The Role of Coupled Versus Uncoupled Reanalyses for Initialization of Decadal Climate Predictions

耦合与非耦合再分析对于十年气候预测初始化的作用

• 批准号: 436413914
• 负责人: Dr. Iuliia Polkova
• 金额: --
• 依托单位: Centrum für Erdsystemforschung und Nachhaltigkeit (CEN)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/436413914?language=en
• 关键词: Role; Coupled; Versus; Uncoupled; Reanalyses

The need for reliable climate prediction is growing in demand for various socio-economic sectors. Coincidently, studies that investigate predictability of the climate system at interannual to decadal timescales demonstrated that the initialization of Earth System Models (ESMs) with the available oceanic and atmospheric observations can improve the ability of models to predict regional surface temperature up to several years ahead. However, the decadal predictions are shown to suffer from model errors and initialization shocks which limit predictability. The magnitude of this effect remains unclear. To eliminate initialization shocks and improve decadal predictions, we need ESMs that are able to estimate coupled initial conditions in a dynamically consistent way. The current project will be concerned with quantifying the impact of dynamically balanced initial conditions on the decadal prediction skill.Among a variety of coupled data assimilation (CDA) methods, the adjoint method is one of the most promising because its result is dynamically consistent with the ESM’s equations. Thus, a dynamically self-consistent space-time evolution of the climate state produced with the adjoint is suitable for initialization of decadal predictions. To this end, we will use the coupled adjoint model developed for the ESM of intermediate complexity CESAM (Centrum für Erdsystemforschung und Nachhaltigkeit Erdsystem Assimilations-Modell) to produce a coupled ocean-atmosphere reanalysis, which will serve as a source of initial conditions for ensembles of retrospective decadal predictions. These simulations will then be compared against the available observations to estimate the prediction skill of CESAM. A decadal prediction framework, which will be implemented within CESAM, will focus on the multiannual variability of large-scale processes and feedbacks acting within the coupled climate system. The advantage of the proposed research is the availability and the computational efficiency of the adjoint and forward CESAM. As programming adjoint codes for ESMs is not a trivial task, it is currently hindering widespread application of the adjoint-based assimilation for initialization of decadal predictions. Therefore, the merits of the adjoint CDA for decadal predictions are still to be understood and demonstrated; this is the major objective of the proposed research project. Thus, in a model-consistent approach, the project will compare initializations based on the coupled ocean-atmosphere reanalysis and based on the widespread strategy in decadal prediction studies of nudging toward the un-coupled reanalyses. Results of the project will serve to guideline future initialization developments for comprehensive ESMs.

社会经济各部门对可靠的气候预测的需求日益增加。巧合的是，研究气候系统在年际到年代际时间尺度上的可预测性的研究表明，利用现有的海洋和大气观测数据初始化地球系统模式（ESM）可以提高模式预测未来几年区域表面温度的能力。然而，十年期的预测显示，遭受模式误差和初始化冲击，限制了可预测性。这种影响的程度尚不清楚。为了消除初始化冲击并改善年代际预测，我们需要能够以动态一致的方式估计耦合初始条件的ESM。本项目主要研究动力平衡初始条件对年代际预报技术的影响，在众多的耦合资料同化（CDA）方法中，伴随方法是最有前途的方法之一，因为它的结果与ESM方程组的结果在动力上是一致的。因此，一个动态自洽的时空演变的气候状态产生的伴随是适合的初始化的年代际预测。为此，我们将使用为中等复杂度CESAM（Centrum für Erdsystemforschung und Nachhaltigkeit Erdsystem Assimilations-Modell）的ESM开发的耦合伴随模式来产生耦合的海洋-大气再分析，这将作为回顾性年代际预测集合的初始条件的来源。然后将这些模拟与可用的观察结果进行比较，以估计CESAM的预测技能。一个十年期预测框架将在空间机械化中心内实施，其重点将是在耦合气候系统内起作用的大尺度过程和反馈的多年变率。所提出的研究的优点是伴随和前向CESAM的可用性和计算效率。由于编程伴随代码的ESM是不是一个微不足道的任务，它是目前阻碍了广泛应用的伴随同化的年代际预测的初始化。因此，伴随CDA的年代际预测的优点仍有待理解和证明，这是拟议的研究项目的主要目标。因此，在一个模式一致的方法，该项目将比较初始化的基础上耦合的海洋-大气再分析和基础上的普遍战略，在十年期预测研究的轻推到非耦合的再分析。该项目的结果将指导今后全面紧急保障措施的启动工作。