3.3. Hazards resulting from atmospheric disturbances Flashcards
1
Q
Define tropical storms
A
a large low pressure system characterised by high winds and heavy rain.
Hurricanes in Americas-Atlantic and Easter Pacific
Typhoons in SE Asia-Western Pacific
Cyclone-South Asia-Bay of Bengal and Indian Ocean
2
Q
Structure of a typhoon
A
- The eye: clear calm centre, typically 0-50km with low winds speed, lowest air pressure (880-970mb) and warm temperatures. In the eye, cold dry air descends from upper atmosphere producing clear skies
- They eyewall: a ring of towering cumulonimbus (thunderstorm clouds) around the eye. Formed by intense convection and uplift. Has the strongest wind and torrential rain. Temperatures drop but air pressure rises
- Rainbands of heavy could and rain surround the eyewall. Up to 6 cloud cells can form around the eyewall
3
Q
Conditions for tropical storms
A
- Sea temperatures must be 27 degrees Celsius to a depth of 60m (warm water gives off large quantities of heat when it is condensed - this is the heat that drives the tropical storm)
- The low pressure area has to be far enough away from the equator so that the Coriolis force creates rotation in the rising air mass. If it is too close to the equator, there will be insufficient rotation => storm cannot develop
- Air needs to be unstable so it will continue rising
- High humidity that provides source of latent heat => keeps air unstable
- Rapid outflow of air in upper atmosphere to allow for the continual rise of air as it draws up water vapour and hence more latent heat energy
4
Q
Formation of tropical storms
A
- Warm water must be 60m deep becaue storms stir up the ocean
- Warm air from the ocean meets cold air. Warm air slowly rises above the cold air, forming a low pressure zone
- Trade winds blow in the opposite directions cause the storm to spin
- As the rising warm air reaches higher elevations, the liquid in it condenses and forms clouds and rain, causes pressure to decrease at higher altitudes. Condensation also releases heat which causes air to continue to rise
- Cool air rushes in to fill the low pressure zone, pushing more warm air up and creating a cycle that can result in high winds and storms
5
Q
3 stages of a typhoon
A
- Embryo cyclones: a collection of thunderstorms with no discernable eye and little rotation
- Mature cyclones: wind speeds of at least 74mph, heavy rain and storm surges
- Decay: when a cyclone moves over the land or cooler water and therefore dissipate its energy source
6
Q
Distribution and timing
A
- Found between 8 and 20 degrees North and South of the equator
- Originate in oceans and track westwards and then north in Northern Hemisphere and South in the Southern Hemisphere
- Move in an anticlockwise direction in the northern hemisphere and clokwise in the southern hemisphere due to the Coriolis effect
- Occur between june and december in NH and between december and june in SH
7
Q
What is the Coriolis force?
A
The deflection of moving objects caused by easterly (West to East) rotation of the Earth
8
Q
Explanation of the Coriolis force
A
- Near the equator where the Earth is widest, the outer edge of the Earth’s atmosphere is moving faster than it does around the poles => atmosphere gains a more west to east spin at the equator
- Flies upwards to the NH => to the right/east (nhin tu pole xuong equator)
- Flies downwards to the SH => to the left/west
9
Q
Why do storms spin?
A
- As air flows from high to low pressure, the Coriolis force comes into effect, making the wind follow a curved path
- In the NH, the wind turns to the right/east direction => rotates anti-clockwise
- In the SH, the wind turns to the left/west direction => rotates clockwise
10
Q
Hazards associated with hurricanes
A
- Strong winds: 74-156mph
- Torrential rain: 2 billion tons is picked up per day then dropped. Can cause large scale flooding especially if rivers break their banks
- Storm surges: biggest - 13m in Australia, 1899.
- Large waves at sea: can reach 15m in height
11
Q
How is a tropical storm measured?
A
Using the Saffir-Simpso scale. Developed in 1969 by a civil engineer Herbert Saffir and Bob Simpson - director of US National Hurricane Centre
12
Q
Category 1 of Saffir-Simpson scale
A
- 74-95mpgh or 119-153km/h
- Damage primarily to trees and unanchored mobile homes
- Some coastal flooding
13
Q
Category 2 of Saffir-Simpson scale
A
- Winds 154-177km/h
- Storm surge generally 1.8-2.4m above normal
- Some damage to roofing materials, doors and windows
- Considerable damage to vegetation, mobile homes and piers
- Coastal and low-lying escape routes flood 2-4 hours before arrival of the tropical storm eye
- Small craft in unprotected anchorages break moorings
14
Q
Category 3 of Saffir-Simpson scale
A
- Winds 178-209km/h
- Storm surge generally 2.7-3.6m above normal
- Some structural damage to small residences and utility buildings
- Mobile homes are destroyed
- Flooding near the coast destroys smaller structures with larger structures damaged by floating debris
- Land below 1.5m above mean sea level may be flooded inland 13km or more
- Evacuation of low lying residences close to the shoreline may be necessary
15
Q
Category 4 of Saffir-Simpson scale
A
- Winds: 210-249km/h
- Storm suge generally 3.9-5.5m above normal
- Some complete roof structure failures on small residences.
- Complete destruction of mobile homes
- Extensive damage to doors and windows
- Land below 3m above sea level may be flooded, requiring massive evacuation of residential areas as far inland as 10km
