[Thread Prev][Thread Next][Index]

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



__________________________________
Yahoo! Mail for Mobile
Take Yahoo! Mail with you! Check email on your mobile phone.
http://mobile.yahoo.com/learn/mail


[Thread Prev][Thread Next][Index]

Dept of Commerce / NOAA / OAR / PMEL / TMAP

Contact Us | Privacy Policy | Disclaimer | Accessibility Statement