JRA-55: Japanese 55-year Reanalysis, Daily 3-Hourly and 6-Hourly Data

Important Notice: Update of JRA-55 data will terminate at the end of January 2024. Please use Japanese Reanalysis for Three Quarters of a Century (JRA-3Q) [https://rda.ucar.edu/datasets/d640000/] at that time.

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.

重要通告：JRA-55 数据集的更新将于2024年1月底终止。届时，请使用《日本气象厅三季度再分析数据集》（JRA-3Q）[https://rda.ucar.edu/datasets/d640000/]进行查询。

日本气象厅（JMA）实施了JRA-55项目，即第二个日本全球大气再分析工程。该数据集覆盖了55年历史，追溯至1958年，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基于一种新的数据同化与预测系统（DA），显著改进了首份日本再分析中发现的诸多不足。这些改进得益于实施了更高空间分辨率的（TL319L60）、新的辐射方案、四维变分数据同化（4D-Var）结合变分偏差校正（VarBC）应用于卫星辐射，以及引入了具有时间变化浓度的温室气体。整个JRA-55的生产于2013年完成，此后将实时更新。

针对JRA-55的早期质量评估结果显示，相较于JRA-25，通过新的辐射方案和VarBC的应用（亦降低了不合理的温度变化），低层对流层中的温度偏差得到了显著降低。此外，亚马逊盆地的干燥陆地异常也得到了缓解，总体预报评分也相较于JRA-25有显著提升。

JRA-55所使用的观测数据大部分与JRA-25相同。此外，EUMETSAT和MSC/JMA分别提供了新处理的METEOSAT和GMS数据。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、存档并处理，包括将TL319L60网格转换为规则的经纬度高斯网格（320个纬度，640个经度，名义上为0.5625度）。所有RDA JRA-55数据均可通过互联网下载，包括完整的子集和数据处理格式转换服务。