Arctic mixed-phase clouds from the micro- to the mesoscale: insights from high-resolution modeling

• Main Author: Eirund, Gesa K.
• Other Authors: Lohmann, Ulrike, Field, Paul R., Possner, Anna
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: ETH Zurich 2019
• Subjects: Boundary layer clouds; Arctic clouds; Boundary layer dynamics; Modeling; STRATOCUMULUS (METEOROLOGY); Aerosols and Clouds; info:eu-repo/classification/ddc/500; Natural sciences; Arctic; Arctic Ocean; Sea ice
• Online Access: https://hdl.handle.net/20.500.11850/404229; https://doi.org/10.3929/ethz-b-000404229

Clouds play a key role in the local Arctic radiative budget and the hydrological cycle. In particular, cloud presence, vertical and horizontal extent, micro- and macrophysical characteristics, temperature, and thermodynamic phase are relevant properties determining the cloud's interaction with its environment. Especially Arctic low-level clouds have been found to strongly interact with atmospheric radiation and to have a net warming effect on the Earth surface during most of the year through the emission of longwave radiation. Low-level clouds reside within the boundary layer and are often mixed-phase, i.e. they contain a mixture of cloud ice and liquid water. Even though the coexistence of ice and liquid is thermodynamically unstable, low-level Arctic mixed-phase clouds (MPCs) have been found to be particularly persistent, a phenomenon that has puzzled the scientific community for decades. Yet, a profound understanding of the processes controlling Arctic MPC persistence, microphysics, and dynamics is so far missing. In order to contribute to the current understanding of processes controlling Arctic low-level MPC properties, semi-idealized cloud-resolving model simulations are explored. At high horizontal (120-200 m) and vertical (25-50 m within the atmospheric boundary layer) resolutions, cloud driven circulations are accurately resolved, while cloud microphysical properties are parameterized. All simulations are based on MPC observations obtained during the Aerosol-Cloud Coupling and Climate Interactions in the Arctic (ACCACIA) campaign in March 2013. In the first part of this work, cloud properties over varying surface conditions (i.e. open ocean and sea ice) are investigated. As sea ice has been retreating in recent years, altered cloud dynamics in response to surface forcing provide valuable insights of future cloud occurrence in the Arctic. In addition, with retreating sea ice the Arctic Ocean becomes more accessible for shipping, such that Arctic clouds are likely to be exposed to higher levels of ...