Re: How to remove semi-annual signals?

There is no explicit function to remove the semi-annual signal.

You can do it yourself. Say you have x(time,lat,lon)

One approach :

[1]
xtime = x(lat|:,lon|:time|:)

[2]

xTaper = *taper*(xtime, 0.1, 0)

[3]
xCoef = *ezfftf* <http://www.ncl.ucar.edu/Document/Functions/Built-in/ezfftf.shtml>(xTaper) ; some minor variance is lost

[4]
Set the xCoef frequency corresponding to 6 months
[n6mo] to zero.

xCoef(:,:,:,n6mo) = 0.0 ; (2,nlat,mlon,...)

[5]
xTIME = *ezfftb* (xCoef, xCoef@xbar)

[6]
if desired, copy meta data [contributed.ncl]

copy_VarMeta(xtime,xTIME)
printVarSummary(xTIME)

[7]
if desired,

xNew = xTIME(time|:,lat|:,lon|:)

=================
Good Luck

On 01/17/2010 09:47 AM, Changlin Chen wrote:
> Hi,
> In ncl, rmMonAnnCycLLT
> <http://www.ncl.ucar.edu/Document/Functions/Contributed/rmMonAnnCycLLT.shtml>
> can be used to removes the annual cycle from "monthly" data, but how
> to remove the semi-annual cycle? Is there the function? Thanks!
>

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Received on Tue Jan 19 14:21:58 2010