ERA-Interim Project, Single Parameter 6-Hourly Surface Analysis and Surface Forecast Time Series

ERA-Interim represents a major undertaking by ECMWF (European Centre for Medium-Range Weather Forecasts) to produce a reanalysis with an improved atmospheric model and assimilation system which replaces those used in ERA-40, particularly for the data-rich 1990s and 2000s, and to be continued as an ECMWF Climate Data Assimilation System (ECDAS) until superseded by a new extended reanalysis. Preliminary runs indicated that several of the inaccuracies exhibited by ERA-40 such as too-strong precipitation over oceans from the early 1990s onwards and a too-strong Brewer-Dobson circulation in the stratosphere, were eliminated or significantly reduced. Production of ERA-Interim, from 1989 onwards, began in summer of 2006. (The period 1979-1988 was prepended in 2011.)Through systematic increases of computing power, 4-dimensional variational assimilation (4D-Var) became feasible and part of ECMWF operations since 1997, paving the way to base ERA-Interim on 4D-Var (rather than 3D-Var as in ERA-40). Enhanced computing power also allowed horizontal resolution to be increased from T159 (N80, nominally 1.125 degrees for ERA-40) to T255 (N128, nominally 0.703125 degrees), and the latest cycle of the atmospheric model (IFS CY31r1 and CY31r2) to be used, taking advantage of improved model physics. ERA-interim retains the same 60 model levels used for ERA-40 with the highest level being 0.1 hectopascal. In addition, data assimilation of ERA-Interim also benefits from quality control that draws on experience from ERA-40 and JRA-25, variational bias correction of satellite radiance data, and more extensive use of radiances with an improved fast radiative transfer model.ERA-Interim uses sets of observations and boundary forcing fields acquired for ERA-40 through 2001, and from ECMWF operations thereafter. Noteworthy exceptions include new ERS (European Remote Sensing Satellite) altimeter wave heights, EUMETSAT (European Organisation for the Exploitation of Meteorological Satellites) reprocessed winds and clear-sky radiances, GOME (Global Ozone Monitoring Experiment) ozone data from the Rutherford Appleton Laboratory, and CHAMP (CHAllenging Minisatellite Payload), GRACE (Gravity Recovery and Climate Experiment), and COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) GPS radio occultation measurements processed and archived by UCAR (University Corporation for Atmospheric Research).NCAR's Data Support Section (DSS) is performing and supplying a grid transformed version of ERA-Interim, in which variables originally represented as spectral coefficients or archived on a reduced Gaussian grid are transformed to a regular 512 longitude by 256 latitude N128 Gaussian grid. In addition, DSS is also computing horizontal winds (u-component, v-component) from spectral vorticity and divergence where these are available. Processing of single parameter 6-hourly surface analysis and surface forecast time series has been completed for January 1979 through December 2014 (inclusive), or at least 36 years, and will continue as ERA-Interim becomes available thereafter. Data is currently available via NCAR's High Performance Storage System (HPSS), or by delayed mode request which transfers files from the HPSS to our web server for internet download, or via direct internet download, or NCAR's GLADE file system.

ERA-Interim是欧洲中期天气预报中心（ECMWF, European Centre for Medium-Range Weather Forecasts）开展的一项重大科研项目，旨在研发一套改进的大气模式与同化系统，替代ERA-40所使用的对应系统，尤其针对数据富集的1990年代与2000年代，并将以ECMWF气候数据同化系统（ECDAS, ECMWF Climate Data Assimilation System）的形式持续运行，直至被新一代扩展再分析产品取代。
初步试运行结果显示，ERA-40存在的诸多缺陷已被消除或显著改善，例如1990年代初以来海洋区域降水强度偏高的问题，以及平流层内布鲁尔-多布森环流偏强的问题。ERA-Interim数据集的生产工作始于2006年夏季，覆盖1989年及以后的时段；1979年至1988年的时段则于2011年补充追加至数据集中。
随着计算性能的系统性提升，四维变分同化（4D-Var, 4-dimensional variational assimilation）自1997年起成为ECMWF的业务化可行技术，为ERA-Interim采用4D-Var（而非ERA-40所使用的三维变分同化3D-Var）奠定了基础。更强的计算能力还使得水平分辨率从ERA-40所采用的T159（对应N80格点，标称分辨率约1.125°）提升至T255（对应N128格点，标称分辨率约0.703125°），并得以使用最新版本的大气模式——集成预报系统（IFS）CY31r1与CY31r2，充分利用了改进后的模式物理过程。ERA-Interim沿用了ERA-40所使用的60层模式垂直结构，最高层气压为0.1百帕。此外，其数据同化流程还受益于借鉴ERA-40与JRA-25经验的质量控制方案、卫星辐射数据的变分偏差校正，以及借助改进的快速辐射传输模型更广泛地应用辐射观测数据。
ERA-Interim所使用的观测数据与边界强迫场，一部分来自ERA-40项目在2001年及之前收集的资料，另一部分则来自ECMWF后续的业务运行数据。值得注意的例外包括：新的欧洲遥感卫星（ERS, European Remote Sensing Satellite）高度计获取的海浪高度数据、欧洲气象卫星开发组织（EUMETSAT, European Organisation for the Exploitation of Meteorological Satellites）再处理的风场与晴空辐射数据、卢瑟福阿普尔顿实验室提供的全球臭氧监测实验（GOME, Global Ozone Monitoring Experiment）臭氧观测数据，以及由大学大气研究联合会（UCAR, University Corporation for Atmospheric Research）处理并归档的挑战微卫星载荷（CHAMP）、重力恢复与气候实验（GRACE）以及气象、电离层与气候星座观测系统（COSMIC）的GPS无线电掩星观测数据。
美国国家大气研究中心（NCAR, National Center for Atmospheric Research）的数据支持部门（DSS）正在处理并提供ERA-Interim的网格转换版本：将原本以谱系数形式表示或存储于缩减高斯网格的变量，转换为规则的512经度×256纬度的N128高斯网格。此外，当谱涡度与散度数据可用时，DSS还将基于这些数据计算水平风场的u分量与v分量。针对1979年1月至2014年12月（含首尾）的单参数6小时地表分析与地表预报时间序列的处理工作已完成，共计36年，后续随着ERA-Interim数据陆续发布，该处理工作也将持续推进。目前可通过以下途径获取该数据集：NCAR的高性能存储系统（HPSS）、延迟模式请求（即从HPSS传输文件至网页服务器以供互联网下载）、直接互联网下载，或是NCAR的GLADE文件系统。

搜集汇总

背景与挑战

背景概述

ERA-Interim数据集是ECMWF提供的高分辨率历史再分析数据，覆盖1979-2019年，包含6小时一次的地表分析和预报，适用于气候和气象研究。数据集通过改进模型和同化系统，显著提升了数据质量，并包含多种关键气象变量。