联合BDS/GPS的北斗广域差分实时电离层延迟格网改正方法研究

研究并实现中国区域北斗广域差分实时电离层延迟格网改正算法,针对北斗单系统实时建立电离层延迟格网的不足,提出联合BDS/GPS的北斗广域差分实时电离层延迟改正方法。比较BDS、GPS以及BDS/GPS观测的实时电离层延迟格网,并利用北斗单频单点伪距定位进行精度验证。结果表明,在有效格网点覆盖充足的地区,BDS与GPS实时电离层延迟格网定位效果相当;而联合BDS/GPS观测的实时电离层延迟格网极大提高了偏远地区的单频定位精度与可定位历元数,也使原本单系统格网覆盖充足的地区定位效果得到进一步增强和稳定。     

GPS/PWV时间序列特征提取方法的研究

针对GAMIT/GLOBK软件解算得到的4 a GPS/PWV时间序列的特征提取问题,提出基于滤波辅助的部分集成经验模态分解（PEEMD）与Hilbert谱分析相结合的特征提取方法。首先,在PEEMD方法的基础上,结合滤波辅助的PEEMD方法与Hilbert谱分析,建立GPS/PWV时间序列特征提取模型;然后,将所提出的方法应用于TNML测站4 a的GPS/PWV长时间序列和7 d的GPS/PWV短时间序列分析中,并将滤波辅助的PEEMD结果与传统的小波分解结果进行对比。结果表明,该特征提取方法能准确有效地提取出 GPS/PWV时间序列中的周年周期和日周期特征分量,滤波辅助的PEEMD分解结果与小波分解结果一致,且提取的特征分量与原始信号更加吻合。     

Comparisons of several evaporation/precipitation datasets for the Bohai Sea based on salinity simulation

Evaporation (E) rate and precipitation (P) rate are two significant meteorological elements required in the ocean baroclinic modeling as external forcings. However, there are some uncertainties in the currently used E/P rates datasets, especially in terms of the data quality. In this study, we collected E/P rates data from ERA-40, NCEP/NCAR Reanalysis, HOAPS for the Bohai Sea and nine routine stations around Laizhou Bay, and made comparisons among them. It was found that the differences in E/P rates between land and sea are remarkable, which was due to the difference in underlying surfaces. Therefore, the traditional way of using E/P rates acquired on land directly at sea is not correct. Since no final conclusion has been reached concerning the net water transport between the Bohai Sea and the Yellow Sea, it is unfeasible to judge the adequacy of the four kinds of data by using the water budget equation. However, the E/P rates at ERA-40 sea points were considered to be the optimal in terms of temporal/spatial coverage and resolution for the hindcast of salinity variation in the Bohai Sea. Besides, using the 3-D hydrodynamic model HAMSOM (HAMburg Shelf Ocean Model), we performed numerical experiments with different E/P datasets and found that the E/P rates at sea points from ERA-40 dataset are better than those from NCEP/NCAR Reanalysis dataset. If NCEP/NCAR Reanalysis E/P rates are to be used, they need to be adjusted and tested prior to simulation so that more close-to-reality salinity values can be reproduced.     

Baja California 边缘PC14 岩芯海水表层温度及生产力变化的百年尺度记录

加利福尼亚流是北太平洋环流的重要组成部分,它的变化对全球气候及碳循环有重要影响.对位于东北太平洋低纬区BajaCalifornia外海的PC14柱状样进行了有机地球化学分析,重建了过去14ka来这一地区百年尺度的海水表面温度及生产力变化,发现其存在明显的B/A(Bling-Aller)和YD(Younger Drays)事件,但B/A和YD事件温度变化幅度小于中纬度地区.与中纬度加利福尼亚流系早中全新世温度降低不同,PC14全新世温度无明显变化趋势.这些结果表明了东太平洋低纬地区对高纬地区的气候响应以及沿岸上升流和ENSO现象对加利福尼亚流系中纬和低纬地区的影响不同.从冰消期到全新世,PC14生产力呈现阶段上升趋势,指示了由E1 Nino气候向La Nifia气候的转化以及沿岸上升流加强的总体趋势.在全新世中后期(6.5-3.8ka)生产力的降低,则可能是受ENSO加强的影响.在B/A暖期,PC14生产力增加不多,但氧最小层强度增加,这表明生产力变化不是东太平洋边缘海的氧最小层强化的控制因素.     

Perturbed solution of sea-air oscillator for the E1 Ni(n)o/La Ni(n)a-Southern Oscillation mechanism

A class of coupled system of the E1 Ni(n)o/La Ni(n)a-Southern Oscillation (ENSO) mechanism is studied. Using the perturbed theory, the asymptotic expansions of the solution for ENSO model are obtained and the asymptotic behavior of solution for corresponding problem is considered.     

Effects of vegetation and sewage load on mangrove crab condition using experimental mesocosms

Constructed wetlands, especially mangroves, have been studied for their usefulness in sewage treatment but the effects of mangrove vegetation and a sewage load on mangrove macrofauna have been given little attention. Ocypodid crabs are important components of mangrove forests and constitute good bioindicators of the functioning of the ecosystem as a whole. In constructed mangrove mesocosms, three vegetation treatments (bare substratum, and Avicennia marina and Rhizophora mucronata seedlings) were subjected to 0, 20, 60 and 100% sewage loads from a nearby hotel. The physiological condition of introduced Uca annulipes and Uca inversa was evaluated in terms of their RNA/DNA ratio after one, five and twelve months, and used as an indicator of ecological function in the system. Crab condition in 0% sewage load was similar to that of wild crabs throughout, suggesting no significant effects of the mesocosms on their RNA/DNA ratio. Overall, both species coped well with the administered sewage loads, suggesting good ecological function in the system. Both species manifested similar patterns in RNA/DNA ratio, being more affected by seasonal fluctuations than by sewage load and vegetation presence and type. Higher RNA/DNA ratios were recorded in the long compared to the short rainy season. Sewage enhanced crab condition in the bare substratum and R. mucronata treatments, especially after one year, probably as a result of enhanced food availability. Uca inversa may be more sensitive to sewage pollution than U. annulipes. In A. marina, no difference in crab condition was observed between sewage loads, and this mangrove yielded the best reduction in sewage impacts. Our results support the usefulness of constructed mangrove areas in sewage treatment, especially if planted with A. marina and inhabited by physiologically healthy ocypodid crabs to enhance the system's performance.     

Resolving physically and biologically driven suspended particulate matter dynamics in a tidal basin with a distribution-based model

Understanding suspended particulate matter (SPM) dynamics in coastal waters is crucial to assess changes in coastal sediment budgets and biogeochemical fluxes. SPM dynamics are subject to various physical and biological factors and processes such as, e.g. tidal currents and aggregation which can be enhanced by extracellular polymeric substances (EPS) that are produced by algae and bacteria. It is still unclear how the different factors and processes interact and together determine SPM dynamics. To unravel the interacting processes and factors, we propose a new distribution-based modeling approach. Based on the derivation of explicit equations for size distribution characteristics of SPM such as the average radius, we derived a model of reduced complexity characterized by low initialization and parameterization effort as well as low computational cost. The proposed 0D model includes the processes of aggregation and fragmentation due to shear, aggregation due to differential settling, deposition, resuspension and tidal exchange, and describes the evolution of the SPM concentration in the water column linked by the settling velocity to the change of the mass average radius of the aggregate distribution. A systematic parameter variation for critical bottom shear stress of erosion, the size of resuspended aggregates, the fractal dimension, the collision efficiency, and the aggregate strength has been performed and compared to observations in the back-barrier basin of Spiekeroog Island in the German Wadden Sea. This analysis confirms the hypothesis that in winter biological influences on SPM dynamics are smaller compared to summer. This is mainly reflected by a significant shift in the various parameters. We hence conclude that biological control mechanisms have a much more quantitative relevance for SPM dynamics than currently represented by state-of-the-art SPM transport models.     

Cadmium and phosphorus cycling in the water column of the South China Sea: The roles of biotic and abiotic particles

The concentrations of cadmium, phosphorus, and aluminum in size-fractionated phytoplankton, zooplankton, and sinking particles are determined using ICPMS to evaluate the roles of biotic and abiotic particles on the cycling and ratios of Cd and P in the water column. Plankton were collected with a filtration apparatus equipped with 10-, 60-, and 150-μm aperture plankton nets on two occasions (2002 and 2006), and sinking particles were sampled by moored sediment traps deployed at depths of 120, 600, and 3500 m from 2004 to 2005. In contrast to what our previous study revealed, i.e., that most of the other bioactive trace metals in plankton were strongly correlated with abiotic Al and adsorbed on phytoplankton [Ho, T.Y., Wen, L.S., You, C.F., Lee, D.C., 2007. The trace metal composition of size-fractionated plankton in the South China Sea: biotic versus abiotic sources. Limnol Oceanogr 52, 1776–88.], Cd/P ratios, ranging from 0.12 to 0.34 mmol/mol P, did not vary with Al and exhibited fairly consistent values among different sizes of plankton, showing that Cd was mostly incorporated on an intracellular basis. In terms of the sinking particles, fluxes in Cd and P as well as in Cd/P ratios were strongly influenced by both biotic and abiotic particles. Overall, the Cd/P ratios in the sinking particles ranged from 0.03 to 1.2 mmol/mol, with the highest value observed in traps at 120 m during the productive season. The lowest value was observed in deep water during high flux periods for lithogenic particles. At surface depth, flux and Cd/P ratios were elevated during the most productive season in the region. The elevated ratios in the traps at 120 m were most likely related to preferential uptake of Cd for the dominant species (coccolithophores) during the productive period. Relatively, Cd/P ratios sharply decreased with increasing Al flux in deep water and ratios were much lower than the expected Cd/P ratios obtained from the relative portion of lithogenic and biogenic particles, indicating that the adsorption of soluble P into lithogenic particles was significant in the deep water during high lithogenic particle flux periods. Using averaged annual fluxes and standing stock in the water column, the residence time of biogenic Cd and P are 0.10 and 0.20, 250 and 100, and 9100 and 5000 years respectively in the top 120 m, 600 m, and water column as a whole, also showing preferential removal for Cd in the euphotic zone but relatively higher removal rates for P in the deep water. Our study suggests that the shift in microalgal community structure along with input of lithogenic minerals are both potentially important factors in influencing Cd/P ratios in oceanic water on a geological time scale.     

Velocity potential formulations of highly accurate Boussinesq-type models

The highly accurate Boussinesq-type equations of Madsen et al. (Madsen, P.A., Bingham, H.B., Schäffer, H.A., 2003. Boussinesq-type formulations for fully nonlinear and extremely dispersive water waves: Derivation and analysis. Proc. R. Soc. Lond. A 459, 1075–1104; Madsen, P.A., Fuhrman, D.R., Wang, B., 2006. A Boussinesq-type method for fully nonlinear waves interacting with a rapidly varying bathymetry. Coast. Eng. 53, 487–504); Jamois et al. (Jamois, E., Fuhrman, D.R., Bingham, H.B., Molin, B., 2006. Wave-structure interactions and nonlinear wave processes on the weather side of reflective structures. Coast. Eng. 53, 929–945) are re-derived in a more general framework which establishes the correct relationship between the model in a velocity formulation and a velocity potential formulation. Although most work with this model has used the velocity formulation, the potential formulation is of interest because it reduces the computational effort by approximately a factor of two and facilitates a coupling to other potential flow solvers. A new shoaling enhancement operator is introduced to derive new models (in both formulations) with a velocity profile which is always consistent with the kinematic bottom boundary condition. The true behaviour of the velocity potential formulation with respect to linear shoaling is given for the first time, correcting errors made by Jamois et al. (Jamois, E., Fuhrman, D.R., Bingham, H.B., Molin, B., 2006. Wave-structure interactions and nonlinear wave processes on the weather side of reflective structures. Coast. Eng. 53, 929–945). An exact infinite series solution for the potential is obtained via a Taylor expansion about an arbitrary vertical position z = zˆ. For practical implementation however, the solution is expanded based on a slow variation of zˆ and terms are retained to first-order. With shoaling enhancement, the new models obtain a comparable accuracy in linear shoaling to the original velocity formulation. General consistency relations are also derived which are convenient for verifying that the differential operators satisfy a potential flow and/or conserve mass up to the order of truncation of the model. The performance of the new formulation is validated using computations of linear and nonlinear shoaling problems. The behaviour on a rapidly varying bathymetry is also checked using linear wave reflection from a shelf and Bragg scattering from an undulating bottom. Although the new models perform equally well for Bragg scattering they fail earlier than the existing model for reflection/transmission problems in very deep water.