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| Titel |
Regular in situ measurements of HDO/H216O in the northern and southern hemispherical upper troposphere reveal tropospheric transport processes. |
| VerfasserIn |
Emanuel Christner, Christoph Dyroff, Shahrokh Sanati, Carl Brenninkmeijer, Andreas Zahn |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250082473
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| Zusammenfassung |
| Atmospheric water in form of water vapor and clouds is an enormously crucial trace
species. It is responsible for ~70 % of the natural greenhouse effect (Schmidt et al.,
JGR, 2010), carries huge amounts of latent heat, and is the major source of OH in
the troposphere. The isotopic composition of water vapor is an elegant tracer for
a better understanding and quantification of the extremely complex and variable
hydrological cycle in Earth’s atmosphere (evaporation, cloud condensation, rainout,
re-evaporation, snow), which in turn is a prerequisite to improve climate modeling and
predictions.
In this context, water-isotopologues (here the isotope ratio HDO/H216O) can be used to
study the atmospheric transport of water and in-cloud processes. As H216O and HDO differ
in vapor pressure and molecular diffusion, fractionation occurs during condensation and
rainout events. For that reason the ratio HDO/H216O preserves information about the
transport and condensation history of an air mass.
The tunable diode-laser absorption spectrometer ISOWAT was developed for airborne
measurements of the water-isotopologue concentrations of H216O and HDO, probing
fundamental rovibrational water-absorption lines at around 2.66 μm. Since April 2010 the
spectrometer is regularly operated aboard the CARIBIC passenger aircraft (Civil
Aircraft for the Regular Investigation of the atmosphere Based on an Instrument
Container – Lufthansa, Airbus 340-600), which measures ~100 trace gases and
aerosol components in the UTLS (9-12 km altitude) on four long-distance flights per
month.
During several flights across the equator (Africa) or close to the equator (Venezuela and
Malaysia) an increase of HDO/H216O from the subtropics towards the tropics was measured
(by more than 100 permil) at an altitude of ~12 km. This isotopic gradient can partly be
attributed to differences in humidity. In addition there is a humidity independent latitudinal
gradient (by more than 50 permil), revealing the strong influence of convection on the
isotopic composition of water in the upper troposphere. This finding is consistent with the
well-known regions of deep convection over Africa, Malaysia and South America. |
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