©1996, west publishing company (modified by asper, 1997; revised by lohrenz, 2000) slide 1 lesson...

©1996, West Publishing Company (Modified by Asper, 1997; revised by Lohrenz, ©1996, West Publishing Company (Modified by Asper, 1997; revised by Lohrenz, 2000)2000)

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Lesson #10Hurricanes!

Vernon Asper

USM


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Hurricanes!

• We’ve covered this before but we’re going to review it again with more detail:– Low presure areas

– Coriolis deflection

– Tropical weather

– The ocean’s connection

– Hurricane impacts

– The future?


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• Low pressure areas are “low” because the air in them has low density– Warm

– Humid (water vapor content)

• This causes the air to rise• This draws air to the center• Coriolis causes rotation

Accentnetwork.orgAccentnetwork.org

http://www.air.ky.govhttp://www.air.ky.gov


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Lows continue to spin until the low pressure has been equalizedLows continue to spin until the low pressure has been equalized(http://www.hi.is/~oi/satellite_photos.htm)(http://www.hi.is/~oi/satellite_photos.htm)


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• On a weather map, low pressure areas show up as the center of “isobars” where pressure is low in the middle

• “warm,”

rainy

conditions

usually

accompany

lows

L=992L=992

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• This all applies to the tropics (near the Equator)• But here, things are more complicated• Solar heating results in super low pressure• WARM• HUMID

• Rising air• Clouds

form• General

westward motion

http://www.uvi.edu/http://www.uvi.edu/


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• As the air mass moves to the west, the flow “flutters”– Like a flag in the

breeze

• The flutters turn to “waves

http://upload.wikimedia.orghttp://upload.wikimedia.org

http://www.ccrc.sr.unh.eduhttp://www.ccrc.sr.unh.edu


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• Waves can intensify• Stronger waves

become “depressions”• The “depressed” part

is because of the low pressure

• This causes wind to increase

• By definition, depressions have winds from 28-33 knots

http://www.wunderground.comhttp://www.wunderground.com


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• What causes the storm to intensify?– Water vapor: the storm MUST be over the ocean!

– Lack of shear

• The longer it is over warm water, the stronger it gets

• Cold water or moving over land will kill it


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“Latent Heat” (a review)• Latent heat of evaporation is

the heat (energy) absorbed by water when it evaporates– Sweating cools you because of

this

• When the water condenses somewhere else, it gives off this heat– Condensation on a window

pane

• Water vapor forming clouds warms the air at that altitude– This feeds the storm


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• Moist air rises, cools• Moisture condenses; warms the air• Warmed air rises more, etc.• Absolutely depends on moisture (latent heat of

evaporation / condensation)


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Areas of Tropical Cyclone Formation


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Storm Effects• Storms have more effect

on shaping the shoreline than “normal” conditions

• Storm surges are extreme high water events

• Caused by high winds that pile water up along the shoreline.

•


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Hurricane Andrew


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Slide Slide 1919


Slide Slide 2020

Isaac

Katrina


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Isaac: 8/29/12


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• Here are before and Here are before and after picturesafter pictures

• Hurricane Georges Hurricane Georges (October 1998) (October 1998) removed most of this removed most of this island.island.

2002: recovery has started


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Project Stormfury 1962-1983

• Can hurricanes be artificially dissipated?

• YES!!! (well, maybe)• These guys seeded several

storms with silver iodide• Idea was to create ice that

would kill the storm• It appeared to work but

the storms re-intensified when seeding stopped

• One appeared to change course!

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com

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com


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• This project and others were all cancelled– They had no “controlled experiment” to prove that

they were effective

– Computer models indicated that they had had no effect

– Funding was pulled

• Several movies have been made of this:– “Maximum Velocity”

– “Storm Tracker”


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Climate Change?• Possible impacts of Global

Warming:• 1) warmer oceans

– More energy in the oceans means

more frequent and more powerful

storms

• 2) higher sea levels– The closer a community is to

the beach, the more vulnerable

it is to hurricanes

• This is the logic,

but what is the reality?

Christmas Island


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• The total number of hurricanes “may” be increasing

• But the trend isn’t clear• Normal cyclicity?

Hurricane strength measurements, west of 69WHurricane strength measurements, west of 69Whttp://www.climateaudit.org/?p=1000http://www.climateaudit.org/?p=1000


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• More people live near the coast

• We continue to invest in vulnerable areas

• US Gov’t encourages and subsidizes it!

http://maps.csc.noaa.gov/hurricanes/pop.jsphttp://maps.csc.noaa.gov/hurricanes/pop.jsp


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• "Based on a range of models, it is likely that future tropical cyclones (typhoons and hurricanes) will become more intense, with larger peak wind speeds and more heavy precipitation associated with ongoing increases of tropical SSTs. There is less confidence in projections of a global decrease in numbers of tropical cyclones. The apparent increase in the proportion of very intense storms since 1970 in some regions is much larger than simulated by current models for that period." – http://www.usgcrp.gov (US Global Change Research

Program


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This year’s forecast:

• “ We continue to foresee well above-average activity for the 2012 Atlantic hurricane season. “

• PROBABILITIES FOR AT LEAST ONE MAJOR (CATEGORY 3-4-5) HURRICANE LANDFALL ON EACH OF THE FOLLOWING COASTAL AREAS:

• 1) Entire U.S. coastline - 72% (average for last century is 52%)

• 2) U.S. East Coast Including Peninsula Florida - 48% (average for last century is 31%)

• 3) Gulf Coast from the Florida Panhandle westward to Brownsville - 47% (average for last century is 30%)


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Summary

• Hurricanes are born in the ocean due to the low pressure at the Equator

• They are intensified by the addition of heat energy through the condensation of water vapor

• Most predictions for warmer climate expect stronger and possibly more abundant storms in the future

• Impacts of the storms will be greater as more people live on the coast and as sea level rises

©1996, west publishing company (modified by asper, 1997; revised by lohrenz, 2000) slide 1 lesson...

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