ageostrophic flow and jet streak dynamics

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ageostrophic flow and jet streak dynamics

• sources
• Holton, p. 172-174
• Koch, http//legacy.ncsu.edu/classes/mea444-sekoc
  h/
• Uccellini, Louis W., Paul J. Kocin, 1987 The
  Interaction of Jet Streak Circulations during
  Heavy Snow Events along the East Coast of the
  United States. Weather and Forecasting Vol. 2,
  No. 4, pp. 289309.

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Review ageostrophic flows around a jet streak
(slides from S. Koch)
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partitioning ageostrophic flow in its isallobaric
and advective components
(QG momentum eqns b term is ignored)
isallobaric advective term
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ageostrophic flow interpretation
isallobaric term
advective term
The ageostrophic flow has two terms - a
transient component (isallobaric) - a
steady-state component (due to curved jet flow
and jet streak flow)
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isallobaric and advective terms in a eastward-
moving baroclinic wave (Holton Fig 6.15)
300 mb
850 mb
weaker wind, isallobaric part dominates
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advective term, more generally
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CV
PVA
NVA
PVA
NVA
AV
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interpretation

• Equation of motion argument (du/dtfva)
• QG argument
• Energy conservation argument (parcel trajectory)

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kjcj
Curved jet streaks
Alternative method Holton, section 3.2 use
natural coordinates to obtain gradient wind Vgr,
define VaVgr-Vg
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(jet streaks in troughs are rather rare!)
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CAA
Low-level Thermal advection
WAA
Iso-thickness lines are distorted due to LL
thermal advection
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Application 1 2 Nov 1996 (rather straight jet)
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Application 2 8 Nov 1996 (highly curved jet)
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con
jet axis
jet axis
div
jet streak deceleration
div
con
jet streak acceleration
div
con
sub-geostrophic
con
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21 hrs later
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