MODAS试验数据统计分析

模块化海洋数据同化系统（MODAS）通过同化卫星遥感测得的海面温度和海面高度,产生一种动态气候态,能够更接近地预报出海洋的真实状况。介绍了MODAS基本原理,并选择试验海区,对MODAS数据进行了统计和分析。     

中国海及邻近海域卫星观测资料同化试验

利用1个基于POMgcs海洋模式和多重网格三维变分同化方法建立的中国海及邻近海域海面高与三维温盐流数值预报模型,通过一系列数值试验,研究了同化卫星测高和卫星遥感海面温度观测资料对该模型预报能力的影响。试验结果表明,同化卫星测高资料可明显改善海面高度与三维温度和盐度的分析预报效果,使1 200 m以上的温度预报误差减小0.16℃,并能有效提高对海洋中尺度现象的预报能力;同化卫星遥感海面温度对100 m以上的温度和盐度的预报效果有所改善,可使海面温度的预报误差减小10%。     

卫星遥感海表温度资料和高度计资料的变分同化

利用国家气候中心正在发展的第二代全球海洋资料同化系统(BCC_GODAS2.0),针对多变量同化的协调性问题,发展了一种基于三维变分框架(3DVAR)下的高度计和海表温度(SST)相互约束的同化方法。该方法使海面高度和SST资料在同一个动力约束关系下进行同化。在一般方法中,海面高度和SST观测项是代价函数中2个独立的观测项,海面高度项引入动力高度计算公式,海表温度项用统计关系进行垂向投影。在代价函数的实际求解的计算过程中,虽然其总体积分效应受海面高度观测的约束,但整个水柱中各层温盐分析变量的调整是无序的。针对这个问题,文章提出一种新的同化方案。该方案将SST的观测项并入海面高度观测项中,海面高度的一部分,确切说是上层海洋部分,由SST决定,因此至少在SST的统计关系能影响到深度的上层海洋,在代价函数的求解过程中,温盐的调整是受较强的统计关系约束的,而这种统计关系的有效性已经在很多SST的同化试验中被其他学者广泛应用并证明。利用该方法,对1993—1997年的AVHRR卫星遥感海表温度资料进行变分同化试验,用TAO、OISST和SODA数据集进行检验证明,通过对卫星遥感资料的同化能够有效改进对海洋温度和盐度的估...     

卫星遥感SSH数据在水下温度垂直分布反演中的应用研究

结合MODAS基本原理,应用动态气候态的数据同化概念,阐述应用卫星遥感SSH数据反演水下温度垂直分布的理论和方法,并利用西太平洋海区的ARGO数据进行试验,建立了单点的温度剖面,通过引入SSH数据进行水温反演,演示结果显示了卫星遥感SSH资料同化的有效性,并得出分析结论。     

南海北部海洋四维变分同化试验研究

为了研究四维变分同化方法在南海北部海洋数值预报中的适用性,使用海洋区域模式(ROMS),建立了南海北部海洋资料四维变分同化系统,进行了温盐廓线和海面温度数据同化试验,初步对比分析了三种四维变分实现方法的同化效果。研究结果表明,四维变分同化方法具有较好的同化效果,其中,增量强约束方法(I4DVar)具有较好的稳定性,其稳定性高于4DPSAS和R4DVar。本文研究成果为建立南海业务化海洋四维变分同化及预报系统奠定技术基础。     

基于ROMS模式的南海SST与SSH四维变分同化研究

卫星遥感观测获得了大量高分辨率的海面实时信息,包括海面温度（SST）和海面高度（SSH）等,同化进入数值模式可有效提升模拟精度。本文基于ROMS模式与四维变分同化方法（4DVAR）,使用AVHRR SST和AVISO SSH数据,开展了南海区域同化实验。为检验同化的效果,分别利用HYCOM再分析资料和Argo温盐实测数据分析了同化结果的海面高度、流场及温盐剖面的精度。对比结果表明,SST和SSH的同化能够改善ROMS的模拟结果:同化后海面高度场能够更为准确地捕捉海洋的中尺度特征,与HYCOM海面高度再分析资料相比,平均绝对偏差和均方根误差分别为0.054 m和0.066 m;与HYCOM 10 m层流场相比,东向与北向流速平均绝对偏差分别为0.12 m/s和0.11 m/s,相比未同化均提升约0.01 m/s;温盐同化结果与Argo温盐实测具有较高的一致性,温度和盐度平均绝对偏差为0.45℃、0.077,均方根误差为0.91℃、0.11,单个的温盐廓线对比说明,同化结果与HYCOM再分析资料精度相当。     

利用卫星观测海面信息反演三维温度场

基于历史观测的温盐剖面资料,采用回归分析方法统计出海面温度异常、海面动力高度异常与温度剖面异常之间的相关关系;然后利用高分辨率的卫星遥感海表面温度(SST)和卫星观测海面高度(SSH)信息重构了三维海洋温度场。在台湾岛周边海域建立了时间分辨率为天、空间分辨率为0.25°×0.25°的三维温度分析场。通过与实测资料的比较分析,文章所构建的分析场能够较好地描述海洋三维温度场的结构特征,能够较为真实地反映海洋的中尺度变化过程。该分析场可以作为海洋数值模式的初始场,也可以作为伪观测同化到海洋数值再分析和预报系统中,进而改善三维温、盐、流的数值再分析和预报。     

气候模式中海洋数据同化对热带降水偏差的影响

本文采用海洋卫星观测海表温度(SST)和海面高度异常(SLA)数据,对国家海洋局第一海洋研究所地球系统模式FIO-ESM(First Institute of Oceanography Earth System Model version 1.0)中海洋模式分量进行了集合调整卡尔曼滤波(EAKF)同化,对比分析了大气环流、湿度和云量对海洋数据同化的响应,探讨了海洋同化对热带降水模拟偏差的影响。结果表明:海洋数据同化能有效改善海表温度和上层海洋热含量的模拟,30°S~30°N纬度带内年平均SST的绝均差降低60%。同化后大气模式模拟的赤道两侧信风得到明显改善,上升气流在赤道以北热带地区增强而在赤道以南热带地区减弱,热带降水模拟的动力结构更为合理,水汽和云量分布也更切合实际。热带年平均降水的空间分布和强度在同化后均得到改善,赤道以南的纬向年平均降水峰值显著降低,降水偏差明显减小,同化后30°S~30°N纬度带内年平均降水绝均差降低35%。     

南海TOPEX海面高度资料的混合同化试验

应用普林斯顿海洋模式（POM），对冬季南海由TOPEX／Poseidon得到的卫星遥感海面高度资料进行混合（blending)同化试验。混合同化的权重系数由以下两者决定：南海POM模式对冬季风强迫产生响应的海面高度场之标准方差；对应期间ＴＯＰＥＸ海面高度资料的标准方差。同化结果表明，混合同化方法不失为一种简单而又有效的同化方案。同化得到的南海环流结构与未同化的模式响应场比较可以发现：海面高度资料的同化试验能够有效地修正南海环流的若干大尺度特征，特别是对冬季黑潮入侵南海东北部的动力过程，同化结果有了更准确的描述。同时，另一个重要的修正表现在：同化试验中瞬变的中等尺度涡旋得到加强，体现了南海海洋天气尺度涡被资料同化所“唤醒”（trigger)。这种“唤醒”不仅明显地反映在表层环流场中，对南海次表层动力、热盐结构也有一定的影响。     

海洋环境数值预报检验方法的探讨与测试

对获得的海浪有效波高、海表温度、剖面温度和水位等要素的实测数据以及历史CTD资料,通过对这些数据进行分析和处理,检验WW3海浪、三维温盐流以及MODAS(模块化数据同化系统)等模式的数值预报产品,并设计相应的软件进行各时次的实时比对和旬月统计,自动生成客观的旬月检验报告.为改进预报模式、提高数值预报的准确性和预报产品的使用率提供可靠的依据.     

Evaluation of the U.S. Navy’s Modular Ocean Data Assimilation System (MODAS) Using South China Sea Monsoon Experiment (SCSMEX) Data

The Navy’s Modular Ocean Data Assimilation System (MODAS) is an oceanographic tool to create high-resolution temperature and salinity on three-dimensional grids, by assimilating a wide range of ocean observations into a starting field. The MODAS products are used to generate the sound speed for ocean acoustic modeling applications. Hydrographic data acquired from the South China Sea Monsoon Experiment (SCSMEX) from April through June 1998 are used to verify the MODAS model. MODAS has the capability to provide reasonably good temperature and salinity nowcast fields. The errors have a Gaussian-type distribution with mean temperature nearly zero and mean salinity of −0.2 ppt. The standard deviations of temperature and salinity errors are 0.98°C and 0.22 ppt, respectively. The skill score of the temperature nowcast is positive, except at depth between 1750 and 2250 m. The skill score of the salinity nowcast is less than that of the temperature nowcast, especially at depth between 300 and 400, where the skill score is negative. Thermocline and halocline identified from the MODAS temperature and salinity fields are weaker than those based on SCSMEX data. The maximum discrepancy between the two is in the thermocline and halocline. The thermocline depth estimated from the MODAS temperature field is 10–40 m shallower than that from the SCSMEX data. The vertical temperature gradient across the thermocline computed from the MODAS field is around 0.14°C/m, weaker than that calculated from the SCSMEX data (0.19°–0.27 °C/m). The thermocline thickness computed from the MODAS field has less temporal variation than that calculated from the SCSMEX data (40–100 m). The halocline depth estimated from the MODAS salinity field is always deeper than that from the SCSMEX data. Its thickness computed from the MODAS field varies slowly around 30 m, which is generally thinner than that calculated from the SCSMEX data (28–46 m).     

Oceanographic and sound speed fields for the ESME workbench

The authors describe the effort to provide three-dimensional global thermohaline and sound speed fields for use in the effects of sound in the marine environment (ESME) workbench suite of programs. The primary fields used are from the modular ocean data assimilation system (MODAS), developed by Fox et al. The system provides global thermohaline and sound speed fields on a daily basis using environmental inputs from the U.S. Navy as well as remote sensing of sea surface temperature and sea surface height. To examine the MODAS fields, the authors also used data from the Southern California Bight collected by the California Cooperative Fisheries Investigations as well as high-resolution hydrographic data collected over the continental shelf south of New England as part of the shelfbreak PRIMER experiment. MODAS performs well for features such as large-scale boundary currents and eddies but is more limited in resolving features such as shelfbreak and coastal fronts, which have small spatial and temporal correlation scales. Because of the considerable computational needs of other ESME modules and its use as a planning tool, the authors present a pragmatic approach for future applications.     

Sensitivity of Satellite Altimetry Data Assimilation on a Weapon Acoustic Preset

The purpose of this research is to assess the benefit of assimilating satellite altimeter data for naval undersea warfare. To accomplish this, sensitivity of the weapon acoustic preset program (WAPP) for the Mk 48 variant torpedo to changes in the sound-speed profile (SSP) is analyzed with SSP derived from the modular ocean data assimilation system (MODAS). The MODAS fields differ in that one uses altimeter data assimilated from three satellites while the other uses no altimeter data. The metric used to compare the two sets of outputs is the relative difference in acoustic coverage area generated by WAPP. Output presets are created for five different scenarios, two anti surface warfare (ASTJW) scenarios, and three antisubmarine warfare (ASW) scenarios, in each of three regions: the East China Sea, Sea of Japan, and an area south of Japan that includes the Kuroshio currents. Analysis of the output reveals that, in some situations, WAPP output is very sensitive to the inclusion of the altimeter data because of the resulting differences in the subsurface predictions. The change in weapon presets can be so large that the effectiveness of the weapon may be affected.     

Decadal Current Variations in the Southwestern Japan/East Sea

Absolute geostrophic velocities were calculated along TOPEX/Poseidon (T/P) groundtracks located in the Ulleung Basin of the southwestern Japan/East Sea (JES) from a combined analysis of nearly a decade of T/P data and two years of pressure-gauge-equipped inverted echo sounder (PIES) data obtained during the United States Office of Naval Research’s JES Program. Geostrophic velocities have been calculated daily for the Ulleung Basin from June 1999 to July 2001 from a three-dimensional mapping of temperature and salinity produced by PIES data interpreted via the Gravest Empirical Mode (GEM) technique combined with the Navy’s Modular Ocean Data Assimilation System (MODAS). These velocities were then used to convert T/P velocity anomalies to absolute velocities for the T/P time period of 1993 to 2002. Current intensities and variabilities associated with the East Korean Warm Current, Ulleung Warm Eddy, and Offshore Branch are examined. Spatial and temporal variations of the sea surface circulation are strong. Intensification of the currents generally occurred during the fall season. The flow pattern in individual years differed greatly from year to year and differed from climatology in important qualitative ways.     

吕宋海峡两侧中尺度涡统计

利用1993-2000年间的T/P卫星高度计轨道资料的时间序列和MODAS同化产品中的卫星高度计最优插值资料对南海东北部海区中尺度涡旋进行动态追踪。按照给定的标准从2种资料中提取了涡旋信息并对其特征量进行统计分析。结果表明,南海东北部海区中尺度涡旋十分活跃,平均每年6个,其中暖涡4个,尺度一般为200~250 km,平均地转流速为44 cm/s;冷涡每年平均2个,尺度一般为150~200 km,平均地转流速为-37 cm/s。吕宋海峡两侧涡旋的比较分析表明,南海东北部海区仍属于西北太平洋副热带海区的涡旋带,冷、暖涡旋处于不断的形成—西移—消散过程中。南海东北部中尺度冷涡大多是南海内部产生的,而暖涡与吕宋海峡外侧暖涡有一定的联系又具有相对的独立性。分析认为西北太平洋的西行暖涡在到达吕宋海峡时,受到黑潮东翼东向下倾的等密度面的抑制和岛链的阻碍,涡旋停滞于吕宋海峡外侧并逐渐消弱,被阻挡于吕宋海峡东侧涡旋释放的能量,形成一支横穿吕宋海峡(同时横穿过黑潮)的高速急流,把能量传递给吕宋海峡西侧的涡旋,使其得到强化,这是吕宋海峡两侧涡旋联系的一种重要机制。     

Validation of interannual simulations from the 1/8° global Navy Coastal Ocean Model (NCOM)

A 1/8° global version of the Navy Coastal Ocean Model (NCOM) is used for simulation of upper-ocean quantities on interannual time scales. The model spans the global ocean from 80°S to a complete Arctic cap, and includes 19 terrain-following σ- and 21 fixed z-levels. The global NCOM assimilates three-dimensional (3D) temperature and salinity fields produced by the Modular Ocean Data Assimilation System (MODAS) which generates synthetic temperature and salinity profiles based on ocean surface observations. Model-data intercomparisons are performed to measure the effectiveness of NCOM in predicting upper-ocean quantities such as sea surface temperature (SST), sea surface salinity (SSS) and mixed layer depth (MLD). Subsurface temperature and salinity are evaluated as well. An extensive set of buoy observations is used for this validation. Where possible, the model validation is performed between year-long time series obtained from the model and time series from the buoys. The statistical analyses include the calculation of dimensionless skill scores (SS), which are positive if statistical skill is shown and equal to one for perfect SST simulations. Model SST comparisons with year-long SST time series from all 83 buoys give a median SS value of 0.82. Model subsurface temperature comparisons with the year-long subsurface temperature time series from 24 buoys showed that the model is able to predict temperatures down to 500 m reasonably well, with positive SS values ranging from 0.18 to 0.97. Intercomparisons of MLD reveal that the model MLD is usually shallower than the buoy MLD by an average of about 15 m. Annual mean SSS and subsurface salinity biases between the model and buoy values are small. A comparison of SST between NCOM and a satellite-based Pathfinder data set demonstrates that the model has a root-mean-square (RMS) SST difference of 0.61 °C over the global ocean. Spatial variations of kinetic energy fields from NCOM show agree with historical observations. Based on these results, it is concluded that the global NCOM presented in this paper is able to predict upper-ocean quantities with reasonable accuracy for both coastal and open ocean locations.     

南海暖水形态特征

利用Levitus资料 ,分析了南海各月某些标准层上的海温水平分布、南北向温度断面垂直分布 ,阐述了南海暖水水平和断面温度分布的阶段性特征 ,给出了南海暖水中心点 ( 1 1 3°E ,8°N)海温垂直结构特征。使用 3次自然样条函数 ,将格点资料插值到每米的深度上 ,求出各格点 2 8℃海温的深度 ,得出各月 2 8℃等温包络面。结果表明 :4～ 1 1月份 2 8℃等温包络面呈现大小不等和深浅不同的盆状 ,其各月的变化形象化地表示了暖水的演变过程。分析南海暖水中心点各标准层温度的季节变化表明 :30m以上海水温度季节变化基本一致 ,冬季 1月最低 ,春季 5月最高 ,次高出现在 1 0月份 ;50m海水温度最低值延至 3月份 ,最高在 7月份 ,次高也在 1 0月份。 2 8℃等温包络面所包体积的季节变化是一个较为规则的单峰型     

青岛近百年气候变化趋势的初步分析

人类活动造成的气候变暖及海平面升高问题已成为当前海洋学与气侯学研究的热点。在全球及全国大部分地区海平面升高的总趋势下,青岛地区海平面不是上升而是下降了。本文根据青岛近百年的年平均气温和年降水量资料分析了青岛气候变化趋势。