Numerical Simulation of Convective Cloud Development During a Marine Cold-Air Outbreak From COMBLE

Cold-air outbreak (CAO) events are an understudied yet common aspect of the Arctic climatology. By creating relatively shallow boundary layers with wide zonal and narrow meridional scales, they often fall in the grey zone of forecasting. Numerical weather and climate models tend to overlook CAOs, potentially leading to the Arctic’s large discrepancy between forecasts and observations. The Cold-Air Outbreaks in the Marine Boundary Layer Experiment (COMBLE; December 2019 - May 2020) was a campaign aimed to characterize CAOs coming off of the Arctic sea ice by gathering data from two main areas of interest: Andenes, Norway, where they stationed an ARM Mobile Facility (AMF1), and Bear Island, Norway, where a reduced set of instruments were deployed. The COMBLE dataset is important for improving the representation of mixed-phase cloud processes in large-eddy simulations and large-scale models.

In this study, the Weather Research and Forecasting (WRF) model is utilized to simulate a strong CAO event on March 28th, 2020 and compare the CAO conditions on Bear Island to those in Andenes. This CAO event spanned over a relatively large meridional and zonal flow, proving to be significant for both locations simultaneously. Two convection-permitting WRF simulations, with 3 km horizontal resolution inner nests centered around Andenes and Bear Island, were conducted driven by ERA5 reanalysis data. A sensitivity test was completed between two WRF microphysics schemes, Thompson and P3. Results show that both WRF simulations captured general characteristics of the CAO event, however, specific parameters differed. Comparing the observations from the AMF1 and Bear Island sites to the model outputs, the WRF simulations are able to reproduce the vertical profiles of temperature and dewpoint for roughly half of the soundings. Both simulations overestimate the reflectivity of the CAO clouds, with the P3 simulation showing clear cloud streets, but the Thompson closer to the observed reflectivity.