AFES–LETKF experimental ensemble reanalysis

ALERA is an experimental atmospheric reanalysis dataset for about one and a half years from 1 May 2005 produced on the Earth Simulator. It provides not only the ensemble mean but also spread of the ensemble members. The spread could be used as a measure of the analysis error.

This datatset is produced under the collaboration among the Japan Meteorological Agency (JMA), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), and Chiba Institute of Science (CIS). ALERA 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 T159/L48 (about 80-km in the horizontal and 48 layers in the vertical). The ensemble size is chosen to be 40. Observational data excluding satellite radiances are assimillated using the LETKF (local ensemble transform Kalman filter).

How to Access

Download data

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

Available Data

  • From 1 May 2005 to 10 Jan 2007
  • Horizontal resolution: 1.25°×1.25° (288×145 points)
  • Variables: Winds (u, v m/s), temperature (T K), dew point depression (T−Td K), geopotential height (z m) and sea-level pressure (slp hPa)
  • Levels: 1000, 925, 850, 700, 600, 500, 400, 300, 250, 200, 150, 100, 70, 50, 30, 20, 10 (17 levels)
  • Original 6 hourly snapshots and daily-, pentad- and monthly-means


  • Miyoshi, T., and S. Yamane, 2007: Local ensemble transform Kalman filtering with an AGCM at a T159/L48 resolution. Mon. Wea. Rev., 135, 3841–3861, doi:10.1175/2007MWR1873.1.
  • Miyoshi, T., S. Yamane, and T. Enomoto, 2007: The AFES-LETKF experimental ensemble reanalysis: ALERA. SOLA, 3, 45–48, doi:10.2151/sola.2007-012.


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