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| Titel |
First airborne water vapor lidar measurements in the tropical upper troposphere and mid-latitudes lower stratosphere: accuracy evaluation and intercomparisons with other instruments |
| VerfasserIn |
C. Kiemle, M. Wirth, A. Fix, G. Ehret, U. Schumann, T. Gardiner, C. Schiller, N. Sitnikov, G. Stiller |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 8, no. 17 ; Nr. 8, no. 17 (2008-09-04), S.5245-5261 |
| Datensatznummer |
250006362
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| Publikation (Nr.) |
 copernicus.org/acp-8-5245-2008.pdf |
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| Zusammenfassung |
| In the tropics, deep convection is the major source of uncertainty in water
vapor transport to the upper troposphere and into the stratosphere. Although
accurate measurements in this region would be of first order importance to
better understand the processes that govern stratospheric water vapor
concentrations and trends in the context of a changing climate, they are
sparse because of instrumental shortcomings and observational challenges.
Therefore, the Falcon research aircraft of the Deutsches Zentrum für
Luft- und Raumfahrt (DLR) flew a zenith-viewing water vapor differential
absorption lidar (DIAL) during the Tropical Convection, Cirrus and Nitrogen
Oxides Experiment (TROCCINOX) in 2004 and 2005 in Brazil. The measurements
were performed alternatively on three water vapor absorption lines of
different strength around 940 nm. These are the first aircraft DIAL
measurements in the tropical upper troposphere and in the mid-latitudes
lower stratosphere. Sensitivity analyses reveal an accuracy of 5% between
altitudes of 8 and 16 km. This is confirmed by intercomparisons with the
Fast In-situ Stratospheric Hygrometer (FISH) and the Fluorescent Advanced
Stratospheric Hygrometer (FLASH) onboard the Russian M-55 Geophysica
research aircraft during five coordinated flights. The average relative
differences between FISH and DIAL amount to −3%±8% and between
FLASH and DIAL to −8%±14%, negative meaning DIAL is more humid.
The average distance between the probed air masses was 129 km. The DIAL is
found to have no altitude- or latitude-dependent bias. A comparison with the
balloon ascent of a laser absorption spectrometer gives an average
difference of 0%±19% at a distance of 75 km. Six tropical DIAL
under-flights of the Michelson Interferometer for Passive Atmospheric
Sounding (MIPAS) on board ENVISAT reveal a mean difference of −8%±49%
at an average distance of 315 km. While the comparison with MIPAS is
somewhat less significant due to poorer comparison conditions, the agreement
with the in-situ hygrometers provides evidence of the excellent quality of
FISH, FLASH and DIAL. Most DIAL profiles exhibit a smooth exponential
decrease of water vapor mixing ratio in the tropical upper troposphere to
lower stratosphere transition. The hygropause with a minimum mixing ratio of
2.5 µmol/mol is found between 15 and 17 km. A high-resolution (2 km
horizontal, 0.2 km vertical) DIAL cross section through the anvil outflow of
tropical convection shows that the ambient humidity is increased by a factor
of three across 100 km. |
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