forecast time

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forecast time

Postby Hadja » Fri Jun 22, 2012 9:06 am

Hi everybody,

Currently, I try to use WRF model in order to forecast solar irradiance. Can you please tell me which variable correspond to the forecast time (in hours for example) once I generate the NetCDF forecast file (wrfout_d01_2005-08-28_00:00:00 for example) with the ./wrf.exe command?

I can extract solar irradiation data but I don't know for which forecast time (in year/month/day : hour/mn/s) it is.

Thank you
Hadja
 
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Re: forecast time

Postby AchternDiek » Mon Jun 25, 2012 6:52 am

Hi Hadja,

The namelist variable 'history interval' tells you in what time interval your output is written to an output file.
The namelist variable 'frames_per_outfile' tells you how many of those 'history intervals' are written to the same output file.

Here an example:
For history interval = 360 (minutes) and frames_per_outfile = 4
your file 'wrfout_d01_2005-08-28_00:00:00' contains results from four time steps, being 00:00, 06:00, 12:00, and 18:00 model time.


AchternDiek
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Re: forecast time

Postby Hadja » Wed Jun 27, 2012 9:08 am

Thank you very for your response.

In this case, what is the rule of time_step variable?
Hadja
 
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Re: forecast time

Postby AchternDiek » Thu Jun 28, 2012 6:40 am

The basic rule is:
time_step = 6 * dx (in km)

I often go with even smaller values just to be on the safe side.
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Re: forecast time

Postby Hadja » Thu Jun 28, 2012 9:23 am

Thank you AchternDiek. I understand now.

I try to forecast 16/01/2012 based on grib data from 01/01/2012 to 15/01/2012 run WRF with namelist.wps and namelist.input (see below).

However When I read Times variable from wrfout_d01_2012-01-01_00:00:00, It contains this value:
2012/01/01 - 00:00:00
2012/01/01 - 03:00:00
2012/01/01 - 06:00:00
2012/01/01 - 09:00:00
2012/01/01 - 12:00:00
2012/01/01 - 15:00:00
2012/01/01 - 18:00:00
2012/01/01 - 21:00:00
2012/01/02 - 00:00:00

What I have to do in order to obtain data forecast for the times 2012/01/16?

File namelist.wps contains :
&share
wrf_core = 'ARW',
max_dom = 2,
start_date = '2012-01-01_00:00:00','2012-01-01_00:00:00',
end_date = '2012-01-15_18:00:00','2012-01-15_18:00:00',
interval_seconds = 21600,
io_form_geogrid = 2,
/
...
File namelist.input contains:
&time_control
run_days = 0,
run_hours = 24,
run_minutes = 0,
run_seconds = 0,
start_year = 2012, 2012,
start_month = 01, 01,
start_day = 01, 01,
start_hour = 00, 00,
start_minute = 00, 00,
start_second = 00, 00,
end_year = 2012, 2012,
end_month = 01, 01,
end_day = 15, 15,
end_hour = 18, 18,
end_minute = 00, 00,
end_second = 00, 00,
interval_seconds = 21600
input_from_file = .true.,.true.,
history_interval = 180, 60,
frames_per_outfile = 1000, 1000,
restart = .false.,
restart_interval = 5000,
io_form_history = 2
io_form_restart = 2
io_form_input = 2
io_form_boundary = 2
debug_level = 0
/
&domains
time_step = 8,
time_step_fract_num = 0,
time_step_fract_den = 1,
max_dom = 2,
...
Hadja
 
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Re: forecast time

Postby AchternDiek » Fri Jun 29, 2012 4:10 am

Your model run time is set to 24 hours (run_hours = 24) and your model run starts at 01/01/2012.
That explains the content of your wrfout_d01_2012-01-01_00:00:00.
You simply have to adjust your model run time, so it matches your start and end time.

Be aware that you need boundary conditions from WPS for the whole model run time.
If you want your model run to include 16/01/2012, you will need grib data for this day as well.

--AchternDiek
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Re: forecast time

Postby Hadja » Fri Jun 29, 2012 7:29 am

Thank you AchternDiek. You help me a lot.

I have difficulties to understand WRF forecasting. I thought that it is able to forecast future data like solar irradiation from past data. Is my understanding correct?

If I need grib data for all the period I want to calculate with WRF, what is the purpose of WRF forecasting?

I use GFS grib data downloaded at http://rda.ucar.edu/cgi-bin/datasets/dataaccess?dsnum=083.2. This data are available only for past time. How to get grib data for futur time?
Hadja
 
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Joined: Fri Jun 22, 2012 9:00 am


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