa Kei Sakamoto Norihisa Usui Hideyuki Nakano Goro Yamanaka 《Climate Dynamics》2013,41(9-10):2287-2318
The effects of large-scale wind forcing on the bimodality of the Kuroshio path south of Japan, the large meander (LM) and non-large meander (NLM), were studied by using a historical simulation (1948–2007) with a high-resolution Ocean general circulation models (OGCM). The Kuroshio in this simulation spent much time in the NLM state, and reproduced several aspects of its long-term path variability for the first time in historical OGCM simulation, presumably because the eddy kinetic energy was kept at a moderate level. By using the simulated fields, the relationships between wind forcing (or Kuroshio transport) and path variation proposed by past studies were tested, and specific roles of eddies in those variations were investigated. The long-term variation of the simulated net Kuroshio transport south of Japan was largely explained by the linear baroclinic Rossby wave adjustment to wind forcing. In the simulated LM events, a triggering meander originated from the interaction of a wind-induced positive sea surface height (SSH) anomaly with the upstream Kuroshio and was enlarged by cyclonic eddies from the recirculation gyre. The cyclonic eddy of the trigger meander was followed by a sizable anticyclonic eddy on the upstream side. Subsequently, a weak (strong) Kuroshio favored the LM (NLM). The LM tended to be maintained when the Kuroshio transport off southern Japan was small, and increasing Kuroshio transport promoted decay of an existing LM. The supply of disturbances from upstream, which is related to the wind-induced SSH variability at low latitudes, contributed to the maintenance of an existing LM. 相似文献
3.
The formation of the Kuroshio large meander in summer 2004 was investigated by using the cruise data,Argo profiles data,and satellite remote sensing data.The authors validated the point that cyclonic eddies contrib-uted to the large meander.Besides,.the impacts of ty-phoons on Kuroshio meanders were also studied.From 29 July to 4 August,the typhoons stirred the ocean and up-welled the deep water,which enhanced the existed cyc-lonic eddy,and immediately made a drastic meander of the Kuroshio.Moreover,the unexpected typhoons in June 2004 also contributed to the initial meander at the Tokara Strait.The result suggests an alternative meander mecha-nism of the Kuroshio path via the typhoon-eddy-Kuroshio interactions.It is argued that typhoons accompanied with cyclonic eddies,might play crucial roles in meanders of the Kuroshio.This will provide a more comprehensive understanding of the dynamics of the western boundary flows,like the Kuroshio and the Gulf Stream,and will be useful in eddy-resolution models. 相似文献
4.
黑潮延伸体中尺度涡年代际变化与北太平洋风暴轴变化之间的关系 总被引：5，自引：1，他引：4
利用18年带通滤波的卫星高度计资料,通过引入黑潮延伸体中尺度涡能量(EKE)的面积指数,分析了黑潮延伸体中尺度涡EKE的强度和位置的年代际变化特征,并使用回归分析等方法分析了它们与北太平洋风暴轴之间的关系。结果表明,黑潮延伸体中尺度涡增强与北太平洋风暴轴的增强相对应,而EKE位置偏北(南)时对应的北太平洋风暴轴也偏北(南),同时当EKE的位置偏东(偏西)时北太平洋风暴轴则西退(东移)。此外,北太平洋风暴轴的变化对黑潮延伸体也可能有一定的反馈作用,黑潮延伸体中尺度涡EKE强度的变化与北太平洋风暴轴EOF第一和第三个模态(第二个模态)回归的海表面高度距平模态有明显的3~4年滞后的正(负)相关,而黑潮延伸体中尺度涡EKE位置的变化则相反。这种滞后相关可能是通过北太平洋风暴轴驱动的遥相关型环流改变海表面风应力旋度并强迫出的海表面高度距平的西传导致的。 相似文献
5.
Masafumi Kamachi Tsurane Kuragano Noriya Yoshiok Jiang Zhu Francesco Uboldi 《大气科学进展》2001,18(5):767-786
l. IntroductionLinear dynamics ls domlnant as a response to atmospheric forcing in the equatrialregion. In the mid-- to high--latitudes, ocean represents nonlinear phenomena such as strongcurrents and meso--scale eddies. Heat and water fluxes are also important. The resultantscales of the phenomena are rather small. We developed, for the mid-- to high--latitudes, anocean data assimilation system COMPASS--K: Comprehensive Ocean ModeIing, Prediction,Analysis and Synthesis System in the K… 相似文献
6.
北半球阻塞高压的维持Ⅰ:准地转和Ertel位涡分析 总被引：2，自引：3，他引：2
从北半球不同地区的４个阻塞高压个例，研究了阻塞高压维持机制及其地域性差异。对阻塞高压区域３００ｈＰａ时间平均准地转让涡低值区的维持机制的分析表明，该位涡低值区的维持机制存在显著的地域性差异。其中，在２个太平洋阻高个例中，时间平均流的位涡平流使低位涡向阻高西北部输送，从而有利于位涡低值区经向度的维持；时变扰动的位涡输送则有抵消平均流作用的倾向，从而对位涡低值区的维持起耗散作用。在大西洋和东亚阻高个例中，平均流的位涡平流使低位涡区向东移动，而时变扰动的位涡输送则有抵消平均流位涡平流的作用，从而有利于位涡低值区在原地稳定维持。以上主要是相对涡度输送的差异所致。等熵面Ｅｒｔｅｌ位涡分析表明，阻高区域３３０Ｋ时间平均等熵位涡低值区的维持机制与３００ｈＰａ时间平均准地转位涡低值区的维持机制十分相似，从而表明以上等压面准地转位涡分析可以近似用来代表等熵Ｅｒｔｅｌ位涡分析。 相似文献
7.
Eight-year daily mean output of a quasi-global eddy-resolving model is examined with a focus on the large-scale dynamical characteristics of the North Atlantic Ocean in a framework of potential vorticity (PV) and its derivatives. The model has reproduced some of the observed features of the mean potential vorticity field well. The three-dimensional structure of the mean potential vorticity supports baroclinic instability in most of the basin. Eddies are found to play important roles in the formation and maintenance of the mean potential vorticity fields. The contribution of relative vorticity to the mean potential vorticity field is found to be negligible for the most part. However, relative vorticity contribution to the source/sink of potential vorticity and eddy potential enstrophy is not negligible. We also find that eddies are not necessarily diffusive even on a basin-scale. 相似文献
8.
A mechanism for the generation of intrathermocline eddies (ITEs) at wind-forced fronts is examined using a high resolution numerical simulation. Favorable conditions for ITE formation result at fronts forced by “down-front” winds, i.e. winds blowing in the direction of the frontal jet. Down-front winds exert frictional forces that reduce the potential vorticity (PV) within the surface boundary in the frontal outcrop, providing a source for the low-PV water that is the materia prima of ITEs. Meandering of the front drives vertical motions that subduct the low-PV water into the pycnocline, pooling it into the coherent anticyclonic vortex of a submesoscale ITE. As the fluid is subducted along the outcropping frontal isopycnal, the low-PV water, which at the surface is associated with strongly baroclinic flow, re-expresses itself as water with nearly zero absolute vorticity. This generation of strong anticyclonic vorticity results from the tilting of the horizontal vorticity of the frontal jet, not from vortex squashing. During the formation of the ITE, high-PV water from the pycnocline is upwelled alongside the subducting low-PV surface water. The positive correlation between the ITE’s velocity and PV fields results in an upward, along-isopycnal eddy PV flux that scales with the surface frictional PV flux driven by the wind. The relationship between the eddy and wind-induced frictional PV flux is nonlocal in time, as the eddy PV flux persists long after the wind forcing is shut off. The ITE’s PV flux affects the large-scale flow by driving an eddy-induced transport or bolus velocity down the outcropping isopycnal layer with a magnitude that scales with the Ekman velocity. 相似文献
9.
北半球阻塞高压的维持Ⅱ:瞬变扰动强迫和平均流位涡平流的形成 总被引：4，自引：2，他引：4
着重探讨大西洋阻高和东亚阻高个例中瞬变扰动位涡（涡度）输送强迫和太平洋阻高中平均流位涡平流的形成机理。结果表明，扰动在阻高西南部西风分流区因形变而产生的扰动拟能向更小尺度串级过程，并不是扰动位涡输送强迫形成的必要机理。扰－流相互作用在阻高西（北）部非分流气流中也十分显著。数值试验表明，这一相互作用也可能是扰动强迫作用形成的机理。而青藏高原和附近海陆对比的强迫作用则可能是太平洋阻高中平均流的位涡平流形成的重要因素。对比分析表明，阻高维持机制的地域性差别可能与其上游（如青藏高原地区、落基山脉）地形和热源强迫作用不同有关。 相似文献
10.
11.
The local budget of eddy kinetic energy (EKE) for both high-frequency (HF, 2–6 days) and intermediate-frequency (IF, 7–29 days) eddies are evaluated for Northern Hemisphere boreal winter using the 31-year (1979/80–2010/11) NCEP-DOE reanalysis. A new form of EKE equation is used to isolate the kinetic energy generation/destruction due to interactions among eddies of different timescales. The main source of HF EKE is baroclinic conversion that is concentrated in the mid-lower troposphere. Barotropic conversion mainly damps HF EKE and shows positive contributions to IF EKE on the northern flank of the winter-mean tropospheric jet. Interaction between HF and IF eddies acts as a sink for HF EKE and a main source for IF EKE, especially over the eastern ocean basins, confirming the substantial role of synoptic-scale transients in the development of IF phenomena such as atmospheric blocking. Large interannual variability is found for various EKE budget terms. The HF EKE response to El Niño is characterized by a dipole (tri-pole) anomaly over the North Pacific (North Atlantic). Baroclinic conversion is the main driver of the observed changes in HF EKE while barotropic conversion, interaction between HF and IF eddies, and energy flux convergence all play non-negligible roles in determining the final meridional structure of the HF EKE anomalies. Associated with El Niño, IF EKE generally decreases over the North Pacific and increases over the North Atlantic, which mainly result from changes in baroclinic conversion and EKE conversion due to eddy–eddy interactions. The latter is dominated by interaction between IF and LF (low-frequency, 30–90 days) eddies over the North Pacific, and by interactions between HF and IF eddies, and between IF and LF eddies over the North Atlantic. 相似文献
12.
河北中南部一次大暴雨个例的成因诊断 总被引：1，自引：0，他引：1
利用NCEP 1°×1°再分析资料和常规资料,分析了一次河北中南部罕见短时特大暴雨的环流背景,计算了暴雨发生过程的干位涡、湿位涡值以及暴雨区域垂直螺旋度的大小.然后利用这些物理量从动力、热力学方面对河北暴雨进行综合分析.结果发现:500 hPa干位涡正压项能较好地表征冷空气和辐合区的强度和移动方向,斜压项负值由小到大引发降水强度的增加,斜压项负值的减小预示着降水的减弱.在此暴雨个例中,强对流发生区域与湿位涡异常的移动方向有较好的相关性,强对流出现在湿位涡移动方向前部的等值线密集区,且短时暴雨靠近零线一侧.正MPV1异常与负MPV2异常相叠置区域,即大气对流稳定时,因垂直涡度得到发展,激发出强对流.低层螺旋度正值中心的出现并增大,预示着强对流的发生,同一经度相邻正负螺旋度中心的存在有利于正螺旋度区域暴雨强度的增大. 相似文献
13.
Mid-latitude atmospheric responses to heat and vorticity forcing using a linear baroclinic model 总被引：1，自引：0，他引：1 
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下载免费PDF全文 Based on diagnostic analysis of reanalysis data for 58-year, the distribution characteristics of decadal variability in diabatic heating, transient eddy heating and transient eddy vorticity forcing related to the sea surface temperature (SST) anomalies over the North Pacific, as well as their relationship with anomalous atmospheric circulation have been investigated in this paper. A linear baroclinic model(LBM) was used to investigate atmospheric responses to idealized and realistic heat and vorticity forcing anomalies, and then to compare relative roles of different kinds of forcing in terms of geopotential height responses. The results illustrate that the responses of atmospheric height fields to the mid-latitude heating can be either baroclinic or barotropic. The response structure is sensitive to the relative horizontal location of heating with respect to the background jet flow, as well as to the vertical profile of heating. The response to the idealized deep heating over the eastern North Pacific, mimicking the observed heating anomaly, is baroclinic. The atmospheric response to the mid-latitude vorticity forcing is always barotropic, resulting in a geopotential low that is in phase with the forcing. The atmospheric responses to the realistic heat and vorticity forcing show the similar results, suggesting that diabatic heating, transient eddy heating and transient eddy vorticity forcing can all cause atmospheric anomalies and that the vorticity forcing plays a relatively more important role in maintaining the equivalent-barotropic structure of geopotential height anomalies. 相似文献
14.
西北太平洋纬向扰动海温经验正交函数（EOF）分解第一和第三模态、第二和第四模态分别代表同期黑潮延伸体和亲潮强弱的配置关系,将两者的典型位相合成,可以分别得到延伸体收缩和扩张状态时的典型模态海温,本文以此及气候态海温作为初始海温强迫场,利用CESM1.2.0模式,讨论了延伸体的系统变异对北太平洋风暴轴的影响及其在不同能量转换过程的主要影响机制,结果表明,延伸体收缩状态下,北太平洋风暴轴强度整体加强,而扩张模态下强度减弱。空间分布上,收缩模态下,风暴轴主要体现为经向方向的变化,中心及其以北强度加强,中心以南减弱;扩张状态下,则主要表现为纬向方向的差异,中心及以西强度减弱明显,中心以东有所增强。对能量转换的诊断分析表明,正压能量转换过程对涡动动能的变化贡献很小,且在风暴轴中心附近,其作用主要为消耗涡动动能,延伸体收缩状态下其消耗作用增强,而扩张状态下消耗作用减弱,这一差异主要是由于不同海温异常强迫下瞬变涡旋的形变不同造成;斜压有效位能释放比正压能量转换大一个量级以上,该过程几乎全部通过基流的经向温度梯度和经向涡动热量输送的相互作用完成,在这一过程中大气斜压性（经向温度梯度）起了关键性作用,大气斜压性异常、基流经向温度梯度异常、斜压有效位能释放异常与风暴轴异常的空间分布均具有较好的对应关系,该过程可能也是延伸体海温异常影响北太平洋风暴轴的主要物理过程;涡动有效位能需要进一步转换为涡动动能才能产生瞬变涡旋运动,涡动有效位能释放的量级与斜压有效位能的释放相当,但数值要小,这一过程通过冷暖空气的上升下沉运动完成,延伸体异常模态下,扰动垂直速度和扰动温度的负相关性的变化与涡动有效位能向涡动动能转换的变化也有较好的对应关系。 相似文献
15.
东北低压爆发性发展过程的诊断分析 总被引：1，自引：1，他引：0
本文对一次东北低压的快速强烈发展过程做了扰动动能、扰动有效位能及涡度收支平衡分析。结果表明:1.气旋爆发性发展前后,扰动动能的产生项变化剧烈,是主要的扰动动能源。气旋爆发性发展前期,以斜压过程为主,而在爆发期,由正压过程制造的扰动动能也有大量增加,同样是不可忽视的,且这时扰动动能通过系统边界与外界的交换很小。2.扰动有效位能在气旋强烈发展前有大幅度增长,由潜热释放造成的扰动有效位能的产生数值很小,平均有效位能向扰动有效位能的转换是扰动有效位能的主要来源。3.在气旋的爆发期,对流层中层及上层的涡度变化最为显著,涡度平衡中,散度项对对流层中下层正涡度的增长贡献最大,而网格尺度及次网格尺度的垂直输送项和涡度平流项对中上层正涡度的迅速增加有着重要意义。 相似文献
16.
位涡外部源汇是驱动大气环流的原动力。文中详细介绍了地表位涡制造和位涡密度强迫的联系,讨论了不同坐标系中位涡密度方程的特点及其在应用中应当注意的问题。还以2008年初南方低温雨雪冰冻灾害为例,探讨了青藏高原地表位涡密度强迫及东传对下游地区对流性天气发生的影响,拟由此揭示青藏高原位涡密度强迫激发中国东部激烈天气发生的一种新机制。伴随着青藏高原地表正位涡密度的东传,下游地区对流层中高层出现纬向正绝对涡度平流,气旋性环流增强,从而促使低空南风发展,为南方地区提供充沛的水汽条件。另外,南风的增强有利于低空经向负绝对涡度平流的加强,从而使南方地区高、低空形成绝对涡度平流随高度增大的大尺度环流背景,有利于上升运动的发展。上升运动的加强又促进低空南风气流的增强,使高、低空绝对涡度平流随高度增大的环流背景进一步增强,最终导致降水的产生。 相似文献
17.
Four observed blocking anticyclones in different regions of the Northern Hemisphere are in-vestigated.Analyses show that there exist distinct differences in the maintenance of the time-meanquasi-geostrophic potential vorticity(PV)low in 300 hPa within blocking areas.In two Pacificblocking cases,the PV advection by time-mean flow tends to flow the PV low to northwestern partof the blocking highs,and thus is beneficial to the maintenance of the blockings'strength.Thetransfer by transient eddies acts to balance the effect of the time-mean flow.In the Atlantic andAlaska blocking cases,however,the advection of mean flow tends to flow the PV low eastward.The PV transfer by transient eddies acts to flow potential vorticity low to the western part of theblocking ridges and also to balance the time-mean flow's effect.Thus,in the latter two cases,it isthe transfer by the transient eddies that acts to maintain the blockings. 相似文献
18.
利用2016年1月1日至31日的FNL资料,对一次极端寒潮天气过程进行了等熵位涡分析。结果表明:高位涡主体由极涡分裂而来,前面低位涡区的阻挡与后侧低位涡大气的北上加强了位涡的经向交换,高位涡空气不断由极地向南输送,使得高位涡主体不断加强维持。高位涡在由北向南移动的同时,也由对流层顶向下输送。此次寒潮过程主要有3股冷空气由上而下发展,位置均在高空急流轴的北侧,最南端的一股下沉气流最旺盛,这是其与高空急流相互作用的结果。强盛的冷空气下沉使得寒潮影响范围触及我国华南地区。随着高位涡的向南向下传输,一方面引起对流层中高层低涡系统迅速发展,当它移到中国东部地区时,东亚大槽迅速加深,使槽后强冷空气迅速向南爆发;另一方面,在高位涡输送的过程中,其后侧有强烈的下沉运动,使得地面冷高压快速发展,导致强寒潮天气的爆发。 相似文献
19.
位涡诊断在黄土高原强对流风暴预报中的应用 总被引：4，自引：0，他引：4
利用位涡理论,对2004年6月15~16日宁夏、内蒙、陕西、山西和河南出现大范围的强对流风暴和局地冰雹天气过程作了诊断分析。个例分析发现,干位涡空间结构表现为:从风暴区下游到风暴区形成随高度向西倾斜的大值正位涡柱,风暴区形成对流层高层大值正位涡中心和对流层中低层伴有位涡梯度增强的位涡等值线密集区的叠置。对流层低层干位涡场特征表现为,风暴区形成干位涡等值线密集区和风场切变的耦合。对流层低层湿位涡场特征表现为,风暴区形成湿位涡正压项小于0对流不稳定舌和湿斜压中心以及湿位涡斜压项等值线密集区的耦合。风暴发生前,对流层中层500hPa河套生成经向位涡等值线密集区,500hPa蒙古地区强偏北气流中同时出现正位涡扰动和指向河套的正位涡平流,对黄土高原大范围强对流风暴的发生有指示意义。 相似文献
20.
The effect of the high frequency (synoptic) variability of wind and heat fluxes upon the surface ocean off south-central Chile (west coast of South America) is investigated using a regional ocean model. We focus our analysis in austral summer, when the regional wind experiences significant day-to-day variability superimposed on a mean, upwelling favorable flow. To evaluate the nature and magnitude of these effects, we performed three identical simulations except for the surface forcing: the climatological run, with long-term monthly mean wind-stresses and heat fluxes; the wind-synoptic run, with daily wind stresses and climatological heat fluxes; and the full-synoptic run, with daily wind-stresses and daily fluxes. The mean currents and surface geostrophic EKE fields show no major differences between simulations, and agree well with those observed in this ocean area. Nevertheless, substantially more ageostrophic EKE is found in the simulations which include synoptic variability of wind-stresses, impacting the total surface EKE and diffusivities, particularly south of Punta Lavapie (37° S), where the lack of major currents implies low levels of geostrophic EKE. Summer mean SSTs are similar in all simulations and agree with observations, but SST variability along the coast is larger in the runs including wind-stress synoptic variability, suggesting a rather linear response of the ocean to cycles of southerly wind strengthening and relaxation. We found that coastal SST variability does not change significantly in the first tenths of kilometers from the shore when including daily heat fluxes, highlighting the prominent role of wind-driven upwelling cycles. In contrast, in the offshore region situated beyond the 50 km coastal strip, it is necessary to include synoptic variability in the heat fluxes to account for a realistic SST variability. 相似文献