DESCRIPTION:
ECMWF ERA-40 archive High Resolution Upper Air Analyses data set at T85 resolution on 23 pressure levels containing monthly means at synoptic hours: 00Z, 06Z, 12Z and 18Z.
SOURCE: Data Support Section Dataset ds126.1
HISTORY:
This dataset is a netCDF version of ds126.1 which is archived in GRIB format. The original dataset was implemented and computed by NCAR's Data Support Section (DSS). It 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, ERA-40 00Z, 06Z, 12Z, and 18Z monthly mean upper air variables on 23 pressure levels were transformed from either spherical harmonics (geopotential, temperature, vertical pressure velocity, vorticity, divergence, relative humidity), or a reduced N80 Gaussian grid (potential vorticity, specific humidity, ozone mass mixing ratio), to a 256x128 regular Gaussian grid at T85 spectral truncation. In addition, horizontal wind components were derived from spectral vorticity and divergence and also archived on a T85 Gaussian grid. All scalar fields were transformed using routines from the ECMWF EMOS library, whereas the horizontal winds were obtained using NCAR's Spherepack library. 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 ds126.1 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 at 00Z, 06Z, 12Z and 18Z
DATES: September 1957 - August 2002
LEVELS:
23 pressure (hPa) levels: 1, 2, 3, 5, 7, 10, 20, 30,
50, 70, 100, 150, 200, 250, 300, 400,
500, 600, 700, 775, 850, 925, 1000
FIELDS:
netCDF
Description Name units
-------------------------------------------------------------------------
Geopotential Z m2/s2
Divergence DIV 1/s
Ozone Mass Mixing Ratio O3 kg/kg
Potential Vorticity PV K m2/kg/s
Relative Humidity RHUM %
Specific Humidity Q kg/kg
Temperature T K
U-component of Wind U m/s
V-component of Wind V m/s
Vertical Pressure Velocity OMEGA Pa/s
Vorticity (relative) VORT 1/s
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.pl.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.pl.t85.t.1958.nc would be the file containing the twelve monthly means for Temperature in 1958 at 00Z, 06Z, 12Z and 18Z..MSS FILE SIZE:
Each file is 144.7MB/variable.
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.pl.t85.t.1958 {
dimensions:
time = UNLIMITED ; // (48 currently)
lev = 23 ;
lat = 128 ;
lon = 256 ;
variables:
double time(time) ;
time:info = "time corresponds to the first day of the month" ;
time:calendar = "gregorian" ;
time:long_name = "initial time" ;
time:units = "hours since 1800-01-01 00:00" ;
int lev(lev) ;
lev:positive = "down" ;
lev:units = "hPa" ;
lev:long_name = "pressure" ;
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" ;
float T(time, lev, lat, lon) ;
T:units = "K" ;
T:long_name = "Temperature" ;
// global attributes:
:title = "\n",
"ERA40 Monthly Mean T85 Analysis on Pressure Surfaces: 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",
"T159 spectral resolution in spherical harmonics. " ;
:story = "\n",
"DS126.1 represents a new data set implemented and computed \n",
"by NCAR\'s Data Support Section, and forms a substantial part \n",
"of ongoing efforts to produce an archive of selected segments \n",
"of ERA-40 on a standard transformation grid. In this case, \n",
"ERA-40 upper air variables on 23 pressure levels have been \n",
"transformed from either spherical harmonics (geopotential, \n",
"temperature, vertical pressure velocity, vorticity, divergence,\n",
"relative humidity), or a reduced N80 Gaussian grid (potential \n",
"vorticity, specific humidity, ozone mass mixing ratio), to a \n",
"256x128 regular Gaussian grid at T85 spectral truncation. \n",
" \n",
"In addition, horizontal wind components have been derived \n",
"from spectral vorticity and divergence and also archived on a \n",
"T85 Gaussian grid. All scalar fields have been transformed \n",
"using routines from the ECMWF EMOS library, whereas the \n",
"horizontal winds have been obtained using NCAR\'s Spherepack \n",
"library. The choice of a T85 Gaussian grid was based on \n",
"considerations of limiting the volume of new data generated \n",
"to a moderate level, and to match the resolution of the latest \n",
"generation of CCSM, NCAR\'s Community Climate System Model. \n",
"" ;
:source_NCAR = "\n",
"Data Support Section \n",
"Scientific Computing Division \n",
"Dataset ID: ds126.1 \n",
"http://dss.ucar.edu/datasets/ds126.1/ \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/U78137" ;
:source_availability = "\n",
"The data are available for non-commercial research in the U.S. \n",
"and at UCAR member institutions. Users are required to submit \n",
"a permission form before access is granted. All data files are \n",
"available directly from the NCAR MSS. This requires an NCAR \n",
"computing account. Permission is automatically granted and \n",
"users are obligated not to redistribute the data. \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 Mar 18 15:24:28 MST 2005" ;
:Conventions = "CF" ;
}
Back to the CAS Data Catalog
Back to the CAS Home PageDennis Shea: shea@ucar.edu