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Re: [netcdfgroup] Questions about NetCDF file - How can I interpret the nc file



This looks to be (at least mostly) a CF-compliant file. So you can learn about what all those attribute mean here:

http://cfconventions.org/

-Chris


On Thu, May 21, 2015 at 8:01 AM, Ted Mansell <address@hidden> wrote:
The information you need is there in the variable information:

Âshort Wind_U(time, lat, lon) ;
 Wind_U:long_name = "Wind U Component" ;
 Wind_U:units = "m/s" ;
 Wind_U:scale_factor = 0.01f ;
 Wind_U:valid_range = -100s, 100s ;
 Wind_U:missing_value = -9999s ;
 Wind_U:_FillValue = -9999s ;
 Wind_U:coordinate = "lon lat" ;

So the values are in m/s but need a scale factor of 0.01 applied because it is stored as a short integer rather than a float. Thus 155 is 1.55 m/s.

As for the ordering, these are in the C convention (opposite of Fortran) 'time' is the slowest index, whereas 'lon' is stride one. [In the Fortran interface, the arrays are automatically switched to (lon, lat, time)]

Thus:

Wind_U(time=0, lat=-90, lon=0) = 155Â -> 1.55 m/s
Wind_U(time=0, lat=-90, lon=0.5) = 158 -> 1.58 m/s
Wind_U(time=0, lat=-90, lon=1.0) = 161 -> 1.61 m/s

etc.

-- Ted
__________________________________________________________
| Edward Mansell <address@hidden>
| National Severe Storms Laboratory
|--------------------------------------------------------------
| "The contents of this message are mine personally and
| do not reflect any position of the U.S. Government or NOAA."
|--------------------------------------------------------------


I suggest getting a viewing tool like ncview to peruse the data graphically.

On May 20, 2015, at 9:58 PM, ëí <address@hidden> wrote:

> Dear NetCDF suppot team
>
>
> Hello
>
> I am DH from Korea.
>
> I am going to use netcdf file soon to get the weather information at my company.
>
> But the problem is I am the first one in my company so don't know how to interpret the nc file.
>
> (I can just convert to txt file with ncdump, and read the letters...)
>
>
> below is the netcdf file which I should interpret...(it contains global wind information)
>
>
> ========================================================================================
>
> netcdf GFS20150520 {
> dimensions:
>Â lon = 720 ;
>Â lat = 361 ;
>Â time = UNLIMITED ; // (57 currently)
> variables:
>Â float lat(lat) ;
>Â Âlat:long_name = "Latitude" ;
>Â Âlat:units = "degrees_north" ;
>Â Âlat:missing_value = -99999.f ;
>Â Âlat:_FillValue = -99999.f ;
>Â float lon(lon) ;
>Â Âlon:long_name = "Longitude" ;
>Â Âlon:units = "degrees_east" ;
>Â Âlon:missing_value = -99999.f ;
>Â Âlon:_FillValue = -99999.f ;
>Â int time(time) ;
>Â Âtime:long_name = "forecast time" ;
>Â Âtime:units = "minutes since 2015-05-20 00:00" ;
>Â Âtime:standard_name = "time" ;
>Â Âtime:reference = "UTC" ;
>Â Âtime:missing_value = -99999 ;
>Â Âtime:_FillValue = -99999 ;
>Â short Wind_U(time, lat, lon) ;
>Â ÂWind_U:long_name = "Wind U Component" ;
>Â ÂWind_U:units = "m/s" ;
>Â ÂWind_U:scale_factor = 0.01f ;
>Â ÂWind_U:valid_range = -100s, 100s ;
>Â ÂWind_U:missing_value = -9999s ;
>Â ÂWind_U:_FillValue = -9999s ;
>Â ÂWind_U:coordinate = "lon lat" ;
>Â short Wind_V(time, lat, lon) ;
>Â ÂWind_V:long_name = "Wind V Component" ;
>Â ÂWind_V:units = "m/s" ;
>Â ÂWind_V:scale_factor = 0.01f ;
>Â ÂWind_V:valid_range = -100s, 100s ;
>Â ÂWind_V:missing_value = -9999s ;
>Â ÂWind_V:_FillValue = -9999s ;
>Â ÂWind_V:coordinate = "lon lat" ;
>
> // global attributes:
>Â Â:title = "Environmental data" ;
>Â Â:version = "1.0" ;
>Â Â:institution = "ASA" ;
>Â Â:Contact = "address@hidden" ;
>Â Â:source = "NCEP NOAA" ;
>Â Â:reference = "Created by DAN_GRIB2NC2 Version 3.0d at 05/20/15 18:14:53" ;
> Â:default_view = "10 meter Wind U, Wind V " ;
>Â Â:netcdf_class = "2" ;
>Â Â:netcdf_class_description = "Multi point, static, ..." ;
>Â Â:time_var = "time" ;
>Â Â:lat_var = "Lat" ;
>Â Â:lon_var = "lon" ;
>Â Â:view_style = "1" ;
>Â Â:Conventions = "CF-1.0" ;
> data:
> lat = -90, -89.5, -89, -88.5, -88, -87.5, -87, -86.5, -86, -85.5, -85,
>Â Â Â-84.5, -84, -83.5, -83, -82.5, -82, -81.5, -81, -80.5, -80, -79.5, -79,
>Â Â Â-78.5, -78, -77.5, -77, -76.5, -76, -75.5, -75, -74.5, -74, -73.5, -73,
>
> .....(oimt).....
>
>Â lon = 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8,
>Â Â Â8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5,
>Â Â Â16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 20.5, 21, 21.5, 22, 22.5, 23,
>Â Â Â23.5, 24, 24.5, 25, 25.5, 26, 26.5, 27, 27.5, 28, 28.5, 29, 29.5, 30,
>
> .....(oimt).....
>
> time = 0, 180, 360, 540, 720, 900, 1080, 1260, 1440, 1620, 1800, 1980, 2160,
>Â Â Â2340, 2520, 2700, 2880, 3060, 3240, 3420, 3600, 3780, 3960, 4140, 4320,
>Â Â Â4500, 4680, 4860, 5040, 5220, 5400, 5580, 5760, 5940, 6120, 6300, 6480,
>Â Â Â6660, 6840, 7020, 7200, 7380, 7560, 7740, 7920, 8100, 8280, 8460, 8640,
>Â Â Â8820, 9000, 9180, 9360, 9540, 9720, 9900, 10080 ;
>
> Wind_U =
>Â Â155, 158, 161, 164, 166, 168, 171, 175, 177, 179, 182, 184, 188, 190, 192,
>Â Â Â194, 197, 200, 203, 204, 207, 209, 212, 214, 216, 220, 222, 224, 227,
>Â Â Â229, 230, 233, 235, 237, 239, 241, 245, 247, 249, 251, 253, 255, 256,
>
> .....(oimt).....
>
> Wind_V =
>Â Â-310, -309, -308, -307, -306, -304, -303, -301, -300, -298, -297, -295,
>Â Â Â-292, -291, -289, -287, -286, -284, -282, -281, -280, -278, -276, -274,
>Â Â Â-272, -270, -267, -265, -263, -262, -259, -257, -256, -254, -252, -250,
>Â Â Â-248, -246, -244, -241, -238, -236, -234, -232, -230, -228, -226, -223,
>
> .....(oimt)
>
> ========================================================================================
>
>
> For example, at the above file, the first value of Wind_U, 155 is simply meaning Wind_U(time, lat, lon)=Wind_U(0, -90, 0) ?
>
> Then what about the second value of Wind_U, 158 ? Is that meaning Wind_U(0, -90, 0.5) ? or Wind_U(180, -90, 0) ?
>
> I am not sure this is right and I don't know about the order...
>
>
> Please reply me with brief explanation.
>
> Thank you for reading.
>
>
> Best Regards
>
> DH HAN
>
>
>
> _______________________________________________
> netcdfgroup mailing list
> address@hidden
> For list information or to unsubscribe, visit: http://www.unidata.ucar.edu/mailing_lists/


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--

Christopher Barker, Ph.D.
Oceanographer

Emergency Response Division
NOAA/NOS/OR&R Â Â Â Â Â Â(206) 526-6959ÂÂ voice
7600 Sand Point Way NE ÂÂ(206) 526-6329ÂÂ fax
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