Developing a common, flexible and efficient framework for weakly coupled ensemble data assimilation based on C-Coupler2.0

Abstract

Abstract. Data assimilation (DA) provides initial states of model runs by combining observational information and models. Ensemble-based DA methods that depend on the ensemble run of a model have been widely used. In response to the development of seamless prediction based on coupled models or even Earth system models, coupled DA is now in the mainstream of DA development. In this paper, we focus on the technical challenges in developing a coupled ensemble DA system, especially how to conveniently achieve efficient interaction between the ensemble of the coupled model and the DA methods. We first propose a new DA framework, DAFCC1 (Data Assimilation Framework based on C-Coupler2.0, version 1), for weakly coupled ensemble DA, which enables users to conveniently integrate a DA method into a model as a procedure that can be directly called by the model ensemble. DAFCC1 automatically and efficiently handles data exchanges between the model ensemble members and the DA method without global communications and does not require users to develop extra code for implementing the data exchange functionality. Based on DAFCC1, we then develop an example weakly coupled ensemble DA system by combining an ensemble DA system and a regional atmosphere–ocean–wave coupled model. This example DA system and our evaluations demonstrate the correctness of DAFCC1 in developing a weakly coupled ensemble DA system and the effectiveness in accelerating an offline DA system that uses disk files as the interfaces for the data exchange functionality.

C-Coupler3.0: an integrated coupler infrastructure for Earth system modeling

“…Sun et al (2021) confirmed the effectiveness of the module-integration framework, as the DA framework DAFCC1 employs the module-integration framework for integrating the codes of DA methods and for online data exchange between the model and DA methods. To further evaluate the effectiveness, we use the Community Earth System Model (CESM;Hurrell et al, 2013) version 1.2.1 (called the baseline version) as well as the air-sea flux algorithm used in the model.…”

“…This framework can automatically and efficiently handle argument passing between a model and a module, even when they use different data structures, grids, or parallel decompositions. 4) C-Coupler3.0 includes a common framework (Sun et al, 2021) for conveniently developing a weakly coupled ensemble data assimilation (DA) system. This framework provides online data exchanges between a model ensemble and a DA method, for better parallel performance.…”

A Global Coupled Atmosphere-Wave Model System Based on C-Coupler2. Part I: Model Description

“…C-Coupler2, the 2.0 version of C-Coupler developed at Tsinghua University, has following outstanding advantages: 1) the flexible coupling configuration interfaces, including coupling frequencies and model grids; 2) automatic coupling processing like data interpolation; 3) dynamic three-dimensional coupling capability; 4) promote model nesting and incremental operation; 5) capability of adaptive restart capability. C-Coupler2 has been applied in a few coupled models and coupled ensemble data assimilation [2] [15].…”