Arctic mixed-phase clouds simulated by the WRF model: Comparisons with ACLOUD radar and in situ airborne observations and sensitivity of microphysics properties
Résumé
The microphysical properties of two mixed-phase clouds (MPCs), one over sea ice, and another over open ocean, are investigated using in situ measuring probes and a cloud radar installed on-board two aircraft during the Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) field campaign, west of Svalbard on 17 June 2017. Comparisons between observations and different configurations of the Weather and Research Forecasting (WRF) model are conducted and reveal discrepancies in the vertical profile of the ice crystal concentrations for both MPCs due to slightly higher temperatures (by approx. 1-2°C) in WRF than observed, affecting the ice formation. A comprehensive sensitivity analysis is carried out to address the impact of assumptions used for the microphysics (MP) and the atmospheric boundary layer (ABL) schemes on the simulated vertical properties of the MPC systems. The role of the vertical resolution of the large scale data used for model initialisation is also investigated. Results show that the model performance improves for large-scale initialisation with more numerous levels close to the surface. Moreover, modifying the ABL or MP scheme influences the altitudes of the cloud top and base as well as the liquid and ice water amounts. Our study also highlights how an increase in the cloud condensation nuclei and droplet number concentrations can impact the vertical profiles of the liquid and ice water amounts.
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