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1.
Chlorophyll blooms consistently develop in the oligotrophic NE Pacific in late summer, isolated from land masses and sources of higher chlorophyll waters. These blooms are potentially driven by nitrogen fixation, or by vertically migrating phytoplankton, and a better understanding of their ubiquity could improve our estimate of the global nitrogen fixation rate. Here, global SeaWiFS chlorophyll data from 1997 to 2007 are examined to determine if similar blooms occur in other oligotrophic gyres. Our analysis revealed blooms in five other areas. Two of these are regions where blooms have been previously identified: the SW Pacific and off the southern tip of Madagascar. Previously, unnoticed summer blooms were also identified in the NE and SW Atlantic and in a band along 10°S in the Indian Ocean. There is considerable variation in the intensity and frequency of blooms in the different regions, occurring the least frequently in the Atlantic Ocean. The blooms that develop along 10°S in the Indian Ocean are unique in that they are clearly associated with a hydrographic feature, the 10°S thermocline ridge, which explains the bloom within a conventional upwelling scenario. The environment and timing of the blooms, developing in oligotrophic waters in late summer, are conducive to both nitrogen fixers and vertically migrating phytoplankton, which require a relatively stable water column. However, the specific locations of the chlorophyll blooms generally do not coincide with areas of maximum levels of nitrogen fixation or Trichodesmium. The NE Pacific chlorophyll blooms develop in a region with a very high SiO4/NO3 ratio, where silicate will not be a limiting nutrient for diatoms. The blooms often develop between eddies, wrapping around the periphery of anti-cyclonic features. However, none of the areas where the blooms develop have particularly high eddy kinetic energy, from either a basin-scale or a mesoscale perspective, suggesting that other factors, such as interactions with a front or dynamics associated with the critical latitude, operate in conjunction with the eddy field to produce the observed blooms. 相似文献
2.
Tian Yongxiang 《Acta Meteorologica Sinica》1995,9(3):338-348
The tropical cyclone motion is numerically simulated with a quasi-geostrophic baroclinic model.The flow field of a tropical cyclone is decomposed into its axisymmetric and asymmetric components.The relation between the ventilation flow vector and the motion vector of the tropical cyclone is investigated.The results of numerical experiments indicate:(1) There are both large-scale beta gyres and small-scale gyres in the asyrnmetric flow field.(2) The interaction between small-scale gyres and large-scale beta gyres leads to the oscillation of translation speed and translation direction for the tropical cyclone.(3) There are the large deviations between the ventilation flow vector calculated by means of Fiorino and Elsberry's method and the motion vector of tropical cyclone.(4) The ventilation flow vector computed using the improved method closely correlates with the motion vector of the tropical cyclone. 相似文献
3.
VENTILATION FLOW IN A BAROCLINIC VORTEX RELATED TO TROPICAL CYCLONE MOTION 总被引：1，自引：0，他引：1 
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下载免费PDF全文 田永祥 《Acta Meteorologica Sinica》1995,(3)
The tropical cyclone motion is numerically simulated with a quasi-geostrophic baroclinic model.The flow field of a tropical cyclone is decomposed into its axisymmetric and asymmetric components.The relation between the ventilation flow vector and the motion vector of the tropical cyclone is inves-tigated.The results of numerical experiments indicate:(1) There are both large-scale beta gyres andsmall-scale gyres in the asyrnmetric flow field.(2) The interaction between small-scale gyres andlarge-scale beta gyres leads to the oscillation of translation speed and translation direction for the tropi-cal cyclone.(3) There are the large deviations between the ventilation flow vector calculated bymeans of Fiorino and Elsberry's method and the motion vector of tropical cyclone.(4) The ventila-tion flow vector computed using the improved method closely correlates with the motion vector of thetropical cyclone. 相似文献
4.
相同强度双台风相互作用的物理机制 总被引：2，自引：1，他引：1
在无基本气流的假定下,应用无辐数正压模式研究双台风相互作用的物理机制。台风Ａ位于观风Ｂ以西,两台风相距６０ｋｍ,且具有相同的强度。在台风Ａ（台风Ｂ）的非对称流场中,由台风Ａ（台风Ｂ）的线性β效应产生的非对称涡旋的方位相位与由台风Ｂ（台风Ａ）形成的非对称涡旋方位相位相反（相同）。因此,台风Ａ（台风Ｂ）的大尺度非对称涡旋较弱（较强）。小尺度涡旋逆时针旋转导致台风Ａ逆时将打转。稳定的偏南非对称气流使台风 相似文献
5.
1 INTRODUCTION Measuring the velocity of ocean currents is one of the most important tasks in physical oceanography research. Many centuries ago, mariners had begun to obtain the sea surface cur- rents from vessel drift records. As early as in 1870s instr… 相似文献
6.
Based on the Simple Ocean Data Assimilation(SODA) products,we study the mean properties and variations of the Southern Hemisphere subpolar gyres(SHSGs) in this paper.The results show that the gyre strengths in the SODA estimates are(55.9±9.8)×10~6m~3/s for the Weddell Gyre(WG),(37.0±6.4) ×10~6m~3/s for the Ross Gyre(RG),and(27.5±8.2)×10~6m~3/s for the Australian-Antarctic Gyre(AG),respectively.There exists distinct connectivity between the adjacent gyres and then forms an oceanic super gyre structure in the southern subpolar oceans.And the interior exchanges are about(8.0±3.2)×10~6m~3/s at around 70°E and(4.3±3.1)×10~6m~3/s at around 140°E.The most pronounced variation for all three SHSGs occurs on the seasonal time scale,with generally stronger(weaker)SHSGs during austral winter(summer).And the seasonal changes of the gyre structures show that the eastern boundary of the WG and AG extends considerably further east during winter and the interior exchange in the super gyre structure increases accordingly.The WG and RG also show significant semi-annual changes.The correlation analyses confirm that the variations of the gyre strengths are strongly correlated with the changes in the local wind forcing on the semi-annual and seasonal time scales. 相似文献
7.
The effect of Stokes drift on Ekman transport in the open sea 总被引：5，自引：5，他引：0
By introducing the wave-induced Coriolis-Stokes forcing into ageostrophic motion equation,the Eulerian transport is modified by the wave-induced Stokes drift.The long-term mean contributions of the Stokes transport with remotely generated swells being included to the ageostrophic transport are analyzed using the ECMWF(European Centre for Medium-Range Weather Forecasts) reanalysis data.The ratio of Stokes transport to Ekman transport in north-south(N-S) direction can reach a maximum of over 50% in the subtropical region.The preliminary influence of the Stokes transport on the North Pacific gyre is all year persistent,while the effect on the North Atlantic gyre is only obvious in boreal winter and early spring. 相似文献
8.
Residual (i.e. non-tidal) components of flow in the Dover Straits are determined from measurements recorded by the OSCR H.F. Radar system. The data are divided into 10 monthly sets, obtained from 5 months of dual radar deployments on the English side of the Straits and a corresponding 5 months from the French side. For each of these sets the tidal component was removed by subtracting constituents derived from separate (monthly) harmonic analyses.In each deployment, surface currents were measured at 700 locations at 20-min intervals, providing spatial resolution on a grid as fine as 660 m. This fine spatial resolution reveals distinct patterns of monthly-mean residual circulations never previously recognized. In particular, a residual gyre is shown to be a dominating feature along the French side, with currents exceeding 20 cm s-1 and a diameter of 20 km. The previous obscurity of this feature may be attributable to the large (> 1·5 m s-1) and strongly spatially variable tidal currents. In these conditions, tidal advection will rapidly smear any surface signature obtained from satellite observations. Likewise, fine resolution (grid spacings of an order of 1 km) is required to reproduce these gyre dynamics in numerical models.The time-varying residual currents were correlated with wind recordings. Significant correlations were obtained for an 'open-sea' response (as represented by Ekman theory), with the wind-driven surface current veering at angles of up to 45° to the right of the wind direction. This 'open-sea' response is modified close to the coast where the generation of surface gradients force the currents to align with the topography.Larger-scale residual motions were identified from modal analyses. The primary modes, on both sides, involved large-scale flows through the Straits partially correlated with local winds. However for winds aligned approximately north-south, the components of these flows on the English and French sides are in opposition. These modes also revealed large oscillatory motions with periods of between 20 and 40 h.Estimates of net residual flows through the Straits from the radar measurements confirm earlier calculations of the range of variability in this parameter. However the increasing complexity of the flow patterns revealed in this study emphasizes the difficulty in quantifying the long-term net flow. 相似文献
9.
非对称环流的细致结构与台风路径的摆动 总被引：3，自引：1，他引：3
田永祥 《南京气象学院学报》1994,17(4):399-404
应用准地转三层斜压模式数值模拟热带气旋的移动，详细分析热带气旋非对称环流的三度空间结构及其与热带气旋移动的关系。结果表明：非线性涡度平流与线性β项相结合不但可以产生大尺度β涡旋对，而且还可产生小尺度涡旋对；这两种不同尺度的非对称涡旋不断相互作用，导致热带旋移速的振荡和移向的摆动。 相似文献
10.
Sadhuram Y. Rao B. P. Rao D. P. Shastri P. N. M. Subrahmanyam M. V. 《Natural Hazards》2004,32(2):191-209
Monthly maps of cyclone heat potential (CHP) in the Bay of Bengalhave been prepared by using Levitus climatological data set. Seasonal variability ofCHP in the Bay of Bengal has been studied using the CTD data sets collected duringfive cruises during the period, 1993–1996. High value (>30 kcal/cm2) of CHP coincided with anticyclonic gyre (ACG) and the low value of CHP (16 kcal/cm2) coincided with thecyclonic gyre (CG). This emphasizes the importance of gyres in the distribution ofCHP, which play an important role in the intensification of cyclones/depressions.CHP is >14 kcal/cm2 over Andaman Sea, southern and Central Bay of Bengal where the generation and movement of cyclones take place during post south west monsoon season (October–November). A depression formed on 07.11.95 at 11°N; 91°E and intensified into a cyclonic storm by 8th November evening and crossed Orissa Coast on 9th November 1995. A few days before its formation, the value of CHP at the origin of thiscyclone was about 20 kcal/cm2. To understand the exact role of CHP in theformation and intensification of cyclones/depressions over Bay of Bengal, more intense and systematic data sets are essential. 相似文献