Atmo: Cyclones Flashcards
What conditions are necessary in the formation of cyclones?
1) source of warm air (>27degrees) to provide the necessary heat and moisture
2) sufficient spin from coriolis force, which increased with latitude (cyclones do not form within 5degrees of the equator)
How are tropical cyclones formed? 8 steps
1) low pressure develops over warm oceans which heat the air above it [5-30N/S >27degrees]
2) less dense air rises, bringing vast quantities of water vapour
3) rising air cools adiabatically and condenses to form cumulonimbus clouds and rains
4) latent heat will be liberated to fuel the cyclone
5) release of latent heat energy warms the air locally and cause further decrease in pressure
6) more winds rushes in, inward spiralling wind whirls upwards
7) coriolis force causes rising column to twist, releasing more heat and moisture
8) produce cumulonimbus clouds where cloud tops are carried outwards by high pressure aloft at 8-10km altitude
Define tropical cyclones
Intense cyclonic storms that originate over warm tropical seas arranged in a pinwheel formation, with bands of thick clouds and heavy thunderstorms. The storms centre an area of very low pressure with strong winds blowing at a speed of over 119km/h
Where are cyclones formed?
Between 5-30degrees latitude over tropical oceans. No cyclones at cold ocean currents
Describe the eye as a feature of cyclones
- averages 25km in diameter
- a zone where precipitation ceases and winds subside
- air descends and heats adiabatically by compression, making it the warmest part of the storm
- does not have clear blue skies
- brief lull until the opposite side of eye wall arrives and storm conditions resume
Describe the eye wall as a feature of the tropical cyclone.
Has the greatest wind speeds, thickest cloud cover and heaviest rainfall. Presence of steep hpressure gradient from the outer edge of yclone (high) to the centre (lower). Velocity increase inwards. As moist surface air approaches the core of the storm, it ascends in a ring of cumulonimbus towers.
In what circumstances cyclones diminish in intensity? 3
1) when they move over cool ocean waters that cannot support warm moist air.
2) when they reach a location where large scale flow aloft is unfavourable (subsidence of air is occurring)
3) when they move onto land
What are the 3 impacts of tropical cyclones?
Storm surge
Wind damage
Heavy rainfall
What is storm surge?
A phenomenon whereby water is physically piles up along a coastline by low pressure and strong winds. Large waves up to 15high can cause extensive flooding. It is a dome of water 65-80km long that sweeps across the coast near the point where eye makes landfall. Strong winds can drag surface waters forward.
Describe wind damage as an impact of tropical cyclones
Sustained winds can reach 250km/h and high wind velocities constitute the main agent for crop destruction. Force of wind can cause buildings to implode while suction can lift up roofs and buildings. They can create a dangerous barrage of flying debris. Eg. Hurricane Andrew had winds that produced >US$20billion of damage in southern Florida
Describe heavy rainfall as an impact of tropical cyclones
1) water seepage into buildings
2) inland flooding by swollen rivers
3) mass movement on slopes as heavy rain lubricates slope materials, reduces their coherence and friction
Eg. Hurricane Agnes in 1972 created >US$2 billion in damage due to flooding in the NE in US
Describe 1 prediction method of cyclones
Aircraft reconnaissance
- when a cyclone is within range, specially instrumented aircraft can fly directly into a threatening storm and accurately measure details of its position and current state of development my measuring wind speed, air pressure, temp and humidity.
Meteorological satellites
- remote censors that can provide data on the size intensity and movement of storms. However it’s not accurate all the time since they are only remote censors. A combination of observing systems is therefore necessary for accurate forecasts and warning
What does the US do as a mitigation measure for cyclones?
A hurricane watch is an announcement aimed at specific coastal areas, within 36hours, allowing people to evacuate in time. Delicate balance between over warning and needing to protect the public. Over warning is costly and ruins credibility.
Why do tropical cyclones diminish when they move onto land?
1) energy source of warm moist water is depleted
2) land is usually cooler than the ocean, the low-level air is chilled rather than warmed
3) increased surface roughness increases friction -> reduction in wind speeds
4) upper level winds shearing off the cyclones
What is the arrangement of thunderstorms in cyclones?
Cyclones contain a large number of thunderstorms arranged in a pinwheel formation
