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ES5001- Natural Hazards and Society > Week 11 > Flashcards

Week 11 Flashcards

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Sociology 101 flashcards
1
Q

Definition

A
  • Cyclone: from the greek “kuklos” = circle
  • Hurricane: from “hurican” = the caribbean god of evil
  • typhoon: from the greek “tuphon” = whirlwind, reinforced by the chinese “tai fun” = big wind
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2
Q

Cyclone, hurricane or typhoon

A
  • typhoons: northwest pacific
  • hurricanes: carribbean western and atlantic NE pacific
  • cyclones: everywhere else with the right conditions
  • 40 - 50 per year worldwide
  • approximately 25 cyclones
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3
Q

What causes a cyclone

A
  1. warm water to provide energy
  2. a favorable atmospheric profile
  3. strong coriolis force
  4. initial disturbance
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4
Q

Warm water to provide energy

A
  • more than 26 degrees C to at least 50 m depth (generally around 5 to 20 degrees N and S of the equator)
  • strong latitudinal control on temperature
  • western parts of the basins are warmer
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5
Q

Ocean currents

A
  • ocean currents play a key role
  • cold currents inhibit the development of cyclones
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6
Q

A favorable atmospheric profile

A
  • Warm, supersaturated air up to around 6 km above sea level: latent heat from condensation leads to warm air
  • low variation in wind speed with height: otherwise the rotating, rising air is sheared off
  • cool air at height: to prevent warm air continually rising
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7
Q

An initial disturbance

A
  1. Tropical disturbance: towering thunderstorm/s with maximum sustained winds less than 40 km/hr
  2. Tropical depression: inward flowing air starts to rotate under coriolis for defined surface circulation. Maximum sustained winds less than 63 km/hr
  3. Tropical storm: winds 70-120 km/ hr
  4. Cyclone: air descends into the storm centre where rotation is weakest, warms, thus evaporating cloud and forming the ‘eye’ winds greater than 120 km/hr
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8
Q

Physical processes in a cyclone

A
  • diameter range from 300 to less than 1,500 km
  • air pressure less than 1,000 hPa near the edge, as low as 950 hPa or less in the central eye. Minimum recorded eye pressure was 870 hPa. Pressure is important for storm surge
  • Winds around 30 km/hr near the edge, at the edge of the eye winds may be consistently faster than 240 km/hr. In the eye itself, winds might be light and variable
  • Speed of forward motion is generally less than 40 km/hr. They are faster in more temperate climates where other air systems are moving faster. Nearer the equator their forward speed is slower
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9
Q

Hazards

A
  1. strong winds
  2. storm surge:
    - Piling up of water from onshore winds
    - Low pressure - elevated ocean surface
    - bathymetry - shallowing water increases wave height
    - greatest hazard associated with cyclones
    - storm surges flood low lying terrain and provide a base for high waves to move further inland
    - often it is poorer informal communities that are the most vulnerable
    - often, people will rebuild straight back in the same place after a cyclone
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10
Q

Storm surge levels depend on

A
  • size of the storm: larger wind field = bigger storm surge
  • the forward speed
    1. slower storms = bigger storm surge inland
    2. faster storms = bigger storm surge on open coast
  • the angle of approach (geometry): perpendicular to coast = more storm surge
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11
Q

Impacts

A
  1. property
  2. People:
    - drownings = 90% of cyclone related fatalities
    - other causes: building damage, wind-blown debris and landslides
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12
Q

Damage and deaths

A
  • Global costs related to cyclones have dramatically increased
    1. rapidly growing population along coast
    2. more expensive buildings
  • number of deaths has decreased
    1. improved ability to predict landfall locations
    2. coordinated ability to evacuate populations at risk
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13
Q

Warning and monitoring

A
  • Since tropical cyclones move relatively slowly (compared to seismic waves), and are so large, satellite and ship-borne platforms can monitor their path
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14
Q

Cyclone warning systems

A
  • Provide information on
    1. location
    2. Intensity
    3. Movement up to five days ahead
  • analysis and forecasts with lead times of up to 24 hours are usually updated every 3 hours
  • when a TC moves within the vicinity of a region, analysis information is issued hourly and more detailed forecasts with 3 hourly information covering the period up to 24 hours ahead are issued to advise the public of possible impending disaster conditions
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15
Q

Mitigation

A
  • boarding up windows to defend against wind damage
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16
Q

Cyclone vamei

A
  • december 27, 2001, in the south china sea, 1.5 degrees N, about 150km, north of the equator weather forecasters note the appearance of cyclone vamei
17
Q

Thunderstorms

A
  • most common in latitudes near equator
  • from as unstable, warm and moist air rapidly rises into colder air and condenses, releasing heat and causing updraft
  • water droplets freeze in anvil-shaped cumulonimbus clouds
  • cold air pushing under warm air along cold front is common triggering mechanism
  • lightning strikes can kill people, while strong winds knock down trees, power lines and buildings. Thunderstorms can also cause wildfires, hail and tornadoes
18
Q

Lightning basics

A
  • lighting is an electric discharge, or spark, that occurs in thunderstorms (usually) 80% occurs within clouds 20% occurs between cloud and ground
  • Lightning is ubiquitous, with more than 6,000+ ground strikes per minute from 40,000+ thunderstorms per day worldwide
19
Q

Lighting pt 1

A
  • results from the strong separation of charge that builds up between top and bottom of cumulonimbus cloud
  • charge separation increases as water droplets and ice particles are carried in droplets and collide with downward-moving ice particles or hail
  • the top of cloud carries a strong positive charge
  • the bottom of cloud carries a strong negative charge
  • negative charges near bottom of clouds attract positive charges toward ground surface, especially to tall objects
  • eventually, electrical resistance in the air cannot keep opposite charges apart
20
Q

Lightning pt 2

A
  • negatively charged step leaders angle their way toward the ground
  • leaders generally fork as they find different paths to ground
  • positive leaders reach upward toward them from elevated objects on ground
  • when one of pairs of leaders connects, massive negative charge follows the conductive path of leader stroke from cloud to ground
  • followed by return stroke moving back towards the cloud along established connection
  • instantly heats air to temperatures about 28,000 degrees C
  • accompanying expansion of air at supersonic speed is thunder
21
Q

Charge separation

A
  • Lightning requires the separation of different charges into different regions of a cloud
  • Lightning only occurs in cold clouds with super cooled droplets and temps below -15 degrees C
  • Thus, the ice crystal processes responsible for precipitation in cold clouds is likely to play a critical role in charge separation
22
Q

One theory

A
  • Hailstones are covered by a layer of liquid water
  • The thin layer of liquid is positively charged
  • When hailstones and ice crystals collide, some of liquid molecules stick to the ice crystals
  • along with the mass transfer, positive ions transfer from the hailstones to the ice crystals
  • the heavier, negative hail falls to cloud bottom. The lighter, positive ice crystals drift to cloud top
  • produces negative lower cloud and positive upper cloud
23
Q

A second theory

A
  • top of cloud top has positive charge
  • lower and middle of cloud has a negative charge
  • charge separation in cloud maintains the earth’s fair weather electric field denoted by the arrow E
  • E points towards positive polarity
24
Q

Fair weather electric field

A
  • an electric potential exists between the ionsphere (positive) and surface (negative)
  • potential varies between 200,000 and 500,000 volts
  • average current is 2 x 10^-12 Amps/ m2
  • power is less than 10^-6 W/m2
25
Q

What causes thunder

A
  • lightning rapidly heats air 300,000 degrees C +
  • the intense heating causes the air to expand rapidly
  • the expanding air cools, then contracts rapidly and generates sound waves
26
Q

How far away is it

A
  • we see lightning instantly
  • but sound travels around 340m/s
  • we hear thunder from closest part of flash first, farthest part last. This is what causes the rumble sound
27
Q

Downbursts and other hazards associate with thunderstorms

A
  • small areas of rapidly descending air can develop in strong thunderstorms
  • as fast as 200 km/hr
  • accompanied by descending mass of cold air, sometimes rain
  • cause wind shear, which can cause planes to plummet to ground as they lose lift from under wings
  • damage sometimes mistake for tornado, but evidence will show straight line winds, rather than rotational damage from tornadoes
28
Q

Hail

A
  • Causes $US 2.9 billion in annual damages to cars, roofs, crops and livestock in the USA
  • Hailstones appear when warm and humid air in thunderstorm rises rapidly into upper atmosphere and freezes
  • upward and downward movement accumulates layers of ice until heavy enough to overcome updrafts and fall to ground
29
Q

Twisters and waterspouts

A
  • a waterspouts is an intense columnar vortex that occurs over a body of water and is connected to a cloud
  • while it is often weaker than most of its land counterparts, stronger version do occur
  • waterspouts do not suck up water, the water seen in the main funnel cloud is actually water droplets formed by condensation

ES5001- Natural Hazards and Society (12 decks)

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