A03: Impact of low-level clouds on Arctic atmospheric boundary layer turbulence and radiation
PIs: Christof Lüpkes, Manfred Wendisch
This project will quantify the impact of low–level clouds on the energy budget in the Arctic Atmospheric Boundary Layer (ABL) and, thus, is closely related to the topic of Arctic Amplification. Vertical profiles of radiative and turbulent fluxes of energy and momentum will be studied by (i) using data from previous ship–borne and aircraft campaigns, and (ii) collecting and analysing new measurements from two planned aircraft deployments over the Arctic Ocean. The two new campaigns involve the AWI research aircraft Polar 5 & 6 to measure the vertical flux profiles as a function of cloud and sea ice cover and for varying synoptic conditions. The aircraft observations are scheduled for May/June 2017 and March 2019, thus covering periods with strong (late winter) and weak (early summer) Arctic Amplification. We expect significant differences between the measurements collected in the two campaigns with a rather surface–dominated flux regime in late winter and more cloud–driven flux patterns in early summer. The campaign in 2017 will be coordinated with the Research Vessel (RV) Polarstern, which will be operated for four weeks in the northern Fram Strait pack ice region. Onboard RV Polarstern and at an ice–floe camp, additional ship–based and balloon-borne flux observations will be carried out (projects A01 and A02). While the aircraft observations (this project) will focus on the horizontal variability and upper levels, the ship–based and balloon–borne measurements will concentrate on the temporal variability and lower levels. The analysis of measurements combined with mesoscale modelling will improve the understanding of the complex interactions between cloud dynamics, turbulent processes over heterogeneous sea ice cover, and atmospheric radiation. It will help to quantify drawbacks of turbulence and radiation parameterizations used in models of different complexity ranging from state–of–the–art climate and weather prediction models to sophisticated radiative transfer schemes.
Hypothesis: The net effect (warming/cooling) of Arctic low–level clouds varies regionally and seasonally, and exhibits a major dependence of sea ice cover.
Specific questions which will be answered in the project are:
- How do ABL clouds modify vertical profiles of turbulent and radiative fluxes of energy and momentum as compared to cloudless conditions?
- Do turbulence parameterizations used in state–of–the–art climate models need improvements to realistically represent the cloudy and cloudless polar ABL?
- What is the seasonal dependence of the cloud impact on the Arctic ABL characteristics?
- What is the relative importance of surface albedo, large scale meteorological forcing, and clouds on the energy budget of the ABL?
The project will help to improve the comprehension of the ongoing climate changes in the Arctic. It will deliver data for validation of models that are essential to identify weaknesses in the representation of processes that significantly contribute to Arctic Amplification.
Role within (AC)³
- Aircraft data form the core of cooperations
- A03 parametrizations developed on the basis of observations and modelling (projects in A03 and B/D/E) will be made available
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