OHD/HL/DMIP2 - Energy Forcing Data

We provide the following Information for those participants who wish to compute time series of potential evaporation.

A. North American Regional Reanalysis (NARR) Data

1. Data websites

The NCEP NARR home page is at: http://www.emc.ncep.noaa.gov/mmb/rreanl/.

Follow the instruction ‘Click here to download data’ to website:
http://nomads.ncdc.noaa.gov/,

Then click ‘access’ under ‘Data’, you will go to: http://nomads.ncdc.noaa.gov/data.php?name=access.

Click on North American Regional Reanalysis (NARR) (32km, 1979 to present) under ‘Reanalysis’, you will go to
http://nomads.ncdc.noaa.gov/data.php?name=access#narr_datasets.

You probably want to choose NARR-A instead of NARR-B.
(Please refer to http://nomads.ncdc.noaa.gov/data.php?name=narrdiffs for difference between NARR A and B files.)

2. Download data

The volume of NARR data is large. ‘It is advised that the FTP4u subsetting tool be used for downloading large time-series of this data’.

i. Define your collection by setting dates and time series
The time required to collect all desired files relies on whether the system is busy.
If the surface 2m air temperature, relative humidity, 10m wind (U and V), surface downward long radiation data are downloaded, you could start with 10 months for all circles (8 times per day) and adjust the data length according to the waiting time.

ii. Click on ‘Select Files for FTP’

ii. Select the files and fill out the FTP information.

After selecting files (just put in ‘*’, in the dialogue frame for all files) and selecting parameters (need to select parameters and levels), it is very important to define a sub-region to reduce the file size.

In Oklahoma, the box covering the entire state for the soil moisture experiments could be defined by: [32N, 39N] for latitudes and [105W, 92W] for longitude.

For the Blue river basin, the sub-region could be [98W, 95W] and [33N, 36N];
For the Illinois and Elk River basins together, the sub-region could be [96W, 93W] and [34N, 38N];

iii. Then follow the instructions to retrieve data from NCDC server:

3. Decode data
NARR data are stored in GRIB format.
i. To read the data, the GrADS is a very useful tool.
http://grads.iges.org/grads/grads.html

The resolution may change when the data are downloaded for sub-regions. To open and read the sub-region files, control files (.ctl) need to be updated by running grib2ctl.pl.
(grib2ctl.pl could be downloaded at http://www.cpc.ncep.noaa.gov/products/wesley/grib2ctl.html)
Then run ‘gribmap -0 –i filename.ctl’ to update the index file.
Now, the files are ready to be opened in GrADS environment.

To extract the time series for one variable, just edit one .ctl file,
Use ‘dset ..narr-a_221_%y4%m2%d2_%h200_000.grb’ in the .ctl files to include all the files in a year, then set the start time and record length.
Produce an index file for the new .ctl file using gribmap (gribmap -0 –i filename.ctl).
Then it is fairly easy to write out the time series in any format in GrADS environment.

ii. NARR data are also stored at UCAR. there are sample codes in FORTRAN and C.
Go to http://dss.ucar.edu/pub/narr/,
under ‘Applications & Software’, select DSS GRIB Software and you will see links to decoding codes in FORTRAN and C.

B. Short Wave (SW) Flux Data

NCEP/NARR has surface downward short wave flux data calculated from radiative transfer models. NOAA/NESDIS has surface downward short wave flux derived from GOES satellites observations. The NESDIS SW data are stored and distributed at University of Maryland, College Park server: http://www.atmos.umd.edu/~srb/gcip/gcipsrb.htm

1. To download the operational data, which are available from 1995 to present, follow the link to ‘Data Access’, click on ‘Historic data’, then select ‘surface downward flux’, there are ‘instantaneous’, ‘hourly average’, ‘daily average’, and ‘monthly average’ surface downward SW flux. (Partial year data are at ‘Current Data’ link instead of ‘Historic Data’ link).

2. NESDIS SW data have been re-processed for the period of 1996-2000. These data are available at ½ and 1/8 degree resolution. To download the re-processed data, go to http://www.atmos.umd.edu/~srb/gcip/gcipsrb.htm,
follow the link to ‘GCIP/GAPP at ½ degree reprocessed from 1996 to 2000’ or ‘GCIP/GAPP at 1/8th degree reprocessed from 1996-2000’.

At the data access pages, there are sample codes in FORTRAN and GrADS to read and display the SW data.