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| Titel |
Radon as a tracer of mixing in terrestrial convective boundary layers |
| VerfasserIn |
A. G. Williams, W. Zahorowski, S. Chambers, A. D. Griffiths, P. Schelander, A. Element, S. Werczynski |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250022418
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| Zusammenfassung |
| The vertical distribution of the natural radioactive tracer radon–222 through the atmospheric
boundary layer (ABL) is a quantitative indicator of exchange and mixing between the
terrestrial surface and the lower atmosphere. Radon is therefore a useful tool in the effort
to reduce systematic errors in the representation of boundary layer processes in
weather and climate prediction models. We present surface time series and vertical
profiles of radon and meteorological quantities in daytime boundary layers over
rural inland Australia, obtained during winter and summer field campaigns with
samplers based on the ground and mounted on motorized gliders. Cases range from
light-wind strong convection to high-wind near-neutral conditions, and from clear
skies to moderately developed fair-weather cumulus and stratocumulus. Due to its
3.8-day half–life, radon concentrations in the free atmosphere are constrained to
be 1–3 orders of magnitude lower than near-surface values. This ensures that a
large radon jump is always maintained between the ABL and the air high above.
As a consequence of the “top-down” mixing process, radon displays a range of
gradients in the upper mixed layer of the ABL that are sensitive to the degree of
exchange (entrainment) across the interface. In the presence of active boundary layer
clouds, the venting of air from the sub-cloud layer is strongly enhanced, leading
to radon concentrations that remain high within the main part of the cloud layer
and only diminish towards its top. Vertical profiles from a number of flight case
studies are related to the time series of surface radon concentrations, which exhibit
a huge variability in diurnal amplitude between periods of light-wind clear-sky
conditions (large amplitude) and high-wind cloudy conditions (small amplitude). |
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