Toward Reanalysis of the Arctic Climate System - Sea Ice Ocean Reconstruction with Data Assimilation

An Integrative Data Assimilation for the Arctic System (IDAAS) has been recommended for development by a special interagency research program "A Study of Environmental Arctic Change" (SEARCH, 2005). While existing operational reanalyses assimilate only atmospheric measurements, an IDAAS activity would include non-atmospheric components: sea ice, oceanic, terrestrial geophysical and biogeochemical parameters and human dimensions data. The IDAAS was recommended for development "because recent global reanalyses of the atmosphere have received widespread use by the research community and because they are regarded as one of the major success stories of the past decade in atmospheric research" (SEARCH, 2005). Atmospheric reanalysis products play a major role in the arctic system studies and are used to force sea ice, ocean and terrestrial models, and to analyze the climate system's variability and to explain and understand the interrelationships of the system's components and the causes of their change. Motivated by this success and the major goals and recommendations of SEARCH, we develop an integrated set of assimilation procedures for the ice-ocean system that is able to provide gridded data sets that are physically consistent and constrained to the observations of sea ice and ocean parameters. Building on our past research activities in sea ice and ocean data assimilation, we make some first steps toward the creation of an Arctic Climate System Reanalysis that uses modern four-dimensional variational (4D-Var, adjoint) data assimilation methods. We employ sea ice and ocean models with new data assimilation procedures to maximize the integration of model results with observations and thus attempt to provide the arctic research community with complete and accurate data sets, ultimately for at least the last three decades. Here we describe three digital data sources made available for community by this project activities, namely: Observational hydrographic data interpolated into PIOMAS grid; Currents data in the original format as it was organized by Greg Holloway who collected these data and provided these data for our project; Our project results: Monthly hydrography and circulation averaged for three periods: 1972-1978, 1989-1996 and 1997-2006.北极系统综合数据同化（Integrative Data Assimilation for the Arctic System, IDAAS）已被跨机构特别研究项目“北极环境变化研究”（A Study of Environmental Arctic Change, SEARCH, 2005）推荐开展研发工作。当前主流业务化大气再分析仅同化大气观测数据，而IDAAS项目将纳入非大气组分数据，包括海冰、海洋、陆地地球物理与生物地球化学参数，以及人文维度数据集。之所以推荐开发IDAAS，“是因为近年来全球大气再分析产品已被科研学界广泛使用，且被视为近十年大气研究领域的重大成功成果之一”（SEARCH, 2005）。大气再分析产品在北极系统研究中发挥核心支撑作用，被用于驱动海冰、海洋与陆地模式，分析气候系统变异性，阐释并理解系统各组分间的相互关系及其变化成因。 受此成功经验以及SEARCH项目的核心目标与推荐内容的启发，我们研发了一套面向冰-海洋系统的综合同化流程，可生成物理自洽且受海冰与海洋参数观测约束的网格化数据集。依托此前在海冰与海洋数据同化领域的研究基础，我们迈出了构建北极气候系统再分析的第一步，该再分析采用现代四维变分（four-dimensional variational, 4D-Var，伴随）数据同化方法。我们使用搭载新型数据同化流程的海冰与海洋模式，最大化实现模式结果与观测数据的融合，旨在为北极科研学界提供完整且精准的数据集，最终覆盖至少过去三十年的时段。 本文介绍本项目面向学界开放的三类数字数据源，具体包括：1. 插值至PIOMAS网格的观测水文数据；2. 由格雷格·霍洛威（Greg Holloway）整理收集并为本项目提供的原始格式海流数据；3. 本项目成果：三个时段的逐月平均水文与环流数据，时段分别为1972-1978年、1989-1996年及1997-2006年。