Re: EASE Ice Motion Vectors

Hi Andy,

It would be great to have this information on our EASE examples page:

http://www.ncl.ucar.edu/Applications/ease.shtml

Would you have any examples to contribute? I would only need an NCL script, a PS, PDF, or PNG file, and a
short description of the plot.

Or, Graham, if you want to contribute your new script… :-)

Thanks much.

--Mary

On Oct 5, 2012, at 1:08 AM, Graham Simpkins wrote:

> Thanks so much for the information and code Andy! It worked perfectly, with the ice motion vectors plotted correctly.
>
> Thanks again,
> Graham
>
>
> On 05/10/2012, at 6:26 AM, Andy Barrett wrote:
>
>> Hi Graham
>>
>> The NSIDC EASE-grid ice motion u and v vectors are parallel to the x and y coordinates of the grid, not lat and lon (e.g. not zonal and meridional components). This is in the documentation somewhere but I couldn't find it immediately when I looked just now. We'll have to deal with that.
>>
>> You have to rotate the u and v vectors based on longitude. A script to do this for the Arctic is below. It should work for the Antarctic.
>>
>> Andy Barrett
>>
>> NSIDC
>> University of Colorado at Boulder
>>
>>
>> ;;**********************************************************************
>> ;; coord_rotate - performs a coordinate rotation for vector data.
>>
>> undef ("coord_rotate")
>> procedure coord_rotate ( x1:numeric, y1:numeric, theta:numeric, \
>> x2:numeric, y2:numeric )
>> local rtheta, dtor
>> begin
>>
>> dtor = 0.0174533 ;; converts degrees to radians
>>
>> rtheta = theta * dtor
>>
>> x2 = ( x1 * cos( rtheta ) ) + ( y1 * sin( rtheta ) )
>> y2 = ( y1 * cos( rtheta ) ) - ( x1 * sin( rtheta ) )
>>
>> end
>> ;;**********************************************************************
>>
>> <snip>
>>
>> ; icef is ice motion file
>> umotion = icef->umotion ; u vector of ice motion
>> vmotion = icef->vmotion ; v vector of ice motion
>> lat2d = icef->lat2d ; 2d lat array
>> lon2d = icef->lon2d ; 2d lon array
>>
>> ;;----------------------------------------------------------------------
>> ;; Ice motion vectors are relative to EASE grid coordinate. These
>> ;; must be rotated according to longitude. Western hemisphere vectors
>> ;; must be rotated clockwise and eastern hemisphere vectors anti-
>> ;; clockwise. Longtitudes are multiplied by -1.0 to achieve this.
>>
>> urot = umotion
>> vrot = vmotion
>> coord_rotate( umotion, vmotion, lon2d, urot, vrot )
>>
>> <snip>
>
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Received on Fri Oct 5 12:30:01 2012