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.
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Definition
Using the classical definition of advection, moisture advection is defined as:
in which V is the horizontal wind vector, and
Moisture Flux
In terms of mixing ratio, horizontal transport/advection can be represented in terms of moisture flux:
in which q is the mixing ratio. The value can be integrated throughout the atmosphere to total transport of moisture through the vertical:
where
And its divergence (convergence) imply net evapotranspiration (precipitation) as adding (removing) moisture from the column:
where P, E, and the integral term are—precipitation, evapotranspiration, and time rate of change of Precipitable water, all represented in terms of mass per unit area (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).