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Moisture advection is the horizontal transport of
water vapor (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/( kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Heat capacity , 1.864 kJ/(kg·K) Water vapor, water vapour or aqueous vapor is the gaseous pha ...
by the
wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hou ...
. 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 cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere, the ...
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 co ...
s,
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 influ ...
,
temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...
,
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, dew, or fog to be present. Humidity depe ...
thermal comfort indices and
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
. 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 at ...
(mass fraction) in reanalyses or
dew point The dew point is the temperature to which air must be cooled to become saturated with water vapor, assuming constant air pressure and water content. When cooled below the dew point, moisture capacity is reduced and airborne water vapor will cond ...
(temperature to partial vapor pressure saturation, 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, dew, or fog to be present. Humidity depe ...
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 (hydrostatic balance, 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. In the planetary ...
approximation. And its divergence (convergence) imply net
evapotranspiration Evapotranspiration (ET) is the combined processes by which water moves from the earth’s surface into the atmosphere. It covers both water evaporation (movement of water to the air directly from soil, canopies, and water bodies) and transpi ...
(
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
) 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, 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.


See also

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Haar (fog) In meteorology, haar or sea fret is a cold sea fog. It occurs most often on the east coast of Great Britain between April and September, when warm air passes over the cold North Sea. The term is also known as harr, hare, harl, har and hoar. C ...
*
Water cycle The water cycle, also known as the hydrologic cycle or the hydrological cycle, is a biogeochemical cycle that describes the continuous movement of water on, above and below the surface of the Earth. The mass of water on Earth remains fairly cons ...
*
Positive vorticity advection Positive vorticity advection, or PVA, is the result of more cyclonic values of vorticity advecting into lower values of vorticity. It is more generally referred to as "Cyclonic Vorticity Advection" (CVA). In the Northern Hemisphere this is positive ...


References


External links


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