Drought - El Niño effect
-The El Niño effect is where normal ocean-current events are reversed.
-Normally, there is warm surface water in the western ocean, off the coast of Australia, meaning the warm air rises to form thrunderstorms, causing floods. Also, there is usually cooler surface water in the east, off Peru and Chile, where dry, sinking air causes drought.
-Sometimes, this is reveresed, where the Trade winds change direction, causing Australia to suffer from droughts and Peru and Chile getting thunderstorms and floods.
Tropical Storms - Description
-An eye in the middle
-At least 600 miles wide
-Anit-clockwise in the Northern Hemisphere
-Clockwise in Southern Hemisphere
Tropical Storms - Characteristics
-Can be hundreds of kilometres wide
-Eye is calm, with no clouds, no rain and low wind speeds
-Eyewall just surrounding eye has torrential rain and very strong winds, which lessens the further frpm the eye it gets
-Lose energy when they hit land, as there is no water to fuel them
-Storm surges = with low pressure, ocean levels near a tropical storm can rise up to 5m above normal level
-Cause secondary hazards of flooding, mudslides, and landslides
Tropical Storms - What do they need to occur?
-Ocean temperatures over 27°C
-Ocean depth over 60m
-High heat and humidity
-Major winds (Trade winds) blowing in the same direction
-5°-15° north and south of the Equator, due to the coriolis effect, at the hottest times of the year
Tropical Storms - Coriolis Effect
-Air would move in straight paths, towards the equator, if the earth did not rotate
-Rotation of the earth causes winds to take curved paths and be diffracted
-Wind blows constantly in a westwards direction, due to the earth's rotation
Tropical Storms - How do they form?
1 - Heat causes ocean water to evaporate and rise quickly
2 - This creates low pressure
3 - The system sucks in more air from the Trade winds to fill the space from where the air has risen.
4 - Trade winds are from an angle, so this causes the spinning/spiralling of the system
5 - Humid air at the top cools and condenses quickly, so the air sinks, creating an area of calm in the eye.
Tropical Storms - Categories
1 - 74-95mph - damage to mobile homes, trees and crops
2 - 96-110mph - crops heavily damage
3 - 111-130mph - mobile homes destroyed, plus roofs and structures damaged
4 - 131-155mph - significant damage to roofs and other structures
5 - over 155mph - wide-ranging destruction