Re: Spectral analysis problems - file sizes ?

I think I understand what specx is doing a bit better, now that I
have found some information on array definitions in NCL. One of the
things I want to do is a temporal spectrum. The output I have been
producing gives a snapshot - i.e. results at a specific time. I will
need to get output at a sequence of different times in order to
follow the temporal variation. However, I am wondering what the best
way is to achieve this ?. My question is, does specx require the
results at different times to all be in the same netcdf file ?.

A typical snapshot at a single time produces a netcdf output file of
size around 160 M (I am running at relatively high resolution). In
order to analyse the time variations in any meaningful way, I might
need to make use of outputs for around 100 different times. I know
that there is a way within the model I am using (CAM) to print
multiple time outputs into a single file. However, this could (I
believe) end up producing a file around 16 G in size. This would be
completely unmanageable in every way, even if I could even work out a
way of ftp-ing it from the computer where it is run.

This is why I am wondering whether specx requires all of tie output
to be in the same file, and if so, is there a way around this ?.

Thanks,
Helen.

On Feb 3, 2009, at 9:24 AM, Dennis Shea wrote:

> [a]
> You have:
> spec = specx_anal(u(lev|kl:kl,lat|nl:nl,lon|ml:ml,time:),d,sm,pct)
> the "time:" should be "time|:"
> spec = specx_anal(u(lev|kl:kl,lat|nl:nl,lon|ml:ml,time|:),d,sm,pct)
> possibly clearer
> spec = specx_anal(u(lev|kl, lat|nl, lon|ml ,time|:),d,sm,pct
>
> This will yield the temporal power spectrum the the specified grid
> point.
>
> ===============
> As far as finding the major *temporal* periodicities in the data, the
> fact that your data are cyclic in longitude is immaterial.
>
> If you are looking at *spatial* wave patterns in longitude, then,
> because the data are periodic [cyclic] in longitude, you can use
> a simple fft
> http://www.ncl.ucar.edu/Document/Functions/Built-in/ezfftf.shtml
>
> perhaps better, see the fourier_info function:
> http://www.ncl.ucar.edu/Document/Functions/Built-in/fourier_info.shtml
>
> Good luck
> Helen Parish wrote:
>> I am trying to do spectral analysis on a netcdf file.
>>
>> a. Firstly I want to find out what the major periodicities are in
>> the data (these may vary from months to several years). I am
>> assuming they are periodic in longitude. I would like to plot the
>> range of periods which are present, as a function of pressure
>> and / or height at a given latitude. I would also like to plot the
>> period present as a function of latitude at a given height or
>> pressure. There are a lot of possible routines available, and I am
>> not sure if I am using the right one(s) (see below).
>>
>> b. I would also like to be able to find a way to follow a specific
>> wave as it travels upwards (or downwards), and to plot this. I am
>> not sure what the best routine to use would be, and how to plot
>> this?.
>>
>>
>> in order to do a. above, I have tried to incorporate specx_anal
>> into a script, but I am not sure how I should be inputting the
>> arguments, and whether this will do what I want if I succeed ?.
>> The error I am getting is below, and underneath that is the script
>> I have been trying to use (please bear in mind that my pressure
>> levels apply to Venus, and the magnitudes are correct).
>>
>> I am not sure how to do b. above/
>>
>> Thanks,
>> Helen.
>>
>> Here is the error message:
>>
>> (0) T: interpolated and written to netCDF
>> (0) Q: interpolated and written to netCDF
>> (0) U: interpolated and written to netCDF
>> (0) V: interpolated and written to netCDF
>> fatal:syntax error: line 76 in file four.ncl before or near time
>> spec = specx_anal(u(lev
>> -------------------------------------------------------^
>>
>> fatal:Error in subscript, named subscripting is being used, make
>> sure each subscript has a name
>> fatal:syntax error: function specx_anal expects 4 arguments, got 0
>> fatal:error at line 76 in file four.ncl
>>
>> fatal:Syntax Error in block, block not executed
>> fatal:error at line 114 in file four.ncl
>>
>>
>> Here is the script I have been trying to use:
>>
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
>> begin
>> ; input file
>> diri = "./"
>> fili = "rand09125k.cam2.h0.0026-01-17-00000.nc"
>> fi = addfile (diri+fili, "r")
>> ; output file
>> diro = "./"
>> filo = "helen.nc"
>> system ("/bin/rm -f "+diro+filo) ; remove any pre-exist file
>> fo = addfile (diro+filo, "c")
>> ; add any file attributes
>> fo_at_title = fi_at_title + ": Selected Variables at pressure levels"
>> fo_at_history = systemfunc ("date")
>> fo_at_source = fi_at_source
>> fo_at_case = fi_at_case
>> fo_at_Conventions = fi_at_Conventions
>>
>> Var = (/ "T" , "Q", "U", "V"/) ; select variable to be interpolated.
>> nVar = dimsizes (Var)
>> ; desired output levels
>> ;lev_p = (/ 91500., 90000., 87500., 80000., 67500., 50000.,
>> 30000., 20000., 10000., 5000., 3000., 1500., 750., 390., 200., 100.,
>> 50.,25., 20., 15.,10., 8., 5.,3.,1. /)
>> ;lev_p = (/ 91500., 90000., 87500., 80000., 67500., 50000.,
>> 30000., 20000., 10000., 5000., 3000., 1500., 750., 390., 200., 100.,
>> 50.,25., 14., 7., 3.5, 1.9, 0.95, 0.4, 0.1, 0.01 /)
>> lev_p = (/ 91500., 90000., 87500., 80000., 67500., 50000., 30000.,
>> 20000., 10000., 5000., 3000., 1500., 750., 390., 200., 100.,
>> 50.,25., 14., 7., 3.5, 1.9, 0.95, 0.4, 0.1, 0.03 /)
>> ;lev_p = (/ 91500., 90000., 87500., 80000., 67500., 50000.,
>> 30000., 20000., 10000., 5000., 3000., 1500., 750., 390., 200., 100.,
>> 50.,25., 14., 7., 3.5, 2.0 /)
>> lev_p!0 = "lev_p" ; variable and dimension name the same
>> lev_p&lev_p = lev_p ; create coordinate variable
>> lev_p_at_long_name = "pressure" ; attach some attributes
>> lev_p_at_units = "hPa"
>> lev_p_at_positive = "down"
>>
>> hyam = fi->hyam ; read hybrid info
>> hybm = fi->hybm
>> PS = fi->PS
>> P0mb = 0.01*fi->P0
>>
>> do n=0,nVar-1 ; loop over the variables
>> X = fi->$Var(n)$
>> Xp = vinth2p (X, hyam, hybm, lev_p ,PS, 1, P0mb, 2, True)
>> copy_VarAtts(X, Xp)
>> fo->$Var(n)$ = Xp ; write to netCDF file
>> print (Var(n)+": interpolated and written to netCDF")
>> end do
>>
>> end
>> ;***********************
>> ; zonal.ncl
>> ;***********************
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
>> ;***********************
>> begin
>> f = addfile ("helen.nc","r")
>> print(f)
>> u = f->U
>> printVarSummary( u )
>>
>> dimu = dimsizes( u )
>> ntim = dimu(0)
>> klvl = dimu(1)
>> nlon = dimu(2)
>> mlon = dimu(3)
>>
>> uavg = dim_avg_Wrap(u)
>>
>> ;***********************
>> ; Create Plot
>> ;***********************
>> d = 0
>> sm = 3
>> pct = 0.1
>>
>> kl = 10
>> nl = 95
>> ml = 40
>> spec = specx_anal(u(lev|kl:kl,lat|nl:nl,lon|ml:ml,time:),d,sm,pct)
>>
>> wks = gsn_open_wks ("pdf", "rand09125k260117spec" ) ; open
>> workstation
>> gsn_define_colormap(wks,"rainbow") ; choose colormap
>>
>> res = True
>> res_at_cnFillOn = True
>> res_at_lbLabelAutoStride = True
>> res_at_gsnMaximize = True ; if [ps, eps, pdf] make large
>> res_at_gsnSpreadColors = True ; span color map
>>
>> do nt=0,ntim-1
>>
>> res_at_gsnCenterString = "rand09125k260117spec"
>> res_at_tiXaxisString = "Frequency"
>> res_at_tiYaxisString = "Variance"
>>
>> plot = gsn_csm_xy(wks,spec_at_frq,spec_at_spcx,res)
>>
>> ; plot = gsn_csm_pres_hgt(wks, u(nt,:,:,40), res ) ; (lev,lat)
>> ;; plot = gsn_csm_pres_hgt(wks, uavg(nt,:,:), res ) ; (lev,lat)
>> ; plot = gsn_csm_contour (wks, uavg(t,:,:), res ) ; (lev,lat)
>>
>> res_at_trYReverse = True
>> ; plot = gsn_csm_contour (wks, u(nt,:,:,0), res ) ; (lev,lat)
>> ; plot = gsn_csm_contour (wks, u(nt,:,0,:), res ) ; (lev,lon)
>>
>> kl = 5
>> res_at_mpFillOn = False
>> res_at_mpGridAndLimbOn = True
>> res_at_mpGridLineDashPattern = 2
>> res_at_mpOutlineBoundarySets = "NoBoundaries"
>> res_at_mpCenterLonF = 180.
>> res_at_gsnCenterString = res_at_gsnCenterString+" p="+u&lev_p(kl)
>> ; plot = gsn_csm_contour_map_ce (wks, u(nt,kl,:,:), res )
>>
>> end do
>>
>> end
>>
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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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Received on Tue Feb 03 2009 - 20:59:57 MST