The Flux Model of Orographic Rain

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The Flux Model of Orographic Rain

• Orographic Influences on Rainfall and Track
  Deflection Associated with the Passage of a
  Tropical Cyclone.
• Lin et al. 2002, Mon. Wea. Rev., 130, 2929-2950.

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Percipitation

• E the precipitation efficiency
• Ls the horizontal scale of the convective system
• Cs the propagation speed of the convective
  system

the three-dimensional
orographic moisture flux the general
vertical moisture flux
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Orographic Vertical Moisture Flux
General Vertical Moisture Flux
3-h rainfall
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Orographic Vertical Moisture Flux
General Vertical Moisture Flux
3-h rainfall
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Orographic Vertical Moisture Flux
General Vertical Moisture Flux
3-h rainfall
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Orographic Vertical Moisture Flux
General Vertical Moisture Flux
3-h rainfall
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Discussion

• The flux model, along with coarser horizontal
  resolution model-simulated wind and moisture
  fields, may be used to help predict the
  distribution of heavy orographic rainfall
  associated with landfalling typhoons interacting
  with mesoscale mountains.
• The rainfall that occurred over the mountains was
  strongly controlled by the orographic forcing,
  rather than by the original rainbands associated
  with the typhoon.

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Domain 3 (6.67km) 7/29-12
Orographic Vertical Moisture Flux
General Vertical Moisture Flux
6-h rainfall
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Domain 3 (6.67km) 7/29-18
Orographic Vertical Moisture Flux
General Vertical Moisture Flux
6-h rainfall
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Domain 3 (6.67km) 7/30-00
Orographic Vertical Moisture Flux
General Vertical Moisture Flux
6-h rainfall
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Domain 4 (2.22km) 7/29-12
Orographic Vertical Moisture Flux
General Vertical Moisture Flux
6-h rainfall
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Domain 4 (2.22km) 7/29-18
Orographic Vertical Moisture Flux
General Vertical Moisture Flux
6-h rainfall
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Domain 4 (2.22km) 7/30-00
Orographic Vertical Moisture Flux
General Vertical Moisture Flux
6-h rainfall
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Supertyphoon Bilis (2000)
SFC
700

• NOGAPS-analyzed surface chart at 8/22/00UTC.
• It produced maximum winds of 75 m/s and heavy
  rainfall (949 mm in 20h in northeast Taiwan).

500
300
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• Model COAMPS (Coupled Ocean-Atmosphere Mesoscale
  Prediction System)
• horizontal grid size 45- 15- and 5-km
• 30 vertical layers
• 1-km terrain databases

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• Cold start is initialized from the 1.0oX1.0o
  NOGAPS global model dataset.
• Warm start is restarted from a previous COAMPS
  simulation using NOGAPS boundary conditions.

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Experiments Design

• Control experiments (CON)
• CON-45, CON-15, CON-5
• No-terrain experiments (NT)
• NT-45, NT-15, NT-5
• All experiments started without implementing a
  bogus vortex.

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