Reanalysis

The need for quantitative assessment of past and current climate conditions gives rise to the requirement for a high-quality dataset with homogeneity in space and time to support climate research and related services such as seasonal forecasts, extreme weather analysis and climate monitoring.

The quality of analysis produced by the operational numerical weather prediction (NWP) system has improved remarkably in recent years due to advances made with the system. Consequently, the difference in the quality of analysis produced with previous operational NWP systems and the current system creates a lack of long-term data homogeneity.

To produce a high-quality homogeneous dataset, a constant state-of-the-art data assimilation system is used in reanalysis. In addition, as many observations as possible are collected, including those used in past operational systems and delayed observations as well as digitized observations. High-quality reprocessed satellite data are also assimilated where available. These approaches enable the production of a higher-quality and more homogeneous dataset for a variety of meteorological variables covering the last several decades.

Global reanalysis has been conducted at a number of major NWP centers (for more information, see https://reanalyses.org/). In this context, the Japan Meteorological Agency (JMA) and the Central Research Institute of Electric Power Industry (CRIEPI) in Japan jointly conducted the Japanese 25-year Reanalysis (JRA-25, covering the period from 1979 to 2004 and completed in 2006), and JMA conducted the Japanese 55-year Reanalysis (JRA-55, covering the period from 1958 onward and completed in 2013).

Japanese Reanalysis for Three Quarters of a Century (JRA-3Q)

JMA is currently conducting the Japanese Reanalysis for Three Quarters of a Century (JRA-3Q), which covers the period from September 1947 onward to extend the current period of data coverage and improve the quality of long-term reanalysis. The project involves a sophisticated data assimilation system (based on the operational set-up as of December 2018) incorporating development results from the operational NWP system and sea surface temperature analysis achieved since JRA-55 (based on the operational set-up as of December 2009). New datasets of past observations are also assimilated, including rescued historical observations and reprocessed satellite data supplied by meteorological and satellite centers worldwide. Many of the deficiencies of JRA-55 are alleviated in JRA-3Q, providing a high-quality homogeneous reanalysis dataset that covers the previous 75 years.

JRA-3Q comprehensive report

Related progress with report submission to the Journal of the Meteorological Society of Japan will be updated here.

Reference JRA-3Q data in scientific or technical papers before the JRA-3Q comprehensive report should be cited to Kobayashi et al. (2021) as per the references below.

References

• Kobayashi, S., Y. Kosaka, J. Chiba, T. Tokuhiro, Y. Harada, C. Kobayashi, and H. Naoe, 2021: JRA-3Q: Japanese Reanalysis for Three Quarters of a Century. Joint WCRP-WWRP Symposium on Data Assimilation and Reanalysis/ECMWF Annual Seminar 2021, online, 13-17 September 2021, O4-2.
• Harada, Y., S. Kobayashi, Y. Kosaka, J. Chiba, and T. Tokuhiro, 2021: Early results of the evaluation of the JRA-3Q reanalysis, EGU General Assembly 2021, online, 19-30 April 2021, EGU21-3762, https://doi.org/10.5194/egusphere-egu21-3762.
• Naoe, H., S. Kobayashi, Y. Kosaka, J. Chiba, T. Tokuhiro, and Y. Harada, 2021: Evaluation of a new Japanese reanalysis (JRA-3Q) in a pre-satellite era, EGU General Assembly 2021, online, 19-30 April 2021, EGU21-6881, https://doi.org/10.5194/egusphere-egu21-6881.

Link

• Joint WCRP-WWRP Symposium on Data Assimilation and Reanalysis and 2021 ECMWF Annual Seminar on Observations

Collaborative organizations providing JRA-3Q data

JRA-3Q data are provided by collaborative organizations for non-commercial purposes.
Please note the following in regard to downloading data from these organizations:

• Collaborative organizations are separate entities from JMA and are solely responsible for their own web portals and data access procedures.
• User registration and agreement to terms and conditions of data service usage are required individually for each organization.

Collaborative organizations

1. DIAS: Data Integration & Analysis System

   Data access to JRA-3Q : https://search.diasjp.net/en/dataset/JRA3Q
   

   • Data for September 1947 to December 1990 and May 2013 onward will be released in spring 2023.

Data source acknowledgement

JRA-3Q data should be acknowledged in scientific and technical reports.

• Example

  This report references JRA-3Q reanalysis data from the Japan Meteorological Agency.

Remaking metafiles for JRA-3Q data visualization

Data descriptor files (*.ctl) and index files (*.idx) can be used in addition to JRA-3Q data for visualization of JRA-3Q data with multi-purpose Grid Analysis and Display System (GrADS) software.

When information in data descriptor files (e.g., time periods and other variables) is changed, the corresponding index files need to be remade.

• To remake an index file

  $ gribmap -b -i [data descriptor file]