scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
Observation of Descending Mesospheric Air above the Arctic during the Winters of
2007 to 2010 by Ground-based Microwave Radiometry
Hoffmann Christoph Gregor 1 , Raffalski Uwe 2 , Palm Mathias 1 , Golchert Sven H. W. 1 , Hochschild
Gerd 3 , Notholt Justus 1
1 Institute of Environmental Physics, University Bremen, 2 Swedish Institute of Space Physics, Kiruna,
Schweden, 3 Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology
In the mesosphere and lower thermosphere (MLT), NOx is produced by solar high-energy
radiation. It can then be transported into the polar winter stratosphere by the large-scale
circulation of the middle atmosphere.
In this region, NOx acts as catalyst for ozone destruction. Parts of the ozone variability can
therefore be induced by either the varying NOx production in the MLT region or the varying
strength of the downward transport into the stratosphere.
For the quantification of the latter, the influence of dynamics, observations of the respective
descent rates are needed. They can be obtained from measurements of CO profiles, since CO
is a tracer for dynamics in this region.
We have been performing ground-based microwave observations of CO since 2007 above
Kiruna, Sweden (67.8°N), covering an altitude range of 40 km to 80 km. We present the
analysis of the measured timeseries for the three winters from 2007/2008 to 2009/2010
together with an estimation of the descent rates. In addition to the analysis of the vertical
motion, the measurements might be used to investigate meridional mixing across the vortex
border in the upper stratosphere. That is because the data set contains features that indicate a
weakening of the polar vortex in the upper stratosphere, while it remains stable in the lower
stratosphere.