- Created by: mbull
- Created on: 13-01-18 17:56
Air circulates between high and low pressure belts at surface winds
- There is an overall movement of air between the equator and the poles that affects the Earth's climate.
- Winds are large scale movements of air caused by differences in air pressure.
- Differences in air pressure are caused by differences in temperature between the equator and the poles.
- Winds move from the areas of high pressure to the area of low pressure.
- Winds are part of global atomospheric circulation loops (or cells.) These loops have warm rising air which creates a low pressure belt, and cool falling air which creates a high pressure belt.
- There are 3 loops in each hemisphere.
Global Atmospheric Circulation
1.) At the equator the sun warms the Earth, which transfers heat to the air above, causing it to rise. This creates a low pressure belt with rising air, clouds and rain.
2.) As the air rises it cools and moves out to 30 degrees north and south of the equator.
3.) 30 degrees north and south of the equator the cool air sinks, creating a high pressure belt with cloudless skies and very low rainfall.
4.) The cool air reaches the ground surface and moves as surface winds either back to the equator or towards the poles:
- Surface winds blowing towards the equator and called trade winds.
- They blow from the south east in the southern hemisphere and from the north east in the northern hemisphere. At the equator, these trade winds meet and are heated by the sun.
- Surface winds blowing towards the poles are called westerlies. They blow from the north west in the southern hemisphere and from the south west in the northern hemisphere.
More on Global Atmospheric Circulation
5.) 60 degrees north and south of the equator the warmer surface winds meet colder air from the poles. The warmer air is less dense than the cold air so it rises, creating low pressure.
6.) Some of the air moves back towards the equator, and the rest moves towards the poles.
7.) At the poles the cool air sinks. creating high pressure. The high pressure air is drawn back towards the equator as surface winds.
- Global atmospheric circulation causes areas to have some types of weather more often than others - it affects the Earth's climate.
Air moves in loops (called cells) from the equator to the poles and back. This gives us surface winds and creates belts of high and low pressure that affect the climate - they're why deserts are so dry and rainforests are so wet.
Global Atmospheric Circulation Diagram
Tropical storms have intense low pressure weather system with heavy rain and strong winds that spiral around the centre.
They have a few different names:
- The majority of storms occur in the northern hemisphere (especially over the Pacific,) in late summer and autumn, when sea temperature are highest.
- Tropical storms form at low latitudes - between 5 degrees and 30 degrees north and south.
The formation of tropical storms
The formation of tropical storms:
1.)Tropical storms develop when the sea temperature is 27 degrees or higher and when the wind shear (the difference in windspeed) between higher and lower parts of the atmosphere is low.
2.)Warm, moist air rises and condensation occurs.
3.)This releases huge amounts of energy, which makes the storms powerful.
4.)The rising air creates an area of low pressure, which increases surface winds.
5.)Tropical storms move towards the west because of the easterly winds near the equator.
6.)The Earth's rotation deflects the paths of the winds, which causes the storms to spin.
7.)The storm gets stronger due to energy from the warm water, so wind speeds increase. They lose strength when they move over land/cooler water because the energy supply from the warm water is cut off.
The features and structure of a tropical storm
- Are circular in shape.
- Hundreds of kilometrres wide.
- Usually last 7-14 days.
- Spin anticlockwise in the northern hemisphere.
- Spin clockwise in the southern hemisphere.
Eye ---> the centre of the storm.
- Up to 50km across.
- Caused by descending air.
- Very low pressure.
- Light winds.
- No clouds.
- No rain.
- High temperature.
More features and structure of a tropical storm
- Surrounds the eye.
- Spiralling rising air.
- Very strong winds.
- Storm clouds.
- Torrential rain.
- Low temperature.
- Towards the edges of the storm the wind speed falls, the clouds become smaller and more scattered. The rain becomes less intense and the temperature increases.
Climate change and tropical storms
- Global temperatures are expected to rise as a result of climate change.
- This means that more of the world's oceans could be above 27 degrees.
- More places in the world may experience tropical storms.
- Oceans will stay at 27 degrees or higher for more of the year - so the number of tropical storms each year could increase.
- Higher temperatures also mean tropical storms will be stronger causing more damage.
Tropical storms - Primary Effects
When tropical storms hit land, they can have serious effects on people and the environment.
Primary effects of a tropical storm are the immediate impacts of stong winds, high rainfall and storm surges (large rises in sea level caused by the low pressure and high winds of a storm.)
- Buildings and bridges are destroyed.
- Rivers and coastal areas flood.
- People drown, or they're injured/killed by debris that is blown around.
- Roads, railways, ports and airports are damaged.
- Electricity cables are damaged, cutting off supplies.
- Sewage overflows due to flooding. The sewage often contaminates water supplies.
The more settlements built and businesses set up in an area, the greater the effect becuase there are more people and properties to be affected by a tropical storm.
Tropical storms - Secondary effects
- People are left homeless, which can cause distress, poverty and ill health/ death due to lack of shelter.
- There's a shortage of clean water and a lack of proper sanitation - this makes it easier for diseases to be spread.
- Roads are blocked/destroyed - aid and emergency vehicles cannot get through.
- Businesses are damaged/destroyed - causing unemployment.
- There can be shortages of food if crops are damaged, livestock are killed or supply lines are blocked.
Tropical Storms Immediate responIses
Immediate responses --> happens when a storm is forecast to hit a populated area, while it is happening, and immediately afterwards.
Long term responses --> to do with restoring the area to the condition it was before the storm struck, and reducing the impact of future storms.
- Evacuate people before the storm arrives.
- Rescue people who have been cut off by flooding and treat injured people.
- Set up temporary shelters for people whose homes have been flooded or damaged.
- Provide temporary supplies of water, food, electricity, gas and communications systems if regular supplies have been damaged.
- Recover any dead bodies to prevent the spread of disease.
- Foreign governments or NGOs may send aid workers, supplies, equipment or financial donations to the area.
- Tech companies may set up disaster response tools, allowing damage to be recorded, people to confirm their safety and alerts about areas at risk from the storm to be shared.
Tropical Storms Long-Term responses
Long term responses
- Repair homes or rehouse people who have been displaced due to damaged buildings.
- Repair/replace damaged infrastructure.
- Repair and improve flood defence systems, e.g, levees and flood gates.
- Improve floodcasting techniques to give people more warning in the future.
- Provide aid, grants or subsidies to residents to repair and strengthen homes.
- Promote economic recovery in the area and encourage people to return to the area,e.g, with tax breaks or other incentives.
- Improve building regulations so more buildings withstand hurricanes, or change planning rules so homes can't be built in the most risky areas.
Ways of reducing the effects of tropical storms
- Scientists use data from things like radar, satellites and aircraft to monitor storms.
- Computer models used to calculate a predicted path for the storm.
- Predicting where/when a tropical storm is going to happen gives people time to evacuate and protect their homes and businesses. E.g, boarding up windows.
- Future developments. E.g, new houses can be planned to avoid the areas most at risks.
- Emergency services can train and prepare for disasters. E.g, practising rescuing people from flooded areas with helicopters. Reduces number of people killed.
- Governments can plan evacuation routes to get people away from storms quickly.
- Buildings can be designed to withstand tropical storms. E.g, by using reinforced concrete, buildings can be put on stilts so they're safe from floodwater.
- Flood defences can be built along rivers (e.g, levees) and coasts (e.g, sea walls.)
- All of these reduce the number of buildings destroyed, so fewer people will be killed, injured, made homeless and made unemployed.
UK Weather Hazards
Types of weather hazards in the UK
- Too much rain in too short a time can cause flooding.
- Can damage homes and posessions, disrupt transport networks and can cause death by drowning.
- Can also force businesses to close, and recovering from flooding can cost millions of pounds.
Snow and Ice:
- Can cause injuries due to slipping and deaths due to cold.
- Schools and businesses may be forced to shut.
- Major disruption to road, rail and air travel - causing economic impacts.
- Cold snaps can damage crops and other plants.
- Makes driving dangerous.
- Can damage property and destroy crops.
More weather hazards in the UK
- Lack of precipitation.
- Water supplies can run low causing economic impacts such as crop failure.
- Rules to conserve water have to be introduced.
- Strong winds can damage properties and cause disruption to transport.
- Uprooted trees and debris can injure/kill people.
- Forests can be damaged when trees are blown over.
- Winds are strongest in the coastal areas of the UK.
More weather hazards
- Heavy rain, lightning and strong winds occur in thunderstorms.
- Most common in summer in the south and east of the UK.
- Lightning can occasionally cause death and fires.
- Long periods of hot weather can caues deaths from heat exhaustion or breathing difficulties.
- Disruption to transport from rails buckling or roads melting - can cause economic impacts.
Extreme weather and management strategies
- Temperatures have become more extreme in recent years.
- It is raining more.
- Major flooding occurs often.
- Warning systems give people time to prepare for extreme weather.
- Individuals and local authorities prepare for extreme weather before it happens. Eg, salt and grit.
- Emergency services and local councils plan how to deal with extreme weather events in advance. E.g, closing schools.
- Areas of high pressure where air sinks to the earth's pressure
- As the air sinks it warms so condensation does not occur and there are very few clouds
- This gives clear skies
- Low wind speeds
- Widely spaced isobars
- Stable conditions
- Only involve one type of air mass which usually cover large areas
- Do not have any fronts
- Occur in winter and summer
- Can be very large - much wider than depressions
- Can give several days of settled weather
- Areas of low atmospheric pressure
- Produce cloudy, rainy and windy weather
- Often begin in the Atlantic, moving eastwards towards the UK
- Responsible for the UKs changeable weather
- Under a depression air is rising, forming an area of low pressure at the surface.
- This rising air cools and condenses and helps encourage cloud formation, so the weather is often cloudy and wet.
- In the Northern Hemisphere winds blow in anticlockwise direction around a depression.