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| Titel |
Observation and modelling of stable isotopes in precipitation for midlatitude weather systems in Melbourne, Australia |
| VerfasserIn |
Vaughan Barras, Ian Simmonds |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250034828
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| Zusammenfassung |
| The application of stable water isotopes as tracers of moisture throughout the hydrological
cycle is often hindered by the relatively coarse temporal and spatial resolution of
observational data. Intensive observation periods (IOPs) of isotopes in precipitation have
been valuable in this regard enabling the quantification of the effects of vapour recycling,
convection, cloud top height and droplet reevaporation (Dansgaard, 1953; Miyake et al.,
1968; Gedzelman and Lawrence, 1982; 1990; Pionke and DeWalle, 1992; Risi et al., 2008;
2009) and have been used as a basis to develop isotope models of varying complexity (Lee
and Fung, 2008; Bony et al., 2008).
This study took a unified approach combining observation and modelling of stable
isotopes in precipitation in an investigation of three key circulation types that typically bring
rainfall to southeastern Australia. The observational component of this study involved the
establishment of the Melbourne University Network of Isotopes in Precipitation
(MUNIP). MUNIP was devised to sample rainwater simultaneously at a number of
collection sites across greater Melbourne to record the spatial and temporal isotopic
variability of precipitation during the passage of particular events. Samples were
collected at half-hourly intervals for three specific rain events referred to as (1)
mixed-frontal, (2) convective, and (3) stratiform. It was found that the isotopic content
for each event varied over both high and low frequencies due to influences from
local changes in rain intensity and large scale rainout respectively. Of particular
note was a positive relationship between deuterium excess and rainfall amount
under convective conditions. This association was less well defined for stratiform
rainfall.
As a supplement to the data coverage of the observations, the events were simulated using
a version of NCAR CAM3 running with an isotope hydrology scheme. This was done by
periodically nudging the model dynamics with data from the NCEP Reanalysis
(Noone, 2006). Results from the simulations showed that the model represented
well the large scale evolution of vapour profiles of deuterium excess and 18O for
the mixed-frontal and stratiform events. Reconstruction of air mass trajectories
provided further detail of the evolution and structure of the vapour profiles revealing
a convergence of air masses from different source regions for the mixed-frontal
event.
By combining observations and modelling in this way, much detail of the structure and
isotope moisture history of the observed events was provided that would be unavailable from
the sampling of precipitation alone.
References
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isotopic composition (?18O and ?D) of precipitation and water vapor in the tropics: 1.
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doi:10.1029/2008JD009942.
Dansgaard, W. (1953), The abundance of 18O in atmospheric water and water vapor.
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Gedzelman, S. D., and J. R. Lawrence (1982), The isotopic composition of cyclonic
precipitation. J. App. Met., 21, 1385-1404.
Gedzelman, S. D., and J. R. Lawrence (1990), The isotopic composition of precipitation
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Lee, J., and I. Fung (2008), ‘Amount effect’ of water isotopes and quantitative analysis of
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Miyake, Y., O. Matsubaya, and C. Nishihara (1968), An isotopic study on meteoric
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