Re: On the significant test of the wavelet analysis

Hello everyone,
    I am a newer to NCL. Could you tell me whether NCL can deal with the
unstructured grid data directly, such FVCOM model output? And we don't
neet to do interpolate. Thanks.

Xueming Zhu ÖìѧÃ÷
Key Laboratory of Research on Marine Hazards Forecasting(LoMF),SOA
National Marine Environmental Forecasting Center(NMEFC)
No.8, Dahuisi Road, Haidian District, Beijing , 100081
People's Republic of China
Tel:+86-10-82481923

ÓÚ 2013/5/24 14:29, liuyong дµÀ:
>
> Dear everyone,
>
> I encounter one problem on the significant test of the
> wavelet analysis. Based on description of the NCL website, the wavelet
> function is to calculates the wavelet transform of a time series and
> significance levels, and the return values contain the wave@power,
> wave@scale, wave@signif, wave@dof, and, etc. The wave@sigif is one
> dimensional array of length jtot (same type as wave) containing
> significance level versus scale. So I think the significance level of
> the wavelet result can be achieved from the two values (wave@scale,
> wave@signif). While, the examples of the wavelet analysis give me a
> different way to calculate the significance, which is shown as follows:
>
> This example reads a time series of seasonal mean sea surface
> temperatures. It mimics the example provided at the above URL.
>
> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
>
> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
>
> begin
>
> f = *addfile* <addfile.html>
> ("/fs/cgd/home0/shea/ncld/test/sst_nino3.nc", "r")
>
> x = f->SST
>
> N = *dimsizes* <dimsizes.html>(x) ; number of elements [here 504]
>
> mother = 0 ; Morlet wavelet
>
> param = 6.0 ; common for Morlet
>
> dt = 0.25
>
> s0 = 0.25
>
> dj = 0.25 ; 4 sub-octaves per octave
>
> jtot = 44 ; =subScale*11
>
> npad = 1024 ; pad with extra zeros
>
> nadof = new( 2,float) ; ignored
>
> noise = 1 ; test vs red noise
>
> siglvl = 0.05
>
> isigtest= 0
>
> w = *wavelet*(x,mother,dt,param,s0,dj,jtot,npad, \
>
> noise,isigtest,siglvl,nadof)
>
> ; create coordinate arrays for plot
>
> power = *onedtond* <onedtond.html>( w@power, (/jtot,N/) )
>
> power!0 = "period" ; Y axis
>
> power&period = w@period
>
> power!1 = "time" ; X axis
>
> power&time = x&time
>
> power@long_name = "Power Spectrum"
>
> power@units = "C^2"
>
> * ; compute significance ( >= 1 is significant)*
>
> * SIG = power ; transfer metadata*
>
> * SIG = power/conform <conform.html> (power,w@signif,0)*
>
> wks = *gsn_open_wks*
> <../../Graphics/Interfaces/gsn_open_wks.html>("x11","example")
>
> ; PLOT (only up to periods of 64)
>
> ; power
>
> res = True
>
> res@/cnFillOn/ <../../Graphics/Resources/cn.html#cnFillOn> = True
>
> res@/trYReverse/ <../../Graphics/Resources/tr.html#trYReverse> = True
>
> res@/gsnSpreadColors/
> <../../Graphics/Resources/gsn.html#gsnSpreadColors> = True
>
> plot = *gsn_csm_contour*
> <../../Graphics/Interfaces/gsn_csm_contour.html>(wks,power({0:64},:),res)
>
> ; significance
>
> RES = True
>
> RES@/cnLevelSelectionMode/
> <../../Graphics/Resources/cn.html#cnLevelSelectionMode> =
> "ManualLevels" ; set manual contour levels
>
> RES@/cnMinLevelValF/
> <../../Graphics/Resources/cn.html#cnMinLevelValF> = 1.0
> ; set min contour level
>
> RES@/cnMaxLevelValF/
> <../../Graphics/Resources/cn.html#cnMaxLevelValF> = 4.0
> ; set max contour level
>
> RES@/cnLevelSpacingF/
> <../../Graphics/Resources/cn.html#cnLevelSpacingF> =
> 3.0 ; set contour spacing
>
> RES@/trYReverse/ <../../Graphics/Resources/tr.html#trYReverse> = True
>
> pSIG = *gsn_contour*
> <../../Graphics/Interfaces/gsn_contour.html>(wks,SIG({0:64},:),RES)
>
> end
>
> The example tells us the *SIG = power/conform <conform.html>
> (power,w@signif,0), and SIG >= 1 is significant at 0.95 level.
> However, what the value of SIG corresponds to the significance at 0.99
> or 0.90 level. So my question is ¡°is there an universal way to
> calculate the significance of the wavelet analysis¡±*
>
> -------------------------------------------------------
>
> -------------------------------------------------------
>
> Liu Yong
>
> Center for Monsoon Research Center, Institute of the Atmospheric Physics,
>
> Chinese Academy of Sciences, Beijing, China
>
> EMAIL: liuyong@mail.iap.ac.cn
>
> PHONE: 82995289/62659180
>
> -------------------------------------------------------
>
> -------------------------------------------------------
>
>
>
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Received on Fri May 24 07:32:45 2013