| Airborne high resolution in situ measurements of a large set of trace gases
including ozone (O3) and total water (H2O) in the upper troposphere and
the lowermost stratosphere (UT/LMS) have been performed above Europe within
the SPURT project. SPURT provides an extensive data coverage of the UT/LMS in
each season within the time period between November 2001 and July 2003.
In the LMS a distinct spring maximum and autumn minimum is observed in O3,
whereas its annual cycle in the UT is shifted by 2–3 months later towards
the end of the year. The more variable H2O measurements reveal a maximum
during summer and a minimum during autumn/winter with no phase shift between
the two atmospheric compartments.
For a comprehensive insight into trace gas composition and variability in the
UT/LMS several statistical methods are applied using chemical, thermal and
dynamical vertical coordinates. In particular, 2-dimensional probability
distribution functions serve as a tool to transform localised aircraft data
to a more comprehensive view of the probed atmospheric region. It appears
that both trace gases, O3 and H2O, reveal the most compact arrangement
and are best correlated in the view of potential vorticity (PV) and distance
to the local tropopause, indicating an advanced mixing state on these
surfaces. Thus, strong gradients of PV seem to act as a transport barrier
both in the vertical and the horizontal direction. The alignment of trace gas
isopleths reflects the existence of a year-round extra-tropical tropopause
transition layer. The SPURT measurements reveal that this layer is mainly
affected by stratospheric air during winter/spring and by tropospheric air
during autumn/summer.
Normalised mixing entropy values for O3 and H2O in the LMS appear to be
maximal during spring and summer, respectively, indicating highest
variability of these trace gases during the respective seasons. |