流形群运动目标自动识别与跟踪技术研究——以MCS自动追踪方法为例

从流形群运运目标的形状特征及其本质属性出发，提出了多种适合计算机自动识别与跟踪流形群运运目标的匹配模板的构建技术。充分顾及流形群运动目标的区域整体描述、几何形状特征、不变矩特性，以及流形群目标的本质属性(纹理特征)，通过最大欧几里得贴近度的择近原则，实现模板匹配，完成目标识别；通过交替更新匹配模板元素参量及交叉匹配算法，实现目标跟踪。应用这种算法，对1998年6月至8月的青藏高原上空中尺度对流系统(MCS)进行了识别与跟踪实验。实验结果表明，这种技术较适合计算机自动识别和跟踪类似MCS的流形群运动目标，与专家目测屏幕扫描跟踪法相比，准确率达90％。同Amaud等人提出的面积重叠跟踪法相比，其准确率提高了一个多数量级。     

Phytoplankton patchiness: the role of lateral stirring and mixing

Explanations for the patchy distribution of marine phytoplankton are critically reviewed with the focus on the role played by lateral advection and mixing. Generating mechanisms for what is increasingly seen as a ubiquitous feature of the oceans have been sought in biology, behaviour, population dynamics, physics and various combinations thereof. As the mesoscale and sub-mesoscale (1-500 km) contain the “weather” of the ocean—eddies and fronts capable of strong stirring and mixing of any tracers advected by them—the physical circulation in this regime may have a strong role in the generation of patchiness. As a consequence, the focus here is on the ways the turbulent currents at these scales can interact with other processes to produce the complex spatial structures in phytoplankton distributions seen in countless satellite images and cruise data. The mechanisms reviewed include patch formation (KiSS theory), filamentation, Turing and related instabilities, diffusion waves, shear effects and turbulent stirring. Parallel to this is a discussion of observations and of the techniques that have been used to analyse them, particularly spectral analysis. It will be seen that many of the limitations in extant theories stem from a paucity of data and ambiguity in its interpretation. A synthesis of recent developments in sampling, instrumentation, image analysis and turbulence theory is used to suggest alternatives to conventional approaches, to highlight important work in related fields and to motivate new lines of research.     

Mesoscale eddies dominate surface phytoplankton in northern Gulf of Alaska

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.     

NPZ response to eddy-induced upwelling in a Brazil Current ring: A theoretical approach

This work explores the effect of a cyclonic mesoscale feature of the Brazil Current (BC) moving northward off SE Brazil (20° S–23° S) in the Nutrients-Phytoplankton-Zooplankton (NPZ) dynamics. We employ the contour dynamics technique in a quasi-geostrophic, inviscid, 1½-layer model set as a meridional jet flowing southward along a rigid western boundary. This hydrodynamical model is coupled to a conventional NPZ model. We evaluate two distinct scenarios: (1) Plankton in a mixed layer (ML) with time-variable depth and no entrainment and; (2) Plankton in an ML held at a fixed depth, which allows entrainment. We perform simulations with different ML depths representing summer (42 m) and winter (86 m) for the region of interest. The presence of the western boundary allows the cyclonic ring to propagate northward due to image effect. The eddy motion produces upwelling (downwelling) in the leading (trailing) edge resulting in different responses in the two scenarios examined. In the variable ML depth simulations, Z is favored relative to P because there is no injection of N. On the other hand, in the fixed ML depth simulations, P is favored relative to Z due to dilution. All simulations show P enrichment within the eddy, but winter simulations show a greater response to the physical forcing. We conclude that the cyclonic eddy shed from BC provides favorable conditions for planktonic growth. Winter-like conditions seem to be more favorable than summer-like ones and, therefore, present more intense blooms associated with the ring.     

青岛─石岛近海反气旋中尺度涡旋存在证据及数值模拟

系统整理的历史实测海流和温盐资料显示出青岛─石岛近海水域全年都存在着中尺度反气旋式涡旋运动．利用二维数值模式,首次模拟出该涡旋的存在,并对这一涡旋的形成机制进行了探讨,数值模拟结果和实测吻合良好．数值计算表明：在冬季盛行风的作用下,山东半岛南岸出现减水,迫使北上的黄海暖流中的一部分向西北方向延伸,在到达山东半岛近海后向右转向,形成东北向沿岸流,这样,与绕过山东半岛大约沿40～50m等深线南下的黄海沿岸流作用,在青岛─石岛近海形成一个中尺度反气旋涡旋．夏季由于偏南风的作用,致使山东半岛南部近海浅水区域海水都向东北方向流动,与沿黄海冷水团锋面南下的黄海沿岸流相作用,由于流速切变也形成了上述涡旋．     

Mesoscale slope current variability in the Gulf of Lions. Interpretation of in-situ measurements using a three-dimensional model

The ECOLOPHY experiments aimed at investigating physical exchanges between coastal and open sea. They were carried out in June and December 2005 over the shelf-break in the North-eastern part of the Gulf of Lions (Northwestern Mediterranean Sea). This area is considered to be the generation zone for the eddy and meandering structures of the Northern Current (NC). The objective of the present work is to examine mesoscale variability of this coastal slope current in the light of available data. Numerical modeling is used to support the field data analysis. ADCP current measurements over a one-year period show that mesoscale activity is maximal in late winter, correlating with the seasonal variability of the NC and, also, partly with local winds. Measured currents exhibit mesoscale fluctuations with periods ranging from 3 to 30 days, in agreement with previous analyses. Fluctuations of periods longer than 10 days are found to be mainly oriented in the direction of the mean current, whereas more frequently observed high frequency fluctuations tend to be oriented cross-slope, suggesting a relationship with the NC mesoscale meandering. Moreover, trajectories of surdrift buoys launched in the NC vein exhibit mesoscale phenomena, such as current meanders or eddies and on-shelf intrusions. Numerical modeling provides a synoptic point of view and is used hereafter to support physical interpretation of punctual eulerian or lagrangian measurements. Therefore, modeled hydrodynamic fields are used to analyze surdrift buoy trajectories and computed vertically averaged current and Ertel potential vorticity provide a better understanding of these behaviors.     

“080527”湖北老河口短历时暴雨的中尺度天气成因分析

以2008年5月27日发生在湖北老河口的短历时暴雨为例,利用NCEP客观再分析资料,开展中尺度天气系统诊断分析。结果表明：干线、500 hPa冷温度槽、冷切尾部辐合区、中低层湿区及地面风场辐合线等中尺度天气系统的活动与暴雨发生、发展密切相关。干空气自北向南、自上而下侵入湿区,具有典型的湖北干侵入暴雨特征。干侵入使干冷空气与暖湿空气汇合上升,同时激发冷切尾部辐合区中的正涡度柱沿假相当位温锋区向上发展,配合地面中尺度辐合线,增强对流上升运动。500 hPa冷温度槽活动及干侵入造成垂直方向上对流不稳定,冷式切变线尾部由于冷暖平流、干湿平流交汇构成水平方向不稳定区,不稳定区受露点锋生扰动,从而触发强对流天气。中低层深厚湿区的维持和水汽辐合为老河口中尺度暴雨提供了水汽来源。     

东亚副热带高空急流区中尺度扰动分布特征及可能机理

东亚副热带高空急流强度变化和天气气候密切相关,本文利用WRF模式输出的高时空分辨率模拟资料研究了东亚副热带高空急流区的中尺度扰动特征,并结合动力学理论,揭示了急流区中尺度扰动产生的可能机制.研究表明,急流轴南侧更容易出现水平尺度为几十公里的高频扰动,这些扰动的时空分布具有波动特征.对高空急流区中出现中尺度扰动区域的拉格朗日Rossby数、Richardson数以及绝对涡度的计算发现,高空急流轴南侧中尺度扰动出现的物理机制与非地转平衡流的不稳定发展有关,并且高空急流强度的大尺度整体变化与急流区中尺度扰动变化的累积效应有关.因此,开展高空急流强度变化规律研究不能忽视其内部中尺度动力过程的作用.     

东北冷涡内部中尺度涡旋引起的冰雹天气数值模拟

利用NCEP格点资料模拟了2011年8月21日沈阳地区的冰雹天气过程,结合机场自动观测数据、多普勒雷达资料和卫星云图等分析了冰雹的形成机制。结果表明：此次冰雹天气是由冷涡内部的中尺度涡旋引起的,卫星云图上的中尺度云团是中尺度涡旋的产物;0℃等温线位于600 hPa,-20℃位于450 hPa附近,两者之间厚度在2KM左右;冰雹发生前,斜升气流的最大上升速度为20 m·s^-1以上,水汽累积区位于0℃层以上,保证了水分累积区都由过冷水滴组成;高层干冷空气倾斜下侵到中低层的暖湿空气中,对强对流的发生发展起到了至关重要的作用;低层MPV1为强对流提供了对流不稳定机制,中层MPV2为强对流提供了对称不稳定机制,高层两种不稳定共存,均为对流发展贡献力量;对流有效位能积累、释放随时间的演变对冰雹的出现有一定的指示意义;10:30多普勒雷达图显示回波强度随高度增强,速度图上存在西南低空急流,有利于对流的发展。     

2007年8月8日乌拉盖地区暴雨天气分析

应用常规气象观测资料、卫星云图和T213数值预报产品,对2007年8月8日乌拉盖地区对流性暴雨天气的成因进行了分析,给出了产生暴雨的对流云团演变特征。