Editing Advection (section)

{{Short description|Transport of a substance by bulk motion}}
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In the fields of [[physics]], [[engineering]], and [[earth science]]s, '''advection''' is the [[transport]] of a substance or quantity by bulk motion of a fluid. The properties of that substance are carried with it. Generally the majority of the advected substance is also a fluid. The properties that are carried with the advected substance are [[Conservation of energy|conserved]] properties such as [[energy]]. An example of advection is the transport of [[pollutant]]s or [[silt]] in a [[river]] by bulk water flow downstream. Another commonly advected quantity is energy or [[enthalpy]]. Here the fluid may be any material that contains thermal energy, such as  [[water]] or [[air]]. In general, any substance or conserved [[Intensive and extensive properties|extensive]] quantity can be advected by a [[fluid]] that can hold or contain the quantity or substance.

During advection, a fluid transports some conserved quantity or material via bulk motion. The fluid's motion is described [[Mathematics|mathematically]] as a [[vector field]], and the transported material is described by a [[scalar field]] showing its distribution over space. Advection requires currents in the fluid, and so cannot happen in rigid solids.  It does not include transport of substances by [[molecular diffusion]].

Advection is sometimes confused with the more encompassing process of [[convection]], which is the combination of advective transport and diffusive transport.

In [[meteorology]] and [[physical oceanography]], advection often refers to the transport of some property of the atmosphere or [[ocean]], such as [[heat]], humidity (see [[water vapor|moisture]]) or [[salinity]].  
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Meteorological or oceanographic advective transport is perpendicular to isobaric surfaces and is therefore predominantly [[Horizontal plane|horizontal]].  
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Advection is important for the formation of [[orographic]] clouds and the precipitation of water from clouds, as part of the [[hydrological cycle]].