Lagrangian process attribution of isotopic variations in near-surface water vapour in a 30-year regional climate simulation over Europe
Stable water isotopes are naturally available tracers of moisture in the atmosphere. Due to isotopic fractionation, they record information about condensation and evaporation processes during the transport of air parcels, and therefore present a valuable means for studying the global water cycle....
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doaj-45249f5afae94f6bb46ca88f3a78aea22020-11-24T21:11:57ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242018-02-01181653166910.5194/acp-18-1653-2018Lagrangian process attribution of isotopic variations in near-surface water vapour in a 30-year regional climate simulation over EuropeM. Dütsch0S. Pfahl1M. Meyer2H. Wernli3Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, SwitzerlandInstitute for Atmospheric and Climate Science, ETH Zurich, Zurich, SwitzerlandInstitute for Atmospheric and Climate Science, ETH Zurich, Zurich, SwitzerlandInstitute for Atmospheric and Climate Science, ETH Zurich, Zurich, SwitzerlandStable water isotopes are naturally available tracers of moisture in the atmosphere. Due to isotopic fractionation, they record information about condensation and evaporation processes during the transport of air parcels, and therefore present a valuable means for studying the global water cycle. However, the meteorological processes driving isotopic variations are complex and not very well understood so far, in particular on short (hourly to daily) timescales. This study presents a Lagrangian method for attributing the isotopic composition of air parcels to meteorological processes, which provides new insight into the isotopic history of air parcels. It is based on the temporal evolution of the isotope ratios, the humidity, the temperature, and the location of the air parcels. Here these values are extracted along 7-day backward trajectories started every 6 hours from near the surface in a 30-year regional climate simulation over Europe with the isotope-enabled version of the model of the Consortium for Small-Scale Modelling (COSMOiso). The COSMOiso simulation has a horizontal resolution of 0.25° and is driven at the lateral boundaries by a T106 global climate simulation with the isotope-enabled version of the European Centre Hamburg model (ECHAMwiso). Both simulations are validated against measurements from the Global Network of Isotopes in Precipitation (GNIP), which shows that nesting COSMOiso within ECHAMwiso improves the representation of <i>δ</i><sup>2</sup>H and deuterium excess in monthly accumulated precipitation. The method considers all isotopic changes that occur inside the COSMOiso model domain, which, on average, correspond to more than half of the mean and variability in both <i>δ</i><sup>2</sup>H and deuterium excess at the air parcels' arrival points. Along every trajectory, the variations in the isotope values are quantitatively decomposed into eight process categories (evaporation from the ocean, evapotranspiration from land, mixing with moister air, mixing with drier air, liquid cloud formation, mixed phase cloud formation, ice cloud formation, and no process). The results show that for air parcels arriving over the ocean, evaporation from the ocean is the primary factor controlling <i>δ</i><sup>2</sup>H and deuterium excess. Over land, evapotranspiration from land and mixing with moister air are similarly important. Liquid and mixed phase cloud formation contribute to the variability of <i>δ</i><sup>2</sup>H and deuterium excess, especially over continental Europe. In summary, the presented method helps to better understand the linkage between the meteorological history of air parcels and their isotopic composition, and may support the interpretation of stable water isotope measurements in future.https://www.atmos-chem-phys.net/18/1653/2018/acp-18-1653-2018.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
M. Dütsch S. Pfahl M. Meyer H. Wernli |
spellingShingle |
M. Dütsch S. Pfahl M. Meyer H. Wernli Lagrangian process attribution of isotopic variations in near-surface water vapour in a 30-year regional climate simulation over Europe Atmospheric Chemistry and Physics |
author_facet |
M. Dütsch S. Pfahl M. Meyer H. Wernli |
author_sort |
M. Dütsch |
title |
Lagrangian process attribution of isotopic variations in near-surface water vapour in a 30-year regional climate simulation over Europe |
title_short |
Lagrangian process attribution of isotopic variations in near-surface water vapour in a 30-year regional climate simulation over Europe |
title_full |
Lagrangian process attribution of isotopic variations in near-surface water vapour in a 30-year regional climate simulation over Europe |
title_fullStr |
Lagrangian process attribution of isotopic variations in near-surface water vapour in a 30-year regional climate simulation over Europe |
title_full_unstemmed |
Lagrangian process attribution of isotopic variations in near-surface water vapour in a 30-year regional climate simulation over Europe |
title_sort |
lagrangian process attribution of isotopic variations in near-surface water vapour in a 30-year regional climate simulation over europe |
publisher |
Copernicus Publications |
series |
Atmospheric Chemistry and Physics |
issn |
1680-7316 1680-7324 |
publishDate |
2018-02-01 |
description |
Stable water isotopes are naturally available tracers of moisture in the
atmosphere. Due to isotopic fractionation, they record information about
condensation and evaporation processes during the transport of air parcels,
and therefore present a valuable means for studying the global water cycle.
However, the meteorological processes driving isotopic variations are complex
and not very well understood so far, in particular on short (hourly to daily)
timescales. This
study presents a Lagrangian method for attributing the isotopic composition
of air parcels to meteorological processes, which provides new insight into
the isotopic history of air parcels. It is based on the temporal evolution of
the isotope ratios, the humidity, the temperature, and the location of the
air parcels. Here these values are extracted along 7-day backward
trajectories started every 6 hours
from near the surface in a 30-year regional climate simulation over
Europe with the isotope-enabled version of the model of the Consortium for
Small-Scale Modelling (COSMOiso). The COSMOiso simulation has a horizontal
resolution of 0.25° and is driven at the lateral boundaries by a T106
global climate simulation with the isotope-enabled version of the European
Centre Hamburg model (ECHAMwiso).
Both simulations are validated against
measurements from the Global Network of Isotopes in Precipitation (GNIP),
which shows that nesting COSMOiso within ECHAMwiso improves the
representation of <i>δ</i><sup>2</sup>H and deuterium excess in monthly accumulated
precipitation. The method considers all isotopic changes that occur inside
the COSMOiso model domain, which, on average, correspond to more than half of
the mean and variability in both <i>δ</i><sup>2</sup>H and deuterium excess at the air
parcels' arrival points. Along every trajectory, the variations in the
isotope values are quantitatively decomposed into eight process categories
(evaporation from the ocean, evapotranspiration from land, mixing with
moister air, mixing with drier air, liquid cloud formation, mixed phase cloud
formation, ice cloud formation, and no process). The results show that for
air parcels arriving over the ocean, evaporation from the ocean is the
primary factor controlling <i>δ</i><sup>2</sup>H and deuterium excess. Over land,
evapotranspiration from land and mixing with moister air are similarly
important. Liquid and mixed phase cloud formation contribute to the
variability of <i>δ</i><sup>2</sup>H and deuterium excess, especially over continental
Europe. In summary, the presented method helps to better understand the
linkage between the meteorological history of air parcels and their isotopic
composition, and may support the interpretation of stable water isotope
measurements in future. |
url |
https://www.atmos-chem-phys.net/18/1653/2018/acp-18-1653-2018.pdf |
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