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

The atmospheric and ocean surface initial and boundary conditions have been obtained from the ERA5 global reanalysis, which has a horizontal grid of 0.25˚ [12]. From September 2007 onwards, ERA5 uses the Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) product for the sea surface temperature (SST), and the Ocean and Sea Ice Satellite Application Facilities (OSI SAF) product for the sea ice concentration (SIC). The CRCM6/ GEM4 is hourly (daily) driven by the atmospheric (ocean surface) fields of ERA5. The ocean surface condition is temporally interpolated. The land surface initial conditions have been obtained from the Canadian Meteorological Centre analyses. Eight simulations were con- ducted by initialising the model every 6 hours from 23 March at 0000 UTC to 24 March at 1800 UTC. All simulations ended on 26 March at 0600 UTC. In what follows, we will refer to each simulation by its initialisation date; for instance, the simulation initialised on 24 March at 1200 UTC will be referred to as 24d12h. Several variables at screen level have been output to compare them with conventional observations. It is important to note that the model computes the wind gusts using the wind gust estimate method developed by Brasseur [38]. This approach assumes that turbulent eddies lead to the downward deflection of air parcels located at higher levels in the boundary layer, producing surface wind gusts. Therefore, the mean wind and the turbulent structure of the atmosphere are included in the computation of wind gusts. This method provides a wind gust

estimate as well as a bounding interval around this estimate. For this study, we use the instan- taneous wind gust estimate that is output every hour. Fig 1. Location of the drifting buoys and surface stations whose data has been used for the verification of the simulations of the PL. The observations used are sea level pressure (SLP), 2-m temperature (T2m), 2-m dewpoint temperature (Td,2m), 2-m relative humidity (RH2m), 10-m wind (V10m), 10-m maximum wind gusts (WG10m,max), and 1-h accumulated precipitation (PR). The region showed is the domain of the simulation excluding the sponge zone. The dataset used to plot the geographic contours has been obtained from the Global Self-consistent, Hierarchical, High-resolution Geography Database (GSHHG; [33]) under a CC BY license, with permission from Dr. Paul Wessel. https://doi.org/10.1371/journal.pone.0292250.g001 PLOS ONE Assessment of simulations of a polar low with the canadian regional climate model PLOS ONE | https://doi.org/10.1371/journal.pone.0292250 October 5, 2023 4 / 28