Extreme Weather: Tropical Storms And Drought Flashcards
What are the normal conditions in the pacific
- trade winds blow towards the warm water of the western pacific, and coasts of Australia and Indonesia
- rising air occurs due to water heating up atmosphere
- trade winds then push the warm water westwards from Peru to Australia
- In the eastern pacific, the thermocline allows wind to pull up water from below
- Resulting in the pressure of the trade winds pushing the water westwards
What is the thermocline
- the point a t which the temp changes from warmer surface waters to deeper,colder water.
- It is this that creates the optimum conditions for fishings, as there’s an abundance of phytoplankton within the cold water, supplying the fish with food
What happens during El Niño
- trade winds weaken
- This causes a 30cm rise (of warm water from Australasia) in sea level around Peru and prevents the usual cold upwelling
- Now there’s more warm water in Peru’s coast, leading to rising air and low pressure
- Peru therefore experiences more rainfall than normal
- In Australasia, the water becomes cooler and there is less air rising, resulting in high pressure and stable, dry conditions
How do we know if it is an El Niño year
- Better satellite coverage looking for oceanic patterns
- Design of Buoys has improved —> they can now measure sea surface temp, surface winds, air temp and humidity
- Buoys transmit to weather forecasting systems, sometimes every hour
- biological recordings —> e.g. during El Niño; phytoplankton won’t grow because there’s no upwelling of cold water in the eastern Pacific
What happens during La Niña
- the impacts are opposite to that of an El Niño
- described as being a more exaggerated version of normal conditions
- because trade winds strengthen, sending more water westward
What is a tropical storm
- it begins as a low-pressure system originating in the tropics, known as a tropical depression and can develop into a tropical cyclone
- it causes high winds and heavy rain
What wind speeds need to be met in order for a tropical storm to become a tropical cyclone
119 km/h
What are tropical cyclones known as in the North Atlantic Ocean and east Pacific
Hurricanes
What are tropical cyclones known as in the northwest Pacific
Typhoons
What are tropical cyclones known as in northern Indian Ocean
Tropical cyclones
Where do tropical storms occur
- Coast of North America
- Northwest of Australia
- Indian Ocean
- Island of Mauritius
How does the Coriolis effect help in the formation of tropical storms
- the rotations of the Earth CAUSES winds to take curved paths
Which is the most destructive part of the storm
- Towards the centre, around the eye wall
- it has high winds and heavy rainfall
What happens inside the storm eye
- wind speed decreases
- clear skies
- warm temps
- low pressure
How frequently do tropical storms occur
- Tropical oceans generate approximately 80 storms over year
- the most powerful occur in the western pacific
- during late summer months from June to November in the northern hemisphere
- and November to April in the southern hemisphere
How has the frequency of tropical storms occurring changed over time
- increased in the Atlantic since 1995
- but no obvious global trend
- they are getting more intense —> energy released by av. hurricane has increased by 70% in the past 3 yrs
What is a drought
When a region experienced below average precipitation
What are the physical causes for drought
- An above avg presence of dry-high pressure systems
- El Niño brings descending air and high pressure over Indonesia and Australia, leading to drought
- As global temps increase, more water is needed to grow crops and more water is lost through evaporation
- The intertropical convergence zone (ITCZ)
What are the human activities that make droughts worse
- excessive irrigation
- Dam building
- Over-grazing exposes soil to wind erosion
- Deforestation — reduced transpiration; reduces the soil’s ability to hold water and it dries out
- soil erosion — impacts the ability of the soil to capture and store water
- over-farming and intensive farming
Explain why tropical storms only occur over tropical and sub-tropical oceans
- Temperatures are higher over tropical oceans
- This causes high rates of evaporation over the oceans
- Rapid evaporation/pressure gradient creates high wind speeds
- Tropical oceans have depths of at least 50-60 metres
- This provides a vast source of water for evaporation
- Rapid evaporation and condensation create high levels of precipitation
Explain the causes of the extreme weather conditions linked to tropical storms.
- can cause: high wind speeds and heavy rainfall.
- The most severe tropical storms can exceed 150 mph wind speeds and over 1,000mm of rain can fall in 24 hours.
- High wind speeds and heavy rainfall are caused by rapid evaporation and condensation.
- Tropical storms form over areas of warm, deep ocean water north and south of the equator (50-60m depth).
- High temperatures cause rapid evaporation of the ocean water.
- The rising warm, moist air cools and condenses to form storm clouds up to 15,000 metres high.
- The spiralling, rising air around the eye generates high wind speeds and the storm clouds release heavy rainfall causing extreme weather conditions.
Suggest how global warming could affect the frequency of drought in the future.
- Drought events could affect places not previously susceptible to drought
- Scientists/climatologists are not sure about how global warming could affect the frequency of drought in the future
- Global warming may increase the frequency of El Niño/La Niña events leading to drought
- Global warming may affect the migration of the ITCZ leading to drought
What is the ITCZ
- low pressure belt which encircles the world around the equator
- where trade winds from the northeast and southeast meet
- due to Earth being tilted, the ITCZ will migrate between the Tropics of Cancer and Capricorn with seasons
