Re: spectral analysis

NCL has no idea about the sampling frequency.
As noted in the documentation

http://www.ncl.ucar.edu/Document/Functions/Built-in/specx_anal.shtml

the first frequency is at (1/N) and last spectral estimate corresponds
to the Nyquist frequency (=0.5). You, the user, assigns the appropriate
units.

Further, the documentation states that the "frq" attribute returned
by the function is a

--
frq
     A one-dimensional array of length N/2 representing frequency 
(cycles/time).
---
In your case, cycles/day.
---
The confidence band is based on a 1st order Markov process.
On 09/21/2010 06:19 AM, Sudheer Joseph wrote:
> Dear Users,
>                                I have modified the script spec_3.ncl
> which is from http://www.ncl.ucar.edu/Applications/Scripts/spec_3.ncl
> to suite the attached data bps_iso_box.nc and obtained the attached
> figure.
> But I have the below questions on this
> 1) the original script was for monthly data and the xaxis is coming as
> cycles/month can ncl take care of the time axis? ie my in put data is
> daily so does ncl recognise this and do the need full so that if I
> simply change the x axis title will the plot be correct? or do I need
> to change some where in library and make ncl know that I am imputing
> daily data?
>
> 2) The confidence level looks some thing odd (to me) do I need to
> modify some where so that the confidence level will be computed as per
> my input data?
> kindly answer the above 2 questions if any one used these excellent
> functions earlier.
>
>
>
>
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Dennis J. Shea                  tel: 303-497-1361    |
P.O. Box 3000                   fax: 303-497-1333    |
Climate Analysis Section                             |
Climate & Global Dynamics Div.                       |
National Center for Atmospheric Research             |
Boulder, CO  80307                                   |
USA                        email: shea 'at' ucar.edu |
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