Lecture 17

Question 1

What is a hurricane?

Answer 1

Tropical cyclone with sustained winds >119km/h
Convert hot water and heat of tropical ocean to winds
Creates waves, surges and flooding
Energy generation (from latent heat of condensation to form clouds and rain, 2500 joules/g water) is 200 times greater than worldwide capacity to generate electricity
The energy released during condensation is 400 times more than the energy of its winds

Question 2

Source regions of hurricanes

Answer 2

Cape Verde
Caribbean Sea
Gulf of Mexico

Question 3

Tropical cyclone

Answer 3

Generic term for a non-frontal synoptic scale low-pressure system over tropical or sub-tropical waters with organized convection (i.e. thunder-storm activity) and definite cyclonic surface wind circulation

Question 4

What conditions must exist (6)

Answer 4

1) Upper 60m ocean should be at least 27*C
2) Moist convection (a thunderstorm) in an atmosphere that cools quickly with height
3) Moist mid layer in the troposphere (5 km)
4) 500 km from the equator to feel enough Coriolis force to balance pressure gradient winds
5) Upper-level winds should be weak, blowing in direction storm is moving
6) Low vertical shear (winds traveling from sea level to tropopause)

Question 5

Evolution of a hurricane (6)

Answer 5

1) Tropical disturbance: low pressure zone draws in clusters of thunderstorms, but not fully organized
2) Tropical depression: surface winds strengthen, flow more efficiency around and into centre of storm
3) Cyclonic rotation: counterclockwise
4) Convergence of surface winds: chimney effect, warm moist air to stratosphere, wind spiral up core walls
5) Condensation of vapour: latent heat is emitted during condensation, increases the updraft, increases inward flow of surface winds
6) Tropical storm: sustained winds > 62km/h

Question 6

Eye

Answer 6

Region of mostly calm weather at the center of strong tropical cyclones. The eye of a storm is a roughly circular area, typically 30–65 km (20–40 miles) in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the most severe weather and highest winds occur

Question 7

Atlantic

Answer 7

Hurricane

Question 8

North Pacific

Answer 8

Typhoon

Question 9

South Pacific

Answer 9

Tropical cyclone

Question 10

Indian ocean

Answer 10

Cyclonic storm

Question 11

Cape Verde

Answer 11

African Eastern waves
Driven by temperature contrasts between the Sahara and adjacent cooler regions
Period of 3-4 days, 2000-2500km
60% of all tropical storms
85% of all major hurricanes
Almost all pacific cyclones

Question 12

Latent heat

Answer 12

Heat absorbed or released during phase change

When water vapour cools to form droplets, release latent heat which helps propel more rising of air

Question 13

Advection

Answer 13

Movement of air of different masses

Wind speed >0

Question 14

Pressure gradient force

Answer 14

Difference in adjacent barometric pressures, operates perpendicular to isobars and an begin to accelerate winds from zero wind speed

Question 15

Centrifugal force

Answer 15

(tangential wind velocity)^2/(radius of curvature)
Force that opposes centripetal force
Centripetal force causes an object to bend its trajectory
Centrifugal pulls outward from the centre of a turn
Wind speed >0

Question 16

Coriolis force

Answer 16

Caused by rotation of the Earth, wind speed must be >0, defects winds to the right in the Northern hemisphere

Question 17

Pressure gradient

Answer 17

Change in pressure over some distance and air density, in the direction of the distance
(deltaP)/(airdensity * deltaX)

Question 18

Angular momentum

Answer 18

p= mvr*sin(theta)

Angular momentum is the same at every point on an orbit, therefore size and rotation speed are inversely proportional

Question 19

Rainbands

Answer 19

Contain showers and thunderstorms outside of the eye wall