Physical Geography - Challenges of Weather and Climate

Weather -

• Day to day conditions of the atmosphere involving, for example, a description of temperature, cloud cover and wind direction.
• Can be observed at a local scale and weather stations forecast future weather up to a week in advance.

Climate -

• The average weather conditons recorded over a period of at least 30 years.
• Measured on a climate graph.

• North Atlantic Drift - warm, moist wind from the Gulf of Mexico.

• Prevailing Winds - creates mild, damp climate ( aka. South Westerley's)

• Maritime Influence - the sea's affect on the climate

• Continetality - the effect of being close or being too far away from the coast

• Altitude - being high upland means greater amount of rainfall and colder temperatures

Depression - An area of low atmospheric pressure

Front - A boundary between cold and warm air

Occluded Front - Front formed when the cold front catchest up with the warm front

Warm Sector - An area of warm air between a warm front and a cold front

Warm Front - A boundary with cold air ahead of warm air

Cold Front - A boundary with warm air ahead of cold air

• At the warm front - lighter, warmer air from the south (tropical maritime air) meets cooler air from the north (polar maritime air) and rises gradually over it.
• As the warm air slowly rises it cools, its water content condenses and clouds form (nimbostratus then altostratus).
  • The result is steady rain, later giving way to drizzle and finally clearer skies with higher cirrus clouds.
• Behind the warm front is an area of warm, rising air and low pressure - the centre of the low pressure system. As this part of the depression passes over, there may be a short period of clear, dry weather. However, at the trailing cold front, heavier, cooler air meets the warm air at the centre of the depression, undercutting it and forcing it steely upwards. Quickly moving air masses produce high winds and cooler temperatures.
• As the rapidly rising warm air cools, its water condenses and clouds form (cumulonimbus then cumulus). The result is heavy rain or thunderstorms, giving way to showers and finally to clear skies as the cold front moves away eastwatds.

• Anticyclones - An area of high atmospheric pressure

• Frost - Results from the temperature of the ground dropping below 0 degrees celcius.

• Fog - Water that has condensed close to the ground to form low cloud and poor visibility

Anticyclones are the opposite to depressions in most ways.

• As the air is sinking, not rising, no clouds or rain are formed. 
  • This is because as the air sinks, it warms, meaning that it can hold more water.

• The absence of fronts means winds may be very light.

• Consequently, high-pressure areas are often associated with settled, dry and bright conditions.

24th July 2008 - 

In Summer, anticyclones bring dry, hot weather

In Winter, clear skies may bring cold nights and frost

2nd February 2006 -

Anticyclones may also bring fog and mist.

This is because the cold forces moisture in the air to condense at low altitudes

Extreme Weather -

• A weather event such as a flash flood or severe snowstorm that is significantly different from average.

Global Warming -

• An increase in the worlds temperature as a result of the increase in greenhouse gases (carbon dioxide, methane, CFC's and nitrous oxide) in the atmosphere brought about my burning of fossil fuels, for example.

Monday 16th August 2004

What Happened?
A small village in Cornwall was hit by a thunderstorm 
About 200mm of rain fell in 24hrs
Steep sided valley slopes and intense rainfall made the River Valency burts its banks

Effects -
Nobody killed, 58 buildings flooded, 25 business properties destroyed, 84 wrecked cars, 32 cars washed out to sea, cost of the damage(£15million), tourism was affected (major tourist resort lost revenue)

Responses -
Traffic Light System to warn people about approaching extreme weather, early warnings of severe extreme weather, some modifications were made to the stream and the bridge, a flash warning is issued when confidence is over 80% on an extreme event happening within the next few hours.

• Instrument Readings - readings from precise thermometers

• Glacier Retreat - Glaciers across the globe are melting and therefore becoming smaller (e.g. Glacier National Park, USA)

• Arctic Ice Cover - Over the last 30 years, Arctic Ice is half its earlier thickness

• Ice Cores - Water and Carbon Dioxide molecules trapped in ice give scientists exact evidence of gas concentrations in the air

• Early Spring - Spring is arriving earlier each year (e.g. birds nesting earlier)

• Burning Fossil Fuels

• Car Exhausts

• Deforestation

• Landfill

• Intensive Farming

• Sewage Treatment

• Fertilisers

• Could melt the worlds glaciers and ice caps - This could lead to an increase in sea levels.
  • Scientists estimate that over the next hundred years, sea levels could rise between 10 to 90cm, making many coastal areas around the world uninhabitable

• Could affect the weather patterns - This would lead to more droughts, flooding and extreme weather such as hurricanes.

• Climatologists argue that the UK climate is changing as a result of global warming - This leaves us with a possibility of more frequent floods, water shortages, and extreme weather conditions

Local -
Conserving energy at home - e.g. low energy light bulbs
Walking and Cycling
Congestion Charge - London
Promote Public Transport - Park and Ride Scheme

Global -
Kyoto Protocol - Agreement to cut emissions of carbon dioxide by 2012
Carbon Credits - Countries that beat their emission targets are able to trade the credits with other countries

National -
Tougher MOT tests on vehicle exhausts
Higher road tax for 'gas guzzlers'
Carbon Dioxide Emissions targets
Power Station Filters

Hurricane -  A powerful tropical storm with sustained winds of over 75mph

Eye -  The centre of the hurricane where sinking air creates clear conditions

Eye Wall -  A high bank of cloud either side of the eye where the wind speeds are high and heavy rain falls 

Track -  The path / course of the hurricane

Hurricanes need a lot of heat to form and a sea temperature of at least 26 degrees celcius, this is why they usually occur over tropical seas. They also need to be between 5 and 20 degrees north or south of the equator.

• When this warm and wet air rises, it condenses to form towering clouds, heavy rainfall
• Rising warm air causes the pressure to decrease at higher altitudes. Warm air is under a higher pressure than cold air, so it moves towards the 'space' occupied by the colder, low pressure air. The low pressure air 'sucks in' air from the warm surroundings, which then also rises.
• Air that surrounds the low pressure zone at the centre flows in a spiral at very high speeds - anti clockwise in the northern hemisphere at speeds of around 75mph.
• Air is ejected at the top of the storm - which can be 15km high  - and falls to the outside of the storm, out and over the top, away from the eye of the storm. As this happens, it reduces the mass of air over the 'eye of the storm'. This causes the wind speed to increase.
• The faster the wind blows, the lower the air pressure in the centre, so the cycle continues.
• The hurricane grows stronger and stronger. The cloud brings heavy rain, thunder and lightning.
• In the centre is the 'eye of the hurricane', about 45km across. Often there will be no clouds in the eye.
• In the northern hemisphere, the prevailing tropical winds tend to steer hurricanes towards land but their courses aren't predictable. As hurricanes move inshore, their power gradually reduces because their energy comes from sucking up moist sea air

2005, North America - New Orleans
6th most powerful hurricane

Effects - 

1863 dead, hundreds of thousands homeless, 3million left without electricity, cost ($89billion)

Short Term Responses -

Rescuing people from floodwater, treating the injured

Long Term Responses -

Rebuilding New Orleans

Evaluation of Warnings -

Katrina had been monitored accurately - 80% people evaccuated

2008, MyanMar (Burma) - It developed in Bay of Bengal 

Effects -

At least 140,000 dead, 2-3million homeless, estimated that 2.5 million were affected, costs ($10billion), government refused foreign aid

Short Term Responses - 

Identification and burial of the dead, treating the injured

Long Term Responses - 

Rebuilding of the homes, reclaiming farmland

Evaluation of Warnings - 

Most people had no idea that the cyclone was approaching