In-situ measurements onboard aircraft

The atmosphere constitutes an extremely complex mixture of thousands of trace constituents that permanently react and re-distribute within the atmosphere itself as well as adjoined compartments such as the biosphere or the ocean. The atmosphere can thus be viewed as a giant natural chemical reactor.

The group Tropopause (TOP) is particularly interested in the budgets of trace gases in the upper troposphere and lower stratosphere (UTLS), i.e. between ~6 km and ~25 km. The layer sandwiched between the two spheres UT and LS, the tropopause, shows an altitude of ~17 km in the tropics and 8-12 km in mid- and polar latitudes. The UTLS plays an essential role in controlling climate on earth. In spite of its importance and due to its extreme dynamical and chemical complexity, the UTLS is still one of the least well understood regions of the atmosphere.

The main scientific objectives of our group are:

• to better understand the (bi-directional) exchange of trace gases between stratosphere and troposphere (STE). We are thus strongly engaged in the dynamics of the UTLS (tropopause dynamics, convection, slow cyclonic lofting).

• to better quantify the budgets of ozone, organic compounds, water (as vapour and in clouds / aircaft contrails), carbon dioxide, and methane in the UTLS, and to better distinguish between variations due to transport and those caused by chemistry.

• and certainly how these trace gas budgets and processes change with time ("global change"), and what are the consequences of these changes for Earth's climate ("climate change").

For achieving this goal we develop, construct and thereafter deploy in-situ instruments on board research and passenger aircraft. Applied techniques are UV photometry, chemiluminescence detection, chemical mass spectrometry, tunable diode laser absorption spectroscopy, photo-acoustic laser spectroscopy, integrated cavity output spectroscopy, and chilled mirror frost point hygrometry. Main project currently is IAGOS-CARIBIC, where we run five in-situ instruments on board an Airbus A340-600 of Lufthansa AG until the beginning of the COVID-19 pandemic. Since 2015 the TOP group is coordinating this european research infrastructure. A new CARIBIC laboratory on board an Airbus A350-900 is under construction at the moment and will become operational in 2023. We further have developed three in-situ instruments for the German research aircraft HALO and contribute to the European research grant MUSICA.