Re: ncl routines for divergence of moisture

From: Jessica Mackaro <jmackaro_at_nyahnyahspammersnyahnyah>
Date: Thu May 13 2010 - 13:18:56 MDT

Marie,

Please see the recently posted response to another similar inquiry:
http://www.ncl.ucar.edu/Support/talk_archives/2010/1113.html

A regular lat/lon grid is the same as a fixed grid in NCL parlance.

Good luck,
Jessica

On 05/13/2010 12:28 PM, Marie wrote:
> Dear NCL users,
>
> I would like to calculate the vertical-integrated divergence of
> moisture div(qU), as well as its components q.div(U) + U.grad(q).
> I am using the UK Met Office HadGEM GCM, which has a regular lat/lon
> grid. I saw that ncl proposes few built-in functions that calculates
> the divergence on Gaussian and Fixed grids using spherical harmonics.
> I tried those, just to see what happens, but because my grid is
> neither gaussian nor fixed, the output field is very noisy. I found
> another routine, which does the calculation for any grid, uv2dv_cfd.
> The output field seems right and smooth, but this function uses
> centered finite differences, which is less accurate than with
> spherical harmonics, so maybe this is not ideal yet.
>
> Moreover, to calculate then grad(q), the only built-in functions are
> gradsf and gradsg for fixed and gaussian grids.
>
> So it seems I need to either compute the divergence and gradient by
> myself, or to convert the regular lat/lon grid onto a fixed cartesian
> grid, and then use the accurate built-in functions uv2dvf and gradsf.
> What would you advice to me? In case I need to compute the divergence
> and gradient by myself, do you provide any source code of your built-
> in functions that I could modify to apply the calculations on a
> regular grid? Otherwise, what ncl code would you suggest to convert
> the regular grid onto a fixed grid? Or is there another routine I
> could use and that I didn't see?
>
> The last thing is that I need then to integrate the divergence
> vertically. My vertical levels are pressure levels, not equally
> spaced: 1000, 925, 850, 700, 600, 500, 400, 300, 250, 200, 150, 100,
> 70, 50, 30, 20. What routine would you suggest to do that calculation?
>
> Thank you very much in advance.
>
> Best regards,
> Marie
>
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-- 
*********************************************************
                    Jessica N. Mackaro			
						
                 Climate Analysis Section			
          Climate and Global Dynamics Division		
        National Center for Atmospheric Research		
                      P.O. Box 3000			
                    Boulder, CO 80307 			
          tel: 303-497-1305   fax: 303-497-1333		
                email:jmackaro@ucar.edu       		
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Received on Thu May 13 13:19:02 2010

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