Re: M flux divergence/convergence

Wei,

Assuming you have both UQ and VQ calculated already,
it is easy to use one of the built in functions to calculate the
*horizontal* divergence at one or more levels.

For *global* grids, it is recommended that you use the spherical
harmonic based functions: uv2dvG or uv2dvF depending on whether you have
a gaussian or fixed (regular) grid. These functions are
quite accurate.

For *limited region* grids that have gaussian or fixed grids, you can
use the slighly less accurate centered finite difference function uv2dv_cfd

For more information on these functions:
http://www.ncl.ucar.edu/Document/Functions/Built-in/uv2dvG.shtml
http://www.ncl.ucar.edu/Document/Functions/Built-in/uv2dvF.shtml
http://www.ncl.ucar.edu/Document/Functions/Built-in/uv2dv_cfd.shtml

or, better, the versions that preserve meta data:

http://www.ncl.ucar.edu/Document/Functions/Contributed/uv2vrG_Wrap.shtml
http://www.ncl.ucar.edu/Document/Functions/Contributed/uv2vrF_Wrap.shtml
http://www.ncl.ucar.edu/Document/Functions/Contributed/uv2dv_cfd.shtml

---
If you want *integrated* flux divergences, you will, after computing the
above have to use:
http://www.ncl.ucar.edu/Document/Functions/Built-in/dpres_plevel.shtml
http://www.ncl.ucar.edu/Document/Functions/Built-in/dpres_hybrid_ccm.shtml
http://www.ncl.ucar.edu/Document/Functions/Built-in/dz_height.shtml
depending upon the vertical coordinate system.
Finally, if your data are on curvilinear grids [eg, WRF, POP, ...] then
you will have to consult with the the creators of those datasets.
Jessica
On 04/21/2010 02:23 AM, wei huang wrote:
> Dear ncl colleagues,
>
> Does anyone have an idea how to compute the moisture flux
> divergence/convergence? Any kind of help will be appreciated.
>
> Thanks
>
> Wei h
>
>
>
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-- 
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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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