Modeling Extreme Warm-Air Advection in the Arctic: The Role of Microphysical Treatment of Cloud Droplet Concentration

• Main Authors: Sotiropoulou, G., Bossioli, E., Tombrou, M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2019
• Subjects: Arctic; Sea ice
• Online Access: https://pergamos.lib.uoa.gr/uoa/dl/object/uoadl:3069001

As the Arctic climate is changing fast, with increasing areas of open water in summer, there is a growing interest in the processes related to the marginal ice zones. Recent studies have indicated that such a critical process may be the advection of warm and moist air from the south. In this study, the performance of the Weather Research and Forecasting (WRF) model is evaluated during an extreme warm advection episode over melting sea ice that occurred near the Arctic ice edge in summer 2014. The model gives a reasonably good representation of the atmospheric conditions and the Arctic boundary layer, characterized by very strong surface inversions and the frequent presence of low-level jets. However, the representation of the highly variable cloud conditions, from optically thick to optically thin, dissipating clouds, is sensitive to the choice of cloud droplet treatment in WRF. Simulations with relatively high cloud droplet number concentrations (Ndrop ≥ 100 cm−3) are more successful in representing the optically thick cloud state, whereas to reproduce optically thin and tenuous clouds Ndrop should be <50 cm−3. The WRF-Chem model, with a realistic treatment of the cloud-aerosol interactions, allows for large variations in Ndrop and hence can reproduce the cloud water properties reasonably well for most of the simulation time. This contributes to an improved representation of the cloud longwave radiative effect, compared to the simulations where a less adaptive treatment of Ndrop is applied. ©2019. American Geophysical Union. All Rights Reserved.