Re: wind curl

[Lynn deWitt <ldewitt@xxxxxxxxxxxxxxxxxxxx>]

Antonio,
   I think it would be difficult to have a standard ferret function 
to calculate wind stress curl because the choice of drag coefficient 
needs to be based on the research being done by an individual 
scientist.  For our "Global" Upwelling Index calculation we use a 
non-linear drag coefficient based on Large and Pond 1981), where the 
draf coefficient is a function of wind speed.  The formulation is 
written out at::

http://las.pfeg.noaa.gov/las/doc/wind_calc_details.html#CD

Our historical upwelling index, however, used a constant drag coefficient.

Once the drag coefficient is known, wind stress curl is easy to 
calculate in Ferret.   Here's one way, using a centered derivative. 
Let u and v be the fields of wind components, rho is density, and Cd 
is drag coefficient:

let uvmag=(u^2 + v^2) ^.5
let taux=rho * Cd * u * uvmag
let tauy=rho * Cd * v * uvmag
let curl=tauy[x=@DDC] - taux[y=@DDC]

Lynn


At 12:19 PM +0200 6/17/02, antonio rodriguez wrote:
> Hi All,
>
> Is there any standard function within Ferret to calculate the wind 
> curl, given u and v wind components, over a specific region.
>
> Thanks in advance
>
> Antonio Rodríguez
> CICEM Agua del Pino
> Huelva, Spain
--------------------------------------------
Lynn deWitt

ldewitt@pfeg.noaa.gov

Pacific Fisheries Environmental Laboratories
1352 Lighthouse Avenue
Pacific Grove, CA 93950-2097
(831)-648-9036