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

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
Trends and stability in the MLT-region - a model study
Grygalashvyly Mykhaylo , Sonnemann Gerd , Berger Uwe , Lübken Franz-Josef
Leibniz-Institute of Atmospheric Physics at the University Rostock in Kühlungsborn, Schloss-Str.6, D-
18225 Ostseebad Kühlungsborn, Germany
The height of the NLC has not noticeably declined since the time of first observation. The
term “equithermal submesopause” was introduced in 1996 and reflects the significant
repeatability of the mean mesopause temperature during the last 40 years. The microwave
measurements of water vapor at high latitudes (ALOMAR, 69°N) during last 14 years do not
show significant positive trends in MLT-region. These facts motivate us to study the
mechanisms of stabilization in the atmosphere and precisely in the summer mesopaus region
which is astonishingly stable in spite of the anthropogenic changes.
We investigate the influence of the rising concentrations of methane, nitrous oxide and carbon
dioxide since 1961 on the chemistry of the mesosphere. We use our global 3D-model LIMA
(Leibniz-Institute Middle Atmosphere) designed for the investigation of the MLT-region and
particularly the extended mesopause region. LIMA uses real tropospheric and lower
stratospheric temperature and horizontal wind up to 35 km altitude from assimilation of
ECMWF/ERA-40. Realtime Lyman-α flux values are employed to determine the water vapor
dissociation rate. The analysis of the long-term behavior of water vapor also utilizes real
methane measurements. The solar influence on the water vapor mixing ratio is insignificant
below about 75-80 km within high latitudes in summer, but becomes increasingly important
above this domain.
Three calculations were carried out and analyzed. 1. We use a constant annual variation of
the model dynamics for all years according to the dynamics of the solar minimum in 1964 and
employ a realistic growth of the anthropogenic gases. 2. We use constant concentrations of
the anthropogenic constituents at the lower border but employ the varying dynamics. 3. The
realistic case considers both, the increase of the anthropogenic minor constituents and yearly
varying dynamics. The analyses of these 3 cases show, that the effect of dynamics reduces the
influence of anthropogenic changes in the upper mesosphere-mesopause-lower thermosphere
region. This probably occurs due to non-linear feed backs effect between dynamics and
chemistry. Therefore, models with climatologically mean dynamics, apparently, overestimate
anthropogenic impact. We also discuss the long-term behavior of water vapor with regard to
the potential impact on NLC. Additionally, we estimate influences on the thermal regime of
MLT-region.