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Re: [ferret_users] geostrophic currents
Hi Sriram,
See the script for calculating surface geostrophic current
from satellite sea level anomaly below. For details see the informations
in the script below and the suggested URL's.
Hope This Helps
With Regards
Jaison
!---------------surface_uv_from_ssh.jnl------------------
\ cancel mode verify
!
! To compute surface geostrophic currents from satellite altimetry.
!
! (this data is obtained from ftp://ftp.cls.fr/pub/oceano/enact/msla/j1/
! & units is cm )
!
! For details of the eqns, please see
! http://oceanworld.tamu.edu/resources/ocng_textbook/chapter10/chapter10_03.htm
! http://oceanworld.tamu.edu/resources/ocng_textbook/chapter10/chapter10_02.htm
!
!--------------------------------------------------------------------------
set data hh_msla_oer_j1_h_20093.nc
let sla = GRID_0001! name of the sea level anomaly variable in the file
let g = 9.8 ! acceleration due to gravity (m/s^2)
let pi = 3.14 ! constant
let omega = 7.292E-5 ! Angular speed of rotation of Earth (rad/s)
let cm2m = 1/100 ! convertion factor ==> from cm to m
let f = 2 * omega * sin(y[gy=sla]*pi/180.0) ! coriolis parameter
! 2*omega*sin(phi)
!
! -g d(eta) g d(eta)
! Us = --- * ------ ; Vs = --- * ------
! f dY f dX
! At equator f --> 0 & hence 1/f --> infinity....so mask the region
! near equator using an IF condition
! @DDC ==> centred derivative
let Us = IF ABS(y[gy=sla]) GT 3.0 THEN (-1*(g/f)*sla[Y=@DDC]*cm2m)
let Vs = IF ABS(y[gy=sla]) GT 3.0 THEN ( (g/f)*sla[X=@DDC]*cm2m)
set var/title="Surface Geostrophic U from Jason's SSH"/units=m Us
set var/title="Surface Geostrophic V from Jason's SSH"/units=m Vs
set reg/x=30:120/y=-30:30
vec/xskip=4/yskip=4/len=0.5 Us, Vs
go land
! save data to a NetCDF file for future use
! sp rm -f surface_uv_from_ssh.nc
! save/file=surface_uv_from_ssh.nc/append Us, Vs
!------------end of surface_uv_from_ssh.jnl------------------
On Fri, 5 Aug 2005, Prakya Shree Ram wrote:
Dear Ferret guru,
How to obtain geostrophic currents from altimeter
data? Please help me with the code if any one has it.
Looking forward to the help.
Thanks in advance,
Sriram
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