Abstract:
Climate change is especially pronounced in the Arctic with an unprecedented decrease of sea ice cover and a much higher increase of temperature than in other regions on Earth in the last decade. This effect, called the Arctic amplification, is in the center of the German research project (AC)3. Participating institutions are the Universities of Leipzig, Cologne and Bremen as well as the Alfred Wegener Institute (AWI) and Leibnitz Institute for Tropospheric Research (TROPOS) and some other international partners. The project has a focus on both modelling and field measurements.
This talk will introduce three (AC)3 aircraft campaigns, which have been carried out from Longyearbyen (Svalbard) since 2017. The main topic concentrates on high frequency measurements of atmospheric quantities like wind and temperature in the lower polar atmospheric layers (boundary layer) over sea ice and the open Arctic ocean. From such measurements the turbulent fluxes of energy and momentum can be derived whose knowledge is essential to understand air-ice-ocean interaction. Our guiding questions are: how are the fluxes influenced by clouds? What are the governing parameters? Are there seasonal dependencies?
Based on several case studies it is shown that clouds have a large impact on the mean and turbulent structure of the atmospheric boundary layer. This is shown by the analysis and comparison of results of data from different types of flight patterns. The data show clearly that turbulence is closely connected with radiation. Cloud top radiative cooling is redistributed by turbulence in the mixed layer. This is visible in different statistical moments of the turbulence, and often, e.g. a peak of the turbulent kinetic energy is measured within the clouds. As discussed in the talk, the detailed structure, depends on many parameters such as the atmospheric temperature and stability, the cloud optical thickness, wind speed and direction relative to the ice edge. Also surface roughness and the related wind shear are shaping profiles of turbulence moments. Finally, it is shown that the existence of multi-layer clouds is one of the most important factors for the turbulence structure of the lower atmospheric layers.
What is the Joint Oslo Seminar (JOS):
Atmospheric and climate sciences have a stronghold in Oslo among the four institutions University of Oslo, the Meteorological Institute, CICERO and NILU. This joint seminar invites renowned international experts to contribute to an informal series of lectures, meant to create interaction with the Oslo atmospheric and climate science community on recent highlights and analysis in the field. All seminars will be held on Thursdays (Noon -1pm).