II Synoptic Atmospheric Destabilization Processes Upper Level Mixed
II. Synoptic Atmospheric Destabilization Processes • • Upper Level Mixed Layer Synoptic Lifting Dynamic Destabilization Differential Advection
Static Stability and Instability • Static Stability: push an air parcel upward (downward) and it will fall (rise) back to its original position transforming the work exerted to accelerate the parcel into the kinetic energy of the parcel’s return movement. • Static Neutrality: push an air parcel upward (downward) and it will continue its motion without further acceleration. • Static Instability: push an air parcel upward (downward) and it will continue to accelerate its motion upward (downward)
Destabilization • Increase Environmental Lapse Rate at middle levels – Mix air vertically – Warm below • Advection • Diabatic – Cool above • Advection • Diabatic – Lifting of a layer increases lapse rate and vise versa • Increase low level moisture and temperature – Daytime heating – Warm moist advection, Sawyer-Elliasen surge • Maintain inversion (cap) separating low level moisture and heat from increased upper level lapse rate
Layer Lifting
Differential Advection • Layer aloft moving at a different velocity than one below • Cold air advection Aloft • Warm or moist air advection below
Differential Advection Caused by Topography
Elevated Mixed Layer • Deep dry mixing of a dry daytime boundary layer produces high lapse rate through deep layer – Deep dry adiabatic layer (steep lapse rate) – Very dry layer, nearly constant vapor mixing ratio – Some of the most intense EMLs formed from regions of very dry near surface air (too make dry lapse rate) found in: • Deserts • High plateau or lee side of a mountain range
Orographically Generated EML • Deep, warm, dry well mixed layer advected over the top of a relatively cool (potential temperature-wise) layer forming a capping inversion • Boundary layer below inversion moistened and warmed creating conditional instability: – Daily heating and evapo-transpiration – Advection from a moist region
EML Moving From Rockies
Sahara Generated EML • Deep, warm, dry well mixed layer of Sahara advected over the top of a relatively cool (potential temperature-wise) marine boundary layer over Mediterranean • Boundary layer below inversion moistened and warmed creating conditional instability: – Air-Sea Interaction
EML Moving over Mediterranean from Sahara
Dynamic Destabilization • Ageostrophic circulation in the right exit region of the jet streak forces subsidence and a capping subsidence inversion • Sawyer-Elliasen Circulation advects warm air under dry destabilized layer completing the formation of “loaded gun” sounding • Progression into the right entrance region initiates rising motion that “pulls trigger”
Load the Gun
Pull the Trigger!
High Elevation Sounding
Loaded Gun Sounding
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