|
|
 |
|
|
Ann. Geophys., 21, 1057-1069, 2003
www.ann-geophys.net/21/1057/2003/
© European Geosciences Union 2003
Observation of an unusual mid-stratospheric aerosol layer in the Arctic: possible sources and implications for polar vortex dynamics
M. Gerding1, G. Baumgarten2, U. Blum3, J. P. Thayer4, K.-H. Fricke3, R. Neuber1, and J. Fiedler2
1Alfred-Wegener-Institut für Polar- und Meeresforschung, Forschungsstelle Potsdam, Telegrafenberg A43, D-14473 Potsdam, Germany
2Leibniz-Institut für Atmosphärenphysik, Schloss-Straße 6, D-18225 Kühlungsborn, Germany
3Physikalisches Institut, Universität Bonn, Nussallee 12, D-53115 Bonn, Germany
4SRI International, Center for Geospace Studies, 333 Ravenswood Avenue, Menlo Park, CA 94025, USA
Abstract. By the beginning of
winter 2000/2001, a mysterious stratospheric aerosol layer had been detected by
four different Arctic lidar stations. The aerosol layer was observed first on
16 November 2000, at an altitude of about 38 km near Søndre Strømfjord,
Greenland (67° N, 51° W) and on 19 November 2000, near Andenes, Norway
(69° N, 16° E). Subsequently, in early December 2000, the aerosol
layer was observed near Kiruna, Sweden (68° N, 21° E) and
Ny-Ålesund, Spitsbergen (79° N, 12° E). No mid-latitude lidar
station observed the presence of aerosols in this altitude region. The layer
persisted throughout the winter 2000/2001, at least up to 12 February 2001. In
November 2000, the backscatter ratio at a wavelength of 532 nm was up to 1.1,
with a FWHM of about 2.5 km. By early February 2001, the layer had sedimented
from an altitude of 38 km to about 26 km. Measurements at several wavelengths
by the ALOMAR and Koldewey lidars indicate the particle size was between 30 and
50 nm. Depolarisation measurements reveal that the particles in the layer are
aspherical, hence solid. In the mid-stratosphere, the ambient atmospheric
temperature was too high to support in situ formation or existence of cloud
particles consisting of ice or an acid-water solution. Furthermore, in the year
2000 there was no volcanic eruption, which could have injected aerosols into
the upper stratosphere. Therefore, other origins of the aerosol, such as
meteoroid debris, condensed rocket fuel, or aerosols produced under the
influence of charged solar particles, will be discussed in the paper.
Trajectory calculations illustrate the path of the aerosol cloud within the
polar vortex and are used to link the observations at the different lidar
sites. From the descent rate of the layer and particle sedimentation
rates, the mean down-ward motion of air within the polar vortex was estimated
to be about 124 m/d between 35 and 30 km, with higher values at the edge of the
vortex.
Key words. Atmospheric composition
and structure (aerosols and particles; middle atmosphere composition and
chemistry) – meteorology and atmospheric dynamics (middle atmosphere
dynamics)
Full Article in PDF (4551 KB) |
|
|
