Re: Area average

Hi Kim,
I'm afraid I'm not clear as to what you are trying to accomplish. The
code you sent won't work for a few reasons:
1) This line: z3 = z0-(z1+z2) will result in an error as you are
subtracting/adding arrays of different sizes, specifically in the
longitude dimension.
2) As you are creating the z3 array from the equation on the other side
of the = sign, meta-data (coordinate variables, attributes) will not be
assigned to the z3 array. Thus, time = z3&time will result in a fatal
error.

You speak of area-averages (normally calculated via wgt_areaave, as I
wrote in my original email) but then you are using the dim_avg_Wrap
function, which will average only the rightmost dimension.

If you could provide a clearer explanation of what you wish to
accomplish that would prove helpful. This is just a guess: If you need
to take an area average of a region that isn't a box (defined by a
latitudinal range and a longitudinal range), then you can set certain
regions to @_FillValue. For instance, let's say you want to take the
area average from 10:20N, and 5:35E, but don't want to include the
region from 12:15N, and 10:20E... Then you can do something like this:
z0(:,{12:15},{10:20}) = z0@_FillValue
z0Area = wgt_areaave_Wrap(z0(:,{10:20},{5:35}),1.0,1.0,0)
Adam

On 03/02/2010 02:03 AM, Kim wrote:
> Dear Adam Phillips , thanks for your kind help. Particularly, in case of
> time vs long, I 'm feeling difficulty to remove the z1& z2 average area
> from the total average area (z0), so that I can calculate the actual
> area averaged, actually my required fig.is in the form of diagonal.
> However, I made some assumption but could not succeed, because the time
> is a problem. kindly have a look on the said assumption given below:
>
> f = addfile("olr.day.mean.nc","r")
>
> z = short2flt(f->olr(120:243,:,:))
>
> printVarSummary(z)
>
> z0 = dim_avg_Wrap(z(time|:,{lon|60:76},{lat|25:40}))
>
> z1 = dim_avg_Wrap(z(time|:,{lon|60:66},{lat|30:36}))
>
> z2 = dim_avg_Wrap(z(time|:,{lon|70:76},{lat|25:28}))
>
> z3 = z0-(z1+z2)
>
> printVarSummary(z3)
>
> time = z3&time
>
> =================
>
> =================
>
> plot = gsn_csm_hov(wks, z3(:,:) , res )
>
> end
> thanks again and regards,
> kim
> --- On *Mon, 3/1/10, Adam Phillips /<asphilli@ucar.edu>/* wrote:
>
>
> From: Adam Phillips <asphilli@ucar.edu>
> Subject: Re: [ncl-talk] Area average
> To: "Kim" <r4rid@yahoo.com>
> Cc: ncl-talk@ucar.edu
> Date: Monday, March 1, 2010, 8:45 AM
>
> Hi Kim,
> I think the following code will do what you want:
> z2 = z(:,{30:40},{60:72}) ; select specific region
> delete(z)
> printVarSummary(z2)
> z2Area = wgt_areaave_Wrap(z2,1.0,1.0,0) ; create area-avg. timeseries
> printVarSummary(z2Area)
> z2_za = dim_avg_Wrap(z2) ; create time x lat array
> z2_ma = dim_avg_Wrap(z2(time|:,lon|:,lat|:) ; create time x lon array
> printVarSummary(z2_za)
> printVarSummary(z2_ma)
>
> printVarSummary is a wonderful tool that you can use to view the details
> of an array. printVarSummary will show the metadata associated with an
> array, as well as the range of the coordinate variables (if there are
> any).
>
> As you are area-averging, you should account for the difference in sizes
> of the grid boxes as the meridians converge at the poles. You can do
> this
> by applying gaussian or cosine weights in the area-averaging
> process. See
> example 1 here:
> http://www.ncl.ucar.edu/Document/Functions/Built-in/wgt_areaave.shtml
>
> If you haven't done so already, I suggest you take a look at the NCL
> Mini-Language Manual available here:
> http://www.ncl.ucar.edu/Document/Manuals/
>
> Good luck,
> Adam
>
>
> > Dear NCL users,
> > I want to calculate only the map area averaged and remove the
> area outside
> > the map (sample Fig.attached). I don’t know how to calculate the
> > required map area and remove the outside area?
> > Furthermore, how does calculate time vs lon and time series plot
> of only
> > map area?
> > Is it correct if I use this function?
> > zArea = wgt_areaave_Wrap(z(:,{30:40},{60:72}),1.0,1.0,0)
> > but how I confirm it is only map area averaged(as indicated in Fig)?
> > Kindly, your guidance regarding this will be appreciated.
> > Thanks in advance,
> > kim
> > Â
> >
> >
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> >
>
>
>

-- 
__________________________________________________
Adam Phillips 
asphilli@ucar.edu
National Center for Atmospheric Research   tel: (303) 497-1726
Climate and Global Dynamics Division         fax: (303) 497-1333
P.O. Box 3000				
Boulder, CO 80307-3000    http://www.cgd.ucar.edu/cas/asphilli
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