波粒相互作用导致环电流质子沉降的卫星共轭观测          下载免费PDF全文

王杰  袁志刚  余雄东  薛祖祥 《地球物理学报》2020,63(6):2131-2140

波粒相互作用是环电流损失的重要机制之一,但波粒相互作用导致的环电流离子沉降而损失迄今为止缺乏直接的观测证据.基于磁层及电离层卫星的协同观测,本文报道了发生在2015年9月7日,由电磁离子回旋波(EMIC波)导致环电流质子沉降的共轭观测事件.在等离子体层的内边界,Van Allen Probe B卫星观测到,存在EMIC波的区域和不存在EMIC波的区域相比,离子通量的投掷角分布的各向异性变弱.我们将Van Allen Probe B卫星沿着磁力线投影到电离层高度,同时在该投影区域内DMSP 16卫星在亚极光区域观测到环电流质子沉降.而且,通过从理论上计算质子弹跳平均扩散系数,我们进一步证实观测的EMIC波确实能将环电流质子散射到损失锥中.本文的研究工作为EMIC波导致环电流质子沉降提供了直接的观测证据,揭示了环电流衰减的重要物理机制:EMIC波将环电流质子散射到损失锥中,从而沉降到低高度大气层中而损失.  相似文献   

Numerical Study on Tidal Mixing in the Bohai Sea     

Yifei Zhao  Ting Yu  Hu Wang 《Marine Geodesy》2019,42(1):46-63

The spatial and temporal variability of tidal mixing in Bohai Sea is studied using a numerical approach. In calculating tidal mixing, accurate barotropic tidal current is obtained via a harmonic analysis package utilizing the simulated current output from a high-resolution regional ocean model. And a “small-scale” roughness map is adopted to describe the detailed topographic features of Bohai Sea. It is shown that the tidal mixing estimated in Bohai Sea is much higher than the level of global background, and fluctuates considerably at some regions within a single day. In Liaodong Bay, Bohai Bay and Bohai Strait, the mixing varies greatly, with the peak value of O (10^?2) m² s^?1. The order of magnitude of mixing in Laizhou Bay is about O (10^?5～10^?3) m² s^?1. Mixing with background level of O (10^?5) m² s^?1 only appears in central area. Result also shows that rough topography plays relatively a more important role than tidal current in enhancing diapycnal mixing in Bohai Sea. The distributions of tidal mixing in selected sections reveal that the vertical stratification in Bohai Sea is not obvious, generally renders a barotropic structure.  相似文献   

周期性的或伴有贯穿流的西边界流跨隙流动的迟滞变异过程     

宋新新  袁东亮  王铮 《海洋学报(英文版)》2019,38(4):90-96

使用1.5层准地转约化重力模式研究了周期性的或伴有贯穿流的西边界流跨隙流动的迟滞变异过程。当西边界流变化的周期比罗斯贝波在缺口处调整的时间尺度大得多时，在雷诺数增加和减少过程的霍夫分叉点都发生延迟，从而产生新的雷诺数迟滞区间；并且西边界流流态转变的临界值变化显著；且周期强迫越短，雷诺数迟滞区间越大。当西边界流变化的周期与罗斯贝波在缺口处调整的时间尺度相当时，西边界流在缺口的流态呈无迟滞的周期性变化，且西边界流入侵西海盆的程度随周期减少而变小。此外，当贯穿流的流量大于西边界流的一半时，会显著影响西边界流在缺口处的迟滞变异过程；西边界流向西入侵程度和流态转变发生的临界雷诺值均发生变化，且贯穿流流量越大变化越大。  相似文献   

Storm-induced turbidity currents on a sediment-starved shelf: Insight from direct monitoring and repeat seabed mapping of upslope migrating bedforms     

Alexandre Normandeau  Daniel Bourgault  Urs Neumeier  Patrick Lajeunesse  Guillaume St-Onge  Louis Gostiaux  Cédric Chavanne 《Sedimentology》2020,67(2):1045-1068

The monitoring of turbidity currents enables accurate internal structure and timing of these flows to be understood. Without monitoring, triggers of turbidity currents often remain hypothetical and are inferred from sedimentary structures of deposits and their age. In this study, the bottom currents within 20 m of the seabed in one of the Pointe-des-Monts (Gulf of St. Lawrence, eastern Canada) submarine canyons were monitored for two consecutive years using Acoustic Doppler Current Profilers. In addition, multibeam bathymetric surveys were carried out during deployment of the Acoustic Doppler Current Profilers and recovery operations. These new surveys, along with previous multibeam surveys carried out over the last decade, revealed that crescentic bedforms have migrated upslope by about 20 to 40 m since 2007, despite the limited supply of sediment on the shelf or river inflow in the region. During the winter of 2017, two turbidity currents with velocities reaching 0·5 m sec⁻¹ and 2·0 m sec⁻¹, respectively, were recorded and were responsible for the rapid (<1 min) upstream migration of crescentic bedforms measured between the autumn surveys of 2016 and 2017. The 200 kg (in water) mooring was also displaced 10 m down-canyon, up the stoss side of a bedform, suggesting that a dense basal layer could be driving the flow during the first minute of the event. Two other weaker turbidity currents with speeds <0·5 m sec⁻¹ occurred, but did not lead to any significant change on the seabed. These four turbidity currents coincided with strong and sustained wind speed >60 km h⁻¹ and higher than normal wave heights. Repeat seabed mapping suggests that the turbidity currents cannot be attributed to a canyon-wall slope failure. Rather, sustained windstorms triggered turbidity currents either by remobilizing limited volumes of sediment on the shelf or by resuspending sediment in the canyon head. Turbidity currents can thus be triggered when the sediment volume available is limited, likely by eroding and incorporating canyon thalweg sediment in the flow, thereby igniting the flow. This process appears to be particularly important for the generation of turbidity currents capable of eroding the lee side of upslope migrating bedforms in sediment-starved environments and might have wider implications for the activity of submarine canyons worldwide. In addition, this study suggests that a large external trigger (in this case storms) is required to initiate turbidity currents in sediment-starved environments, which contrasts with supply-dominated environments where turbidity currents are sometimes recorded without a clear triggering mechanism.  相似文献   

潮汐和风对马六甲海峡海流的影响     

范锦晓  胡松 《热带海洋学报》2020,39(4):13-24

基于非结构有限体积法海洋模型FVCOM(Finite-Volume Community Ocean Model), 建立了马六甲海峡及其毗邻海域高分辨率水动力数值模型, 研究了风和潮流作用下的余环流结构以及水体输运特征。结果表明, 马六甲海峡航道中央潮流运动以往复流为主, 边缘存在旋转流; 主要研究区域内落潮流速略大于涨潮流速, 东南窄道处流速最大; 因峡道束窄变浅, 在涨落潮过程中潮流发生汇聚与分离; 主要研究区域东南段存在3个显著的潮致余环流; 东北季风驱动时模型响应为海峡海流整体向西北方向流动, 西南季风时反之; 季风期间潮致表层余环流结构被破坏, 但底层余流仍存在水平环流结构, 且随着风速增加, 底层余环流的数目、大小、形状、位置均会产生变化; 季风过渡期余环流结构也会发生部分改变, 尤其是小潮期间风场影响效果显著。  相似文献   

Application of computational fluid dynamics simulation for submarine oil spill     

YANG Zhenglong  YU Jianxing  LI Zhigan  CHEN Haicheng  JIANG Meirong  CHEN Xi 《海洋学报(英文版)》2018,37(11):104-115

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基于SODA资料的南海表层风能输入的空间分布与长期趋势研究     

杨倩  崔超然  张宇  刘志宇  管玉平  黄瑞新 《热带海洋学报》2018,37(6):41-48

海面风不仅是驱动上层海洋运动的主要动力, 其能量也是维持海洋表层流动的主要机械能来源。为了分析南海表层流风能输入的变化, 用SODA(Simple Ocean Data Assimilation)(1901—2010)资料估算了风向南海表层流(表层地转流+表层非地转流)的能量输入。结果表明, 风向南海表层流、表层地转流和表层非地转流输入的能量总体均呈减少趋势, 110年间分别减小了约56%、65%和49%。导致风能输入减小的最主要因素是风应力的减弱(减小了35%)。由于南海受季风系统的控制, 风向表层流及其各成分输入的能量呈现出显著的季节性变化。冬季风能输入最强, 高值区位于南海西部及北部区域, 呈一个显著的“回力镖”状结构。这些结果对深入认识南海环流具有理论意义。  相似文献   

重庆红池坝地电场变化分析     

董蕾  龚丽文 《大地测量与地球动力学》2018,38(9):986-990

利用磁静日时序叠加方法和FFT频谱分析方法对红池坝地电场观测资料进行逐月处理，并与巫山建坪台地磁观测资料进行对比，分析红池坝地电场静日变化特征；计算红池坝台站磁暴期间产生的感应电场，与地电场观测数据对比，分析地电暴的特征。结果表明，静日随着月份的变化，相位发生变化，与巫山建坪地磁Sq变化一致；1月、2月、11月、12月的地电场日变幅明显小于其他月份；地电场显著周期成分与磁静日地磁场相同，并且通过周期成分的逐月对比分析得到，地电场与地磁D分量的不同周期成分的频谱值随时间的变化基本一致；某一方向的地电暴与该垂直方向的磁暴和该地区的电性结构有关；地电暴观测值与地磁感应电流计算值呈线性关系；地电暴变化与K值呈指数关系。  相似文献   

弧形海岸裂流的数值模拟研究   总被引：3，自引：0，他引：3  

汪鸿  朱首贤  李训强  张文静  聂屿 《海洋学报(英文版)》2018,37(3):21-30

弧形海岸波浪产生的裂流严重危害人类活动，但是目前对其特征缺乏充分认识。本文对Haller物理模型实验和三亚大东海的数值模拟表明FUNWAVE模式具有较好的裂流模拟能力。基于该模式进行了多种弧形海岸条件的裂流数值模拟，给出裂流的一些特征：（1）海岸弯曲度增大，裂流增强；（2）海岸坡度对裂流有比较大的影响，太陡或太平缓的海岸不利于形成裂流；（3）海岸尺寸减小，裂流减弱；（4）波高和波周期增大，裂流增强，但是对于某些海岸而言，0.4m波高可能就存在危害比较大的裂流。  相似文献   

潮致泥沙全沙净输运解析模式     

储鏖  徐怡  陈永平  郁夏琰  王彪 《海洋工程》2020,38(4):61-72

泥沙运动作为水流和底床相互作用的纽带,是河流、河口及海岸工程研究的重要内容。在潮波作用明显的河口、海岸地区,周期性的动力作用下的泥沙运动具有往复和可逆的特征,因此研究这类水域的泥沙的净输运更具有实际的意义。基于泥沙输运和流速呈指数关系假设,建立潮流环境下的泥沙全沙净输运的解析解公式,并对该公式的计算结果和数值计算以及数学模型的结果进行了检验和验证,结果表明本研究提出的公式能较好地反应潮流环境下的泥沙净输运。由此,基于本公式采用潮流分潮调和常数可计算得到全沙净输运,并可以分析各分潮流及其相互作用与泥沙净输运的关系。研究结果显示,在受径流影响较大的半日潮河口,S2、MS4、M2三潮相互作用对全沙净输运的贡献显著高于通常的潮流不对称作用,即M2、M4的相互作用。此外,河口区域径流导致的余流对泥沙净输运的贡献不可忽略,特别是在洪季,大径流量条件下往往导致余流较大,其对泥沙净输运的贡献所占比例较大。  相似文献