Comparative aerosol studies based on multi-wavelength Raman LIDAR at Ny-Ålesund, Spitsbergen [Elektronische Ressource] / von Anne Hoffmann

Anne Hoffmann

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• Publié par: universitat_potsdam
• Publié le: 01 janvier 2011
• Nombre de lectures: 25
• Langue: English
• Poids de l'ouvrage: 11 Mo

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Comparative Aerosol Studies based on Multi-wavelength
Raman LIDAR at Ny-Ålesund, Spitsbergen
D I SS E R TAT I O N
zur Erlangung des akademischen Grades
Dr. rer. nat.
im Fach Physik
eingereicht an der
Mathematisch-Naturwissenschaftlichen Fakultät
Universität Potsdam
von
Dipl.-Phys. Anne Hoffmann
19.12.1981, Berlin
Präsidentin der Universität Potsdam:
Prof. Dr.-Ing. habil. Dr. phil. Sabine Kunst
Dekan der Mathematisch-Naturwissenschaftlichen Fakultät:
Prof. Dr. Reimund Gerhard
Gutachter:
1. Prof. Dr. Klaus Dethloff
2. Prof. Dr. Thomas Duck
3. Prof. Dr. Justus Notholt
eingereicht am: 20.11.2010
Tag der mündlichen Prüfung: 10.03.2011This work is licensed under a Creative Commons License:
Attribution - Noncommercial - Share Alike 3.0 Germany
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Published online at the
Institutional Repository of the University of Potsdam:
URL http://opus.kobv.de/ubp/volltexte/2011/5242/
URN urn:nbn:de:kobv:517-opus-52426
http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52426 ComparativeAerosolStudiesbasedonMulti-wavelengthRamanLIDARatNy-Ålesund,
Spitsbergen
Anne Hoffmann
Faculty of Mathematics and Natural Sciences, University of Potsdam
Abstract
The Arctic is a particularly sensitive area with respect to climate change due to the high
surface albedo of snow and ice and the extreme radiative conditions. Clouds and aerosols
as parts of the Arctic atmosphere play an important role in the radiation budget, which
is, as yet, poorly quantified and understood. The LIDAR (Light Detection And Ranging)
measurements presented in this PhD thesis contribute with continuous altitude resolved
aerosol profiles to the understanding of occurrence and characteristics of aerosol layers
above Ny-Ålesund, Spitsbergen. The attention was turned to the analysis of periods with
high aerosol load. As the Arctic spring troposphere exhibits maximum aerosol optical
depths (AODs) each year, March and April of both the years 2007 and 2009 were analyzed.
Furthermore, stratospheric aerosol layers of volcanic origin were analyzed for several
months, subsequently to the eruptions of the Kasatochi and Sarychev volcanoes in summer
2008 and 2009, respectively.
The Koldewey Aerosol Raman LIDAR (KARL) is an instrument for the active remote sens-
ing of atmospheric parameters using pulsed laser radiation. It is operated at the AWIPEV
research base and was fundamentally upgraded within the framework of this PhD project.
It is now equipped with a new telescope mirror and new detection optics, which facilitate
atmospheric profiling from 450 m above sea level up to the mid-stratosphere. KARL pro-
vides highly resolved profiles of the scattering characteristics of aerosol and cloud particles
(backscattering, extinction and depolarization) as well as water vapor profiles within the
lower troposphere. Combination of KARL data with data from other instruments on
site, namely radiosondes, sun photometer, Micro Pulse LIDAR, and tethersonde system,
resulted in a comprehensive data set of scattering phenomena in the Arctic atmosphere.
The two spring periods March and April 2007 and 2009 were at first analyzed based on
meteorological parameters, like local temperature and relative humidity profiles as well as
large scale pressure patterns and air mass origin regions. Here, it was not possible to find a
clear correlation between enhanced AOD and air mass origin. However, in a comparison of
two cloud free periods in March 2007 and April 2009, large AOD values in 2009 coincided
with air mass transport through the central Arctic. This suggests the occurrence of aerosol
transformation processes during the aerosol transport to Ny-Ålesund. Measurements on 4
April 2009 revealed maximum AOD values of up to 0.12 and aerosol size distributions
changing with altitude. This and other performed case studies suggest the differentiation
between three aerosol event types and their origin: Vertically limited aerosol layers in
dry air, highly variable hygroscopic boundary layer aerosols and enhanced aerosol load
across wide portions of the troposphere. For the spring period 2007, the available KARL
data were statistically analyzed using a characterization scheme, which is based on optical
characteristics of the scattering particles. The scheme was validated using several case
studies.
Volcanic eruptions in the northern hemisphere in August 2008 and June 2009 arose the
opportunity to analyze volcanic aerosol layers within the stratosphere. The rate of strato-
iiispheric AOD change was similar within both years with maximum values above 0.1
about three to five weeks after the respective eruption. In both years, the stratospheric
AOD persisted at higher rates than usual until the measurements were stopped in late
September due to technical reasons. In 2008, up to three aerosol layers were detected,
the layer structure in 2009 was characterized by up to six distinct and thin layers which
smeared out to one broad layer after about two months. The lowermost aerosol layer was
continuously detected at the tropopause altitude. Three case studies were performed, all
revealed rather large indices of refraction of m = (1.53–1.55) - i0.02, suggesting the presence
of an absorbing carbonaceous component. The particle radius, derived with inversion
calculations, was also similar in both years with values ranging from 0.16 to 0.19 μm.
However, in 2009, a second mode in the size distribution was detected at about 0.5 μm.
The long term measurements with the Koldewey Aerosol Raman LIDAR in Ny-Ålesund
provide the opportunity to study Arctic aerosols in the troposphere and the stratosphere
not only in case studies but on longer time scales. In this PhD thesis, both, tropospheric
aerosols in the Arctic spring and stratospheric aerosols following volcanic eruptions have
been described qualitatively and quantitatively. Case studies and comparative studies
with data of other instruments on site allowed for the analysis of microphysical aerosol
characteristics and their temporal evolution.
ivVergleichende Aerosolstudien mittels Mehrwellenlängen-Raman-LIDAR in Ny-Ålesund,
Spitzbergen
Anne Hoffmann
Mathematisch-Naturwissenschaftliche Fakultät, Universität Potsdam
Zusammenfassung
Die Arktis ist ein bezüglich Klimaveränderungen besonders sensitives Gebiet, d.h. die
globale Erwärmung wirkt sich aufgrund der saisonal hochvariablen Strahlungsbedingun-
gen und der Bodenalbedo dort verstärkt aus. Wolken und Aerosole als Bestandteile der
arktischen Atmosphäre spielen dabei eine besondere Rolle im Strahlungsgleichgewicht.
Die vorliegende Promotionsarbeit leistet mit Hilfe von LIDAR-Messungen (Light Detec-
tion and Ranging) einen Beitrag zum Verständnis von Vorkommen und Eigenschaften
von Aerosolschichten über Ny-Ålesund, Spitzbergen. Besonderes Augenmerk liegt dabei
auf der Analyse von Zeiträumen mit erhöhter Aerosolbelastung. Es wurde zum einen
die arktische Troposphäre zweier Frühjahre (März und April der Jahre 2007 und 2009)
untersucht, da im Frühjahr die Aerosol-optische Dicke (AOD) in der Arktis Maximal-
werte erreicht. Zum anderen wurden stratosphärische Aerosolschichten vulkanischen
Ursprungs analysiert, die in den Sommern 2008 und 2009 nach Ausbrüchen der Kasatochi
und Sarychev Vulkane jeweils für mehrere Monate in der unteren Stratosphäre messbar
waren.
Das an der AWIPEV Forschungsstation betriebene Koldewey Aerosol Raman LIDAR
(KARL), ein Instrument zur optischen Fernerkundung atmosphärischer Parameter mittels
gepulster Laserstrahlung, wurde im Rahmen der Promotion grundlegend überarbeitet
und mit einem neuen Teleskop sowie neuen Detektoroptiken versehen. Dies ermöglicht
die Profilerfassung ab 450 m über dem Meeresspiegel bis in die mittlere Stratosphäre.
KARL liefert hochaufgelöste Messungen der Streueigenschaften von Aerosol- und Wol-
kenteilchen (Rückstreuung, Extinktion und Depolarisation) sowie Wasserdampfprofile
in der unteren Troposphäre. Durch die Kombination von KARL Messungen mit Daten
anderer Messgeräte an der AWIPEV Forschungsstation wie Radiosonden, Sonnenphoto-
meter, Micro Pulse LIDAR und Fesselsonden wurde ein umfassender Datenbestand von
Streuphänomenen in der arktischen Atmosphäre geschaffen.
Die beiden genannten Frühjahreszeiträume März und April 2007 und 2009 wurden zu-
nächst anhand meteorologischer Parameter, wie lokaler Temperatur- und Feuchteprofile
sowie großskaliger Druckmuster und Luftmassenquellgebiete analysiert. Dabei konnte
kein eindeutiger Zusammenhang zwischen Quellgebieten und erhöhter AOD festgestellt
werden. In einem Vergleich zweier wolkenfreier Perioden im März 2007 und April 2009
war jedoch die höhere Aerosolbelastung in 2009 mit dem Transport von Luftmassen durch
die innere Arktis verbunden. Aufgrund der begrenzten Lebensdauer von Aerosolen lässt
das entweder Aerosol-Entstehungsprozesse in der Zentralarkti