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Re: [ferret_users] alongshore wind calculation




On Wed, Aug 29, 2018 at 11:11 AM, Sandeep Mohapatra <sandeepmohapatra21@xxxxxxxxx> wrote:
Hi Satyesh,
I have gone through the link... And i have calculated the alongshore wind according to the mentioned link , but it's not coming correctly.

Hi,

 I may not know the perfect answer to your question, but perhaps you may try this thread https://www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2013/msg00345.html which you might have already seen.    

 I have not done full exercise to find such winds, but as you are going to use etopo bathymetry as one step for calculating wind, in Ferret, you may proceed using finer bathymetry, may be " use etopo5". Then you may regrid your tau or wind to finer grid to match the grid of etopo5 (which may not be recommended as we may want to have output along/cross shore wind in same spatial resolution as the input data and not interpolation, but you may try around this). Then you may follow the above thread. Also as this thread mentions, you may find difference in the result according to your different requirement of the definition of the coast. 
 
Actually i want to calculate alongshore wind along sumatra  coast that makes an angle 135 with the horizontal plane.

^ As you are mentioning the 135 degree angle, we can do some calculation to convert your normal (towards East) and v (towards North) winds to along/cross -shore winds by simplifying the coast to be straight line with your 135 degree angle. If such simplification is fine for you, then 

Along shore wind =    |v| * ( 1/sqrt(2) ) - |u| * ( 1/sqrt(2) )
Cross shore wind= - [ |v| * ( 1/sqrt(2) ) + |u| * ( 1/sqrt(2) )) ]         

   1/sqrt(2) = sin(45) or cos(45). |v| means magnitude of v.

In above formula, I have assumed 'towards North-West direction' as +ve along shore direction and 'towards South-West direction' as +ve offshore direction. Depending upon your convention you may apply -ve / +ve sign.

 This is according to my understandings, hope it helps.

Please help me to solve the code...

On Thu, Aug 9, 2018 at 2:19 PM Satyesh Ghetiya <satyeshghetiya@xxxxxxxxx> wrote:
Hi,

 If I am understanding your question correctly, then perhaps you may look into the old Ferret thread: https://www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2017/msg00931.html  (you may go to next/previous thread in that discussion to get full discussion)

On Thu, Aug 9, 2018 at 12:53 PM, Sandeep Mohapatra <sandeepmohapatra21@xxxxxxxxx> wrote:
Hi,
Can you please tell me how to calculate alongshore wind from zonal and meridional wind in ferret.
Any script for that ?

regards
sandeep mohapatra



G Satyesh




--
G Satyesh


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