黄河中下游地区持续性低温天气成因分析     

孙仲毅  张睿光  靳冰凌  王敏  徐朝晖  黄真文  李忠亮 《安徽农业科学》2010,38(30):17167-17170,17203

利用常规观测资料和我国气象台站温度资料,采用天气学原理、天气动力学和热力学诊断分析方法,对2010年1月上、中旬黄河中下游地区强降温和持续性低温天气过程进行了环流形势、影响天气系统及成因分析。结果表明,500hPa槽后偏北气流引导极地冷空气不断向南输送,东北亚稳定的冷涡中心起到了阻挡冷空气东移、促使冷空气堆积和加强的作用,西伯利亚深厚低槽压迫高压脊崩溃,强冷空气爆发南下。850hPa强盛的温度冷平流是造成气温骤降和持续性低温天气的主要原因,冷平流中心的演变与强冷空气移动路径相一致。黄河中下游地区从高空到低层均有负涡度平流,深厚的负涡度平流输送有利于高压系统的移动,其值越小冷空气越强,负涡度平流中心与强降温中心相对应。冷平流中心比强降温中心提前12～24h出现,＂负涡度平流核＂先于强降温天气出现,这些特征为预报强降温天气提供了有利的参考依据。  相似文献   

一次双急流型沙尘暴过程的数值模拟与诊断     

程海霞  丁治英  帅克杰 《干旱区研究》2007,24(4):543-549

利用MM5模式对2001年4月8～9日的双急流型沙尘暴天气过程进行了数值模拟和诊断分析,结果发现:此次沙尘暴过程中有强的西风动量下传,动量下传主要由北支急流完成;在沙尘暴发展旺盛阶段,南、北两支急流低层的南风和北风分量之间产生的辐散促进了高层动量下传,而高层南北两支急流南风分量的加强和贯通引导南方暖湿气流向北输送,抑制了沙尘暴的发展.南北两支急流的共同作用是造成该次沙尘暴的重要原因,北支急流产生了直接的作用,南支急流有间接的影响.250 hPa两支MPV1正的大值位涡区与南、北两支急流有很好的对应关系,在沙尘暴区域前部,对流层高层存在对称不稳定.  相似文献   

Pacific sand lance of the Port Moller estuary, southeastern Bering Sea: an estuarine^dependent early life history     

MICHAEL D. McGURK  H. DAVID WARBURTON 《Fisheries Oceanography》1992,1(4):306-320

Three waves of spawning Pacific sand lance (Ammo-dytes hexapterus) entered the Port Moller estuary from mid-January to late May 1990. Each wave laid its eggs on sand in lower Moller Bay with the center of egg distribution about 14 km inside the estuary. After incubation for 45 to 94 d, each cohort of eggs hatched out over a 41- to 63-d period. Larvae moved at a rate of 0.21 knvd“¹ toward a deep fjordlike basin at the head of Herendeen Bay inside the estuary about 20 km southwest of the center of hatch. The basin has the lowest flushing rate of the estuary, and unlike the rest of Port Moller, it is vertically stratified, which allows the development of a spring-summer zooplankton community with greater biomass than any other location in the estuary. Larvae may have moved to the basin to enhance growth or to avoid offshore transport to areas of low food abundance, but we cannot demonstrate a direct link between growth and habitat. We conclude that the Port Moller sand lance stock has an estuarine early life history that evolved in response to the unique physical conditions of the Port Moller estuary–a shallow, well-mixed site with sandy substrate that is suitable for incubation of demersal eggs next to a deep, vertically stratified fjord with a rich zooplankton community that is suitable for rearing of larvae.  相似文献   

Effect of horizontal advection induced by intrusion of the Kuroshio water on plankton biomass in the spring fishing period of shirasu on the Pacific coast of Japan     

Joon-Taek  YOO  Hideaki  NAKATA  Takashige  SUGIMOTO 《Fisheries Science》2004,70(6):937-944

ABSTRACT:   This study explored the fundamental process that controls interannual change in plankton biomass on the Pacific coast of Japan, focusing on the spring period of shirasu fishery. A 1-D model of primary production revealed that the strength of horizontal advection induced by warm water intrusion from the Kuroshio into the Pacific coast is the most critical for plankton biomass compared with other factors such as diffusion and production. This conclusion was also confirmed by a sensitivity analysis of the model.  相似文献   

基于粒子图像测速技术的液力变矩器涡轮内流场测试与分析     

柴博森  王玉建  刘春宝  马文星  王文博 《农业工程学报》2015,31(12):92-98

液力变矩器是自动变速器的主要部件,其在乘用车、载重汽车、公共汽车和机车上的应用广泛。液力变矩器内部流动特性影响其外部性能,为了深入研究其内部流动特性,基于粒子图像测速(particle image velocimetry,PIV)技术对液力变矩器涡轮内流场进行试验研究。采用帧频为1 000帧/s的CCD高速相机,在不同工况下(输入与输出的转速比分别取0、0.3、0.5、0.7)采集不同粒子直径、不同粒子浓度下的流动图像,经过图像预处理,对连续两帧图像进行互相关计算,获得涡轮径向切面的速度场和涡量场。通过对流场分布结构和流动区域上复杂流动现象的对比分析,发现投入流场中粒子浓度越高(1 500mL蒸馏水中投入2.4 g粒子)、粒子直径越小(10μm)时,识别并提取流动区域上的流动参数越丰富,流速场和涡量场信息越可靠。液力变矩器内部高梯度流场分布结构和非均匀流速场分布导致出现多尺度涡旋和反向流等复杂流动现象,造成液力变矩器内部流动能量损耗,随转速比提高,涡轮流场结构趋于规律,能耗逐渐降低。该文试验测量与分析结果对于液力变矩器结构优化和性能提升提供了参考。  相似文献   

沈阳市93510大风的天气气候学分析     

裘碧梧  石宇虹 《沈阳农业大学学报》1994,25(1):8-12

１９９３年５月１０日，沈阳市出现了罕见的大风天气．这是１次蒙古气旋冷锋形势下的天气过程．对这次大风过程的特点、产生原因进行了天气气候学分析．对此类大风天气的预报进行了研究，并探讨了预报途径和方法．  相似文献   

南京地区一次罕见锋前增温天气过程分析     

张子仪  李国翠 《绿色科技》2021,(6):145-149

2020年11月18日,我国南京地区出现了罕见的增温异常,利用常规气象资料和11月16日至20日ERA5逐小时1000 hPa至300 hPa的散度、位势高度、气温、水平风和垂直速度等再分析资料,根据高低空的天气系统的配置和槽脊移动的过程,结合散度、暖平流等天气学原理的相关知识分析冷锋过境前的基本环流形势,并主要结合热力学一级能量方程(温度倾向方程)对影响本次增温天气过程的因子进行了评估分析。结果表明:在这次增温中,温度平流和非绝热加热的贡献占主导作用,前者由于西南暖湿气流带来,后者与冷空气把原来占主导地位的暖气团迅速挤压到狭窄区域聚集增温有关;而垂直运动不是最显著的影响因子。  相似文献   

A model of the spring migration into the North Sea by Calanus finmarchicus overwintering off the Scottish continental shelf     

A. Gallego  J. Mardaljevic  M.R. Heath  D. Hainbucher  & D. Slagstad 《Fisheries Oceanography》1999,8(S1):107-125

A particle tracking model was used to investigate the annual spring invasion of the North Sea by Calanus finmarchicus copepodites which overwinter in deep water off the Scottish continental shelf. Flow fields generated by a hydrodynamic model (HDM) were used to simulate the advection of zero drag particles representing the copepods. Particles were released simultaneously from a regular lattice of start positions at a given depth ( D ₁), and ascended at a fixed rate ( dD/dt ) until they reached a final depth ( D ₂) in the surface layers. The proportion of particles reaching target areas in the northern North Sea was relatively insensitive to a moderate degree of variation (±20%) around chosen default values of the vertical migration parameters ( D ₁, D ₂ and dD/dt ), derived from field data. The inclusion of horizontal diffusion velocities and diel vertical migration in surface layers did not significantly affect the results. Sensitivity to wind direction was investigated by applying flow fields from HDM runs with different wind forcing scenarios. For the default vertical migration parameters, only north-westerly winds resulted in particles entering the North Sea from release locations north of the Iceland–Scotland Ridge, where dense aggregations of overwintering copepods were encountered during field surveys. The particle tracking model predicted that the major routes for the spring Calanus invasion into the North Sea were the East of Shetland Atlantic Inflow and the Norwegian Trench Atlantic Inflow, which agreed with seasonal trends observed in Continuous Plankton Recorder data. Overall, despite its relative simplicity, particle tracking was confirmed as a robust tool to explore the causal mechanisms behind the annual invasion of the North Sea by C. finmarchicus emerging from diapause in the deep waters off the Scottish continental shelf.  相似文献   

Nonlocal wind-driven fjord–coast advection and its potential effect on plankton and fish recruitment     

Lars Asplin  Anne Gro Vea Salvanes  & Jon Bent Kristoffersen 《Fisheries Oceanography》1999,8(4):255-263

The Bergen Ocean Model (BOM), a three-dimensional physical coastal ocean model, was used for a numerical simulation experiment to investigate short-term effects of wind-generated coastal upwelling and downwelling on the dynamics of adjacent large outer and smaller inner fjords. The effect of the real alongshore wind regime on advection for an idealized fjord topography, resembling Masfjorden, western Norway, is used as an example. This modelling exercise is a supplement to, and its predictions support, the various hypotheses investigated in ecosystem simulation studies of the Masfjorden. The model predicts that coastal winds from the north cause upwelling and transport the upper water layer out from the fjords. Winds from the south cause downwelling and transport the upper water layer into the fjords. The transport is rapid and ≈50% of the upper water layer may be replaced within 1–2 days. Implications of these physical processes for the dispersal and retention of planktonic organisms and the early life stages of fish are discussed. If strong southerly winds occur frequently, this will transport planktonic organisms into the fjord and may increase the carrying capacity for planktivorous fish. In contrast, frequent strong northerly winds may reduce the abundance of planktonic organisms, including the early life stages of marine fish, and thus possibly reduce recruitment to fjord fish populations. Frequent shifts between southerly and northerly winds would cause an exchange of early life stages between neighbouring fjords and thus enhance genetic exchange.  相似文献   

Connectivity of lobster (Homarus americanus) populations in the coastal Gulf of Maine: part II. Coupled biophysical dynamics     

LEWIS INCZE  HUIJIE XUE  NICHOLAS WOLFF  DANYA XU  CARL WILSON  ROBERT STENECK  RICHARD WAHLE  PETER LAWTON  NEAL PETTIGREW  YONG CHEN 《Fisheries Oceanography》2010,19(1):1-20

We used a coupled biophysical model to investigate larval transport and connectivity patterns in the Gulf of Maine lobster ( Homarus americanus ) population. Biological 'particles' were released at over 21 000 locations every 10 days over a 4-month hatching period, and were followed from hatching through late postlarval stage. In addition to circulation and dispersion, model calculations included spatial patterns of egg production, temporal patterns of hatching, temperature-dependent development, vertical distribution and mortality. We ran the model for three larval production seasons using the same hatching patterns and individual-based modeling parameters but different flow patterns in the coastal current system. Model results gave distribution and abundance patterns of competent postlarvae that closely resembled observed, alongshore patterns of lobster settlement density. We evaluated the relative contribution of all source regions to the total number of competent postlarvae in a series of medium-size zones along the coastal shelf, many of which are used in lobster management. Connectivity depended on many factors, including patterns of egg production and transport, and the location and size of the receiving zones. Self recruitment ranged from a few percent to >90% of competent postlarvae. Although it was common for postlarvae to come from many, often distant, sources, most of the competent postlarvae in a zone originated within one to two zones in the prevailing 'up-stream' direction, forming shorter connections along the coast than the energetic currents might otherwise suggest. Inshore migrations during summer hatching may contribute to these shorter patterns of connectivity. Transport in the prevailing 'upstream' direction was also indicated.  相似文献