WISE: Wave driven isentropic exchange

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Changes in the distributions of trace gases, like water vapor and ozone, and thin cirrus clouds in the upper troposphere and lower stratosphere (UTLS) strongly impact radiative forcing. Uncertainties in the description of mixing introduce large errors to the estimates of the radiative forcing and are thus of key importance for understanding climate change. It is therefore of great importance to quantify the physical and chemical processes (e.g. exchange of air masses, cirrus formation) that govern the composition of the UTLS. The so-called overworld above = 380 K influences directly the composition of the extra-tropical stratosphere with significant contributions of air originating from the Asian monsoon circulation during summer. Breaking planetary waves transport monsoon air to the extratropical UTLS where these contribute to the moisture and tracer budget. The lower boundary of the UTLS, the extra-tropical transition layer (ExTL) is strongly affected by bidirectional (quasi-isentropic) mixing across the tropopause. The upper bound of the ExTL roughly coincides with the tropopause inversion layer (TIL), which constitutes a region of enhanced stability above the tropopause. The impact of radiatively active species like water vapour and ozone on the temperature structure makes the TIL a sensitive indicator for changes of ozone chemistry or changes of tropopause temperatures which directly affect water vapour which in turn feeds back into the static stability. WISE will address the relation between composition and dynamical structure of the UTLS by focusing on the following four main research topics:- Interrelation of the tropopause inversion layer (TIL) and mxing processes on the trace gas distribution- Role of Planetary wave breaking for water vapor transport into the extra-tropical lower stratosphere - Role of halogenated species for ozone in the UTLS- Occurrence and effects of sub-visual cirrus (SVC) in the lowermost stratosphereWISE will addres these objectives with a novel payload combining 2D and 3D measurements of tracers and temperature, drop sondes and highly resolved state-of-the-art in-situ trace gas measurements. A unique combination of limb and nadir remote sensing instruments will be used for innovative studies of optically and vertically thin cirrus clouds in the UTLS region. High-precision in-situ observations provide detailed information on mixing processes and tracer structure with high spatial resolution.WISE will take place in Spetember and October and thus directly measure the impact of the decaying monsoon on the extratropical UTLS. Based on Lagrangian and process oriented models the relative contribution of air from different source regions as well as well as transport times and mixing processes will be quantified.