“dynamical effects of convection” kathryn saussy meteorology 515: analysis & pred. of severe...
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“Dynamical Effects of Convection”Kathryn Saussy
Meteorology 515: Analysis & Pred. of Severe Storms March 1 2006
Bluestein, Howard: Synoptic-Dynamic Meteorology in Midlatitudes, Vol. II.
Oxford Press, 594 pp.
Johnson, Richard H., Mapes, Brian E, 2001: Mesoscale Processes and Severe
Convective Weather. Meteor. Mon. 28 (50), Amer. Meteor. Soc., Boston.
Monteverdi, John. Advanced Weather Analysis Lectures, Spring 2005.
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Dynamical Effects of Convection
I. Development & dynamical consequences of rotation
II. Cold pool-shear interactions
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I. Development & dynamical consequences of rotation
Pressure perturbation forces develop.
2 perturbation dynamic pressures are associated with the wind field:
The linear, p´L , and the nonlinear part, p´NL .
( p´ perturbation upward-directed pressure gradient force that adds to the synoptic-scale upwards directed force…or subtracts from the perturbation pressure change that would occur at that level. )
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Nonlinear pressure perturbation, p´NL
p´NL 2
This says that pressure falls are proportional & opposite in sign to the square of the vertical vorticity.
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Nonlinear pressure perturbation, p´NL
(con’d)Unidirectional shear Initial stage shows pressure
falls (on either flank) that augment the updraft.
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Nonlinear pressure perturbation, p´NL
(con’d)Unidirectional shear Splitting stage shows downdraft
forming; equal preference for R and L-moving storms.
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Nonlinear pressure perturbation, p´NL
(con’d)
On radar, it appears that the storm splits into mirror images.
Note the unidirectional shear on the hodograph.
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Linear pressure perturbation, p´L
p´L v/z 2w´
Unidirectional shear If the wind shear vector (v/z)
lies transverse a buoyant updraft, then pressures rise on the upshear side and fall on the downshear side.
This results in no preferential growth to either of the flanks lying across the shear.
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Linear pressure perturbation, p´L (con’d)
Clockwise shear vector
Leads to pressure falls on the right flank of the storm…and pressure rises on the left.
New growth is favored on the right.
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Linear pressure perturbation, p´L (con’d)
On radar, it appears that new storm growth favors the right flank.
Note the clockwise shear indicated on the hodograph.
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II. Cold pool-shear interactions
Vertical shear enhances ability of outflow (or cold pool) to trigger new storms
Increasing shear interaction between shear and cold pool enhances lifting on preferred storm flank.
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Evolution of a Convective System: Stage 1
The initial updraft leans downshear in response to the surrounding vertical shear.
(C is the strength of the cold pool; u is the strength of surrounding vertical shear. Circular arrows show the most significant horizontal vorticity.)
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Evolution of a Convective System: Stage 2
The circulation generated by the storm-induced cold pool balances the surrounding shear, and the system becomes upright.
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Evolution of a Convective System: Stage 3
The cold pool dominates the surrounding shear and the system tilts upshear, producing a rear-inflow jet. (The rear-inflow jet is indicated by the thick, black arrow.)
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Thank you.