Weather and Climate
Climate: The average weather conditions eg temperature, pressure, precipitation and humidity expected for an area over a period of time, usually thirty years or more.
Weather: day to day changes in temperature, precipitation, wind speed, direction and cloud cover. The weather here and now.
Depressions: areas of low atmospheric pressure, which produce cloudy, rainy and windy weather. A depression usually moves from west to east with a leading warm front and a trailing cold front
Warm front: When warm air is rising over a mass of cold air
Cold front: The cold air is following the warm air, and is gradually moving underneath the warmer air. As the warm air is pushed upwards it will rain heavily.
Anti-Cyclones: are the opposite of depressions, they happen in areas of high atmospheric pressure, there is little or no clouds, it never rains and is rarely wind.
Factors effecting climate
Altitude: Temperature decreases by roughly 1 degree C for every 100m of height.
Prevailing winds: The strongest winds that blow over a country for example in Briton the prevailing wind is from the south west which brings warm wet air from the atlantic contributing to frequent rainfall.
Latitude: The closer you are to the equator the hotter the climate because the sun always shines over the equator. The futher you are away from the equator the colder it is. In the north and south poles, the vast amount of white ice and snow reflect the sun's rays and therefore it is colder.
Distance from the Sea: (Matitime effect) The ocean warms slowly during the summer but cools slowly during the winter. This keeps the land near the cost cooler in the summer and warmer in the winter. Land in the centre of the continent however heats and cools quickly giving more extreme temperatures.
Climate in the UK
- Sunshine hours:are greatest along the south coast of England.
- Day light hours: Scotland has shorter winter days and longer summer days because of it's northernly latitude
- Rainfall: On average it rains on in every three days in the UK. Wetter in the highlands such as Snowdonia, Lake district, Scottish highlands, Peak district
- Average temperature: The UK is warmer at lower latitudes and colder at higher ones But also colder at high altitudes and warmer at lower ones. The average daily maximum temperature at Glasgow in July is 19°C compared with 22°C in London.
- Severe weather: Scotland tends to be worse effected my severe areas than other areas. while snow might fall on the south west of England less than 10 days as year, it will fall on the peaks of the Mountains in scotland over 100 days a year.
Northwest - cool summers, mild winters, heavy rain all year.
Northeast - cool summers, cool winters, steady rain all year.
Southeast - warm summers, mild winters, light rain all year, especially summer.
Southwest - warm summers, mild winters, heavy rain all year, especially winter.
Types of Rainfall
Convectional: The hot sun shines down on the earth. The earth's surface warms up and some surface water is evapourated. Hot air rises. As is rises it cools (because temperature goes down with height) Any water vapour condenses into droplets. Droplets cling together as clouds. Clouds become heavy. The clouds burst and it rains. This rain occurs everyday in equatorial rain forests.
Relief Rain: Warm, moist air is blown over the land, usually from the sea. When this air meets a mountain or highland it must rise over it. As the warm air rises over the mountain, the air begins to cool and water vapour condenses into droplets. Droplets cling together as clouds. The clouds become heavy and usually burst on the other side of the mountain resulting in this being an area with high rainful. This rain is most commin in wales.
Frontal rain: This occurs when warm air and cold air meet at a front. The warm air rises upwards and the cold air sinks. As the air lifts into an areas of lower pressure it expands, cools and condenses into water droplets forming wide flat clouds. When these clouds become heavy they burst and this results in rain.
Depressions - What happens?
Explanation of a depression
- At the warm front light warm air from the south (topical marintime air) meets cooler air from the north (polar maintime air) and rises gradually over it.
- As the warm air slowly rises it cools and it's water content condences into clouds (nimbostratus then altostratus). The result is steady rain, drizzle and then clear skies.
- Behind the warm front there is an area of warm, low pressure air, as this passes over there will be clear, dry weather
- However this doesn't last for long as the trailing cold front meets the warm air, it sharply undercuts it forcing it steeply upwards. This quickly moving air produces fast winds and cool temperatures.
- As the rapidly rising warm air cools, its water condences and clouds form (cumulonimbus, then cumulus) resulting in heavy rain and thunder storms. But eventually giving way to clear skies as the cold front moves away eastwards.
Winter Anti-cyclones: cold, dry and bright. If temperatues are low, Fog or frost may occur during the night which can sometimes take much longer to burn off as the day temperatures don't get warm enough to evapourate it.
Disadvantages: Absence of rainfall causes potential droughout as resevoirs do not fill up. Absence of wind leads to fog and sunless days, affecting driving, planes, sports and leisure, winter smog causes breathing problems. Hypothermia kills old people. Broken bones from accidents on ice.
Summer Anti-cyclones: warm, hot and sunny days with cool/cold nights because there are no clouds. Risk of thunder storms due to convectional rain after heat build up over a few days. At night the air cools quickly forming early morning mist however this burns off quickly the next day.
Disadvantages: Absence of rainfull causes draught, absence of wind causes hazy conditions, summer smog, pollutants are trapped by the high pressure can cause breathing problems. Pollen spores cause hayfever. Heat waves cause dehydration. Ultraviolet radiation causes sunburn and can cause cancer.
AKA: Hurricans, typhoons, cyclones, willywilies
Where do they start?
- Over warm tropical oceans where temperatures are 27 degrees C or more.
- Between lattitudes of 5 degrees and 20 degrees north or south of the Equator.
- Mostly in late summer, early autumn.
Why do Hurricans happen?
Air rising of a very warm water can draw up huge masses of vapour from the ocean. As it rises it cools and starts to spiral. The vapour will then start to condence. This releases masses of energy (one hurrican = 500,000 atomic bombs) This heat energy powers the storm, moving it westwards on an eratic and difficult to predict path. Once reaching land the source of moisture and heat is gone and the hurrican starts to loose power. They can last between 7 and 14 days.
Case study: Tropical storm Hurrican Andrew
Factor Hurricane Mitch LEDC Hurricane
- Location: Florida, USA
- Deaths: over 30
- Missing: over 15
- Homeless: 80000
- Time for help to arrive: several hours
- Prediction: more effective early warning system, people heard about it on the TV or the Radio
- Planning: good emergancy services, lots of hospitals and doctors available, houses strongly built and so were more resistant against the storm.
- Effects on services: no telephones or electricity
- Effect on economy: Some business' had to close, but mostly short term effects
- Secondary effects: Very few
- Time to recover: A couple of days.
Case study: Tropical storms Hurrican Mitch
Hurricane in a LEDC - Hurricane Mitch
- Location: Nicaragua, Honduras, Guatemala, El Salvador
- Deaths: over 12,000
- Missing: over 16,000
- Homeless: over 700,000
- Number effected: 3 million
- Time for help to arrive: Several days
- Effects on services: No telephones, electricity, fresh water or transport
- Effects on economy: crops lost/damaged that were often the only products for sale, long term
- Secondary effects: Shortages of food, clothing, medical supplies
- Prediction: less effective early warning system, some people without radios or TVs to hear the news
- Planning: Limited emergency services. Few available doctors and hospitals. Many houses poorly built and so easily blow down or washed away
- Time to recover: estimated ten years