Moisture advection is the horizontal transport of water vapor by the wind. Measurement and knowledge of atmospheric water vapor, or "moisture", is crucial in the prediction of all weather elements, especially clouds, fog, temperature, humidity thermal comfort indices and precipitation. Regions of moisture advection are often co-located with regions of warm advection.[1]
Using the classical definition of advection, moisture advection is defined as:
Adv(\rhom)=-V ⋅ \nabla\rhom
in which V is the horizontal wind vector, and
\rhom
Adv(Td)=-V ⋅ \nablaTd
In terms of mixing ratio, horizontal transport/advection can be represented in terms of moisture flux:
f=qV
in which q is the mixing ratio. The value can be integrated throughout the atmosphere to total transport of moisture through the vertical:
| infty | |
| F=\int | |
| 0 |
\rhofdz
| 0 | |
| =-\int | |
| P |
| f | |
| g |
dp
where
\rho
And its divergence (convergence) imply net evapotranspiration (precipitation) as adding (removing) moisture from the column:
| P-E- |
| ||||||||
| \partialt |
=-\nabla ⋅ F
where P, E, and the integral term are - precipitation, evapotranspiration, and time rate of change of precipitable water, all represented in terms of mass/(unit area * unit time). One can convert to more typical units in length such as mm by multiplying the density of liquid water and the correct length unit conversion factor.