Reconstruction of vertical thermal structure from several subsurface temperatures in the China Seas and adjacent waters

Empirical Orthogonal Function (EOF) analysis is used in this study to generate main eigenvector fields of historical temperature for the China Seas (here referring to Chinese marine territories) and adjacent waters from 1930 to 2002 (510 143 profiles). A good temperature profile is reconstructed based on several subsurface in situ temperature observations and the thermocline was estimated using the model. The results show that: 1) For the study area, the former four principal components can explain 95% of the overall variance, and the vertical distribution of temperature is most stable using the in situ temperature observations near the surface. 2) The model verifications based on the observed CTD data from the East China Sea (ECS), South China Sea (SCS) and the areas around Taiwan Island show that the reconstructed profiles have high correlation with the observed ones with the confidence level > 95%, especially to describe the characteristics of the thermocline well. The average errors between the reconstructed and observed profiles in these three areas are 0.69A degrees C, 0.52A degrees C and 1.18A degrees C respectively. It also shows the model RMS error is less than or close to the climatological error. The statistical model can be used to well estimate the temperature profile vertical structure. 3) Comparing the thermocline characteristics between the reconstructed and observed profiles, the results in the ECS show that the average absolute errors are 1.5m, 1.4 m and 0.17A degrees C/m, and the average relative errors are 24.7%, 8.9% and 22.6% for the upper, lower thermocline boundaries and the gradient, respectively. Although the relative errors are obvious, the absolute error is small. In the SCS, the average absolute errors are 4.1 m, 27.7 m and 0.007A degrees C/m, and the average relative errors are 16.1%, 16.8% and 9.5% for the upper, lower thermocline boundaries and the gradient, respectively. The average relative errors are all < 20%. Although the average absolute error of the lower thermocline boundary is considerable, but contrast to the spatial scale of average depth of the lower thermocline boundary (165 m), the average relative error is small (16.8%). Therefore the model can be used to well estimate the thermocline.

Neural network retrieval of ocean surface parameters from SSM/I data

A new algorithm based on the multiparameter neural network is proposed to retrieve wind speed (WS), sea surface temperature (SST), sea surface air temperature, and relative humidity ( RH) simultaneously over the global oceans from Special Sensor Microwave Imager (SSM/I) observations. The retrieved geophysical parameters are used to estimate the surface latent heat flux and sensible heat flux using a bulk method over the global oceans. The neural network is trained and validated with the matchups of SSM/I overpasses and National Data Buoy Center buoys under both clear and cloudy weather conditions. In addition, the data acquired by the 85.5-GHz channels of SSM/I are used as the input variables of the neural network to improve its performance. The root-mean-square (rms) errors between the estimated WS, SST, sea surface air temperature, and RH from SSM/I observations and the buoy measurements are 1.48 m s(-1), 1.54 degrees C, 1.47 degrees C, and 7.85, respectively. The rms errors between the estimated latent and sensible heat fluxes from SSM/I observations and the Xisha Island ( in the South China Sea) measurements are 3.21 and 30.54 W m(-2), whereas those between the SSM/ I estimates and the buoy data are 4.9 and 37.85 W m(-2), respectively. Both of these errors ( those for WS, SST, and sea surface air temperature, in particular) are smaller than those by previous retrieval algorithms of SSM/ I observations over the global oceans. Unlike previous methods, the present algorithm is capable of producing near-real-time estimates of surface latent and sensible heat fluxes for the global oceans from SSM/I data.

Impact of spatial resolution and spatial difference accuracy on the performance of Arakawa A-D grids

This paper alms at illustrating the impact of spatial difference scheme and spatial resolution on the performance of Arakawa A-D grids in physical space. Linear shallow water equations are discretized and forecasted on Arakawa A-D grids for 120-minute using the ordinary second-order (M and fourth-order (C4) finite difference schemes with the grid spacing being 100 km, 10 km and I km, respectively. Then the forecasted results are compared with the exact solution, the result indicates that when the grid spacing is I kin, the inertial gravity wave can be simulated on any grid with the same results from C2 scheme or C4 scheme, namely the impact of variable configuration is neglectable; while the inertial gravity wave is simulated with lengthened grid spacing, the effects of different variable configurations are different. However, whether for C2 scheme or for C4 scheme, the RMS is minimal (maximal) on C (D) grid. At the same time it is also shown that when the difference accuracy increases from C2 scheme to C4 scheme, the resulted forecasts do not uniformly decrease, which is validated by the change of the group A velocity relative error from C2 scheme to C4 scheme. Therefore, the impact of the grid spacing is more important than that of the difference accuracy on the performance of Arakawa A-D grid.

Equivalent-barotropic definition of tropospheric mean temperature

An equivalent-barotropic (EB) description of the tropospheric temperature field is derived from the geostrophic empirical mode (GEM) in the form of a scalar function Gamma(p, phi), where p is pressure and phi is 300-850-mb thickness. Baroclinic parameter phi plays the role of latitude at each longitudinal section. Compared with traditional Eulerian-mean methods, GEM defines a mean field in baroclinic streamfunction space with a time scale much longer than synoptic variability. It prompts an EB concept that is only based on a baroclinic field. Monthly GEM fields are diagnosed from NCEP-NCAR reanalysis data and account for more than 90% of the tropospheric thermal variance. The circumglobal composite of GEM fields exhibits seasonal, zonal, and hemispheric asymmetries, with larger rms errors occurring in winter and in the Northern Hemisphere (NH). Zonally asymmetric features and planetary deviation from EB are seen in the NH winter GEM. Reconstruction of synoptic sections and correlation analysis reveal that the tropospheric temperature field is EB at the leading order and has a 1-day phase lag behind barotropic variations in extratropical regions.

Shallow water tidal constituents in the Bohai Sea and the Yellow Sea from a numerical adjoint model with TOPEX/POSEIDON altimeter data

A numerical adjoint model with TOPEX/POSEIDON (T/P) altimeter data was set up to investigate the shallow water tidal constituents in the Bohai Sea and the Yellow Sea. Shallow water tidal constituents W-4, MS4 and M-6) in the Bohai Sea and the Yellow Sea were first extracted from nearly 10 years of T/P data and then assimilated into a nonlinear barotropic tidal model by using adjoint method in order to fully describe the tides in this area. The general patterns of M-4 and MS4 solutions were in good agreement with those of Kang et al. (Cont. Shelf. Res. IS (1998) 739.) and Lefevre et al., (J. Geophys. Res. 105 (2000) 8707.). The RMS values for the principal constituents and coastal constituents were obviously less than those calculated by Kang et al. (1998) and Lefevre et al. (2000). It was shown that the calculated tidal constituents charts obtained in the present study were more accurate than those in other models. In the future the model will be applied to other coastal areas and some semi-enclosed seas. (C) 2004 Elsevier Ltd. All rights reserved.

卫星高度计资料在海洋潮汐研究中的应用

本文依据收集到的392个地面验潮站8个主要分潮（M2、S2、K1、O1、N2、K2、P1及Q1）的调和常数，对现有7个全球大洋潮汐模式的准确度进行了检验，结果显示各模式在深海区域均达到了比较高的准确度，相互之间差别也不大。经验模式GOT00和CSR4.0、同化模式NAO99、反演同化模式TPXO7.0、数值同化模式FES2002和FES2004的M2分潮均方根偏差在3 cm左右，其它分潮（S2、K1、O1、N2、K2、P1及Q1）大约在1～2 cm。本文还依据中国近海18个岛屿的调和常数对其中的5个大洋潮汐模式的准确度进行了检验，结果表明，M2分潮均方根偏差在6～14 cm，明显高于大洋部分的偏差，其中日本国家天文台的潮汐模式NAO99在中国近海的结果相对较准确。 我们利用1992年8月至2008年8月的TOPEX/POSEIDON和JASON-1(T/P-J)卫星高度计资料，对沿卫星轨道的302816个站点进行了14个分潮的潮汐调和分析，得到了全球大洋潮汐的8个主要分潮以及2个气象分潮Sa、Ssa的经验同潮图。主要结果有：（1）各分潮在卫星上升轨道与下降轨道的交叉点(约7000个)相关性分析表明：M2分潮的振幅和迟角的相关系数很高（分别为0.9965和0.9961）；S2，K1，O1和Sa分潮也有较好的相关性（相关系数为0.94～0.99）；（2）该结果与392地面个验潮站吻合较好，其中M2分潮的振幅、迟角和向量的均方根偏差分别为：1.73 cm，2.340和2.93 cm；S2，K1和O1分潮的振幅、迟角和向量的均方根偏差为1 cm左右，5.250～7.270和1.5～2.1 cm，该精度与最近几年国际上的主要大洋潮汐模式的准确度相近；（3）首次通过卫星资料获得了Sa、Ssa分潮的同潮图。周期为1年的Sa分潮与大洋105个地面站相比，振幅、迟角和向量的均方根偏差分别为1.50 cm、18.360和2.16 cm。在此基础上，进一步分析了构成Sa、Ssa气象分潮的两个主要因素（海水密度以及海面气压）在全球的分布。 在T/P-J等卫星资料无法覆盖到南大洋和北冰洋，本文利用Princeton Ocean Model（POM）进行了数值模拟，模拟结果与162个地面实测站（其中南大洋30个，北冰洋132个）的观测比较一致。基于卫星资料分析的结果和数值模拟结果合并得到了全球大洋的8个主要分潮同潮图。在此基础上通过全球潮汐能量耗散的计算得到潮能通量的分布，并得到全球M2、S2、K1和O1分潮的潮汐能量耗散率为2.431TW、0.401TW、0.336TW和0.176TW。 本文还利用卫星资料对南海潮汐进行了研究，在中国南海，获得了主要的半日潮、全日潮、四分日分潮和长周期分潮（M2，S2，N2，K2，K1，O1，P1，Q1，M4, MS4，Sa, Ssa）的经验同潮图。与南海沿岸94个地面验潮站的数据符合得比较好，M2，S2，K1及O1等4个主要分潮的平均振幅差为2～4 cm，均方根偏差分别是9～11 cm.其它4个主要分潮N2，K2，P1，Q1的平均振幅差为1～2 cm，均方根偏差为2～4 cm。此外，本文还利用卫星高度计资料潮汐分析结果沿卫星轨道进行高通滤波，分离得出中国近海的M2，S2，K1及O1分潮的内潮信息。

台风海面风场的动力分析、四维同化及数值试验

台风是最具破坏性的海洋大气系统。台风及其引起的沿海强风暴潮和海上巨浪不仅给沿海地区人民的生命财产造成严重的损失，而且对海上交通运输、军事活动、海洋工程和渔业都带来严重影响。准确的台风海面风场是获得比较真实的海浪、风暴潮等海洋现象的关键所在。由于不准确的海面初始场和台风海面风场数值模式中物理过程不完善等问题，模拟预报台风海面风场的精度达不到要求，极大的影响了海浪、风暴潮等海洋过程的模拟预报精度。因此获得准确真实的台风海面风场不仅对国民经济的顺利健康发展起到至关重要的作用，而且会很好地促进海浪、风暴湖等过程的研究。中尺度大气数值模式MM5在灾害性天气的预报研究方面具有重要的地位，并在暴雨研究方面取得了成功。在本论文中，我们结合气象工作者和海洋学者在台风研究中的不同侧重点，耦合自由大气和边界层过程，考察海气相互作用对台风海面风场的作用，首次将MM5应用于台风海面风场的研究之中，这对台风海面风场的研究来说是一个新的起点。本论文在MM5中，将中国国家气象中心中期预报谱模式T63／T106分析和预报场与常规地面和探空观测资料相结合，合理调整模式参数(海面粗糙度等参数)，建立了一套适用于中国区域的台风海面风场的模拟、预报系统。本论文利用改造过的中尺度大气数值模式MM5对两个台风个例：9608号台风(HERB)和9711号台风(WINNIE)进行数值试验。对海面风场而言，海气热通量交换对海面风场发挥着重要作用。因此本论文研究海面热量通量交换对9608号台风的强度和中心位置的影响，这也是以前国内台风数值模式中疏于考虑的方面。最后将模式模拟风场用于波浪的模拟研究之中，考察模拟海面风场在海洋环境研究中应用的有效性；并与目前国内较先进的LAGFD-WIN海面动力风场模式对比，检验MM5在台风海面风场研究中的性能。研究结果表明，MM5较好的反映出台风特性，并且优于LAGFD-WIN海面动力风场模式结果。在考察台风不稳定扰动特征时，我们区别于以往的本征值方法，利用中尺度二维扰动模式，由MM5提供9711号台风数值试验结果作为扰动模式的初始场，从动力学角度研究台风过程的扰动特征。初始资料问题对台风模式的预报模拟精度来说是一个最大、最重要的问题。因此改善、弥补模式初始场所造成的不足是本研究论文的重点工作之一。目前，在国内关于MM5中的四维资料同化(FDDA)方案试验刚刚起步。在本论文中，我们成功的启动MM5的四维资料同化方案：分析逼近和观测逼近。我们改造模式，同时启动这两种逼近方法，充分发挥探空资料和地面观测资料各自的优越性，I探索不同尺度、不同类型的资料在台风海面风场的应用。尝试卫星高度计风场资料溶于MM5中的同化方案中，这是本研究论文的另一个创新之处。本文的主要结论是(1)对两个台风个例：9608号台风(HERB)和9711号台风(WINNIE)进行了控制试验(CNTL)研究，分析台风模拟过程的温度距平、海平面气压及海面风场分布特点。研究表明，两个台风过程分别在不同高度上具有暖中心结构；模拟出的两个台风环流都呈现出台风的非对称及涡旋型态，模拟出的台风强度令人满意。对移动路径来说，对9608号台风过程，12h模拟台风路径误差为1.3个纬度，0.7个经度，而24h的模拟误差则为0.4个纬度，0.2个纬度；而对于9711号台风过程，其12h模拟台风路径误差为1.2个纬度，1.6个经度；24h路径误差为1.9个纬度，1．5个经度；36h模拟路径误差为3.2个纬度，2.8个经度。我们认为，由于9711号台风过程不准确的初始场，9711号台风模拟路径精度逊色于9608号台风过程的结果。(2)9608号台风过程中感热通量和潜热通量交换，在台风中心附近，热通量较小，但在台风周围，存在热通量的高值压，随着台风强度的减弱，热量通量交换也随之减小。在海面上始终是海水给大气提供热量。海面潜热通量总为正通量，并且都大于相应时刻的感热通量，表明水汽通量对台风系统比感热通量更重要。在分析热通量在不同下垫面演变特征时发现，在下午2h左右，在水陆交界处的次之，上最大，陆地上最小。感热通量在陆地下垫面上最大，其峰值出现而在水域上的最小，对于潜热通量则是水域(3)应用9608号台风的模拟海面风场到海浪的数值模拟研究中，发现由于台风海面风场分布的不对称性(在台风前进方向的右侧风速最大)，也因此造成了海浪有效波高分布的不对称性，同时在台风影响的右前方也传播得较远。随着台风海面风场减弱，风浪能量也逐渐消耗，有效波高也逐渐降低。(4)在台风发展的动力学特征研究方面，首先从不稳定扰动理论角度出发，讨论了台风发展的条件，得到了和天气学分析的台风形成发展条件一致的判据；在台风不稳定扰动的数值试验方面，针对9711号台风过程进行了数值试验，数值试验结果表明：扰动环流型以倾斜的扰动特征出现，并略向西倾斜，这是发展型的扰动型态；促使中尺度扰动发展和维持的能源主要来自于基本流场的有效位能和扰动场的有效位能。(5)利用标准探空资料和卫星高度计风场资料，在MM5中对9608号台风进行了七个试验：一个控制试验，三个分析逼近试验(AW，AWTQ，ATQ)，两个观测逼近试验(IWT，IW)和一个同时进行分析和观测逼近的试验(AWTQ+IWT)。七个试验中海平面气压场都形成了闭合低压中心，海面风场具有台风的气旋型态，再次证明MM5对台风的模拟能力；在定量的描述上，AWTQ+IWT试验较好地模拟出台风的中心位置和强度。因此联合有相对好的垂直分辨率的探空资料以及相对于探空资料有好的时间和水平分辨率的地面资料，能有效地提高台风海面风场的模拟预报精度。由于没有同化SLP的观测资料到模式中，SLP成为确定FDDA有效程度的有力手段。我们发现同时同化风场和质量场(温度场和湿度场)的试验AWTQ对风场和质量场均有一致的正面影响；对由强烈动力作用和大尺度强迫的台风过程，风场优于质量场。试验AWTQ，AW和ATQ的结果表明在风场中只有非常少的质量场诱导信息。试验ATQ，IWT对风场，海平面气压场具有负面影响。而利用包含常规气象观测资料无法拥有的海面风场信息的高度计风场资料，仅进行风场同化的IW试验，对海面气压场有非常好的效果。结果表明而AW，AWTQ，IW，AWTQ+IWT在24h模拟期间，则对SLP的平均RMS有明显的减小，分别约为3％，9％，12％和8％。

复杂介质边界元法数值模拟研究

A major impetus to study the rough surface and complex structure in near surface model is because accuracy of seismic observation and geophysical prospecting can be improved. Wave theory study about fluid-satuated porous media has important significance for some scientific problems, such as explore underground resources, study of earth's internal structure, and structure response of multi-phase porous soil under dynamic and seismic effect. Seismic wave numerical modeling is one of the effective methods which understand seismic propagation rules in complex media. As a numerical simulation method, boundary element methods had been widely used in seismic wave field study. This paper mainly studies randomly rough surface scattering which used some approximation solutions based on boundary element method. In addition, I developed a boundary element solution for fluid saturated porous media. In this paper, we used boundary element methods which based on integral expression of wave equation to study the free rough surface scattering effects of Kirchhoff approximation method, Perturbation approximation method, Rytov approximation method and Born series approximation method. Gaussian spectrum model of randomly rough surfaces was chosen as the benchmark model. The approximation methods result were compared with exact results which obtained by boundary element methods, we study that the above approximation methods were applicable how rough surfaces and it is founded that this depends on and ( here is the wavenumber of the incident field, is the RMS height and is the surface correlation length ). In general, Kirchhoff approximation which ignores multiple scatterings between any two surface points has been considered valid for the large-scale roughness components. Perturbation theory based on Taylor series expansion is valid for the small-scale roughness components, as and are .Tests with the Gaussian topographies show that the Rytov approximation methods improves the Kirchhoff approximation in both amplitude and phase but at the cost of an extra treatment of transformation for the wave fields. The realistic methods for the multiscale surfaces come with the Born series approximation and the second-order Born series approximation might be sufficient to guarantee the accuracy of randomly rough surfaces. It could be an appropriate choice that a complex rough surface can be divided into large-, medium-, and small-scale roughness components with their scattering features be studied by the Kirchhoff or Rytov phase approximations, the Born series approximation, and the perturbation theory, respectively. For this purpose, it is important to select appropriate parameters that separate these different scale roughness components to guarantee the divided surfaces satisfy the physical assumptions of the used approximations, respectively. In addition, in this paper, the boundary element methods are used for solving the porous elastic wave propagation and carry out the numerical simulation. Based on the fluid-saturated porous model, this paper analyses and presents the dynamic equation of elastic wave propagation and boundary integral equation formulation of fluid saturated porous media in frequency domain. The fundamental solutions of the elastic wave equations are obtained according to the similarity between thermoelasticity and poroelasticity. At last, the numerical simulation of the elastic wave propagation in the two-phase isotropic media is carried out by using the boundary element method. The results show that a slow quasi P-wave can be seen in both solid and fluid wave-field synthetic seismograms. The boundary element method is effective and feasible.