About ALERA3

AFES–LETKF experimental ensemble reanalysis 3

ALERA3 is an experimental atmospheric reanalysis dataset from 1 Dec 2018 (ongoing) produced on the Earth Simulator. This dataset is the third generation of ALERA series. In ALERA3, the vertical levels are increased from 48 (about 3 hPa) to 56 (about 0.1 hPa) and the data assimilation system is updated from the previous one, in which an AMSU-A satellite radiance assimilation scheme is implemented (see Yamazaki et al. 2023).

This dataset is produced by Japan Agency for Marine-Earth Science and Technology (JAMSTEC). ALERA3 may be used for research purposes for free under the terms and conditions.

AFES (AGCM for the Earth Simulator) is run at a resolution of T119L56 (about 100 km in the horizontal and 56 layers in the vertical). The PrepBUFR and satellite data compiled by the National Centers for Environmental Prediction (NCEP) and archived at the University Corporation for Atmospheric Research (UCAR) is used for the observational data and assimilated using the LETKF (local ensemble transform Kalman filter).


Near-real time states in ALERA3 is visualized via APL Virtualearth

How to Access

Download data

Data is distributed through GrADS Data Server. Use DODS-enabled applications, such as GrADS or NCL for visualization and NCO (ncks) to slice and download data. Meta data is displayed when accessed with a web browser.

Available Data

  • From 1 Dec 2018
  • Temporal resolution: 6 hourly
  • Horizontal resolution: 1.25°×1.25° (288×145 points)
  • Pressure levels (plev): 37 levels (up to 0.5 hPa)
  • Variables: Winds (U, V m/s), temperature (T K), specific humidity (Q kg/kg), geopotential height (Z m), p-velocity (OMG Pa/s), sea-level pressure (SLP Pa), and surface pressure (PS Pa)
  • Additional data: Ensemble mean (mean) and spread (sprd) of analysis (anal) fields


  • Yamazaki, A., K. Terasaki, T. Miyoshi, and S. Noguchi, 2023: Estimation of AMSU-A radiance observation impacts in an LETKF-based atmospheric global data assimilation system: Comparison with EFSO and observing system experiments. Wea. Forecasting, 38 (6), 953–970, doi:10.1175/WAF-D-22-0159.1.


We encourage you to report your findings, problems and suggestions to esc-oreda AT jamstec.go.jp (replace AT with @).