Chapter 11: Hurricanes
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Transcript of Chapter 11: Hurricanes
Chapter 11: Chapter 11: HurricanesHurricanes
Tropical weatherTropical weather Anatomy of a hurricaneAnatomy of a hurricane Hurricane formation and dissipationHurricane formation and dissipation Some notable hurricanesSome notable hurricanes Hurricane watches, warnings and Hurricane watches, warnings and
forecastsforecasts Modifying hurricanesModifying hurricanes
Tropical WeatherTropical Weather
Tropics: Tropics: 23.5N-23.5S23.5N-23.5S
streamlinesstreamlines tropical wavetropical wave easterly wave,easterly wave,
2500km wavelength,2500km wavelength,
10-20 knots speed10-20 knots speed
• The tropics are close to the equator, where theThe tropics are close to the equator, where theCoriolis force is too small to balance the pressureCoriolis force is too small to balance the pressuregradient force. Thus winds are not geostrophic.gradient force. Thus winds are not geostrophic.
Anatomy of a HurricaneAnatomy of a Hurricane
hurricane (typhoon, cyclone): hurricane (typhoon, cyclone): > 64 knots> 64 knots
eye; eyewalleye; eyewall spiral rainbandspiral rainband
• Hurricanes are Hurricanes are quite similar quite similar to, yet also to, yet also quite different quite different fromfrommid-latitude mid-latitude storms.storms.
Fig. 11-3, p. 302
Sinking air and clear sky in the eye due to high pressure aloft
Hurricane Hurricane Formation and Formation and
DissipationDissipationHurricane forms over tropical waters where winds are light, humidity is high in a deep layer, and surface temperature is warm, typically 26.5C (80F) or greater,over a vast area
SST > 28C
Over Atlantic
The Right EnvironmentThe Right Environment
Convergence triggerConvergence trigger
ITCZ, easterly waves, midlatitude fronts to ITCZ, easterly waves, midlatitude fronts to
tropicstropics Weak trade wind inversionWeak trade wind inversion Weak upper windWeak upper wind
during El Nino over Atlanticduring El Nino over Atlantic Some Coriolis force: Some Coriolis force: 5-20deg latitude5-20deg latitude
The Developing StormThe Developing Storm
Heat engine: heat taken at high T, converted into work, then ejected at Heat engine: heat taken at high T, converted into work, then ejected at low T.low T.
Hurricane: heat taken from warm ocean, converted into kinetic energy Hurricane: heat taken from warm ocean, converted into kinetic energy (wind), lost at its top through radiational cooling (wind), lost at its top through radiational cooling
Maximum wind depends on surface and tropopause temperature Maximum wind depends on surface and tropopause temperature difference and the potential of sea surface evaporationdifference and the potential of sea surface evaporation
The Storm Dies OutThe Storm Dies Out
cutting off the cutting off the storm’s energy storm’s energy supply by moving supply by moving over cooler oceanover cooler ocean
Landfall: lose Landfall: lose energy sourse and energy sourse and increased friction increased friction to reduce windto reduce wind
Hurricane Stages of Hurricane Stages of DevelopmentDevelopment
tropical disturbance: tropical disturbance: unorganized mass of unorganized mass of thunderstorms, weak windthunderstorms, weak wind
tropical depression: tropical depression: 20-34 knots, closed 20-34 knots, closed isobarsisobars
tropical storm: tropical storm: 35-64 knots, with a name35-64 knots, with a name
hurricane: hurricane: > 64 knots, with a name> 64 knots, with a name• This progression of stages is This progression of stages is followed in reverse order as a followed in reverse order as a storm weakens.storm weakens.
Hurricane vs midlattitude Hurricane vs midlattitude stormsstorms
Hurricane: 1) derive energy from warm ocean Hurricane: 1) derive energy from warm ocean and latent heat of condensation; 2) warm core and latent heat of condensation; 2) warm core low; 3) high center aloft; 4) sinking air in the eye; low; 3) high center aloft; 4) sinking air in the eye; 5) strongest wind near surface; 6) stronger wind; 5) strongest wind near surface; 6) stronger wind; 7) smaller size7) smaller size
Midlatitude storms: 1) derive energy from Midlatitude storms: 1) derive energy from horizontal temperature difference; 2) cold core horizontal temperature difference; 2) cold core low; 3) intensifies with height; 4) rising air at low; 3) intensifies with height; 4) rising air at center; 5) strongest wind aloft in the jet stream; center; 5) strongest wind aloft in the jet stream; 6) wind not as strong; 7) larger size6) wind not as strong; 7) larger size
Both are low pressure systems with Both are low pressure systems with counterclockwise motionscounterclockwise motions
Hurricane MovementHurricane Movement
role of the ITCZrole of the ITCZ northward northward
movement due to movement due to subtropical highssubtropical highs
influence of the influence of the westerlieswesterlies
• Because of the Bermuda High, westward-Because of the Bermuda High, westward-movingmovingNorth Atlantic hurricanes often take a North Atlantic hurricanes often take a turn towards the north as they turn towards the north as they approach North America.approach North America.
Fig. 11-10, p. 307
Lack of hurricanes adjacent to South America: cooler water vertical wind shear, unfavorable ITCZ position
Naming Hurricanes and Naming Hurricanes and Tropical StormsTropical Storms
past practices: past practices: female namesfemale names
current protocol: current protocol: female and male names; female and male names; in alphabetic order so that the first hurricane in alphabetic order so that the first hurricane starts with the letter A; then in Greek alphabetstarts with the letter A; then in Greek alphabet
•Letters Q, U, X, Y not used over north Atlantic
•Letters Q, U not used over north Pacific
•Whenever a hurricane has had a major impact, any country affected by the storm can request that the name of the hurricane be retired by the World Meteorological Organization.
Devastating Winds and Devastating Winds and the Storm Surgethe Storm Surge
location of strongest windslocation of strongest winds Ekman transport Ekman transport 10-15 m high waves10-15 m high waves High ocean High ocean due to low due to low
pressurepressure storm surge: storm surge: several several
meter rise of sea levelmeter rise of sea level Flooding: Flooding: due to heavy due to heavy
rain and storm surge; causerain and storm surge; cause
most human casualtiesmost human casualties
Table 11-2, p. 313
Table 11-3, p. 316
Figure 4, p. 319
Katrina, 2005: $75B damage; >1200 deaths;
High winds, large waves, andlarge storm surge caused disastrous breeches in the leveesystem
Hurricane Watches, Hurricane Watches, Warnings and ForecastsWarnings and Forecasts
Hurricane watch:Hurricane watch:
24-48 hr before landing24-48 hr before landing hurricane warning:hurricane warning:
storm will strike an areastorm will strike an area Forecasts:Forecasts: improvement in path;improvement in path;
not in strengthnot in strength
Wrong forecastsWrong forecasts
also cause Economic lossalso cause Economic loss
Modifying HurricanesModifying Hurricanes
cloud seeding to reduce maximum cloud seeding to reduce maximum windwind
monomolecular filmsmonomolecular films