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

timing of its genesis and dissipation (Table 1). The average speed of the PL in 24d18h is the same as that of the observed one, and the total distance travelled is similar. The average speed of the PL and the distance travelled are lower in 24d12h, but they are fairly close to the observed ones. The PL represented in 23d12h is much smaller than the observed PL, and its lifetime is less than half the lifetime of the observed PL. However, its average speed is similar to the observed one. The PL in this simulation forms eleven hours latter than the observed one, but it dissipates at a similar time. Therefore, the distance travelled by the PL in this simulation is significantly lower than the observed one. The PL in ERA5 has shorter lifetime and some- what lower average speed than the observed one, but similar size. The tracks of the PL in the simulations and in ERA5 are reasonably close to that of the observed PL (Figs 5 and 6A). The distance between the simulated and the observed tracks notably increases at the end of the lifetime of the PL, which may be partly due to the high uncertainty when determining the centre of the PL at its dissipation stage. The tracks in 24d12h and 24d18h remain within 100 km from the observed track most of the time, whereas the track in ERA5 remains within 50 km from the observed one. The observed SLP minimum attained near the centre of the PL is 999.1 hPa at 1500 UTC (Fig 6B). However, since the Fig 4. Spaghetti plots showing the SLP isobars (contours every 3 hPa) of the simulations and ERA5 on 25 March 2019 at 1500 UTC, when the mature PL

was affecting the Norwegian coast. The contour lines correspond to the SLP field of (a) the simulations initialised on 23 March at 0000, 0600, 1200 and 1800 UTC, and (b) the simulations initialised on 24 March at 0000, 0600, 1200 and 1800 UTC, and ERA5. The black outlining represents the coastline. The dataset used to plot the geographic contours has been obtained from the GSHHG [33] under a CC BY license, with permission from Dr. Paul Wessel. https://doi.org/10.1371/journal.pone.0292250.g004 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 9 / 28