DESCRIPTION:
ECMWF ERA-40 High Resolution "Other" Surface Analysis dataset at T85 resolution containing monthly means. These are not analyzed fields. These are model forecast fields. (See HISTORY section for details.) When interpreted properly, these additional fields may facilitate insight into assorted research investigations.
SOURCE: Data Support Section Dataset ds126.0 [See also: Data Support Section Dataset ds119.0 and supporting documentation]
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, twenty seven ERA-40 monthly mean surface and single level 6-hour forecast variables were transformed from a reduced N80 Gaussian grid to a 256x128 regular Gaussian grid. Four of the variables are "instantaneous" variables, and the remaining twenty three variables are "accumulated" over the 6-hour forecast time. Because of this offset, we note that 1984123118, valid at 1985010100, is the first time encountered in the file containing monthly means for 1985, for example. In this case, 1984123118 (1985010100) represents the January 1985 monthly mean, 1985013118 (1985020100) represents the February 1985 monthly mean, and so on. Divide the accumulated variables by 21600 seconds to obtain instantaneous values. (Multiplication by minus one may also be necessary to match the sign convention one is accustomed to.) All fields were transformed using routines from the ECMWF EMOS library, including three pairs of stresses which were treated as scalars because of a lack of spectral precursors. 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, top of atmosphere, categorical cloud levels
FIELDS:
As noted in the HISTORY section, the original three pairs of stresses 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. Technically, vector pairs should be derived or interpolated as component pairs. Users should use these fields with this caveat in mind.
netCDF Accumulated
Description Name units (Yes/No)
-----------------------------------------------------------------------------------------
Stress: East-West surface stress EWSS N/m2 s Y
Stress: North-South surface stress NSSS N/m2 s Y
Stress: latitudinal gravity wave LGWS N/m2 s Y
Stress: meridional gravity wave MGWS N/m2 s Y
Stress: instantaneous X IEWS N/m2 No
Stress: instantaneous Y INSS N/m2 No
Precipitation: stratiform
(Large scale precipitation) LSP m Y
Precipitation: convective CP m Y
Moisture flux: instantaneous IE kg/m2/s No
Evaporation E m of water Y
Runoff RO m Y
Snowfall: convective+large scale) SF m of water equivalent Y
Snow evaporation ES m of water Y
Snowmelt SMLT m of water Y
Heat flux: surface latent SLHF W/m2 s Y
Heat flux: surface sensible SSHF W/m2 s Y
Boundary layer height BLH m No
Solar radiation: top TSR W/m2 s Y
Solar radiation: surface SSR W/m2 s Y
Solar radiation: sfc net (clear sky) SSRC W/m2 s Y
Solar radiation: top net (clear sky) TSRC W/m2 s Y
Solar radiation: surface downwards SSRD W/m2 s Y
Thermal radiation: surface STR W/m2 s Y
Thermal radiation: top TTR W/m2 s Y
Thermal radiation: sfc net (clear sky) STRC W/m2 s Y
Thermal radiation: top net (clear sky) TTRC W/m2 s Y
Thermal radiation: surface downwards STRD W/m2 s Y
Note: SSRD is the total solar radiation directed downward at the surface.
SSR is the net solar radiation at the surface, i.e.
SSR = SSRD - (surface_albedo)SSRD = (1 - surface_albedo)SSRD
SSRD and SSR are the only ERA-40 surface solar radiation variables
that can be interpreted as "total", representing contributions from
all components of the shortwave stream affecting the surface.
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.
e4mnth.an.sfc.othr.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.othr.t85.tsr.1958.nc would be the file containing the "Top Solar Radiation" 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.othr.t85.vName.1957-2002.nc For example: e4mnth.an.sfc.othr.t85.tsr.1957-2002.nc would be the file containing the "Top Solar Radiation" for 1957-2002.
MSS FILE SIZES: 6.3MB per yearly file per variable; 283MB/variable for the 1957-2002 files
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:
Note that the "time", "date", "datesec" and "yyyymmddhh" pertain to the time at which the forecast is valid. Each forecast was initiated 6 hours previous to this time. The initial times are denoted by the "time_initial", "date_initial", "datesec_initial" and "yyyymmddhh_initial" variables.
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.othr.t85.tsr.1985 {
dimensions:
time = UNLIMITED ; // (48 currently)
lat = 128 ;
lon = 256 ;
variables:
double time(time) ;
time:units = "hours since 1800-01-01 00:00" ;
time:long_name = "valid time" ;
time:calendar = "gregorian" ;
time:info = "This is the time the forecast is valid. USE THIS!" ;
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 = "valid date as 8 digit integer (YYYYMMDD)" ;
int datesec(time) ;
datesec:long_name = "seconds of valid date" ;
int yyyymmddhh(time) ;
yyyymmddhh:long_name = "valid date as 10 digit integer (YYYYMMDDHH)" ;
double time_initial(time) ;
time_initial:info = "This is the time the forecast is initiated" ;
time_initial:calendar = "gregorian" ;
time_initial:long_name = "initial time" ;
time_initial:units = "hours since 1800-01-01 00:00" ;
int date_initial(time) ;
date_initial:long_name = "initial date as 8 digit integer (YYYYMMDD)" ;
int datesec_initial(time) ;
datesec_initial:long_name = "seconds of initial date" ;
int yyyymmddhh_initial(time) ;
yyyymmddhh_initial:long_name = "initial date as 10 digit integer (YYYYMMDDHH)" ;
float TSR(time, lat, lon) ;
TSR:accumulated_variable = "Yes: divide by 21600 seconds for instantaneous value" ;
TSR:units = "W/m2 s" ;
TSR:long_name = "Top solar radiation" ;
// global attributes:
:title = "\n",
"ERA40 T85 Monthly Mean Surface Forecast Fields at 00Z, 06Z, 12Z, 18Z: 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",
"on a 256x128 regular Gaussian. In this case, twenty seven \n",
"ERA-40 00Z, 06Z, 12Z and 18Z monthly mean surface and single \n",
"level 6-hour forecast variables were transformed from a reduced\n",
"N80 Gaussian grid to a 256x128 regular Gaussian grid. All \n",
"variables are valid 6 hours after the forecast was initiated. \n",
"Thus, 00Z 6-hour forecast evaporation is valid at 06Z. \n",
" \n",
"Four of the variables are \n",
"*instantaneous* variables, and the remaining twenty three \n",
"variables are *accumulated* over the 6-hour forecast time. \n",
"Divide the accumulated variables by 21600 seconds to obtain \n",
"instantaneous values. (Multiplication by minus one may also \n",
"be necessary to match the sign convention one is accustomed \n",
"to.) All fields were transformed using routines from the ECMWF \n",
"EMOS library, including three pairs of stresses which were \n",
"treated as scalars because of a lack of spectral precursors. \n",
"The choice of a T85 Gaussian grid was based on considerations \n",
"of limiting the volume of new data generated to a moderate \n",
"level, and to match the horizontal resolution of the Community \n",
"Atmosphere Model (CAM) component of the Community Climate \n",
"System Model (CCSM). \n",
"" ;
:Caveat = "\n",
"THESE ARE NOT ANALYZED FIELDS. THESE ARE MODEL FORECAST FIELDS \n",
"They derived from the forecast initiated at the indicated \n",
"analysis time. These fields apply to six hours after the \n",
"forecast was initiated. Most are ACCUMULATED quantities. \n",
"To compute instantaneous values for the accumulated fields, \n",
"divide all data values by 21,600 seconds. When interpreted \n",
"properly, these additional fields may facilitate insight into \n",
"assorted research investigations. \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/U82552" ;
: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 22 14:32:27 MDT 2005" ;
:Conventions = "CF" ;
}
Back to the CAS Data Catalog
Back to the CAS Home PageDennis Shea: shea@ucar.edu