CH10b: tornadoes and microbursts

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CH10b tornadoes and microbursts
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Fig. 10-38, p. 291
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Fig. 10-27, p. 284
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• Tornado
• 1- a turbulent to convective scale vortex, 100 to
  1000 m in diameter
• 2- life time 2- 20 min, far less than parent Cb
• 3- wind speeds have reached over 300 mph
• 4- pressure gradient must be extreme
• 5- can spin cyclonically or anticyclonically,
  Coriolis
• is not important
• 6- a tornado is declared when the circulation
• reaches the ground

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Fig. 10-42, p. 294
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Fig. 10-32, p. 288
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Figure 3, p. 295
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Fig. 10-39, p. 292
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Table 10-2, p. 288
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Stepped Art
Fig. 10-37, p. 291
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Fig. 10-31, p. 287
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Fig. 10-28, p. 285
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Fig. 10-29, p. 285
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Table 10-1, p. 287
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• What is the critical ingredient that
• differentiates a supercell from a ordinary
• cell? A robust rotating updraft
• How is this achieved? Key mechanism is the
• tilting of a vortex tube, caused by the vertical
• shear of the horizontal wind being lifted by
• an updraft

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Stepped Art
Fig. 10-34, p. 289
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Fig. 10-5, p. 268
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Fig. 10-33, p. 289
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• Microburst a downdraft with a diameter of a
• few km that produces very strong outflows
• Why should you care?
• BOAC 252 at Kano Nigeria, 1956 32 dead
• Eastern 66 at JFK, 1975 112 d.
• Continental 426 at Denver,1975 15 injured
• Pan Am 759 at New Orleans, 1982 152 d.
• Pan Am 806 at Pago-Pago, 1974 86 d.
• Jack Bonham Scholarship for top UH athlete

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Fig. 10-14, p. 273
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Fig. 10-15, p. 273
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• Summary, CH10b
• tornadoes
• 1- last for a few minutes and usually are 100
• m in diameter
• 2- supercells produce the strongest
• 3- can exceed 300 mph
• 4- motion and suction vortices may cause highly
  unusual damage patterns

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• Microburst
• 1- a downdraft that causes strong divergence
  (wind flow in opposite directions)
• 2- often comes from benign looking clouds
• that evaporate rain into very dry air
• 3- major threat to aircraft at landing and
• take-off

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Fig. 10-13, p. 272
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Fig. 10-16, p. 273
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Fig. 10-8, p. 270
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Fig. 10-30, p. 286
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Overshooting top
Anvil
Mammatus
Wind
Mesocyclone
Rear flank downdraft
Rainfree base
Inflow
Inflow
Wall cloud
Light rain
Hail
Tornado
Heavy rain
Editable Text
Fig. 10-35, p. 290