Transcript
Dry Line
Initiation Video URL: http://www.nssl.noaa.gov/users/ziegler/public_html/initiation.html
Dry Lines
or
Dry Lines• Associated with large horizontal gradients in
moisture, but not necessarily temperature.
• Results from the interaction of cyclones and fronts with large-scale terrain.
• Found over the U.S. Midwest, northern India, China, central West Africa and other locations.
• Acts as a focus for convection, and particularly severe convection.
• Most prevalent during spring/early summer in U.S.
Dry Line• Surface boundary between warm, moist air
and hot, dry air.Surface dry line
Inversion or cap
Well-mixed warm air
Typical Dryline
Temperatures indegrees Celsius
©1993 Oxford University Press -- From: Bluestein, Synoptic-Dynamic
Meteorology in Midlatitudes, Volume II
Southern Plains Dry
Line
Temperatures indegrees Celsius
©1993 Oxford University
Press -- From: Bluestein, Synoptic-Dynamic
Meteorology in Midlatitudes,
Volume II
Dry Line
Trajectories
• Fundamentally the dry line represents a trajectory discontinuity between moist southerly flow and flow descending from higher elevations.
• Can only happen relatively close to the upstream barrier (no more than 1000 km) since otherwise air would swing southward behind the low system and thus would be cool and somewhat moist.
L
DRY LINE
Warm, Moist
L
NODRY LINE—Get ColdFront
Dry Line: Tends to Move Eastward During the Day and Westward At
Night• After sunrise, the sun will warm the surface
which will warm the air near the ground.• This air will mix with the air above the
ground.• Since the air above the moist layer is dry, the
mixed air will dry out.• The dry line boundary will progress toward
the deeper moisture.
Dry Line
Warm, Moist Air
Hot, Dry Air—Usually Well MixedTop of moist layer
before mixing
Boundary after mixing
Initial Positionof the Dry Line
Position of theDry Line after
mixing
Dry Line• After sunset, a nocturnal inversion forms and the
winds in the moist air respond to surface pressure features.
• The dry line may progress back toward the west .
West East
Note weak inversion or “cap” over low-level moist layer east of the surface dry line
Sounding West of the
Dryline
NCAR
Very Dry
West Winds
Albuquerque, NM12Z -- 26 June 1998
Sounding East of the
Dryline
NCAR
Moist
South Winds
Oklahoma City, OK12Z -- 26 June 1998
Aircraft Study of the Dry Line
Convection Tends to Focus On the Dryline
Storm Initiation Along a Dry Line
Simulation of a Thunderstorm Initiation Along Dryline in TX Panhandle
Storm
Note converging winds and risingmotion
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