# [ncl-talk] How to get explained variance from spectra

Fri Sep 17 04:41:36 MDT 2021

``` Dear Lyndz,I'm interested about your previous problem with this script which was:fatal:Plus: Dimension size, for dimension number 0, of operands does not match, can't continue
fatal:["Execute.c":8637]:Execute: Error occurred at or near line 39 in file spectral_mean_plot.ncl

I would like to know how did you fix it.Sincerely,Ehsan
On Friday, September 17, 2021, 09:01:12 AM GMT+4:30, Lyndz via ncl-talk <ncl-talk at mailman.ucar.edu> wrote:

Thanks Sir Dennis!
-Lyndz
On Fri, Sep 17, 2021 at 10:39 AM Dennis Shea <shea at ucar.edu> wrote:

As notes in the specx_anal documentation:
-====

These spectra have been normalized so that the area under the curve:

(spcx(0)+spcx(N/2-1))*(df/2) +SUM{spcx(1:N/2-2)*df}
equals the variance of the detrended series, wheredf=(1/N)=frequency spacing.
The units are variance/(unit frequency interval).

====

You know the frequencies corresponding to  5-to-10 days.

5-to-10day variance:   var_510 = SUM{spcx('f5->f10')*df}

fractional_variance = var_510/total_variance

On Thu, Sep 16, 2021 at 2:39 AM Lyndz via ncl-talk <ncl-talk at mailman.ucar.edu> wrote:

Dear NCL-experts,
I have a sample data that I attached here and below is the script that I used to plot the spectra.
I found significant peaks between 5-10 (days).
I would like to ask how to estimate the fractional variance of total rainfall variability explained by this 5-10 days ISO. Im not sure if this can be estimated from the spectra. If not, any suggestions on how to do this NCL?

-Lyndz_______________________________________________
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