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Output Archive
 

Click here for the PDF version of this document (outdated)

Updated 2010/4/30 to reflect changes in filename conventions and 3-D data organization.

General Information

Output will be reported in NetCDF using CF conventions. Variable names and units should be consistent with IPCC. Please consult with the NARCCAP group if inconsistencies are found. More on CF conventions can be found at http://badc.nerc.ac.uk/help/formats/netcdf/index_cf.html.

Output will be on the model’s native horizontal grid. A supplemental archive is planned to provide some variables on a common grid.

File name

File names should follow this structure:

VariableName_ModelName_Time.nc
VariableName_ModelName_DriverName_Time.nc

Where:

"VariableName" is the IPCC/CF-convention Variable Name in the tables below.

"ModelName" is a 4-character, all-caps identifier chosen by the modeling group (please clear it with the archival group beforehand to avoid conflicts)

"DriverName" is either "ncep" or the name of the driving GCM, in all-lowercase. (For the timeslice experiments, the driver is "slice".)

"Time" is the starting time of the file, in the form "YearMonthDayUTC", e.g., 1979010100 for 00 UTC on 1 Jan 1979.

File sizes

(a) two-dimensional fields: files covering 5 years (half a decade).

For consistency with climatological averaging standards, all 2-D files should end on years ending in zero or five (e.g., 1981-1985, 1986-1990, etc.). There may be some odd file sizes at the beginning and end (e.g., 1979-1980), but there is merit in having output from all models cover the same set of periods in their files.

The ending time in a file should be 00 UTC on 1 January, since fluxes are for the 3-hour period preceding that time. For instantaneous fields, the ending time is less important, but for consistency should be the same time.

(b) three-dimensional fields: files covering 1 month

Note that the definition of a month may vary between GCMs and may also differ from the real calendar. The "month" should follow usage in the source of the boundary conditions. The ending time in a file should be 00 UTC on day 1 of the following month (i.e., at midnight UTC separating one month from the next).

Three-dimensional fields are separated by pressure level into 2-D files structured as above. Following CF convention, the pressure level is recorded as a scalar coordinate variable. The pressure level is included in the filename, prefaced by a 'p', between the driver and the time. For example: ta_RCM3_ncep_p750_1981010103.nc is the file containing temperature data at the 750 hPa level for the ncep-driven run of RegCM3 starting Jan 1st 1981.

Further details regarding NetCDF conventions to follow, especially for metadata, appear in Requirements for Standard Output Contributed to the NARCCAP Archive.

 

Two-Dimensional Fields

Table 1: Daily fields

The "day" for minimum and maximum temperatures should be from 06 UTC - 06 UTC, with the date stamp referring to the beginning time. This follows NARCCAP Exp. 0 practice. Thus, for 06 UTC 30 June 1979 - 06 UTC 1 July 1979, the date of the record is 30 June 1979, the calendar day corresponding to the period recorded for North America.

The min/max should be recorded from instantaneous “screen height” temperatures sampled every time step during the course of the day. The “screen height” or “reference height” should be in the range 1.5 – 2 m above the surface.

Long Name Units Variable Name Standard Name
Maximum Daily Surface Air Temperature K tasmax air_temperature (In CF convention: air_temperature with a vertical coordinate in height of 2 m and a cell_methods attribute including time: maximum within days)
Minimum Daily Surface Air Temperature K tasmin air_temperature (In CF convention: air_temperature with a vertical coordinate in height of 2 m and a cell_methods attribute including time: minimum within days)
Maximum Daily 10-Meter Wind Speed

m-s -1

spdmax wind_speed_of_gust (In CF convention: wind_speed with a vertical coordinate in height of 10 m and a cell_methods attribute including time: maximum within days)
Daily Average Sea-ice Fraction fraction in [0,1] sic sea_ice_area_fraction

Table 2: Primary three-hourly surface fields needed for impacts assessment

Each day, values reported at 03 UTC, 06 UTC, … 24 UTC. Solar radiation is averaged over the 3-hr period prior to the reporting time. Precipitation is the 3-hour average prior to the reporting time. Other quantities are instantaneous values as noted. Winds should be the true west-east and south-north winds (i.e., rotated from the model’s grid as needed to the earth’s longitudinal and latitudinal directions).

The surface air temperature and specific humidity should be recorded from “screen height” values. The “screen height” or “reference height” should be in the range 1.5 – 2 m above the surface. Surface winds should be recorded from “anemometer level” values. The “anemometer level” should be 10 meters above the surface.

Note units for precipitation and surface pressure (MKS – following CF standards).

Long Name Units Variable Name Standard Name Notes
Precipitation kg-m-2-s -1 pr precipitation_flux Average
Surface Specific Humidity kg-kg -1 huss specific_humidity (In CF convention: specific_humidity with a vertical coordinate in height of 2 m) Instantaneous
Surface Air Temperature K tas air_temperature (In CF convention: air_temperature with a vertical coordinate in height of 2 m)

Instantaneous

Surface Downwelling Shortwave Radiation W-m -2 rsds surface_downwelling_shortwave_flux_in_air Average, Positive down
Zonal Surface Wind Speed m-s -1 uas eastward_wind (In CF convention: eastward_wind with a vertical coordinate in height of 10 m) Instantaneous, Positive to East
Meridional Surface Wind Speed m-s -1 vas northward_wind (In CF convention: northward_wind with a vertical coordinate in height of 10 m) Instantaneous, Positive to North
Surface Pressure Pa ps surface_air_pressure Instantaneous


Table 3: Additional three-hourly fields, guided by GCM output archived for IPCC Fourth Assessment Report

See https://esg.llnl.gov:8443/about/ipccTables.do for more on IPCC Fourth Assessment Report.

For each day, values reported at 03 UTC, 06 UTC, … 24 UTC, on the model’s native grid.

Quantities that can be used for storage terms in budgets are instantaneous values. Quantities that are fluxes in budgets should be average values for the 3-hr period prior to the reporting time.

Snow depth is snow-water equivalent and is the average depth over the entire grid box, even if the model allows snow to cover a fraction of the grid box.

Long Name Units Variable Name Standard Name Notes
Total Cloud Fraction fraction in [0,1] clt cloud_area_fraction Average
Precipitable Water kg-m -2 prw atmosphere_water_vapor_content Instantaneous
Snow Depth m snd surface_snow_thickness Instantaneous, Snow-water equivalent
Soil Frozen Water Content kg-m -2 mrfso soil_frozen_water_content Instantaneous

Total Soil Moisture Content

kg-m -2 mrso soil_moisture_content Instantaneous
Surface Evaporation of Condensed Water kg-m -2-s -1 evps water_evaporation_flux Average
Snow Melt kg-m -2-s -1 snm surface_snow_melt_flux Average
Surface and Subsurface Runoff kg-m -2-s -1 mrro runoff_flux Average
Surface Runoff kg-m -2-s -1 mrros surface_runoff_flux Average
Convective Precipitation kg-m-2-s-1 prc convective_precipitation_flux Average
Surface Latent Heat Flux W-m-2 hfls surface_upward_latent_heat_flux Average, Pos. up
Surface Sensible Heat Flux W-m-2 hfss surface_upward_sensible_heat_flux Average, Pos. up
Surface Downwelling Longwave Radiation W-m-2 rlds surface_downwelling_longwave_flux_in_air Average, Positive down
Surface Upwelling Longwave Radiation W-m-2 rlus surface_upwelling_longwave_flux_in_air Average, Pos. up
Outgoing Longwave Radiation W-m-2 rlut toa_outgoing_longwave_flux Average, Pos. up
Surface Upwelling Shortwave Radiation W-m-2 rsus surface_upwelling_shortwave_flux_in_air Average, Pos. up
TOA Incident Shortwave Radiation W-m-2 rsdt toa_incoming_shortwave_flux Average, Pos. down
TOA Reflected Shortwave Radiation W-m-2 rsut toa_outgoing_shortwave_flux Average, Pos. up
Surface Downward Flux of Eastward Momentum Pa tauu surface_downward_eastward_stress Average, Pos. down
Surface Downward Flux of Northward Momentum Pa tauv surface_downward_northward_stress Average, Pos. down
Surface (skin) Temperature K ts surface_temperature Instantaneous
Sea Level Pressure Pa psl air_pressure_at_sea_level Instantaneous
500 hPa Geopotential Height m zg500 geopotential_height (ID for singleton level: geopotential_height with a vertical coordinate in pressure of 500hpa) Instantaneous
Atmospheric Boundary Layer Thickness m zmla atmosphere_boundary_layer_thickness Instantaneous

Table 4: Fixed surface fields

For land-cover type, modelers will supply a vegetation index for each grid point along with a table linking each index value to a land-cover description. Models using a mosaic of multiple surface types in a grid box should supply sufficient information to describe the mosaic. On the models’ native grids.

Long Name Units Variable Name Standard Name Notes
Capacity of Soil to Store Water kg-m -2 mrsofc soil_moisture_content_at_field_capacity  
Surface Altitude m orog surface_altitude  
Root Depth m rootd root_depth  
Land-Cover Type - landtyp land_cover  
Longitude of Grid Points degrees east lon longitude  
Latitude of Grid Points degrees north lat latitude  
Land Area Fraction fraction in [0,1] sftlf land_area_fraction land/ocean

Three-Dimensional Fields

Table 5: Three-dimensional atmospheric fields

Reported every three hours (03 UTC, 06 UTC, 09 UTC, 12 UTC, 15 UTC, 18 UTC, 21 UTC, 24 UTC). Instantaneous values every 25 hPa from 1050 hPa to 25 hPa 700 hPa, and every 50 hPa from 750 hPa to 050 hPa. Flag values for levels outside of the model’s atmosphere with the PCMDI missing values flag: 1e20. (Surface pressure is listed in Table 2).

Note that according to the CF conventions, the ice cloud water and the liquid cloud water are each reported as the ratio (cloud-water mass)/(mass of gas+condensed constituents), i.e., more like specific humidity than mixing ratio.

Long Name Units Variable Name Standard Name Notes
Temperature K ta air_temperature Instantaneous
Zonal Wind Component m-s-1 ua eastward_wind Instantaneous
Meridional Wind Component m-s-1 va northward_wind Instantaneous
Vertical Wind Component m-s-1 wa upward_air_velocity Instantaneous
Specific Humidity kg-kg-1 hus specific_humidity Instantaneous
Cloud Ice Fraction of Layer fraction in [0,1] cli mass_fraction_of_cloud_ice_in_air Instantaneous
Cloud Liquid Water Fraction of Layer fraction in [0,1] clw mass_fraction_of_cloud_liquid_water_in_air Instantaneous

For more information on the output archive, contact William Gutowski, Jr. (gutowski@iastate.edu) or Seth McGinnis (mcginnis@ucar.edu).

 
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