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Thread: geostrophic currents from sha

  1. #1
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    geostrophic currents from sha

    hi all
    i need to compute geostrophic currents from sha (SSH anomly) as available from TOPEX/Poseidon. can anyone help me out with the necessary fortran code or at least the required equations

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    geostrophic current from ssh

    Hi Deba

    Geostrophic current from SSH anomaly (TOPEX or whatever) is more straight forward
    (assuming the SSH is the resultant contributions from all the vertical modes)

    The geostrophic balance is
    f.v = g.dh/dx
    f.u = -g.dh/dy ; where h is the SSH anomaly
    f=2.omega.sin(y) ; where 'omega' is angular velocity of earth rotation and 'y' is
    the latitude and 'g' is the gravity.

    If the softwere FERRET is used,

    use ssh_data.nc ! (assuming that the variable is ssh)
    let g=9.8
    let pi=3.141
    let omega = 0.729e-4
    let yy = y[g=giw1] !( please note that this 'giw1' is coming from ferret
    grid, and can be get by using the command 'show grid ssh' after
    loading the data into ferret, It will be different for different data sets)
    let f=2.0*omega*sin(yy*pi/180.0)

    let u = (-1.0*g/f)*ssh[y=@ddc] !(centered difference is used)
    let v = (g/f)*ssh[x=@ddc]

    set reg/x=100e:80w/y=10n:40n
    vec/l=1 u,v

    In FORTRAN, the spatial gradient of SSH can be found in a centered difference
    grid. For example , u = -(g/f)*(h(i,j+1) - h(i,j-1))/2dy and v = (g/f)*(h(i+1,j) - h(i-1),j)/2dx;
    where 2dx and 2dy are the twice the grid size and h(i,j) is the two-D array of SSH.

    There must be a buffer zone at the equator where the 'f' tends to zero
    and geostrophy breaks down. a +/- 5 degree on either side of the
    equator would be fine.


    Thanks

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    hi anyone know how to compute geostrophic velocity anomaly using weekly mean sea level anomaly data (msla) using fortran ? Can u share it here or any tutorial available?

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    Hi,
    Calculation of geostrophic velocity anomaly is given in chapter 2 of this paper.

    http://onlinelibrary.wiley.com/doi/1...08JC005242/pdf

    Thanks

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