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A brief synopsis of Johnson and Mapes: Mesoscale Processes and Severe Convective Weather. From Severe Convective Storms sections 3.3b, 3.3c.1, 3.4 By Matt Gough. overview. Advective Processes and examples that lead to severe weather Dynamical Processes and examples
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A brief synopsis of Johnson and Mapes: Mesoscale Processes and Severe Convective Weather From Severe Convective Storms sections 3.3b, 3.3c.1, 3.4 By Matt Gough
overview • Advective Processes and examples that lead to severe weather • Dynamical Processes and examples • Convective triggering mechanisms
Advective Processes Moisture Advection • Increases CAPE and lowers LFC Synoptic scale Differential Advection • Destabilizes atmosphere • Provides vertical wind shear • establishes capping inversions Convergence Lines • Preconditioning and triggering convection
Examples of mesoscale Differential Advection • Low-level jets with high θ(e) overrunning fronts and cold-pools (bow echoes). • Flow of moist boundary layer air out from beneath an inversion • Transport of clouds and moisture aloft downstream of mountain barriers (dry microbursts) • Short periods of jet streak circulations and boundary layer heating
Examples of Convergence Lines • Warm and cold fronts – associated with Mesoscale cross-front circulations. • Precipitation driven downdrafts (gust fronts) • Drylines – usually needs to be coupled with other mechanisms. • Land and Sea breezes – convergence of offshore or onshore flow. • Mountain/Valley breezes – upslope flow in western US providing convergence and lifting.
Dynamical processes • Upper level jets • Lower level jets • Coupling of upper and lower level jets
Dynamical processes Upper level jets
Dynamical processes Lower level Jets • Enhancement of moisture and temperature advection. • Increased low level convergence • Increase in vertical wind shear Coupling of upper and lower level jets • Upper level conv. forces low level jet Coupling between indirect circulation and cold cold front.
Triggering of convection Mechanisms can operate in isolation • Storms along a gust front or in combination • Gust fronts colliding with each other
Triggering of convection Local Processes Buoyancy driven circulation • Thermals, horizontal convective rolls, overshooting buoyant eddies. Terrain Forcing • Lee-side convergence, thermally-induced lifting, flow deflection, and surface inhomogeneities.
Triggering of convection Advective Processes • Convection along convergence • Cold/warm front lifting • Gust fronts, sea breezes, and drylines Usually the intersection of these features cause severe convection.
Triggering of convection Dynamical Processes: • Horizontal Convective Rolls (operate in conjunction with other processes) • Gravity waves (in tropics – small CIN) • Horizontal shear
Triggering of convection Combined Lifting Processes: • Boundary layer rolls intersecting with convergence lines • HCRs intersecting with sea breezes. • Dryline convection: mesoscale lows, HCRs, fronts, and gravity waves. • Gust fronts with terrain, gravity waves, etc.
