Patterns of upper layer circulation variability in the South China Sea from satellite altimetry using the self-organizing map

Patterns of the South China Sea (SCS) circulation variability are extracted from merged satellite altimetry data from October 1992 through August 2004 by using the self-organizing map (SOM). The annual cycle, seasonal and inter-annual variations of the SCS surface circulation are identified through the evolution of the characteristic circulation patterns. The annual cycle of the SCS gener- al circulation patterns is described as a change between two opposite basin-scale SW-NE oriented gyres embedded with eddies: low sea surface height anomaly (SSHA) (cyclonic) in winter and high SSHA (anticyclonic) in summer half year. The transition starts from July--August (January--February) with a high (low) SSHA tongue east of Vietnam around 12°～14° N, which de- velopa into a big anticyclonic (cyclonic) gyre while moving eastward to the deep basin. During the transitions, a dipole structure, cyclonic (anticyclonic) in the north and anticyclonic (cyclonic) in the south, may be formed southeast off Vietnam with a strong zonal jet around 10°～12° N. The seasonal variation is modulated by the interannual variations. Besides the strong 1997/1998 e- vent in response to the peak Pacific El Nino in 1997, the overall SCS sea level is found to have a significant rise during 1999～ 2001, however, in summer 2004 the overall SCS sea level is lower and the basin-wide anticyclonic gyre becomes weaker than the other years.     

South China Sea wave characteristics during typhoon Muifa passage in winter 2004

The responses to tropical cyclones of ocean wave characteristics in deep water of the western Atlantic Ocean have been investigated extensively, but not the regional seas in the western Pacific such as the South China Sea (SCS), due to a lack of observational and modeling studies there. Since monsoon winds prevail in the SCS but not in the western Atlantic Ocean, the SCS is unique for investigating wave characteristics during a typhoon’s passage in conjunction with steady monsoon wind forcing. To do so, the Wavewatch-III (WW3) is used to study the response of the SCS to Typhoon Muifa (2004), which passed over not only deep water but also the shallow shelf of the SCS. The WW3 model is forced by the NASA QuikSCAT winds and tropical cyclone wind profile model during Typhoon Muifa’s passage from 0000UTC 16 on November to 1200UTC on 25 November 2004. The results reveal the unique features of the SCS wave characteristics in response to Muifa, such as non-decaying, monsoon-generated swell throughout the typhoon period and strong topographic effects on the directional wave spectrum.     

Enhanced seamount location database for the western and central Pacific Ocean: Screening and cross-checking of 20 existing datasets

Seamounts are habitats of considerable interest in terms of conservation and biodiversity, and in terms of fisheries for bentho-pelagic and pelagic species. Twenty previously compiled datasets including seamount/underwater feature lists, bathymetric maps and emerged feature maps from different sources (ship-derived and satellite altimetry-derived) at different spatial scales (from individual cruise to worldwide satellite data) were gathered in order to compile an enhanced list of underwater features for parts of the western and central Pacific Ocean (WCPO). The KL04 dataset [Kitchingman, A., and Lai, S., 2004. Inferences on potential seamount locations from mid-resolution bathymetric data. Fisheries Centre Research Reports 12 (5), 7–12], listing seamount positions and depths as calculated from satellite altimetry-derived bathymetry, provided the baseline data for this study as it covered the entire region of interest and included summit depth information. All KL04 potential seamounts were cross-checked with other datasets to remove any atolls and islands that had been incorrectly classified as seamounts, to add seamounts undetected by KL04, to update the overall database (geolocation, depth, elevation, and name) and to compile a 12-class typology of the different types of underwater features. Of the 4626 potential seamounts identified in KL04, 719 were multiple identifications of the same large underwater features and 373 (10%) were actually emerged banks, atolls and islands, leaving 3534 actual underwater features. Conversely, 487 underwater features were documented in other datasets but not registered by KL04. The screening of all the potential WCPO seamounts produced a final list of 4021 underwater features with agreed upon position and information. This enhanced list should have many applications in oceanography, biodiversity conservation and studies of the influence of seamounts on pelagic ecosystems and fisheries.     

Persian gulf and Oman sea tide modeling using satellite altimetry and tide gauge data (TM-IR01)

Satellite altimetry observations and tide gauge data are invaluable tools to diagnose and resolve tidal constituents over the Oceans and Seas. The aim of this study is to introduce a new purely empirical tide model named TM-IR01 in the Persian Gulf, Oman Sea, and North Indian Ocean. The observations of three altimeter sensors including TOPEX/POSIDON, JASON1, and JASON2 and 13 coastal tide gauge (TG) stations are processed and analyzed in this research. First of all, the least square spectral analysis is utilized to recover the significant tide components and consequently the amplitude and phases of the constituents are found during the tide modeling. Finally, the analysis results are interpolated into a grid of 1/4° using the Kriging method. TM-IR01 model is validated by comparing with TG stations and global tide models. It is shown that for main tidal frequencies M2, S2, K1, and O1 the root mean square error (RMSE) between TM-IR01 and TG stations results are 0.372, 0.130, 0.141, and 0.084?m, respectively, and also the RMSE between TM-IR01 and FES2004 models are 0.231, 0.087, 0.027, and 0.042?m, respectively. Validating with FES2012 and Tpxo7.2, the results obtained are close to the above values.     

Accuracy assessment of global ocean tide models in the South China Sea using satellite altimeter and tide gauge data

In this study, to meet the need for accurate tidal prediction, the accuracy of global ocean tide models was assessed in the South China Sea (0°–26°N, 99°–121°E). Seven tide models, namely, DTU10, EOT11a, FES2014, GOT4.8, HAMTIDE12, OSU12 and TPXO8, were considered. The accuracy of eight major tidal constituents (i.e., Q₁, O₁, P₁, K₁, N₂, M₂, S₂ and K₂) were assessed for the shallow water and coastal areas based on the tidal constants derived from multi-mission satellite altimetry (TOPEX and Jason series) and tide gauge observations. The root mean square values of each constituent between satellite-derived tidal constants and tide models were found in the range of 0.72–1.90 cm in the deep ocean (depth>200 m) and 1.18–5.63 cm in shallow water area (depth<200 m). Large inter-model discrepancies were noted in the Strait of Malacca and the Taiwan Strait, which could be attributable to the complicated hydrodynamic systems and the paucity of high-quality satellite altimetry data. In coastal regions, an accuracy performance was investigated using tidal results from 37 tide gauge stations. The root sum square values were in the range of 9.35–19.11 cm, with the FES2014 model exhibiting slightly superior performance.     

GNSS-R海面测高算法

研究了GNSS-R海面测高的原理和主要误差源,对测高中的两个关键算法进行了研究,包括利用梯度法直接从实测数据中计算镜点位置,利用非线性回归算法计算相关波形峰值点的位置,并在此基础上研究了散射延迟的问题。     

Global ocean tides from Geosat altimetry by Quasi-Harmonic analysis

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基于卫星测高与卫星测温的表层流产品生成方法应用评估

提高海洋表层流的精度与分辨率对于相关应用领域至关重要.研究引入海表面温度(sea surface temperature,SST)信息对高度计导出流场的改进效果,计算了 2018年每日无间隔的全球海洋表层流速度.通过增加热量守恒方程约束,引入卫星测温产品,在地转流基础上生成表层流产品,并与现场漂流浮标速度比较,评估了使...     

联合多种测高数据确定中国边缘海及全球海域的垂线偏差

On the basis of gravity field model （EIGEN_CG01C）, together with multi-altimeter data, the improved deflection of the vertical gridded in 2＇×2＇ in China marginal sea and gridded in 5＇×5＇ in the global sea was determined by using the weighted method of along-track least squares, and the accuracy is better than 1.2^# in China marginal sea. As for the quality of the deflection of the vertical, it meets the challenge for the gravity field of high resolution and accuracy, it shows that, compared with the shipboard gravimetry in the sea, the accuracy of the gravity anomalies computed with the marine deflection of the vertical by inverse Vening-Meinesz formula is 7.75 m.s ^-2.     

联合卫星测高和模式资料研究海水热含量变化

本文在考虑洋底压力变化的情况下,利用2003~2008年融合多颗卫星的测高资料估计了全球和中国近海的海水热含量变化.顾及洋底压力(OBP)变化以及热膨胀系数随海水深度变化的影响,提出的改进方法提高了对中高纬度地区热含量变化的估算精度.在OBP变化较为明显的北太平洋区域I(30°N~50°N,170°E~190°E)、南印度洋区域II(40°S~60°S,100°E~120°E)和南太平洋区域III(40°S~60°S,100°W~120°W),改进方法的均方差较传统方法分别降低了16.3%、60.5%和48.4%.同时研究表明,卫星测高的精度以及盐度变化是影响中高纬度地区热含量估计精度的重要因素.在中国近海地区,东海和黄海的热含量主要表现为周年变化;南海区域的热含量除周年变化外,还存在半周年项和年际变化项,且南海的海水热含量近年有增加的趋势.