mconv.gs

[Eric L. Altshuler]

Sara,

I noticed that in your method you do the vertical integral of moisture
transport before calculating the divergence. In your case, because the
top and bottom pressure you use in the vertical integral are both
constant, the order of operations does not matter. However, in general,
if the upper and/or lower pressure levels for the vertical integral are
not constant (i.e. they vary with x and y), the order of operations is
important and the divergence should be calculated first, followed by the
vertical integral.

To calculate moisture convergence at a single pressure level, just use:

mconv = -hdivg(q*u,q*v)

where q is specific humidity and u,v are the wind components. The units
of mconv will depend on those of q, u and v (usually q is in kg/kg while
u and v are in m/s, so mconv will be in kg/kg/s).

The mconv.gs script uses some strange formulas that I have not seen
elsewhere. I would not advise using it unless you are sure the formulas
are correct. Because there are so many hard-coded constants in the
formulas, it is difficult to determine the units.

Best regards,
Eric L. Altshuler
Assistant Research Scientist
Center for Ocean-Land-Atmosphere Studies
Calverton, MD, USA