Moisture advection


Moisture advection

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.

Contents

Definition

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

Adv(\rho_m)=-\mathbf{V}\cdot\nabla \rho_m \!

in which V is the horizontal wind vector, and ρm is the density of water vapor. However, water vapor content is usually measured in terms of mixing ratio (mass fraction) in reanalyses or dew point (temperature to partial vapor pressure saturation, i.e. relative humidity to 100%) in operational forecasting. The advection of dew point itself can be thought as moisture advection:

Adv(T_d)=-\mathbf{V}\cdot\nabla T_d \!

Moisture Flux

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

\mathbf{f}=q\mathbf{V}\!

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

\mathbf{F}=\int_0^\infty \! \rho \mathbf{f}\,dz \,=-\int_P^0 \! \frac{\mathbf{f}}{g}\,dp \,

which ρ is the density of air, P is pressure at the ground surface. For the far right definition, we have used Hydrostatic equilibrium approximation.

and its divergence (convergence) imply net evapotranspiration (precipitation) is adding (removing) moisture from the column:

P-E-\frac{\partial (\int_0^\infty \! \rho q\,dz \,)}{\partial t}=-\nabla \cdot \mathbf{F}\!

which 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).

See also

External links


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Advection — Advection, in chemistry, engineering and earth sciences, is a transport mechanism of a substance, or a conserved property, by a fluid, due to the fluid s bulk motion in a particular direction. An example of advection is the transport of… …   Wikipedia

  • Mesoscale convective complex — MCC moving through New England: August 2, 2006 0600 UTC A mesoscale convective complex (MCC) is a unique kind of mesoscale convective system which is defined by characteristics observed in infrared satellite imagery. They are long lived,… …   Wikipedia

  • Chad Basin — The Chad Basin, also known as the Lake Chad Basin, is a large lowland area in north central Africa. In all directions from the center of this area the elevation changes are gentle. The Chad Basin is an endorheic (closed) basin its water does not… …   Wikipedia

  • climate — /kluy mit/, n. 1. the composite or generally prevailing weather conditions of a region, as temperature, air pressure, humidity, precipitation, sunshine, cloudiness, and winds, throughout the year, averaged over a series of years. 2. a region or… …   Universalium

  • Fog — For other uses, see Fog (disambiguation). Part of the Nature series on Weather   Calendar seasons Spring  …   Wikipedia

  • Convection — This figure shows a calculation for thermal convection in the Earth s mantle. Colors closer to red are hot areas and colors closer to blue are cold areas. A hot, less dense lower boundary layer sends plumes of hot material upwards, and likewise,… …   Wikipedia

  • Lake-effect snow — Lake Effect redirects here. For the American literary journal, see Lake Effect (journal). Lake effect precipitation coming off Lake Erie and into Western New York, as seen by NEXRAD radar, October 12–13, 2006 …   Wikipedia

  • fog — fog1 fogless, adj. /fog, fawg/, n., v., fogged, fogging. n. 1. a cloudlike mass or layer of minute water droplets or ice crystals near the surface of the earth, appreciably reducing visibility. Cf. ice fog, mist, smog. 2. any darkened state of… …   Universalium

  • Cloud — For other uses, see Cloud (disambiguation). Cumulus cloudscape over Swifts Creek, Australia A cloud …   Wikipedia

  • Numerical weather prediction — Weather models use systems of differential equations based on the laws of …   Wikipedia