On the movement of trofs and ridges

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On the movement of trofs and ridges

• Rossby waves result from the conservation of
  vorticity. The restoring force is b or, more
  generally, the meridional gradient of the
  absolute vorticity. The resulting circulation
  causes the wave to propagate westward.
• In short waves, the advection of relative
  vorticity dominates. The wave propagation speed
  is slow and they move with the prevailing
  westerly flow.
• In long waves, the advection of planetary
  vorticity dominates. Their speed is large and
  they are generally stationary, or may retrograde

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On the movement of trofs and ridges

• Trofs may be cut-off from the westerly flow and
  they become stationary at lower latitudes. They
  may dissipate or they may be kicked back into
  the main current
• The kicker trof needs to approach the cut-off to
  within 2000 km (Henrys rule)
• (see Bluestein p. 69)

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On the movement of trofs and ridges

• If the max cyclonic shear is on the upstream side
  of the trof, the trof will tend to move
  equatorward, and may deepen
• If the max cyclonic shear is on the downstream
  side of the trof, the trof will tend to move
  poleward
• (see Bluestein p. 74)

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The movement of trofs and ridges (500 mb)
1989
Hovmöller diagram
Long-dash short-wave trofs (1 2) -
slow Short-dash group waves (3 4) -
fast Solid stationary long-wave ridge
1990
Contour int 60 m (dash negative)
average
5
blocking

• Most frequently in spring around 50N
• Anomalous long-wave ridge blocks progression of
  short waves
• Occurs during low-index cycles (zonal flow
  weak, meridional flow strong) high index strong
  zonal flow
• 3 types, qualitatively separated
• High-over-low block
• Omega block
• UL ridge
• See Bluestein p. 79-81

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