[ncl-talk] Some comments are needed in mjoclivar_14.ncl on the MJO diagnostics page [SEC=UNCLASSIFIED]
cjschrec at ncsu.edu
Wed Jul 26 09:03:15 MDT 2017
That's a great catch. The way I handle it is:
; calculate the PCs
retVal = eofunc_ts_Wrap( data(var|:,lon|:,time|:), eof, False )
do e = 0, nEof-1
retVal(e,:) = ( retVal(e,:) + retVal at ts_mean(e) ) / pcStddev(e)
Where pcStddev is the standard deviation calculated from the original PCs
over a 30+ year period.
It would be great if eofunc_ts had an option to not subtract the mean
On Tue, Jul 25, 2017 at 12:34 AM, Eun-Pa Lim <eun-pa.lim at bom.gov.au> wrote:
> Dear NCL developers
> My colleagues Harry Hendon and Abhik Santra at the Bureau of Meteorology
> want to report an issue regarding the computation of the RMM1 and RMM2 time
> series (eof_ts_cdata) and the expansion coefficients of olr, u200 and u850
> (ceof_ts) in mjoclivar_14.ncl.
> > eof_ts_cdata = eofunc_ts(cdata,eof_cdata,False)
> Harry and Abhik were trying to replace cdata with forecast data of
> a particular year to see if forecast amplitudes of RMM1 and RMM2 are
> realistic or not.
> Because eofunc_ts_Wrap removes the time mean of the input data by default
> (i.e. 1-year time mean of forecast data for their case), their forecast MJO
> amplitudes were systematically biased.
> This problem will occur when people try to compute the MJO amplitues with
> a subset of a dataset.
> Could you please add a comment where eof_ts_cdata and ceof_ts appear in
> mjoclivar_14.ncl that users should compute the expansion coefficients
> manually rather than using eofunc_ts_Wrap if the removal of the time mean
> of the input data is not intended/desirable?
> Please let me know if what I've explained is not clear.
> Many thanks!
> Research Scientist
> The Australian Bureau of Meteorology
> GPO Box 1289, Melbourne, VIC 3000, AUS
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