Assessment of simulations of a polar low with the Canadian Regional Climate Model

RESEARCH ARTICLE Assessment of simulations of a polar low with the Canadian Regional Climate Model Marta Moreno-Iba´ñezID1,2*, Rene´ Laprise1,2, Philippe Gachon1,3 1 Centre for the Study and Simulation of Regional-Scale Climate (ESCER), University of Quebec in Montreal (UQAM), Montreal, Canada, 2 Department of Earth and Atmospheric Sciences, University of Quebec in Montreal (UQAM), Montreal, Canada, 3 Department of Geography, University of Quebec in Montreal (UQAM), Montreal, Canada * marta.moreno-ibanez@outlook.com Abstract Polar lows (PLs), which are intense maritime polar mesoscale cyclones, are associated with severe weather conditions. Due to their small size and rapid development, PL forecasting remains a challenge. Convection-permitting models are adequate to forecast PLs since, compared to coarser models, they provide a better representation of convection as well as surface and near-surface processes. A PL that formed over the Norwegian Sea on 25 March 2019 was simulated using the convection-permitting Canadian Regional Climate Model version 6 (CRCM6/GEM4, using a grid mesh of 2.5 km) driven by the reanalysis ERA5. The objectives of this study were to quantify the impact of the initial conditions on the simulation of the PL, and to assess the skill of the CRCM6/GEM4 at reproducing the PL. The results show that the skill of the CRCM6/GEM4 at reproducing the PL strongly depends on the initial conditions. Although in all simulations the synoptic environment is favourable for PL development, with a strong low-level temperature gradient and an upper-level

through, only the low-level atmospheric fields of three of the simulations lead to PL develop- ment through baroclinic instability. The two simulations that best captured the PL represent a PL deeper than the observed one, and they show higher temperature mean bias com- pared to the other simulations, indicating that the ocean surface fluxes may be too strong. In general, ERA5 has more skill than the simulations at reproducing the observed PL, but the CRCM6/GEM4 simulation with initialisation time closer to the genesis time of the PL repro- duces quite well small scale features as low-level baroclinic instability during the PL devel- opment phase. 1. Introduction The polar regions experience a variety of climate-related extreme events and high-impact weather conditions such as katabatic winds, blizzards, and polar lows (PLs) [1]. PLs are intense mesoscale maritime cyclones that develop between the poles and the main baroclinic zone, mainly during the cold season. Their diameter varies between 200 and 1,000 km, and their associated near-surface wind speed is over 15 m s-1 [2]. PLs are short-lived phenomena, with PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone.0292250 October 5, 2023 1 / 28 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Moreno-Iba´ñez M, Laprise R, Gachon P (2023) Assessment of simulations of a polar low with the Canadian Regional Climate Model. PLoS ONE 18(10): e0292250. https://doi.org/10.1371/ journal.pone.0292250 Editor: Delei Li, Institute of Oceanology Chinese Academy of Sciences, CHINA

Received: October 31, 2022 Accepted: September 15, 2023 Published: October 5, 2023 Peer Review History: PLOS recognizes the benefits of transparency in the peer review process; therefore, we enable the publication of all of the content of peer review and author responses alongside final, published articles. The editorial history of this article is available here: https://doi.org/10.1371/journal.pone.0292250 Copyright: © 2023 Moreno-Iba´ñez et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: AVHRR channel 4 observations are available from EUMETSAT (https://navigator.eumetsat.int/product/EO:EUM: DAT:METOP:AVHRRL1), and MODIS channel 31 observations and VIIRS channel M15 observations