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Class #23: Friday October 23
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Transcript of Class #23: Friday October 23
Class #23: Friday October 23
The Extratropical or Midlatitude Cyclone
1Class #23: October 23
The story of an extratropical cyclone
• Day 1, Sat., Nov. 8,1975: Low (Panhandle Hook) forms just NE of Amarillo
• Day 2, Sun., Nov. 9: Ship sails at 2 p.m.; Storm has matured to young adult stage
• Day 3, Mon., Nov. 10: The storm is occluding. Ship sinks at 7:20 p.m.
• Day 4, Tues., Nov. 11: The storm is dying • Subtract 7 from date to get Day #
Class #23: October 23 2
Sank on Day 4
Class #23: October 23 3Fig. 10-1, p. 276
Ore freighter Edmund Fitzgerald
Class #23: October 23 4Fig. 10-2, p. 277
North is at lower right. Ship sank near Whitefish Point
Class #23: October 23 5Fig. 10-4, p. 278
Day 1 and Day 2
Class #23: October 23 6Table 10-1a, p. 279
Table 10-1b, p. 2797Class #23: October 23
Day 1 weather maps: Low forms NE of Amarillo, TX
Class #23: October 23 8Fig. 10-5, p. 280
Birth to NW of Amarillo
Class #23: October 23 9Fig. 10-5a, p. 280
Strong westerlies upstream
Class #23: October 23 10Fig. 10-5b, p. 280
Low humidity, clear skies
Class #23: October 23 11Fig. 10-5c, p. 280
Typical cyclone paths
• Depend on topography• Depend on position of the polar front• Depend on upper level winds:– Extratropical cyclones move approximately with
the 500mb wind at about half the speed
Class #23: October 23 12Fig. 10-6, p. 281
Fig. 10-6a, p. 28113Class #23: October 23
Fig. 10-6b, p. 28114Class #23: October 23
Fig. 10-6c, p. 28115Class #23: October 23
Shows Panhandle hook path
Class #23: October 23 16Fig. 10-6d, p. 281
Ingredients for a cyclone
• Cyclone growth is called cyclogenesis• Cyclogenesis requires 3 ingredients:– Surface temperature gradients: a front– A strong jet stream: helps the low grow and the
fronts intensify– Mountains or other surface boundaries (for example,
a coastline along a warm ocean current• Cyclones get their energy in a process called
baroclinic instability—related to horizontal temperature gradients and vertical wind shear
Class #23: October 23 17
Cyclonic spin (or vorticity) is important for cyclogenesis.
Class #23: October 23 18Box 10-1, p. 282
Cyclonic spin is generated by flow over mountains
Class #23: October 23 19Box 10-1, p. 283
Day 2: Young adult stage
Class #23: October 23 20Fig. 10-7, p. 285
Note fronts, Low, and path. Ship sets sail at 2 p.m.
Class #23: October 23 21Fig. 10-7a, p. 285
Note upper-level short-wave trough to west of surface Low
Class #23: October 23 22Fig. 10-7b, p. 285
Back to the story
• The cyclone moves very rapidly, steered by the upper-level winds at 500mb.
• On Day 2 (Nov. 9) gale warnings were issued in the mid-afternoon for the next day (Monday, Day 3, Nov. 10)
• Gale warnings are for winds up to 38 knots (44 mph), not typical, not too unusual
• Ships take the northern, longer route
Class #23: October 23 23
Satellite picture from 10:12 a.m.Note the comma shape of cloud
Class #23: October 23 24Fig. 10-7c, p. 285
A close-up of last slide
Class #23: October 23 25Fig. 10-8, p. 286
Fig. 10-9, p. 28726Class #23: October 23
Fig. 10-10, p. 28827Class #23: October 23
Fig. 10-10a, p. 28828Class #23: October 23
Fig. 10-10b, p. 28829Class #23: October 23
Fig. 10-10c, p. 28830Class #23: October 23
Fig. 10-11, p. 28931Class #23: October 23
Fig. 10-12, p. 29032Class #23: October 23
Fig. 10-13, p. 29133Class #23: October 23
Fig. 10-14, p. 29234Class #23: October 23
Fig. 10-14a, p. 29235Class #23: October 23
Fig. 10-14b, p. 29236Class #23: October 23
Fig. 10-14c, p. 29237Class #23: October 23
Box 10-2, p. 29338Class #23: October 23
Box 10-2, p. 29339Class #23: October 23
Fig. 10-15, p. 29440Class #23: October 23
Fig. 10-16, p. 29541Class #23: October 23
Fig. 10-17, p. 29542Class #23: October 23
Box 10-3, p. 29743Class #23: October 23
Box 10-3, p. 29744Class #23: October 23
Box 10-3, p. 29845Class #23: October 23
Box 10-3, p. 29846Class #23: October 23
Box 10-3, p. 29947Class #23: October 23
Box 10-3, p. 29948Class #23: October 23
Fig. 10-18, p. 30149Class #23: October 23
Fig. 10-18a, p. 30150Class #23: October 23
Fig. 10-18b, p. 30151Class #23: October 23
Fig. 10-18c, p. 30152Class #23: October 23