A large-eddy simulation perspective on Arctic airmass transformation and low-level cloud evolution
The Arctic is currently warming faster than other regions of the Earth. Many processes and feedbacks contribute to the enhanced warming. Among these are the radiative effects of the clouds. Arctic mixed-phase clouds which contain both liquid and ice condensate, have high longevity and can exert sign...
| Main Authors: | , |
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| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
| Published: |
Institutes outside Greece
2022
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| Subjects: | |
| Online Access: | http://hdl.handle.net/10442/hedi/53845 https://doi.org/10.12681/eadd/53845 |
| Summary: | The Arctic is currently warming faster than other regions of the Earth. Many processes and feedbacks contribute to the enhanced warming. Among these are the radiative effects of the clouds. Arctic mixed-phase clouds which contain both liquid and ice condensate, have high longevity and can exert significant surface warming since the amount of solar radiation in the region is relatively low and the surface reflectivity often is high. In this thesis, we study these clouds utilizing a large eddy model coupled with one dimensional thermodynamic sea ice model. The main aim is to understand the interactions between cloud dynamics, microphysics, radiation, and turbulent processes and how these together govern the lifecycle and surface warming of the clouds. By comparing a group of models with observations of the summertime high Arctic we confirm the hypothesis that then when aerosol concentrations are low a small increase in their number concentration can increase the liquid water content of the cloud and turn the surface warming. Idealized simulations of moist intrusions into the Arctic show that the surface temperature may increase by more than 15 Celsius degrees if we allow cloud to form during a moist intrusion compared to if the atmosphere is cloud free. The simulations also show that the large scale divergence rate strongly impacts the maintenance of the liquid layer at the top of these clouds. A main finding of this thesis is that the temperature of the cloud that forms during a moist intrusion is close to the initial dew point temperature. Thus, the surface warming induced by the clouds depends mostly on the initial humidity of the air mass rather than the initial temperature. In addition, the stability of the initial dew point temperature profile largerly controls the turbulent state of the cloud. If the profile is unstable then the cloud can transform from a thin stable stratus to a deeper stratocumulus cloud, which also enhances the surface warming. Consequently, both the initial amount and the vertical ... |
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