This archive contains answers to questions sent to Unidata support through mid-2025. Note that the archive is no longer being updated. We provide the archive for reference; many of the answers presented here remain technically correct, even if somewhat outdated. For the most up-to-date information on the use of NSF Unidata software and data services, please consult the Software Documentation first.
To answer your first question, you can simply use SFPARM = UWND;VWND (for wind in meters/second) or SFPARM = UKNT;VKNT (for knots) in the SF programs to find the U and V components of the wind, provided your surface file has the wind speed and direction parameters. See the SFPARM man page for more information: http://www.unidata.ucar.edu/cgi-bin/gempak/manual/variables_index?sfparm As for your second question, you can check if UWND and VWND are in your grid files with the program GDINFO http://www.unidata.ucar.edu/cgi-bin/gempak/manual/programs_index?gdinfo Finally, UREL and VREL are in meters per second, as defined in the grib product they are decoded from, using table $GEMTBL/grid/wmogrib2.tbl. This table defines the parameter names, units and scaling for the grib parameter id from the model output. To output in knots, you can use KNTV(UREL) and KNTV(VREL) -Michael > dear sir: > > I'm very thanks for your advice to help me solve the problem creating > correct surface file . however there 3 questions to want you help. > > First question, I want to get the wind components u and v by wind > dircetory and speed.could you told me what should I do ? > > sceond question ,are both uwnd and vwnd in the grd files if I want to > draw a streamline by gdstream program? > > finally, could you told me the difference between uwnd and urel? > > thanks > > 2009-08-17 > > > > gcs > > Ticket Details =================== Ticket ID: ULU-782715 Department: Support GEMPAK Priority: Normal Status: Open