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La convection et les orages dans le sud du Québec
beachcp31 posted a topic in Discussions généralesLe 20 novembre, il y a eu un séminaire au Centre ESCER sur les zones de convections dans le sud du Québec. Vraiment très intéressant!!!!! Voici le résumé. Ça explique beaucoup de choses!!! Vendredi 20 novembre, local PK-6610 – 14 h Conférencier : Daniel Kirshbaum, McGill University Titre : Preferred locations of convective storms over southern Québec Résumé : Observations and numerical simulations presented herein reveal strong mesoscale variability in deep-convection occurrence over southern Québec. Based on a 22-year climatology from the McGill radar located just west of Montréal, deep-convection maxima exist (i) within the St. Lawrence valley between Ottawa and Montréal, (ii) within the Champlain valley of upstate New York, extending north to just east of Montréal, and (iii) along the western edge of the Laurentian mountains just northeast of Trois Rivières. These features exhibit clear sensitivity to the background low-to-mid-level geostrophic wind direction, shifting northward as the southerly wind component increases. A meridional axis of suppressed convection also extends from Lake Ontario and the Adirondacks of New York north through Montréal and into the Laurentians. To physically interpret these features, a suite of quasi-idealized, convection-permitting simulations of regional convection events is conducted, which reproduce the observations reasonably well despite neglecting synoptic-scale forcing. Analysis of the pre-convective simulated environment indicates that the deep-convection maxima develop within pockets of moisture and mass convergence at the junctions of major river valleys and in the lee of prominent orography. In these locations, enhancements in water-vapor mixing ratio and Convective Available Potential Energy (CAPE) coincide with near-zero Convective Inhibition (CIN), which both favor convection initiation. In contrast, deep convection is suppressed over and downwind of water bodies, where reduced surface heat fluxes reduce CAPE and increase CIN, and over the higher terrain, where a lack of low-level moisture limits CAPE.