Open AccessTopographic Impacts on the Spatial Distribution of Deep Convection over Southern Quebec
Author(s) -
Michael J. Kovacs,
Daniel J. Kirshbaum
Publication year - 2016
Publication title -
journal of applied meteorology and climatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.079
H-Index - 134
eISSN - 1558-8432
pISSN - 1558-8424
DOI - 10.1175/jamc-d-15-0239.1
Subject(s) - mesoscale meteorology , convection , convective available potential energy , geology , climatology , geostrophic wind , convective storm detection , deep convection , storm , convective inhibition , atmospheric sciences , meteorology , geography , oceanography , natural convection , combined forced and natural convection
Observations and numerical simulations reveal pronounced mesoscale variability in deep-convection occurrence over southern Quebec, Canada. A 22-yr climatology from the McGill radar just west of Montreal shows that deep-convection maxima exist (i) within the St. Lawrence valley surrounding Ottawa; (ii) within the Champlain valley of upstate New York, extending north to just east of Montreal; and (iii) in the lee of the Laurentian Mountains northeast of Trois-Rivières. These features are sensitive to the background low- to midlevel 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 Montreal and into the Laurentians. To physically interpret these features, a suite of quasi-idealized convection-permitting simulations is conducted. Analysis of the simulations, which broadly reproduce the observed extrema in convection occurrence, reveals that the maxima develop within pockets of moisture and mass convergence at the junctions of major river valleys and in the lee of prominent mountain ridges. In these locations, enhanced boundary layer humidity and convective available potential energy (CAPE) coincides with minimal convective inhibition (CIN). The minima occur over and downwind of water bodies, where limited surface heat fluxes reduce CAPE and increase CIN, and over the higher terrain, where reduced low-level moisture limits storm intensity.