Hazards: Tropical Storms Flashcards
What are the characteristics of tropical storms?
- develop in the tropics
- intense low-pressure weather systems
- 200-700km in diameter
- violent storms
- last around 7-14 days
What are the conditions required for tropical storms?
- sea temperature above 27ºC (provides a source of heat for rising air)
- ocean depth of at least 70m
- location of at least 5º N/S of the equator (Coriolis effect is strong enough to make them spin)
- emergence of air in the lower atmosphere, either within the ITCZ or along the boundary between cool and warm air masses (this forces warm air to rise)
Describe the distribution of tropical storms?
- 5º-20º north or south of the Equator (in lateral bands)
- always form over oceans
- in oceans with a depth of a minimum of 70m
- never occur at the Equator
- occur at the ITCZ
- move westerly due to easterly winds in the tropics
Why do tropical storms occur 5º-20º north or south of the Equator (in lateral bands)?
Insolation from the Sun is the greatest at the Equator, warms the ocean and storms need enough energy in the water for evaporation and warm, moist air to rise
Why do tropical storms always form over oceans?
- ocean provides a constant source of rising warm air
Why do tropical storms form in oceans with a minimum depth of 70m?
needs to be enough hot water to give the energy needed to drive a tropical storm
Why do tropical storms never occur at the equator?
coriolis effect is required to change individual storms into tropical storms, by spinning storms together which concentrates the energy
- coriolis effect is very weak at the equator
Why do tropical storms occur at the ITCZ?
Trade winds fuel storms with moisture, air rising will create low pressure at Earth’s surface, wind results in air moving down the pressure gradient (high to low)
What is the ITCZ?
Intertropical Convergence Zone
Tropical storm formation part 1
warm oceans cause warm moist air to rise, by convection, air pressure falls, rising air cools and condenses forming clouds
Tropical storm formation part 2
- condensation releases latent heat
- this warms the air and it rises, cools and condenses and releases further latent heat (forming continuous upward convection currents)
- thick vertical clouds grow rapidly and give heavy rainfall and thunderstorms
- this causes a further fall in air pressure at the surface
Tropical storm formation part 3
- convergence occurs, warm moist air is drawn into the low-pressure system from different directions causing wind
- the rising air rotates and the hurricane follows a spiral path due to the Coriolis force
- upper atmosphere air rotation spreads away from the storm
Explaining the processes of a tropical storm: convection
- heat energy is transferred through a substance from hot water to the cooler air above by convection
- the air above the ocean is heated and as it warms it rises
Explaining the processes of a tropical storm: evaporation
- water changing state from a liquid to a gas
- hot water from the ocean evaporates to become water vapour cooling the ocean
- this provides potential energy
Explaining the processes of a tropical storm: condensation
- water vapour changing state into liquid water, this releases energy
- water vapour cools as it rises in the cool upper atmosphere where it condenses and creates potential for heavy ain
- condensation releases energy which leads to further warming of the air and air is forced to rise, adding more energy to the storm
What is the magnitude of tropical storms?
Varies due to central pressure, wind speed and strom surges
What is the lifespan of a tropical storm?
usually between 7-14 days
- however this is dependent of the magnitude, relative size and the supply of latent heat and moisture
What does is the frequency of tropical storms?
- depends on conditions in the area
- climate change is leading to warmer ocean temperatures, greater frequency and magnitude
- therefore in the future they could occur further than 20º N or S of the equator
What are the primary effects (hazards) of tropical storms?
- winds (can be an extreme of 250km/h)
- heavy rainfall (exceeding 200-300mm)
What are the secondary effects (hazards) of tropical storms?
- storm surges
- landslides
- coastal flooding
- river flooding
Q: Evaluate risk management designed to reduce the impacts of tropicak storms
Reduce the impacts gives context to the question
prediction: hurricane forecasting and modelling are the most effective
protection/preparation: moderate effectiveness
prevention: cloud seeding in the worst
Why is land use planning one of the most effective ways to reduce impacts?
- Development is prevented in vulnerable areas (e.g. in low-lying areas = storm surges
- this dramatically decreases risk to loss of life or loss of property and normality can be restored much faster after the event
- furthermore can help identify extremely vulnerable areas = enforcement
- sea walls, breakwaters and flood barriers can be built
- sea wall that was built to protect Galveston (Texas) from further flooding, after the storm surge of 1900 that killed over 6,000 people, however this was so expensive and will not be repeated elsewhere
Why is land use planning not a very effective way to mitigate impacts?
- it can only be useful in areas that have the capacity to implement that type of strategy
- rapidly urbanised places result in many being forced into living in vulnerable spots as there is no alternative
- for example in Tacloban some areas have over 2000Km^2, limiting options for residents forcing them to live in areas of high risk along the coast
Why is hurricane forecasting and warning systems a effective way of managing tropical storm hazards?
- data from satellites and aircrafts is compiled into supercomputers to predict path of the storm and enables for decisions of warning and evacuations
- reduces social losses, but not property
- individuals can empower themselves and protect themselves
- the National Hurricane Centre in Florida gather data from stalleties in both land and sea and maintains 24/7 surveillance of tropical storms that have the potential to become hurricanes and pose threat to life in the USA
