JRA-55: Japanese 55-year Reanalysis, Monthly Means and Variances

The Japan Meteorological Agency (JMA) conducted JRA-55, the second Japanese global atmospheric reanalysis project. It covers 55 years, extending back to 1958, coinciding with the establishment of the global radiosonde observing system. Compared to its predecessor, JRA-25, JRA-55 is based on a new data assimilation and prediction system (DA) that improves many deficiencies found in the first Japanese reanalysis. These improvements have come about by implementing higher spatial resolution (TL319L60), a new radiation scheme, four-dimensional variational data assimilation (4D-Var) with Variational Bias Correction (VarBC) for satellite radiances, and introduction of greenhouse gases with time varying concentrations. The entire JRA-55 production was completed in 2013, and thereafter will be continued on a real time basis.

Specific early results of quality assessment of JRA-55 indicate that a large temperature bias in the lower stratosphere has been significantly reduced compared to JRA-25 through a combination of the new radiation scheme and application of VarBC (which also reduces unrealistic temperature variations). In addition, a dry land surface anomaly in the Amazon basin has been mitigated, and overall forecast scores are much improved over JRA-25.

Most of the observational data employed in JRA-55 are those used in JRA-25. Additionally, newly reprocessed METEOSAT and GMS data were supplied by EUMETSAT and MSC/JMA respectively. Snow depth data over the United States, Russia and Mongolia were supplied by UCAR, RIHMI and IMH respectively.

The Data Support Section (DSS) at NCAR has processed the 1.25 degree version of JRA-55 with the RDA (Research Data Archive) archiving and metadata system. The model resolution data has also been acquired, archived and processed as well, including transformation of the TL319L60 grid to a regular latitude-longitude Gaussian grid (320 latitudes by 640 longitudes, nominally 0.5625 degree). All RDA JRA-55 data is available for internet download, including complete subsetting and data format conversion services.

日本气象厅（JMA）实施了JRA-55项目，这是继JRA-25之后的第二个日本全球大气再分析计划。该项目覆盖了自1958年至今的55年时间，与全球无线电探空观测系统的建立相吻合。相较于其前身JRA-25，JRA-55基于一套新的数据同化和预测系统（DA），显著改善了首次日本再分析中发现的诸多缺陷。这些改进得益于更高空间分辨率（TL319L60）、新的辐射方案、四维变分数据同化（4D-Var）配合变分偏差校正（VarBC）对卫星辐射的应用，以及引入了随时间变化的温室气体浓度。整个JRA-55的生产工作于2013年完成，此后将实时继续进行。

JRA-55质量评估的早期具体结果指出，与JRA-25相比，通过新的辐射方案和VarBC的应用（这也降低了不切实际的温度变化），中低层大气温度偏差得到了显著降低。此外，亚马逊盆地的干旱地表异常也得到了缓解，整体预报评分相较于JRA-25有显著提升。

JRA-55中使用的观测数据大多与JRA-25相同。此外，来自欧洲气象卫星组织（EUMETSAT）和MSC/JMA的新处理METEOSAT和GMS数据也得到了提供。美国、俄罗斯和蒙古的雪深数据分别由UCAR、RIHMI和IMH提供。

美国国家大气研究中心（NCAR）的数据支持部门（DSS）已使用RDA（研究数据存档）存档和元数据系统处理了JRA-55的1.25度版本。模型分辨率数据也已获取、存档和处理，包括将TL319L60网格转换为规则的经纬度高斯网格（320个纬度由640个经度组成，近似0.5625度）。所有RDA JRA-55数据均可在互联网上下载，包括完整的子集和格式转换服务。

搜集汇总

背景与挑战

背景概述

JRA-55是日本气象厅的55年全球大气再分析数据集，覆盖1958年至2013年，并持续实时更新。该数据集采用改进的数据同化系统，提供高分辨率的月均和方差数据，涵盖多种气象变量和全球范围。