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| | | #REDIRECT: [[Tracer]] |
| #REDIRECT [[tracer]] | |
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| == tracer ==
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| #<div class="definition"><div class="short_definition">A chemical or thermodynamic property of the flow that is conserved during [[advection]].</div><br/> <div class="paragraph">It can be used to track air-parcel movement and to identify the origins of [[air masses]]. Examples are [[absolute humidity]], [[equivalent potential temperature]], [[radioactivity]], and [[CCN]] composition.</div><br/> </div>
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| #<div class="definition"><div class="short_definition">Any substance in the [[atmosphere]] that can be used to track the history of an [[air mass]].</div><br/> <div class="paragraph">It can be chemical or radioactive in nature. The main requirement for a tracer is that its lifetime be substantially longer than the [[transport]] process under study. An example of an inert chemical tracer is SF<sub>6</sub>, which is often released during a field experiment and measured at a later time to assess the extent of dilution of the air mass. Chemicals such as [[methane]] (CH<sub>4</sub>) and [[nitrous oxide]] (N<sub>2</sub>O), which are released at the earth's surface and destroyed slowly in the atmosphere, can be used to infer vertical rates of transport. CO released in the [[boundary layer]] can be used to trace transport in [[convection]]. Radioactive tracers such as <sup>14</sup>C and <sup>90</sup>Sr have been used to test models of stratospheric [[circulation]]. Certain atmospheric gases have also been used as tracers in ocean waters, for example, the [[chlorofluorocarbons]].</div><br/> </div>
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