ENSEMBLES RT1: Experimental set up; initialisation and perturbations

• Corrected Wind Stress Perturbations and Extension to 2006 (05/03/2007)

The wind stress perturbation files prepared at ECMWF in 2005 (scroll down for the corresponding information) showed discontinuities from one month to the next. Pierluigi di Pietro (INGV) has prepared an example for the meridional wind stress perturbations for 1958. Although this feature it is not expected to be a source of problems (such as discontinuities) in generating the ensemble of ocean analyses, Magdalena Balmaseda (ECMWF) has generated a new set with continuous perturbations that are available from ec:/neh/ENSEMBLES/pert_wsrt_crtd_nc/. The new files are also extended to 2006, which is required to create the Stream 2 hindcasts.

The files are in NetCDF format and use the suffix wsx and wsy for zonal and meridional wind stress, respectively. There is a file with daily data per month and perturbation, with files available for 8 perturbations and the period January 1958 to December 2006.

The error is not expected to have a significant influence in the ocean analyses. Most of the ocean initial conditions used to initialize the Stream 1 hindcasts employed the discontinuous perturbations, and so did the ocean initial conditions used in the ECMWF operational forecast System 3. We apologize for the inconveniences.

• Ocean Forcing Fields and Initial Conditions for 2002-2006 (14/02/2007)

Magdalena Balmaseda has prepared a set of GRIB files from the operational analyses with fluxes to force ocean models. The data are in a T85 Gaussian grid. They can be obtained from 2002 onwards from ECFS at:

ec:/emos/OCEA/3/0001/forcing/odnpa_85_*

These are the fluxes used to create the operational analysis for System 3. The files contain daily fields of specified sea surface temperature, absorbed solar radiation, U stress, V stress, specified surface heat flux, precipitation - evaporation and runoff. Bear in mind that the precipitation has not been corrected as in ERA40 and, therefore, the climatologies are different.

The atmospheric operational analyses are available from MARS. You can use the attributes described in:
http://www.ecmwf.int/services/archive/d/catalog/class=od/stream=oper/expver=1/type=an/

• SST and Wind Stress Perturbations in ECFS (09/10/2006)

The perturbation files prepared at ECMWF are in ECFS in the directory ec:/ENSEMBLES/pert. The files use the suffix wsx and wsy for zonal and meridional wind stress and sst for SST. They are in NetCDF format, so the way they are organized and the grid information is easily readable. There are monthly files with daily data for the wind stress perturbations (only one perturbation in each file) and one file per month with four instantaneous SST perturbations.

• Documentation of the Impact of Wind Stress Perturbations on the Ocean Analysis at ECMWF (12/12/2005)

A document on the ECMWF ocean analysis with respect to the impact of the wind stress perturbations can be downloaded here. The effect of the new vs. old wind stress perturbations and assimilating ocean data are discussed, and the DEMETER vs. ENSEMBLES stream1 ocean analyses are compared.

• Documentation of the SST and Wind Stress Perturbations at ECMWF (12/12/2005)

A document describing how the SST and wind stress perturbations are estimated can be obtained here.