Collaborative Research: A Pilot Study of Simultaneous Parameter and State Estimation in Coupled Ocean-Atmosphere General Circulation Models Using the Ensemble Kalman Filter

海洋大气环流模式（OAGCM）表现出明显的模式偏差，例如，热带辐合带冷舌复合体中的热带偏差。这种偏差的一个重要部分是由于模型参数的不确定性。然而，到目前为止，在OAGCM参数调整仍然是基本的。这个合作项目将开发一种新的策略，系统参数优化OAGCMs，使用集合为基础的数据同化策略，专注于突出的热带偏差问题。建立在现有的耦合数据同化系统，自适应耦合集合卡尔曼滤波系统（AcEnKF）的模式参数和状态的同时估计，将开发。将研究不同的同化技术，以寻找一种有效的方法，参数优化OAGCMs，以及耦合动力学参数优化相关的热带气候系统的气候学和气候变率。这项工作预计将首次对OAGCM中基于集合的参数优化策略进行全面评估。该研究还将揭示热带气候系统的耦合动力学机制及其对模式参数的敏感性。尽管存在潜在的困难，但这一试点研究是在改进OAGCM方面迈出的重要一步。这项活动具有重大的广泛影响：它将为系统地改进OAGCM以及更广泛地说，未来的耦合地球系统模型奠定基础。

Ocean Atmosphere General Circulation Models (OAGCM) exhibit significant model biases, e.g., the tropical bias in the Intertropical Convergence Zone cold tongue complex. A significant part of such biases is due to uncertainties in the model parameters. Thus far, however, parameter tuning in OAGCMs remains rudimentary. This collaborative project will develop a novel strategy for systematic parameter optimization in OAGCMs, using an ensemble based data assimilation strategy, focusing on the outstanding tropical bias problem. Building on an existing coupled data assimilation system, an adaptive coupled ensemble Kalman Filter system (AcEnKF) for a simultaneous estimation of model parameter and state, will be developed. Different assimilation techniques to search for an effective method of parameter optimization in OAGCMs will be studied, as also coupled dynamics relevant to parameter optimization in the tropical climate system for both the climatology and climate variability. The work is expected to give the first comprehensive evaluation of the ensemble based strategy for parameter optimization in OAGCMs. The study will also shed light on the mechanism of the coupled dynamics of the tropical climate system and its sensitivity to model parameters. In spite of potential difficulties, this pilot study represents a significant step forward in the improvement of OAGCMs. This activity has significant broader impacts: it will lay a foundation for a systematic improvement of OAGCMs and, more generally, future coupled earth system models.