Horizontal Pressure Differences
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Pressure
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Higher along horizontal
red line in warm air
than in cold air
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Pressure difference is a
non-zero force
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Pressure Gradient Force
or PGF (red arrow)
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Air accelerates from
column 2 towards 1
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Pressure falls at bottom
of column 2, rises at 1
1000 mb
H
L
Ahrens, Fig. 6.2
PGF