General characteristics of
tropospheric trace constituent layers observed in the MOZAIC
program
We present a statistical study on tropospheric layers as allowed by
the most extensive ozone and water vapor data base up to now
available. Considering O3 and H2O deviations
from an automatically calculated background we define four types of
layers. These tropospheric layers are a common feature with the
percentage of the troposphere occupied by such layers varying from 7%
to 33% depending on the region and the season. Most of the layers are
found between 4 and 8 km altitude and the median thickness is about
500 m. At northern mid-latitudes we find four times more layers in
summer than in winter, while in tropical Asia we observe a spring
maximum in the occurrence of the layers. The most abundant layer type
everywhere is O3+ H2O- and corresponds to the
signature of stratospheric intrusions or continental pollution. This
suggests that stratosphere-troposphere exchanges or at least their
influence are not negligible in summer at mid-latitudes or in the
tropics. A complete understanding of the layers could lead to a
better empirical assessment of the different tropospheric ozone
sources and to an assessment of the potential vorticity fluxes in the
troposphere.
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