Re: Wavelets and time

> I am learning how to use the wavelet script along with a wrf idealized model
> run.
> My question concerns the use of a variable and its association with time as in
> the following from the wavelet_1.ncl script:
>
> power&time = time
>
> What does this statement actually do?
>
> Is "time" supposed to be defined in the netcdf file as an attribute?
> Thanks for any insight.
==========================================================

The wavelet example

  f = addfile ("/cgd/cas/shea/TEST/wavelet/NAO_b053.03_0000-0999.nc","r")
  nao = f->NAO ; one value/year
  time = nao&time ; time values

  w = wavelet(nao.....)
  power = onedtond(w_at_power,(/jtot,N/))

You could plot 'power' directly without creating coordinate
variables.

  plt = gsn_csm_contour(wks,power,res)

It just makes for a nicer plot to include coordinate information.

=========

A quick lesson on NCL variables.

NCL variables are based upon the netCDF variable model:
(a) an array or scalar; (b) [possibly] attributes; (c)
[possibly] named dimensions; (d) [possibly] coordinate variables.

A brief descripion of netCDF files and variables is at:
    http://www.ncl.ucar.edu/Training/Workshops/lectures.shtml
    netCDF (describes netCDF)
             [A 'picture' of NCL variables may be seen as the
              5th power point slide.]

;************************************
; manually create coordinate arrays [will be used by gsn_csm_comtour]
;************************************

  power!0 = "period" ; Y axis
  power&period = w_at_period

  power!1 = "time" ; X axis
  power&time = time ; assign time values
                                                     ; to the named dimension
                                                     ; will be used for plot
[SNIP]
;************************************
; NCL's gsn_csm* are 'meta-data aware'
; They will use the coordinate values for plotting.
;************************************

plot(0) = gsn_csm_contour(wks,power,res)

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Received on Fri Jan 12 2007 - 09:24:48 MST