Vector arrows for primary wave direction
Nathan Cool
nathan at NATHANCOOL.COM
Wed Nov 4 14:59:31 EST 2009
Thanks Matthias and James! That did the trick. I sure do appreciate all the
help on this.
btw: I ended up having to use 270 to convert to the proper angle:
d skip(cos((270-DIRPWsfc) * 3.14159/180),3,3); skip(sin((270-DIRPWsfc) *
3.14159/180),3,3)
Thanks again,
-Nathan
On Wed, Nov 4, 2009 at 10:18 AM, Matthias Fripp <matthias.fripp at eci.ox.ac.uk
> wrote:
> That's right -- I just checked this page (
> http://polar.ncep.noaa.gov/waves/products.html
> ), which reports that the datasets use the "oceanographical
> convention", and this page (
> http://www.aims.gov.au/pages/facilities/oceanographic-buoys/ob-1.html
> ), which says that the oceanographic convention is to show "the
> direction the current is flowing towards, measured in degrees
> clockwise from North".
>
> If you replace DIRPWsfc with (90 - DIRPWsfc), you can convert between
> the two conventions. So that would give you
>
> set gxout vector
> display cos((90-DIRPWsfc) * 3.14159/180); sin((90-DIRPWsfc) *
> 3.14159/180)
>
> Sorry about that -- I'm so used to the physicists' approach to angles
> that I forgot about the real world!
>
> Matthias
>
>
> On Nov 4, 2009, at 6:10 PM, James T. Potemra wrote:
>
> Hi Nathan:
>>
>> Matthias suggestion is correct, but I think you need to be careful
>> with
>> the direction. His calculation
>> presumes that the direction is measured counterclockwise from the east
>> (so a direction of zero would
>> be a wave headed due east, direction 90 would be headed north, and so
>> on). The direction from the
>> model is probably compass heading (0 is north). So, you might have to
>> add an extra step to convert
>> the direction angle.
>>
>> Jim
>>
>> Nathan Cool wrote:
>>
>>> Thanks Matthias. I sure do appreciate the help. That produced some
>>> interesting results, but it didn't seem accurate (arrows pointing in
>>> some rather bizarre directions). Perhaps though this is a data
>>> problem, and I need to grab different GRIB files? Currently, I'm
>>> using
>>> GRIBs from the NCEP server:
>>> ftp://polar.ncep.noaa.gov/pub/waves/latest_run/
>>>
>>> -Nathan
>>>
>>>
>>> On Wed, Nov 4, 2009 at 7:53 AM, Matthias Fripp
>>> <matthias.fripp at eci.ox.ac.uk <mailto:matthias.fripp at eci.ox.ac.uk>>
>>> wrote:
>>>
>>> How about this:
>>>
>>> set gxout vector
>>> display cos(DIRPWsfc * 3.14159/180); sin(DIRPWsfc * 3.14159/180)
>>>
>>> This converts the wave direction from degrees to radians, and then
>>> calculates its u and v components.
>>>
>>> Matthias
>>>
>>> On Nov 4, 2009, at 2:38 PM, Nathan Cool wrote:
>>>
>>> Thanks, but I'm not trying to display "wind" vector arrows;
>>>> instead, I'm trying to display the primary wave direction.
>>>>
>>>> The vars in the Grib are:
>>>> ------------------------
>>>> DIRPWsfc 0 107,1,1 ** surface Primary wave direction [deg]
>>>> DIRSWsfc 0 109,1,1 ** surface Secondary wave direction [deg]
>>>> HTSGWsfc 0 100,1,1 ** surface Sig height of wind waves and
>>>> swell [m]
>>>> PERPWsfc 0 108,1,1 ** surface Primary wave mean period [s]
>>>> PERSWsfc 0 110,1,1 ** surface Secondary wave mean period [s]
>>>> UGRDsfc 0 33,1,1 ** surface u wind [m/s]
>>>> VGRDsfc 0 34,1,1 ** surface v wind [m/s]
>>>> WDIRsfc 0 31,1,1 ** surface Wind direction [deg]
>>>> WINDsfc 0 32,1,1 ** surface Wind speed [m/s]
>>>> WVDIRsfc 0 101,1,1 ** surface Direction of wind waves [deg]
>>>> WVPERsfc 0 103,1,1 ** surface Mean period of wind waves [s]
>>>>
>>>> ...and I can see that others have been able to show the primary
>>>> wave direction (DIRPWsfc) using vector arrows, as is the case on
>>>> the FNMOC models like this one:
>>>>
>>>> https://www.fnmoc.navy.mil/ww3_cgi/dynamic/ww3.w.npac.sig_wav_ht.000.gif
>>>>
>>>> Do you know how this can be done?
>>>>
>>>> Thanks,
>>>>
>>>> -Nathan
>>>>
>>>>
>>>> On Tue, Nov 3, 2009 at 9:58 PM, sushant puranik
>>>> <sushantpuranik at gmail.com <mailto:sushantpuranik at gmail.com>>
>>>> wrote:
>>>>
>>>> Hi
>>>> I am able to generate wind direction. try his
>>>> 'set arrscl 1 30'
>>>> 'set cthick 5'
>>>> 'set arrowhead 0.10'
>>>> 'set clevs 3 5 10 15 20 25'
>>>> 'set ccols 0 4 1 2 3 5 12'
>>>> 'set gxout vector'
>>>> 'd
>>>> skip(UGRDsfc,2,2);skip(VGRDsfc,
>>>> 2,2);skip(sqrt(UGRDsfc*UGRDsfc+VGRDsfc*VGRDsfc),2,2)'
>>>> 'run cbar.gs <http://cbar.gs>'
>>>> 'printim wind(m/s)'
>>>>
>>>> with the help of such script i am able to generate output
>>>> which is attached with this mail.
>>>>
>>>> all the best.
>>>>
>>>>
>>>> On Tue, Nov 3, 2009 at 9:45 PM, Nathan Cool
>>>> <nathan at nathancool.com <mailto:nathan at nathancool.com>> wrote:
>>>>
>>>> Good morning everyone,
>>>>
>>>> I'm generating wave analysis models, but I'm having a
>>>> tough time showing the mean-wave (or primary) wave
>>>> direction arrows.
>>>>
>>>> The vars in the Grib are:
>>>> -------------------------------------------------
>>>> DIRPWsfc 0 107,1,1 ** surface Primary wave direction
>>>> [deg]
>>>> DIRSWsfc 0 109,1,1 ** surface Secondary wave direction
>>>> [deg]
>>>> HTSGWsfc 0 100,1,1 ** surface Sig height of wind waves
>>>> and swell [m]
>>>> PERPWsfc 0 108,1,1 ** surface Primary wave mean
>>>> period [s]
>>>> PERSWsfc 0 110,1,1 ** surface Secondary wave mean
>>>> period [s]
>>>> UGRDsfc 0 33,1,1 ** surface u wind [m/s]
>>>> VGRDsfc 0 34,1,1 ** surface v wind [m/s]
>>>> WDIRsfc 0 31,1,1 ** surface Wind direction [deg]
>>>> WINDsfc 0 32,1,1 ** surface Wind speed [m/s]
>>>> WVDIRsfc 0 101,1,1 ** surface Direction of wind waves
>>>> [deg]
>>>> WVPERsfc 0 103,1,1 ** surface Mean period of wind
>>>> waves [s]
>>>>
>>>> For displaying wind vector arrows it's straightforward as
>>>> there are U and V variables (UGRDsfc and VGRDsfc) for the
>>>> zonal and meridional components. Displaying primary wave
>>>> direction though seems more elusive, yet I see it done on
>>>> many models such as the following:
>>>>
>>>> https://www.fnmoc.navy.mil/ww3_cgi/dynamic/ww3.w.npac.sig_wav_ht.000.gif
>>>>
>>>> ...which was generated using GrADS by FNMOC.
>>>>
>>>> Any help you can provide would be greatly appreciated,
>>>> and thank you for your time.
>>>>
>>>> --
>>>> Nathan Cool
>>>> nathan at nathancool.com <mailto:nathan at nathancool.com>
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Sushant Puranik
>>>> Junior Research Fellow
>>>> Dept. of Atmospheric & Space Sciences,
>>>> University of Pune,
>>>> Pune-07,
>>>> India.
>>>>
>>>>
>>>>
>>>
>>>
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