About ALERA2

AFES–LETKF experimental ensemble reanalysis 2

ALERA2 is an experimental atmospheric reanalysis dataset from 1 Jan 2008 to 5 Jan 2013 produced on the Earth Simulator. This dataset is the second generation of ALERA. In ALERA2, the ensemble size is increased from 40 to 63 and the data assimilation system is updated from the previous one (see Enomoto et al. 2013).

This dataset is produced by Japan Agency for Marine-Earth Science and Technology (JAMSTEC). ALERA2 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 T119L48 (about 100 km in the horizontal and 48 layers in the vertical). The PREPBUFR complied 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 ALERA2 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 Jan 2008 to 4 Jan 2021
    • stream2008: 1 Jan 2008–31 Aug 2010[1]
    • stream2010: 1 Aug 2010–5 Jan 2013
    • stream2013: 20 Dec 2012–24 Sep 2016
    • stream2015: 31 Aug 2015–4 Jan 2021
  • Temporal resolution: 6 hourly
  • Horizontal resolution: 1.25°×1.25° (288×145 points)
  • Pressure levels (plev): 1000, 925, 850, 775, 700, 600, 500, 400, 300, 250, 200, 150, 100, 70, 50, 30, 20, and 10 hPa (18 levels)
  • Type: Analysis (anal) and first guess (gues) fields
  • 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) and first guess (gues) fields on σ surfaces (slev, 48 levels) and the forecast fields related to physical processes (fcst)[2]


  1. ^ Some of the files between 1 Jan to 31 May 2008 are unavailable due to an archiving problem.
  2. ^ Details of the additional data can be found in control files for GrADS.


  • Enomoto, T., T. Miyoshi, Q. Moteki, J. Inoue, M. Hattori, A. Kuwano-Yoshida, N. Komori, S. Yamane, 2013: Observing-system research and ensemble data assimilation at JAMSTEC. In Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications (Vol. II), S. K. Park and L. Xu (eds.), chapter 21, pp. 509–526, Springer, doi:10.1007/978-3-642-35088-7_21.


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