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

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
Particle tracing within noctilucent clouds in the polar summer mesosphere
Kiliani Johannes, Lübken Franz-Josef, Berger Uwe, Baumgarten Gerd, Hoffmann Peter
Leibniz-Institute of Atmospheric Physics
We use the LIMA/ICE Lagrangian model for NLC simulation to investigate the history of
large mesospheric ice particles prior to and after observation and to look into the origin and
development of noctilucent clouds. To that end, we scan given NLC events for large particles
(e.g., > 20nm) and then trace those backward in time to their nucleation and forward to their
evaporation. From this, characteristic properties like mean radius, growth rate, local water
vapor (super-)saturation etc. are plotted in time series to characterize NLC particle
development.
As validation for the trajectory modeling, modeled winds from LIMA are compared to
measurements of radar data from Andenes (69°N) and Juliusruh (55°N).
We observe a generally good agreement of modeled winds with radar winds for the Andenes
latitude, so the focus of trajectory tracing are NLC oberserved near 69°N. Higher and lower
latitudes are also considered, but those results are used more cautiously, as validation for the
winds used in modeling is not as conclusive in this case.
Particle lifetime is dependent on latitude, with NLC particles observed near the pole
remaining small and close to the mesopause much longer than those at lower latitudes. At
69°N, the typical growth and sedimentation process may take a day or longer, while ice
particles observed at the very edge of the NLC latitude range tend to grow within hours before
being observed. This may be explained with much more variability in saturation ratios of air
carrying ice particles in mid-latitudes compared to higher latitudes.
With few exceptions, ice particles growing to visible size evaporate within ~6h of
observation, since they sediment to warmer regions and evaporate quickly once there. Thus,
ice particle lifetime is almost entirely determined by the time the NLC particles take to grow
to visible size.