Using meteorological input data from NCEP

This description is kindly provided by Jooil Kim and Bob Dattore (NCAR) and updated by Michael Schoeppner.

Now there exists a well-managed source of archived windfields from NCEP for use with FLEXPART. Here are the instructions:

1. Go to website: ​http://rda.ucar.edu/datasets/ds093.0/

2. Log in with your ucar account (create one for free if you don't have one yet)

3. Go to "Data Access" -> "Customizable Data Requests" -> "Get a Subset". This opens a window for choosing a customized subset of the CFSR data.

4. Choose your time period, and select "FLEXPART Model Input - 6-hour Forecasts" under the parameter presets. When done, press the "Continue" button on the bottom of the page.

5. On the next window, look for the "Type of Product" menu and select "all available", then press the "Click Here" button to update. . Select all from 1-hour Forecast to 6-hour Forecast in the type-of-product list. For some time periods (e.g. most recent), these may not be available; however, Flexpart might also work with lower time resolution files. Important note: Make sure that under "More date/time options" the box "Split output files into one timestep per file" is checked. When done, push the "Submit Request" button.

6. You will receive an e-mail from UCAR when the data is ready. Follow instructions on the e-mail regarding ways to download the data.

UCAR provides a description of the file nomenclature: ​http://rda.ucar.edu/datasets/ds093.0/#docs/6hrly_filenames.html

Getting the data into FLEXPART

1. The received files should be in the format 201001011300.pgbh01.gdas.20100101-20100105.grb2. Make sure the data is not in format pgbh02.gdas.20100101-20100105.grb2 without the date/time in the beginning. If this is the case, you probably did not check the “Split output files into one timestep per file” box.

2. In case you also downloaded the analysis data (labeled "pgbhnl"): It does not include all of the surface variables like 2 m temperature and 10 m winds, and so can't be used in FLEXPART. Use the 6 h forecast files (labeled “pgbh06”) instead to cover the time steps 00 06 12 and 18. See also the example for the AVAILABLE file below.

3. The files that you want to use in Flexpart have to be listed in the AVAILABLE file like this

DATE TIME FILENAME SPECIFICATIONS

YYYYMMDD HHMISS

20100101 000000 201001010000.pgbh06.gdas.20091226-20091231.grb2 ON DISC

20100101 010000 201001010100.pgbh01.gdas.20100101-20100105.grb2 ON DISC

20100101 020000 201001010200.pgbh02.gdas.20100101-20100105.grb2 ON DISC