Moisture advection is the horizontal transport of

water vapor Water vapor, water vapour, or aqueous vapor is the gaseous phase of Properties of water, water. It is one Phase (matter), state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from th ...

by the

wind Wind is the natural movement of atmosphere of Earth, air or other gases relative to a planetary surface, planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heatin ...

. Measurement and knowledge of atmospheric water vapor, or "moisture", is crucial in the prediction of all

weather Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloud cover, cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmo ...

elements, especially

cloud In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles, suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...

fog Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus and is heavily influenc ...

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...

thermal comfort indices and

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

. Regions of moisture advection are often co-located with regions of warm advection.

Definition

Using the classical definition of advection, moisture advection is defined as: :

Adv(\rho_m)=-\mathbf\cdot\nabla \rho_m \!

in which V is the horizontal wind vector, and

\rho_m

is the density of water vapor. However, water vapor content is usually measured in terms of

mixing ratio In chemistry and physics, the dimensionless mixing ratio is the abundance of one component of a mixture relative to that of all other components. The term can refer either to mole ratio (see concentration) or mass ratio (see stoichiometry). In a ...

(mass fraction) in reanalyses or

dew point The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to produce a relative humidity of 100%. This temperature depends on the pressure and water content of the air. When the air at a temperature above the ...

(temperature to partial vapor pressure

saturation Saturation, saturated, unsaturation or unsaturated may refer to: Chemistry *Saturated and unsaturated compounds, a classification of compounds related to their ability to resist addition reactions ** Degree of unsaturation **Saturated fat or satu ...

, i.e.

relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...

to 100%) in operational forecasting. The advection of dew point itself can be thought as moisture advection: :

Adv(T_d)=-\mathbf\cdot\nabla T_d \!

Moisture flux

In terms of mixing ratio, horizontal transport/advection can be represented in terms of moisture flux: :

\mathbf=q\mathbf\!

in which q is the mixing ratio. The value can be integrated throughout the atmosphere to total transport of moisture through the vertical: :

\mathbf=\int_0^\infty \! \rho \mathbf\,dz \,=-\int_P^0 \! \frac\,dp \,

where

\rho

is the density of air, and P is pressure at the ground surface. For the far right definition, we have used

Hydrostatic equilibrium In fluid mechanics, hydrostatic equilibrium, also called hydrostatic balance and hydrostasy, is the condition of a fluid or plastic solid at rest, which occurs when external forces, such as gravity, are balanced by a pressure-gradient force. I ...

approximation. And its divergence (convergence) imply net

evapotranspiration Evapotranspiration (ET) refers to the combined processes which move water from the Earth's surface (open water and ice surfaces, bare soil and vegetation) into the Atmosphere of Earth, atmosphere. It covers both water evaporation (movement of w ...

(

) as adding (removing) moisture from the column: :

P-E-\frac=-\nabla \cdot \mathbf\!

where P, E, and the integral term are—precipitation, evapotranspiration, and time rate of change of

precipitable water Precipitable water is the depth of water in a column of the atmosphere, if all the water in that column were precipitated as rain. As a depth, the precipitable water is measured in millimeters or inches. Often abbreviated as "TPW", for Total Preci ...

, 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.

References

External links

Moisture Advection DescriptionUsing Moisture Advection to Predict Weather
{{climate-stub Synoptic meteorology and weather Atmospheric dynamics

Definition

Moisture flux

See also

References

External links