Seasonal cycles and variability of O3 and H2O in the UT/LMS during SPURT

[摘要] Airborne high resolution in situ measurements of a large set of trace gasesincluding ozone (O₃) and total water (H₂O) in the upper troposphere andthe lowermost stratosphere (UT/LMS) have been performed above Europe withinthe SPURT project. SPURT provides an extensive data coverage of the UT/LMS ineach 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 towardsthe end of the year. The more variable H₂O measurements reveal a maximumduring summer and a minimum during autumn/winter with no phase shift betweenthe two atmospheric compartments.For a comprehensive insight into trace gas composition and variability in theUT/LMS several statistical methods are applied using chemical, thermal anddynamical vertical coordinates. In particular, 2-dimensional probabilitydistribution functions serve as a tool to transform localised aircraft datato a more comprehensive view of the probed atmospheric region. It appearsthat both trace gases, O₃ and H₂O, reveal the most compact arrangementand are best correlated in the view of potential vorticity (PV) and distanceto the local tropopause, indicating an advanced mixing state on thesesurfaces. Thus, strong gradients of PV seem to act as a transport barrierboth in the vertical and the horizontal direction. The alignment of trace gasisopleths reflects the existence of a year-round extra-tropical tropopausetransition layer. The SPURT measurements reveal that this layer is mainlyaffected by stratospheric air during winter/spring and by tropospheric airduring autumn/summer.Normalised mixing entropy values for O₃ and H₂O in the LMS appear to bemaximal during spring and summer, respectively, indicating highestvariability of these trace gases during the respective seasons.

[学科分类] 大气科学