[ncl-talk] vertically integrated moisture flux convergence in nil

Erik Noble erik.u.noble at gmail.com
Mon Dec 29 12:46:38 MST 2014


Hi. Perhaps the listed examples for the center_finite_difference function will help?
http://www.ncl.ucar.edu/Document/Functions/Built-in/center_finite_diff.shtml <http://www.ncl.ucar.edu/Document/Functions/Built-in/center_finite_diff.shtml> 
This, combined with Dennis’s code will help with determining MFC. 
-Erik Noble

> Date: Mon, 29 Dec 2014 15:46:47 +1100
> From: tms_l <littithomas at gmail.com>
> Subject: Re: [ncl-talk] vertically integrated moisture flux
> 	convergence in	nil
> To: Kyle Griffin <ksgriffin2 at wisc.edu>, "ncl-talk at ucar.edu"
> 	<ncl-talk at ucar.edu>
> Message-ID:
> 	<CA+MEkzs-hk-043YDxHLW+fOgPn4iGRR01Lg=Smzej8M6Opc=bg at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
> 
> hi,
> 
> 
> thank you Kyle
> 
> 
> 
> 
> I have calculated the divergence of wind at 850 hPa  level and multiplied
> by specific humidity (q) at 850 hPa level.
> 
> Moisture flux= q* wind(u,v)
> 
> 
> 
> div=uv2dvG_Wrap(u_850_clim,v_850_clim); divergence at pressure level 850
> 
> moisture flux= div*psl_clim  ;psl_clim ->specific humidity
> 
> 
> 
> Then I tried to use the function dpres_plevel_Wrap to find out the pressure
> level thickness and will be planning to integrate the moisture flux as
> explained in the example number 2 (
> http://www.ncl.ucar.edu/Document/Functions/Contributed/dpres_plevel_Wrap.shtml
> )below
> the explanation for the function dpres_plevel_Wrap.
> 
> 
> 
> When I try to find out dp  = *dpres_plevel*
> <http://www.ncl.ucar.edu/Document/Functions/Built-in/dpres_plevel.shtml>(lev,
> psfc, ptop, 0), I am getting the error as follows:
> 
> 
> 
> warning:dpres_plevel: At one or more grid points the sum of the layer
> thicknesses is not equal to (psfc-ptop). Are units of plev, psfc and ptop
> matching?
> 
> fatal:Mul: Number of dimensions do not match, can't continue
> 
> 
> 
> however, the units of all lev,psfc,ptop are all similar in the ncl script.
> 
> 
> 
> ;==============================
> 
> lev = u_ctl ->z11_p_level ;17 pressure levels from u compont of wind data
> 
> 
> 
> ps_ctl= addfile("ps_197001_200112.nc","r") ;surface pressure data
> 
> psf = ps_ctl->ps
> 
> psfc =psf(:,0:143,:) ; in order to get 144  lat points
> 
> ptop = lev(14) ; pressure level 850hPa
> 
> dsize=dimsizes(psfc)
> 
> lonn=dsize(2)
> 
> latn=dsize(1)
> 
> n2=30
> 
> 
> 
> ps_jjas=new((/n2,latn,lonn/),float)
> 
> 
> 
> do y=0,n2-1
> 
> ps_jjas(y,:,:)=dim_avg_n_Wrap((psfc((4+(y*12)):(7+(y*12)),:,:)),0)  ;
> seasonal mean of 30 years
> 
> end do
> 
> 
> 
> printVarSummary(psfc)
> 
> printVarSummary(ptop)
> 
> printVarSummary(lev)
> 
> 
> 
> dp  = dpres_plevel(lev, ps_jjas, ptop, 0)
> 
> 
> 
> 
> 
> 
> 
> 
> 
> After calculating dp, I would like to use the function *dim_sum_n_Wrap*
> <http://www.ncl.ucar.edu/Document/Functions/Contributed/dim_sum_n_Wrap.shtml>
> to integrate vertically.
> 
> 
> 
> But, I am not sure whether I am moving in a correct way to find out
> vertically integrated moisture flux convergence between two pressure
> levels.
> 
> 
> 
> I am very new to ncl, so I hope some one will  help me to sort out the
> problem.
> 
> 
> any help will be highly appreciated
> 
> 
> thanks
> 
> 
> thomas
> 
> On Sat, Dec 27, 2014 at 1:02 PM, Kyle Griffin <ksgriffin2 at wisc.edu> wrote:
> 
>> Thomas,
>> 
>> This is not an NCL issue, this is a science issue. The functions are
>> well-documented, as you most definitely seem to understand what each
>> function is calculating.
>> 
>> Only YOU can say whether your calculation should include or exclude the
>> boundary levels - generally I would include them, but it depends on the
>> science you want to do.
>> 
>> If you can calculate the moisture flux itself (a simple calculation), I
>> would vertically integrate that and then calculate the divergence of the
>> resulting field as this will be more efficient. However, I'm not sure if it
>> would yield the same result as calculating the moisture flux divergence and
>> then doing the vertical integral - you can certainly try both methods and
>> be aware the second method will take longer to calculate.
>> 
>> Don't forget to look at the code that Dennis sent you in a previous email
>> as well - some or all of it might help outline what you want to do.
>> 
>> Hope this helps. If not, consult the mathematical equations for this field
>> and respond back to ncl-talk if you have issues implementing the
>> calculations within your NCL scripts.
>> 
>> 
>> Kyle
>> 
>> ----------------------------------------
>> Kyle S. Griffin
>> Department of Atmospheric and Oceanic Sciences
>> University of Wisconsin - Madison
>> Room 1421
>> 1225 W Dayton St, Madison, WI 53706
>> Email: ksgriffin2 at wisc.edu
>> 
>> On Thu, Dec 25, 2014 at 9:57 PM, tms_l <littithomas at gmail.com> wrote:
>> 
>>> hi ncl users
>>> 
>>> I have to calculate the moisture flux convergence between pressure levels
>>> 850hpa AND 200hpa pressure levels..and I THINK i need to consider the
>>> specific humidity at 850 & 200 hpa pressure levels too ...finally
>>> integrating between the two pressure levels to get the moisture flux
>>> convergence...
>>> 
>>> I already calculated the wind divergence at two pressure levels using the
>>> function, uv2dvG_Wrap..I am not clear about the next step..
>>> 
>>> can anyone describe it little more..which functions i need to select for
>>> calculating the moisture flux convergence..
>>> 
>>> thanks in advance
>>> 
>>> thomas
>>> 
>>> _______________________________________________
>>> ncl-talk mailing list
>>> List instructions, subscriber options, unsubscribe:
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>>> 
>>> 
>> 
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