Transcript Powerpoint

The Great Plains Dryline
Type 1 - Diurnally-Forced Dryline
Type 2 - Dynamically-Forced Dryline
Type 1 - Diurnally Forced Dryline
Air on upwind (upslope) side of dry line is represented
by a deep mixed layer
Air west of the dryline has broken the inversion and so upper level
dry and warm air from the EML has mixed down
The inversion breaks on its western extremity first because the
inversion is closest to the surface there
As the daytime surface mixed layer deepens to the inversion
throughout the day, the inversion break (dryline position) works its
way eastward
West of the dryline, mixing of the deep EML with the shallow moist
layer produces :
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Gusty westerly surface winds
Very low humidities
Warm temperatures
Type 1 - Diurnally Forced Dryline (Cont'd.)
Air east (downslope) of the dryline is relatively
moist and cool, although there tends to be only a
small virtual temperature contrast across the
dryline
Shallow moist boundary layer
Source of moisture includes
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Evapotranspiration
Advection from east (Gulf)
Moist boundary layer reaches depth of the inversion
at the point of the dryline
Type 1 - Daily Evolution
Late morning and afternoon:
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Boundary layer grows below nocturnal inversion
dryline eats its way eastward
Evening:
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Nocturnal inversion forms
Moisture trapped under inversion
Early morning
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Plants become active and transpire raising moisture under
inversion
Slope flow commences enhancing inversion
Type 2 - Dynamically Forced Dryline
Response to mountain wave drag on the
tropospheric jet stream
Integrates mesoscale downslope flow surges of
momentum and dry air into a coherant streamwise
front
Results in meso-beta and meso-gamma scale
gravity wave-induced bulges of dry air, momentum
and nonconserved isentropic potential vorticity
Severe convection focused in meso-gamma scale
gravity wave-induced bulge locations