基于卫星遥感数据的全球表层流场反演重构

利用2000—2008年的卫星高度计资料和QuikSCAT风场资料,反演了全球的海表的地转流和Ekman流,将两者合成后生成了0.5°×0.5°的逐周全球表层流产品。在计算Ekman流的时候,引入了权重函数,改进了Lagerloef方法中Ekman流在25°S和25°N上的不连续问题。分析表明:卫星资料反演的流产品能够反映出海表流场的特征,将其分别与TAO观测和SCUD流产品进行定量化的比较显示,所得流产品具有较高的反演精度和可信度,说明改进的方法是有效的。     

海表地转流差商计算试验分析

基于卫星高度计海面异常高度资料反演的海表地转流场在海洋学研究中应用广泛。针对Arbic等(2012)提出的海表地转流差商计算改进算法,以南海为试验海区,通过涡动能和中尺度涡自动识别计算试验对差商改进方法进行有效性检验。结果表明,七点中差法计算的海表地转流场比其他常用差商方法更利于中尺度涡旋外边界确定,得出的涡动能分布规律和数值大小也更符合实际。     

基于变分理论的AVHRR海表温度反演应用及效果评估

基于变分理论算法实现了METOP-A卫星AVHRR传感器探测数据的海洋表面温度变分反演,进行了连续1个月的海表温度反演试验,并分别从全球、分纬度带和天气系统活跃区域3个方面,将变分反演结果（VAR SST）与利用统计回归方法反演相同卫星得到的海表温度产品（GBL SST）、其他海温融合产品（OISST）及实际浮标观测数据等进行一系列评估。从全球评估指标看出,以OISST为参照,VAR SST要优于GBL SST;以浮标观测为参照,VAR SST略逊于GBL SST,而且VAR SST还改进了GBL SST随时间波动大的缺点;从分纬度带对比看出,在与OISST对比时,VAR SST在低纬度地区和北半球中纬度地区的质量要优于GBL SST,海温反演精度较高。研究还表明,由于变分方法考虑了大气状态的变化,能够更加有效订正卫星遥感过程中大气的削弱作用,从而反演出精度更高的海表温度,尤其在天气系统较为复杂的区域效果明显。     

基于ARGO资料的MTSAT海温产品误差分析

利用全球海洋观测网计划ARGO浮标的表层海温测量值分析了MTSAT卫星的海温反演误差。结果显示,平均绝对误差为0.73℃,均方根误差为0.885℃,满足应用需要;海温反演异常点多分布在30°N以北的高纬区域。为了确保海温产品数据的可靠性,需要通过数据误差控制技术来检测和控制海表温度反演的异常值,影像边缘和高纬地区的区域数据应谨慎使用。     

HJ-1B 卫星海表温度定量反演业务化算法研究——以中国北部海区为例

利用中国2008年9月发射的自主 HJ-1B 卫星热红外遥感影像数据,基于实测数据对已有海表温度反演的单窗算法进行了改进与简化,重新订正了大气透射率和大气平均作用温度估算方程,建立了基于实测数据验证的 HJ-1B 卫星海表温度定量反演业务化算法.将本算法与段四波等的改进算法用于实验海区海表温度的反演,反演结果与卫星同步实测海温数据的对比表明:本研究算法反演结果与现场同步实测海表温度平均误差约为0.76,℃段四波等改进算法反演结果平均误差约为1.09℃.本算法为 HJ-1B 卫星海表温度产品的业务化应用提供了便捷可行的方案     

基于机器学习的SMAP卫星海表盐度反演

针对传统海表盐度的物理机制反演模型拟合过程复杂且反演精度不高等问题,借助大范围、全天时、L波段探测的SMAP卫星微波海洋遥感产品,以北太平洋(135°～165°E,15°～45°N)范围为研究海域,利用深层神经网络(Deep Neural Network, DNN)和支持向量机(Support Vector Machine, SVM)建立海表盐度(Sea Surface Salinity, SSS)遥感反演模型。验证结果表明:DNN与SVM模型测试集反演SSS与Argo(Array for Real-time Geostrophic Oceanography))实测SSS的均方根误差(Root Mean Square Error, RMSE)分别为0.179 0和0.257 0,平均绝对误差(Mean Absolute Error, MAE)为0.129 3和0.182 1,最小绝对误差为0.642 6和2.038 0,最大绝对误差为1.324 1和2.373 2,反演模型数据与实测Argo数据拟合后的的相关系数分别为0.89和0.84。总体来看,DNN模型比SVM模型的反演精度更高,...     

SMAP卫星的RBF神经网络海表盐度遥感反演

针对传统海表盐度遥感反演精度不高、影响因素较少等问题,本文基于SMAP(Soil Moisture Active Passive)卫星L2C(Level 2 C)数据、Argo(Array for Real-time Geostrophic Oceanography)数据和其他辅助数据,以太平洋部分海域（160°E～120°W,0°～30°N）为研究区域,综合考虑海面粗糙度以及白冠覆盖率等参量,利用径向基神经网络建立RBF亮温增量模型,并对平静海面亮温进行修正,然后基于Meissner-Wentz介电常数模型得到反演后的盐度值。验证结果表明：模型预测盐度和SMAP卫星盐度相对于Argo实测盐度的均方根误差分别为0.4和0.5,平均绝对误差分别为0.3和0.4。实验证明,利用RBF神经网络建立的亮温增量模型可以提高海表盐度反演的精度,对海表盐度反演具有实用意义。     

基于再分析数据的南大洋区域Ekman流时空分布规律研究

南大洋Ekman输运是全球大气-海洋耦合气候系统的重要组成部分,对该区域Ekman动力过程的研究极为重要.首先基于实测数据和文献资料,对GEKCO2 (Geostrophic and Ekman Current Observatory 2)产品提供的Ekman流数据进行了评估,验证了数据的有效性;并结合CCMP(cro...     

NOAA/AVHRR卫星海表温度在西北太平洋的印证及分析

本文详细分析了TeraScan系统反演NOAA/AVHRR卫星海表温度的过程,解决了反演过程中的海陆匹配问题和云检测过程中的误检、漏检问题,处理得到2002年(5°～45°N)、(105°～150°E)区域内的卫星海表温度数据.利用东北亚地区海洋观测系统NEAR-GOOS提供的现场海表温度数据做比较,印证NOAA/AVHRR海表温度在西北太平洋海域的精度,并分析其误差产生的来源.     

基于深度神经网络的海表盐度反演

海表盐度（Sea Surface Salinity,SSS）是研究海洋对全球气候影响的重要参量,欧洲航天局（European Space Agency,ESA）设计研发的SMOS(Soil Moisture and Ocean Salinity)是专用于探测海水盐度的卫星之一。受射频干扰（Radio Frequency Interference, RFI）等因素的影响,SMOS卫星盐度产品的精度难以达到预期效果。为了提高SMOS卫星海表盐度产品精度,本文提出一种基于深度神经网络的海表盐度反演算法。以太平洋中部海域（150°E～180°,5°～30°N）为研究区域,利用Argo浮标实测盐度数据为参考真值,将SMOS卫星L1C、L2级产品与Argo盐度数据进行时空匹配。并根据海洋遥感和辐射传输理论,选取亮温（Brightness Temperature,TB）、海表温度（Sea Surface Temperature,SST）、降雨率（Rain Rate,RR）、波高（Significant Wave Height,SWH）、纬向风速（Zonal Wind Speed,ZWS）、经向风速（...     

An approximate solution of wave-modified Ekman current for gradually varying eddy viscosity

An approximate steady solution of the wave-modified Ekman current is presented for gradually varying eddy viscosity by using the WKB method with the variation of parameters technique. The parameters involved in the solution can be determined by the two-dimensional wavenumber spectrum of ocean waves, wind speed, the Coriolis parameter and the densities of air and water. The solution reduces to the exact solution when the eddy viscosity is taken as a constant. As illustrative examples, for a fully developed wind-generated sea with different wind speeds and a few proposed gradually varying eddy viscosities, the current profiles calculated from the approximate solutions are compared with those of the exact solutions or numerical ones by using the Donelan and Pierson wavenumber spectrum, the WAM wave model formulation for wind input energy to waves, and wave energy dissipation converted to currents. It is shown that the approximate solution presented has an elegant form and yet would be valid for any given gradually varying eddy viscosity. The applicability of the solution method to the real ocean is discussed following the comparisons with published observational data and with the results from a large eddy simulation of the Ekman layer.     

Coupling winds to ocean surface currents over the global ocean

A Wind stress–Current Coupled System (WCCS) consisting of the HYbrid Coordinate Ocean Model (HYCOM) and an improved wind stress algorithm based on Donelan et al. [Donelan, W.M., Drennan, Katsaros, K.B., 1997. The air–sea momentum flux in mixed wind sea and swell conditions. J. Phys. Oceanogr. 27, 2087–2099] is developed by using the Earth System Modeling Framework (ESMF). The WCCS is applied to the global ocean to study the interactions between the wind stress and the ocean surface currents. In this study, the ocean surface current velocity is taken into consideration in the wind stress calculation and air–sea heat flux calculation. The wind stress that contains the effect of ocean surface current velocity will be used to force the HYCOM. The results indicate that the ocean surface velocity exerts an important influence on the wind stress, which, in turn, significantly affects the global ocean surface currents, air–sea heat fluxes, and the thickness of ocean surface boundary layer. Comparison with the TOGA TAO buoy data, the sea surface temperature from the wind–current coupled simulation showed noticeable improvement over the stand-alone HYCOM simulation.     

The effects of random surface waves on the steady Ekman current solutions

The response of near-surface current profiles to wind and random surface waves are studied based on the approach of Jenkins [1989. The use of a wave prediction model for driving a near surface current model. Dtsch. Hydrogr. Z. 42, 134–149] and Tang et al. [2007. Observation and modeling of surface currents on the Grand Banks: a study of the wave effects on surface currents. J. Geophys. Res. 112, C10025, doi:10.1029/2006JC004028]. Analytic steady solutions are presented for wave-modified Ekman equations resulting from Stokes drift, wind input and wave dissipation for a depth-independent constant eddy viscosity coefficient and one that varies linearly with depth. The parameters involved in the solutions can be determined by the two-dimensional wavenumber spectrum of ocean waves, wind speed, the Coriolis parameter and the densities of air and water, and the solutions reduce to those of Lewis and Belcher [2004. Time-dependent, coupled, Ekman boundary layer solutions incorporating Stokes drift. Dyn. Atmos. Oceans. 37, 313–351] when only the effects of Stokes drift are included. As illustrative examples, for a fully developed wind-generated sea with different wind speeds, wave-modified current profiles are calculated and compared with the classical Ekman theory and Lewis and Belcher's [2004. Time-dependent, coupled, Ekman boundary layer solutions incorporating Stokes drift. Dyn. Atmos. Oceans 37, 313–351] modification by using the Donelan and Pierson [1987. Radar scattering and equilibrium ranges in wind-generated waves with application to scatterometry. J. Geophys. Res. 92, 4971–5029] wavenumber spectrum, the WAM wave model formulation for wind input energy to waves, and wave energy dissipation converted to currents. Illustrative examples for a fully developed sea and the comparisons between observations and the theoretical predictions demonstrate that the effects of the random surface waves on the classical Ekman current are important, as they change qualitatively the nature of the Ekman layer. But the effects of the wind input and wave dissipation on surface current are small, relative to the impact of the Stokes drift.     

Response of the western North Pacific subtropical ocean to the slow-moving super typhoon Nanmadol

Based on in-situ observation,satellite and reanalysis data,responses of the western North Pacific subtropical ocean(WNPSO)to the slow-moving category 5 super typhoon Nanmadol in 2011 are analyzed.The dynamical response is dominated by near-inertial currents and Ekman currents with maximum amplitude of 0.39m/s and 0.15m/s,respectively.The near-inertial currents concentrated around 100m below the sea surface and had an e-folding timescale of 4 days.The near-inertial energy propagated both upward and downward,and the vertical phase speed and wavelength were estimated to be 5m/h and 175m,respectively.The frequency of the near-inertial currents was blue-shifted near the surface and redshifted in ocean interior which may relate to wave propagation and/or background vorticity.The resultant surface cooling reaches-4.35℃ and happens when translation speed of Nanmadol is smaller than 3.0m/s.When Nanmadol reaches super typhoon intensity,the cooling is less than 3.0℃ suggesting that the typhoon translation speed plays important roles as well as typhoon intensity in surface cooling.Upwelling induced by the slow-moving typhoon wind leads to typhoon track confined cooling area and the right-hand bias of cooling is slight.The mixed layer cooling and thermocline warming are induced by wind-generated upwelling and vertical entrainment.Vertical entrainment also led to mixed layer salinity increase and thermocline salinity decrease,however,mixed layer salinity decrease occurs at certain stations as well.Our results suggest that typhoon translation speed is a vital factor responsible for the oceanic thermohaline and dynamical responses,and the small Mach number(slow typhoon translation speed)facilitate development of Ekman current and upwelling.     

简单海-气边界层模式中的埃克曼流动Ⅰ——无限深海的情形

近十余年来,海洋和大气相互作用这一课题日益受到人们的关注。从海-气边界层结构以及通过海面的物理量和化学量输送机制的研究到大尺度海洋和大气相互作用的研究都取得了可喜的成果。此外,还从海洋和大气相互作用的观点探索了风暴潮预报的新的可能途径[2]。然而,由于问题的复杂性,通过海面以及海-气边界层的物理量的小尺度输送机制迄未得到澄清,企图从本质上改善大尺度海洋和大气相互作用的理论是不现实的。     

近年来厄尔尼诺期间北赤道流输运的年际变化

为了研究近年来厄尔尼诺期间北赤道流输运的年际变化,本文利用海洋客观分析数据MOAA GPV(Grid Point Value of the Monthly Objective Analysis)以及P-vector方法计算了北太平洋绝对地转流,探讨了2001~2013年期间厄尔尼诺与北赤道流输运之间的关系。在此期间发生的4次厄尔尼诺事件中,北赤道流输运在2002~2003、2006~2007、2009~2010年的厄尔尼诺成熟期都出现了明显的增强,但是在2004~2005年的厄尔尼诺成熟期并没有明显的增强。进一步分析发现,在2002~2003年、2006~2007年、2009~2010年的厄尔尼诺成熟期,10°N以南的热带西北太平洋区域出现了负的海面高度异常和气旋式环流异常,这主要是由热带环流区域出现的西风异常和正的Ekman抽吸通过Rossby波西传到热带西太平洋区域所致;但是在2004~2005年厄尔尼诺成熟期,海面温度异常的分布明显不同,西风异常和正的Ekman抽吸异常明显北移,导致负的海面高度异常和气旋式环流异常出现在了10°N以北的西北太平洋区域,使得北赤道流输运在2004~2005年的厄尔尼诺成熟期没有明显的增强。     

基于高频地波雷达的多时间尺度海流研究

近海海流受多种动力过程及岸线岛屿的作用呈现空间和时间尺度上的复杂变化,而地波雷达由于其探测面积广、时间分辨率高的特点成为研究这些变化的有效手段。本文利用舟山海域多年高频地波雷达资料,通过潮流调和分析、低通滤波和相关性分析对该海域海流潮周期、极端事件、季节、年际尺度的动力过程进行了解译。研究表明,舟山海域属于正规半日潮,潮流运动形式以顺时针旋转流为主,流速大小在空间上为东北方向较大,往西南方向逐渐减小,并在近岸处得到增强。余流的年际变化并不显著,但存在着明显的季节变化,例如冬季为南向流,流速减小,空间分布上近岸较外海大,而夏季与之反向,为北向流,流速较大,空间分布较为均匀。进一步分析了风与余流之间的相关性,在大风期间,风与余流的速度相关系数在0.48～0.90之间,方向相关系数在0.55～0.68之间。极端事件发生时,速度、方向的相关系数分别高达0.92与0.91。总体而言,通过分析高频地波雷达数据能够较好地反映舟山海域海流的时空特征,为海洋灾害监测和污染物、藻华的输运研究提供依据。     

The statistical structure of synoptic variability ocean currents at the continental slope of the Laptev Sea and features of their generation by anemobaric forces

Based on vector-algebraic analysis of random processes, we study the statistical structure of the synoptic variability of currents measured by an ADCP in the upper mixed layer in the central part of the continental slope of the Laptev Sea in 2006–2007. The results of statistical analysis show that in some cases the synoptic currents in the surface layer of the sea are signs of wind drift currents. This is indicated by the high correlation between the tangential friction of wind and currents, as well as the reversal of the depth of current vectors and the major axes of the ellipses of the mean-square deviation of the Ekman spiral. Due to the large variability of wind flows and stratification of water masses, the penetration depth of these currents is small and varies from 6 to 30 m, with pronounced seasonal variation. In deeper layers, no relationship between the currents and anemobaric forces is traced. It is concluded that the fluctuations of synoptic scale currents in the area of the continental slope of the Laptev Sea represent a superposition of Ekman drift currents and movements associated with free baroclinic Kelvin waves. These currents are the dominant contributor in the upper 30-m layer of the ocean, while waves play a key role in deeper waters.