Experimental implementation of an ensemble adjustment filter for an intermediate ENSO model
Experimental implementation of an ensemble adjustment filter for an intermediate ENSO model
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DOI：
10.1175/jcli4245.1
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发表时间：
2007-09-01
影响因子：
4.9
通讯作者：
Anderson, Jeffrey L.
中科院分区：
文献类型：
--
作者：
Karspeck, Alicia R.;Anderson, Jeffrey L.
利用集合平差卡尔曼滤波（EAKF）研究了热带太平洋海气耦合模式对海温（SST）异常的同化。这里使用的中间耦合模型是Zebiak-Cane模型的操作版本，称为LDEO5。在存在不完全状态观测的情况下，应用同化作为估计系统真实状态的一种手段。在本研究的第一部分中，同化是在“完美模式”假设下进行的，其中海温观测是由模式的轨迹综合得出的。重点是过滤器参数（集合大小、协方差定位和协方差膨胀）的变化如何以及为什么会影响分析的质量。结果表明，即使使用少量的集成成员，各向同性协方差定位也不利于分析。这些结果表明，局域化导致的变量之间“平衡”的破坏比由于集合尺寸小而导致的虚假相关更有害。在本研究的第二部分，EAKF被用来同化一个独立的海温观测数据集。EAKF/Zebiak-Cane同化系统能够正确估计赤道东太平洋平均海温异常所测量的ENSO的相位和强度。将本文的分析与独立的风应力和温跃层深度数据集进行比较表明，即使仅同化海温观测，也有可能再现赤道东太平洋和菲律宾群岛沿岸70%以上的温跃层深度年际变化。赤道太平洋中部和西部纬向风应力的年际变化也与独立观测具有良好的相关性（r> 0.75）。
The assimilation of sea surface temperature (SST) anomalies into a coupled ocean-atmosphere model of the tropical Pacific is investigated using an ensemble adjustment Kalman filter (EAKF). The intermediate coupled model used here is the operational version of the Zebiak-Cane model, called LDEO5. The assimilation is applied as a means of estimating the true state of the system in the presence of incomplete observations of the state.In the first part of this study assimilation is performed under the "perfect model" assumption, where SST observations are synthetically derived from a trajectory of the model. The focus is on how and why changes in the filter parameters (ensemble size, covariance localization, and covariance inflation) affect the quality of the analysis. It is shown that isotropic covariance localization does not benefit the analysis even when a small number of ensemble members are used. These results suggest that destruction of the "balance" between variables caused by localization is more detrimental than spurious correlation due to small ensemble size.In the second part of this study the EAKF is used to assimilate an independent dataset of SST observations. The EAKF/Zebiak-Cane assimilation system is able to correctly estimate the phase and intensity of ENSO, as measured by the average SST anomaly in the eastern equatorial Pacific. A comparison of the analysis herein to independent wind stress and thermocline depth datasets suggests that even with the assimilation of only SST observations it is possible to reproduce over 70% of the interannual variability of thermocline depth in the eastern equatorial Pacific and off the coast of the Philippine Islands. The interannual variability of zonal wind stress in the central and western equatorial Pacific is also well correlated with independent observations ( R > 0.75).