Strong Cold Front Hits the BAO Tower

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Strong Cold Front Hits the BAO Tower
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7C in 3 hr criterion
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Fig. 3. Frontal passages on (a) 46 and (b) 810
Mar 2003 from the 1-min data at the Automated
Surface Observing System (ASOS) at OKC (UTC CST
6 h)
temperature decrease of 10C in 2 min
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Using Simple First Order Relationships to Explain
Tilt of Occluded Fronts
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Classic Idea Occlusion Type Determined By
Temperature Contrast Behind Cold Front and in
Front of Warm Front (the temperature rule)
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But reality is very different
From Stoelinga et al 2002, BAMS
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Literature Review

• Schultz and Mass (1993) examined all published
  cross sections of occluded fronts. Found no
  relationship between the relative temperatures on
  either side of the occluded front and the
  resulting structure. Of 25 cross sections, only
  three were cold-type occlusions.
• Of these three, one was a schematic without any
  actual data, one had a weak warm front, and one
  could be reanalyzed as a warm-type occlusion
• Cold-type occlusions appear rare.

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But what controls the slope?

• Virtually all fronts are first-order fronts
  (which the horizontal temperature gradient
  changes discontinuously with frontal passage)
  rather than zero-order fronts (where temperature
  varies discontinuously across the front)
• Historical note in the original Norwegian
  Cyclone Model they suggested all fronts were
  zero-order fronts.

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Basic Relationship
The relative value of the vertical potential
temperature derivative will determine the slope
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• Occluded frontal surfaces generally mark a
  maximum in potential temperature on a horizontal
  surface, so the numerator on the right side of
  (2) is always positive.
• Therefore, the sign of the slope of the occluded
  front is determined only by the denominator on
  the right-hand side of (2), that is, only by the
  static stability contrast across the front, and
  not by the contrast in horizontal potential
  temperature gradient.

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An Improved View The Static Stability Rule of
Occluded Front Slope

• An occluded front slopes over the statically more
  stable air, not the colder air.
• A cold occlusion results when the statically more
  stable air is behind the cold front.
• When the statically more stable air lies ahead
  of the warm front, a warm occlusion is formed.
• The is pretty much always the case.

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An Example
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Another Example