DESCRIPTION:
ECMWF ERA-40 High Resolution Surface Analysist: T85 resolution: monthly means at 00Z, 06Z, 12Z, 18Z
SOURCE: Data Support Section Dataset ds126.0 [See also: Data Support Section Dataset ds119.0]
HISTORY:
This dataset is a netCDF version of ds126.0 which is archived in GRIB format. The original dataset was implemented and computed by NCAR's Data Support Section, and forms an essential part of efforts undertaken in late 2004, early 2005, to produce an archive of selected segments of ERA-40 on a standard transformation grid. In this case, 47 ERA-40 at 00Z, 06Z, 12Z, 18Z monthly mean surface and single level analysis ("instantaneous") variables were transformed from a reduced N80 Gaussian grid to a 256x128 regular Gaussian grid. All fields were transformed using routines from the ECMWF EMOS library, including 10 meter winds which were treated as scalars because of a lack of 10 meter spectral vorticity and divergence. A missing value of 1e+20 occurs in the sea surface temperature and sea ice (SST and CI) fields to mask grid points occurring over land. Fields formerly archived as whole integers, such as vegetation indices and cloud cover, occur as integers plus a fractional part in the T85 version due to interpolation. The choice of a T85 Gaussian grid was based on considerations of limiting the volume of new data generated to a moderate level, and to match the horizontal resolution of the Community Atmosphere Model (CAM) component of the Community Climate System Model (CCSM)
The netCDF version of ds126.0 was produced by the Climate Analysis Section (CAS) as a community service. The contents conform to the netCDF Climate and Forecast (CF) Metadata Convention . The purpose is to facilitate evaluation of the CCSM and to produce datasets that may be more readily analyzed by commonly available software tools.
AVAILABILITY:
The ERA-40 data are available for non-commercial use within the U.S. and at UCAR member institutions. All data are available from the NCAR Mass Storage System (MSS). Use of the data at NCAR does not require the submission of a permission form. However, if you do not have access to the MSS or wish to utilize the data outside of NCAR, then a permission form must be signed. Redistribution of this data under any circumstances is strictly prohibited.
FORMAT: netCDF
GRID: T85 Gaussian (256 x 128)
TIMES: Monthly means: 00Z, 06Z, 12Z, 18Z
DATES: September 1957 - August 2002
LEVELS: Single level fields: at/near surface, categorical cloud levels
FIELDS:
As noted in the HISTORY section, the original U10M and V10M fields are available only on the N80 Gaussian grid. As a result the T85 components were derived using ECMWF's EMOS software as separate scalar components because of a lack of spectral precursors, specifically 10m vorticity and divergence. Technically, vector pairs should be derived or interpolated as component pairs. Users should use these fields with this caveat in mind.
netCDF
Description Name units
-------------------------------------------------------------------------
Mean sea level pressure MSL Pa
Temperature at 2m T2M K
Temperature at 2m: dew point TD2M K
Temperature: skin SKT K
U-component of Wind at 10m U10M m/s
V-component of Wind at 10m V10M m/s
Surface Geopotential PHIS m2/s2
Land-sea mask LSM land=0, sea=1
Sea surface temperature SST K
Sea-ice cover CI fraction
Sea sfc roughness [Charnock par] CHNK
Vegetation cover (low) CVL fraction
Vegetation cover (high) CVH fraction
Vegetation cover (type of low veg) TVL int.fraction
Vegetation cover (type of high veg) TVH int.fraction
Cloud Cover: Total TCC fraction
Cloud Cover: Low LCC fraction
Cloud Cover: Medium MCC fraction
Cloud Cover: High HCC fraction
Albedo AL fraction
Snow: albedo ASN fraction
Snow: density RSN kg/m3
Snow: depth SD m of water equivalent
Snow: temperature of layer TSN K
Surface roughness SR m
Skin reservoir content SRC m of water
Ozone: total column TCO3 kg/m2
Ice surface temperature layer 1 ISTL1 K
Ice surface temperature layer 2 ISTL2 K
Ice surface temperature layer 3 ISTL3 K
Ice surface temperature layer 4 ISTL4 K
Soil temperature level 1 STL1 K
Soil temperature level 2 STL2 K
Soil temperature level 3 STL3 K
Soil temperature level 4 STL4 K
Volumetric soil water layer 1 SWVL1 m3/m3
Volumetric soil water layer 2 SWVL2 m3/m3
Volumetric soil water layer 3 SWVL3 m3/m3
Volumetric soil water layer 4 SWVL4 m3/m3
Orography: Std. Deviation SDOR
Orography: Anisotropy of
sub-gridscale ISOR
Orography: Angle of sub-gridscale
orography ANOR rad
Logarithm of surface roughness
length for heat LSRH
MSS PATH:
/DSS/ERA40/
MSS FILE NAMES:
The MSS file names are based upon ECMWF style file names and are consistent with those suggested by the Data Support Section.
Generic Name: e4mnth.an.sfc.t85.vName.yyyy.nc where yyyy is the 4-digit year and vName is the lower case of the netCDF variable name. For example, e4mnth.an.sfc.t85.u10m.1958.nc would be the file containing the U-component of Wind for January 1958. Special Combined File Because the individual year files for each variable are small, a file which contains the entire Sept 1957-Aug 2002 period was created. Each file has the following form: Generic Name: e4mnth.an.sfc.t85.vName.1957-2002.nc For example: e4mnth.an.sfc.t85.u10m.1957-2002.nc would be the file containing the U-component of Wind for 1957-2002.
MSS FILE SIZES: 6.3MB per year per variable; 283MB/variable for each 1957-2002 file
REFERENCES
Uppala, S.M., P.W. Kallberg, A.J. Simmons, et al,
The ERA-40 Reanalysis
Q.J.R. Meteorol. Soc. (2005): 131, 612, 2961-3012
Uppala, S., P. Kallberg, A. Hernandez, S. Saarinen,
M. Fiorino, X. Li, K. Onogi, N. Sokka, U. Andrae,
V. Da Costa Bechtold (2004):
ERA-40: ECMWF 45-year reanalysis of the global
atmosphere and surface conditions 1957-2002.
ECMWF Newsletter No. 101 - Summer/Autumn 2004: 2-21.
ERA-40 Project Report Series
Climate Analysis Section references using ERA40 data.
Often, these illustrate strengths and weaknesses of the ERA40 dataset.
netCDF metadata:
CAVEAT: longitude coordinate variable
The netCDF files were derived from GRIB files containing the T85 resolution ERA-40 data. The GRIB format allows only three decimal places for the longitude increment. Since the T85 grid has a longitude spacing of 1.40625 degrees, the automatically generated longitudes which use the GRIB spacing are not correct. Users can readily generate the correct longitudes or can download the values from an ascii file.
netcdf e4mnth.an.sfc.t85.u10m.2000 {
dimensions:
time = UNLIMITED ; // (48 currently)
lat = 128 ;
lon = 256 ;
variables:
double time(time) ;
time:calendar = "gregorian" ;
time:long_name = "initial time" ;
time:units = "hours since 1800-01-01 00:00" ;
float lat(lat) ;
lat:units = "degrees_north" ;
lat:long_name = "latitude" ;
float lon(lon) ;
lon:units = "degrees_east" ;
lon:long_name = "longitude" ;
float gw(lat) ;
gw:long_name = "gaussian weights" ;
int date(time) ;
date:long_name = "current date as 8 digit integer (YYYYMMDD)" ;
int datesec(time) ;
datesec:long_name = "current seconds of current date" ;
int yyyymmddhh(time) ;
yyyymmddhh:long_name = "current date as 10 digit integer (YYYYMMDDHH)" ;
float U10M(time, lat, lon) ;
U10M:units = "m/s" ;
U10M:long_name = "10 metre U wind component" ;
// global attributes:
:title = "\n",
"ERA40 T85 Surface Analysis: created at NCAR" ;
:temporal_span = "\n",
"The entire ERA40 archive spans 45 years: September 1957 - August 2002." ;
:source_original = "\n",
"European Center for Medium-Range Weather Forecasts - Reading \n",
"" ;
:story = "\n",
"This dataset is a netCDF version of ds126.0 which is archived \n",
"in GRIB format. The original dataset was implemented and \n",
"computed by NCAR\'s Data Support Section (DSS), and forms an \n",
"essential part of efforts undertaken in late 2004, early 2005, \n",
"to produce an archive of selected segments of ERA-40 on a \n",
"standard transformation grid. In this case, 47 ERA-40 at \n",
"00Z, 06Z, 12Z, 18Z monthly mean surface and single level \n",
"analysis (*instantaneous*) variables were transformed from a \n",
"reduced N80 Gaussian grid to a 256x128 regular Gaussian grid. \n",
"All fields were transformed using \n",
"routines from the ECMWF EMOS library, including 10 meter winds \n",
"which were treated as scalars because of a lack of 10 meter \n",
"spectral vorticity and divergence. A missing value of 1e+20 \n",
"(assigned to the _FillValue attribute) occurs in the sea \n",
"surface temperature (SST) and sea ice (CI) fields to mask \n",
"grid points occurring over land. Fields formerly archived \n",
"as whole integers, such as vegetation indices and cloud cover, \n",
"occur as integers plus a fractional part in the T85 version \n",
"due to interpolation. The choice of a T85 Gaussian grid was \n",
"based on considerations of limiting the volume of new data \n",
"generated to a moderate level, and to match the horizontal \n",
"resolution of the Community Atmosphere Model (CAM) component \n",
"of the Community Climate System Model (CCSM). \n",
"" ;
:source_NCAR = "\n",
"Data Support Section \n",
"Scientific Computing Division \n",
"Dataset ID: ds126.0 \n",
"http://dss.ucar.edu/datasets/ds126.0/ \n",
"Specialist: David Stepaniak, davestep@ucar.edu " ;
:source_format = "\n",
"The original ECMWF and the derived T85 are in GRIB format. \n",
"" ;
:source_file = "\n",
"MSS: /DSS/U82383" ;
:source_availability = "\n",
"The ERA-40 data are available for non-commercial use within \n",
"the U.S. and at UCAR member institutions. All data are \n",
"available from the NCAR Mass Storage System (MSS). Use of \n",
"the data at NCAR does not require the submission of a \n",
"permission form. However, if you do not have access to the \n",
"MSS or wish to utilize the data outside of NCAR, then a \n",
"permission form must be signed. This form is available at \n",
" http://dss.ucar.edu/datasets/common/ecmwf/docs/perms.html \n",
"Redistribution of ERA-40 data under any circumstances is \n",
"strictly prohibited. \n",
"" ;
:netCDF_creation = "\n",
"Climate Analysis Section \n",
"Climate & Global Dynamics Division, NCAR \n",
"http://www.cgd.ucar.edu/cas/catalog/ecmwf/ \n",
"Dennis Shea, shea@ucar.edu \n",
"" ;
:netCDF_creation_software = "\n",
"NCAR Command Language (NCL) \n",
"http://www.ncl.ucar.edu/ [Click Download] \n",
"Contact shea@ucar.edu for NCL script \n",
"" ;
:netCDF_creation_date = "\n",
"Fri Apr 1 07:07:50 MST 2005" ;
:Conventions = "CF" ;
}
Back to the CAS Data Catalog
Back to the CAS Home PageDennis Shea: shea@ucar.edu