POLSTRACC / GW-LCYCLE / SALSA

The Arctic is the region that experiences the largest changes in Earth’s climate, with a rapid decline of Arctic sea ice, a strong warming of the surface atmosphere and changes in the chemistry and dynamics of the UTLS. In the Arctic stratosphere, large depletion of Arctic stratospheric ozone has been observed in recent cold winters, with still large uncertainties how this will respond to future climate change. Changes in the trace gas composition and cirrus cloud occurrence in the UTLS have a large impact on radiative forcing and surface climate. POLSTRACC aims at providing new scientific knowledge on the structure, composition and evolution of the Arctic UTLS. POLSTRACC will investigate chemical and physical processes involved in Arctic stratospheric ozone depletion, transport and mixing processes in the UTLS at high latitudes, polar stratospheric clouds and cirrus clouds. In contrast to previous Arctic aircraft campaigns, a specific focus is set on the Lowermost Stratosphere (LMS), a region where fast horizontal transport processes occur and which is particularly important for the atmospheric radiation budget. Utilizing the combination of field measurements and model simulations, POLSTRACC will help improving our understanding of the polar stratosphere in a changing climate.

POLSTRACC will be performed in four phases: Early winter flights will be performed from Oberfaffenhofen, Germany, in December 2015 with the aim to probe the early polar vortex (Oberpfaffenhofen 1). The main campaign phases will be based in Kiruna, Sweden, at 68°N with extensive flights inside and in the vicinity of the polar vortex at high latitudes. The activities in Kiruna will be split into two phases: from early January to early February 2016 (Kiruna 1) and from the end of February to mid of March 2016 (Kiruna 2). A final campaign phase based in Oberpfaffenhofen, Germany, in the mid of March 2016 (Oberpfaffenhofen 2) will provide the opportunity to study the remants of the dissipating polar vortex in mid-latitudes in spring.

The POLSTRACC activities are coordinated with the BMBF/ROMIC project GW-LCYLCE (Gravity Wave Life Cycle Experiment) and the SALSA project (Seasonality of Air mass transport and origin in the Lowermost Stratosphere using the HALO Aircraft), which will strongly enhance the scientific outreach and capabilities of the individual projects. POLSTRACC furthermore shares a similar payload with the HALO mission WISE (Wave-driven ISentropic Exchange), which addresses complementary scientific objectives.

GW-LCYCLE. The project GW-LCYCLE addresses the fundamental issue of internal gravity wave (IGW) excitation, propagation, and dissipation in the atmosphere. IGWs are one of the most important dynamical coupling processes between the troposphere and the middle atmosphere (10 to 120 km). IGWs couple different atmospheric regions both in the vertical as well as in the horizontal directions by means of momentum and energy transport. Notably, this coupling is effective both from the troposphere upwards, and also in the opposite direction by indirect effects on circulation patterns. While this importance of IGWs for understanding atmospheric structure, dynamics and climate is now widely recognized surprisingly little is still known about the details of the actual life cycle of IGWs.