Thanks Matthias and James! That did the trick. I sure do appreciate all the help on this.<br><br>btw: I ended up having to use 270 to convert to the proper angle:<br><br>d skip(cos((270-DIRPWsfc) * 3.14159/180),3,3); skip(sin((270-DIRPWsfc) * 3.14159/180),3,3)<br>
<br>Thanks again, <br><br>-Nathan<br>
<br><br><div class="gmail_quote">On Wed, Nov 4, 2009 at 10:18 AM, Matthias Fripp <span dir="ltr"><<a href="mailto:matthias.fripp@eci.ox.ac.uk">matthias.fripp@eci.ox.ac.uk</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
That's right -- I just checked this page ( <a href="http://polar.ncep.noaa.gov/waves/products.html" target="_blank">http://polar.ncep.noaa.gov/waves/products.html</a><br>
), which reports that the datasets use the "oceanographical<br>
convention", and this page ( <a href="http://www.aims.gov.au/pages/facilities/oceanographic-buoys/ob-1.html" target="_blank">http://www.aims.gov.au/pages/facilities/oceanographic-buoys/ob-1.html</a><br>
), which says that the oceanographic convention is to show "the<br>
direction the current is flowing towards, measured in degrees<br>
clockwise from North".<br>
<br>
If you replace DIRPWsfc with (90 - DIRPWsfc), you can convert between<br>
the two conventions. So that would give you<br>
<br>
set gxout vector<br>
display cos((90-DIRPWsfc) * 3.14159/180); sin((90-DIRPWsfc) *<br>
3.14159/180)<br>
<br>
Sorry about that -- I'm so used to the physicists' approach to angles<br>
that I forgot about the real world!<br><font color="#888888">
<br>
Matthias</font><div><div></div><div class="h5"><br>
<br>
On Nov 4, 2009, at 6:10 PM, James T. Potemra wrote:<br>
<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hi Nathan:<br>
<br>
Matthias suggestion is correct, but I think you need to be careful<br>
with<br>
the direction. His calculation<br>
presumes that the direction is measured counterclockwise from the east<br>
(so a direction of zero would<br>
be a wave headed due east, direction 90 would be headed north, and so<br>
on). The direction from the<br>
model is probably compass heading (0 is north). So, you might have to<br>
add an extra step to convert<br>
the direction angle.<br>
<br>
Jim<br>
<br>
Nathan Cool wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Thanks Matthias. I sure do appreciate the help. That produced some<br>
interesting results, but it didn't seem accurate (arrows pointing in<br>
some rather bizarre directions). Perhaps though this is a data<br>
problem, and I need to grab different GRIB files? Currently, I'm<br>
using<br>
GRIBs from the NCEP server:<br>
<a href="ftp://polar.ncep.noaa.gov/pub/waves/latest_run/" target="_blank">ftp://polar.ncep.noaa.gov/pub/waves/latest_run/</a><br>
<br>
-Nathan<br>
<br>
<br>
On Wed, Nov 4, 2009 at 7:53 AM, Matthias Fripp<br>
<<a href="mailto:matthias.fripp@eci.ox.ac.uk" target="_blank">matthias.fripp@eci.ox.ac.uk</a> <mailto:<a href="mailto:matthias.fripp@eci.ox.ac.uk" target="_blank">matthias.fripp@eci.ox.ac.uk</a>>><br>
wrote:<br>
<br>
How about this:<br>
<br>
set gxout vector<br>
display cos(DIRPWsfc * 3.14159/180); sin(DIRPWsfc * 3.14159/180)<br>
<br>
This converts the wave direction from degrees to radians, and then<br>
calculates its u and v components.<br>
<br>
Matthias<br>
<br>
On Nov 4, 2009, at 2:38 PM, Nathan Cool wrote:<br>
<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Thanks, but I'm not trying to display "wind" vector arrows;<br>
instead, I'm trying to display the primary wave direction.<br>
<br>
The vars in the Grib are:<br>
------------------------<br>
DIRPWsfc 0 107,1,1 ** surface Primary wave direction [deg]<br>
DIRSWsfc 0 109,1,1 ** surface Secondary wave direction [deg]<br>
HTSGWsfc 0 100,1,1 ** surface Sig height of wind waves and<br>
swell [m]<br>
PERPWsfc 0 108,1,1 ** surface Primary wave mean period [s]<br>
PERSWsfc 0 110,1,1 ** surface Secondary wave mean period [s]<br>
UGRDsfc 0 33,1,1 ** surface u wind [m/s]<br>
VGRDsfc 0 34,1,1 ** surface v wind [m/s]<br>
WDIRsfc 0 31,1,1 ** surface Wind direction [deg]<br>
WINDsfc 0 32,1,1 ** surface Wind speed [m/s]<br>
WVDIRsfc 0 101,1,1 ** surface Direction of wind waves [deg]<br>
WVPERsfc 0 103,1,1 ** surface Mean period of wind waves [s]<br>
<br>
...and I can see that others have been able to show the primary<br>
wave direction (DIRPWsfc) using vector arrows, as is the case on<br>
the FNMOC models like this one:<br>
<a href="https://www.fnmoc.navy.mil/ww3_cgi/dynamic/ww3.w.npac.sig_wav_ht.000.gif" target="_blank">https://www.fnmoc.navy.mil/ww3_cgi/dynamic/ww3.w.npac.sig_wav_ht.000.gif</a><br>
<br>
Do you know how this can be done?<br>
<br>
Thanks,<br>
<br>
-Nathan<br>
<br>
<br>
On Tue, Nov 3, 2009 at 9:58 PM, sushant puranik<br>
<<a href="mailto:sushantpuranik@gmail.com" target="_blank">sushantpuranik@gmail.com</a> <mailto:<a href="mailto:sushantpuranik@gmail.com" target="_blank">sushantpuranik@gmail.com</a>>><br>
wrote:<br>
<br>
Hi<br>
I am able to generate wind direction. try his<br>
'set arrscl 1 30'<br>
'set cthick 5'<br>
'set arrowhead 0.10'<br>
'set clevs 3 5 10 15 20 25'<br>
'set ccols 0 4 1 2 3 5 12'<br>
'set gxout vector'<br>
'd<br>
skip(UGRDsfc,2,2);skip(VGRDsfc,<br>
2,2);skip(sqrt(UGRDsfc*UGRDsfc+VGRDsfc*VGRDsfc),2,2)'<br>
'run <a href="http://cbar.gs" target="_blank">cbar.gs</a> <<a href="http://cbar.gs" target="_blank">http://cbar.gs</a>>'<br>
'printim wind(m/s)'<br>
<br>
with the help of such script i am able to generate output<br>
which is attached with this mail.<br>
<br>
all the best.<br>
<br>
<br>
On Tue, Nov 3, 2009 at 9:45 PM, Nathan Cool<br>
<<a href="mailto:nathan@nathancool.com" target="_blank">nathan@nathancool.com</a> <mailto:<a href="mailto:nathan@nathancool.com" target="_blank">nathan@nathancool.com</a>>> wrote:<br>
<br>
Good morning everyone,<br>
<br>
I'm generating wave analysis models, but I'm having a<br>
tough time showing the mean-wave (or primary) wave<br>
direction arrows.<br>
<br>
The vars in the Grib are:<br>
-------------------------------------------------<br>
DIRPWsfc 0 107,1,1 ** surface Primary wave direction<br>
[deg]<br>
DIRSWsfc 0 109,1,1 ** surface Secondary wave direction<br>
[deg]<br>
HTSGWsfc 0 100,1,1 ** surface Sig height of wind waves<br>
and swell [m]<br>
PERPWsfc 0 108,1,1 ** surface Primary wave mean<br>
period [s]<br>
PERSWsfc 0 110,1,1 ** surface Secondary wave mean<br>
period [s]<br>
UGRDsfc 0 33,1,1 ** surface u wind [m/s]<br>
VGRDsfc 0 34,1,1 ** surface v wind [m/s]<br>
WDIRsfc 0 31,1,1 ** surface Wind direction [deg]<br>
WINDsfc 0 32,1,1 ** surface Wind speed [m/s]<br>
WVDIRsfc 0 101,1,1 ** surface Direction of wind waves<br>
[deg]<br>
WVPERsfc 0 103,1,1 ** surface Mean period of wind<br>
waves [s]<br>
<br>
For displaying wind vector arrows it's straightforward as<br>
there are U and V variables (UGRDsfc and VGRDsfc) for the<br>
zonal and meridional components. Displaying primary wave<br>
direction though seems more elusive, yet I see it done on<br>
many models such as the following:<br>
<a href="https://www.fnmoc.navy.mil/ww3_cgi/dynamic/ww3.w.npac.sig_wav_ht.000.gif" target="_blank">https://www.fnmoc.navy.mil/ww3_cgi/dynamic/ww3.w.npac.sig_wav_ht.000.gif</a><br>
<br>
...which was generated using GrADS by FNMOC.<br>
<br>
Any help you can provide would be greatly appreciated,<br>
and thank you for your time.<br>
<br>
--<br>
Nathan Cool<br>
<a href="mailto:nathan@nathancool.com" target="_blank">nathan@nathancool.com</a> <mailto:<a href="mailto:nathan@nathancool.com" target="_blank">nathan@nathancool.com</a>><br>
<br>
<br>
<br>
<br>
--<br>
Sushant Puranik<br>
Junior Research Fellow<br>
Dept. of Atmospheric & Space Sciences,<br>
University of Pune,<br>
Pune-07,<br>
India.<br>
<br>
<br>
</blockquote>
<br>
<br>
</blockquote></blockquote>
</div></div></blockquote></div><br>