Earth Sciences 240A - Lecture 31- The Big Storms: “Tropical Storms”

Cold Front Involvement

Cold front across tropical region

‘Bulge’ development

Spiral upward

Adiabatic expansion; latent heat supply at dew point

Occlusion of spiral system

Tropical storm birth

Origin of Hurricanes

‘Wind Disturbance’ close to equator; Minimum 26^oC ocean water T

Tropical wave

Characterized by masses of thunderstorms

Tropical Storm; Named

Further development depends upon amount of latent heat energy release

Hurricane Structure

Rain bands surrounding eye

‘Storm-center velocity’

Forward motion

Slowest in tropical regions

Right/Left side wind differences

Hurricane/Ocean Surface

Sea swells: Smooth, long period waves; May be 6-12 hrs ahead of eye

Surge: Associated with low pressure of eye; Responsible for most deaths

Saffir-Simpson Hurricane Scale

Based on: Wind velocity, Air pressure at surface, Potential surge

Category 2 ~= 4x Category 1

Category 3 ~= 40x Category 1

Category 4 ~= 120x Category 1

Category 5 ~= 240x Category 1

Andrew, 1992

Category 4

Florida landfall south of Miami

$25 billion damage; 50 deaths

‘Spin-up votices’

Iniki, 1992

Crossed Central America into Pacific

Over Kauai as Category 4

Prediction

No known measurable conditions that always work!

Factor?

Rainfall in Africa

Evapotranspiration in Western Africa

Adds moisture to already warn air

Enhanced activity in Atlantic

Rely on satellite photos

Huge problem: public awareness

Global warming

Ocean water warming

= more water evaporation

= more latent heat release

= more hurricanes

(? = more violent hurricanes)

Project Stormfury

USA effort to ‘seed’ hurricanes

Aim: to increase dimensions/decrease wind velocities

Technique: Silver iodide or dry ice to initiate growth of ice from super-cooled water (latent heat absorbed)

Experiments:

Esther, 1961 (disaster)

Beulah, 1963 (mild success?)

Debbie, 1969 (good success)

Ginger, 1971 (no change)

Abandoned; insufficient super-cooled water

Hurricane frequency - Atlantic

Achives: http://www.nhc.noaa.gov/pastall/shtml

Ass’n with Mass Extinction??

‘Hypercanes”

Periodically predicted to result from global warming

Seawater at 50oC

Pressures of 200 millibars

Wind speeds 1080 km/h

Next

Climate I

Glossary

HURRICANE: - A warm core tropical cyclone in which the maximum sustained winds are at least 74 mph. Applies to the Atlantic Basin and the Pacific east of the International Date Line.

HURRICANE EYE: - A region in the center of the hurricane where winds are relatively light and skies are clear to partly cloudy.

STORM SURGE: - The dome of water that builds up as a hurricane moves over water.

TROPICAL CYCLONE: - A large scale non-frontal, warm core, low pressure system of tropical origin that forms over tropical waters or subtropical waters and possesses a definite and organized circulation.

TROPICAL DEPRESSION: - A tropical cyclone in which the maximum sustained winds are 38 mph or less.

TROPICAL DISTURBANCE: - An area of thunderstorms, (a discrete system of apparently organized convection), originating in the tropic or subtropics. A tropical disturbance has a non frontal, migratory character and maintains their identity for at least 24 hours.

TROPICAL STORM: - A warm core tropical cyclone in which the maximum sustained winds speeds are from 39 to 73 mph.

TYPHOON: - A hurricane in the north Pacific west of the International Date Line.