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Weather and Climate

  • Types of Weather
  • Measuring and Forecasting Weather
  • UK Weather Roundabout
  • Air Pressure Systems
  • Rainfall
  • Extreme Weather
  • Extreme weather in the UK, The Beast from the East

What is Weather and Climate?

 

The Earth’s atmosphere produces a wide range of weather conditions. Weather is the day to day conditions of the atmosphere, such as temperature and presence of rain, clouds and sunshine. Weather is not the same as climate.

 

Climate is the average atmospheric or weather conditions over a long period of time, usually 30 years. Components of climate include how hot, cold, windy, wet or dry a place is. The weather in Manchester might be that it is raining today, whereas the climate of Antarctica is cold, windy and dry.

 

Weather on Earth is caused by heat from the sun and the movement of air. The Sun heats Earth, but Earth is round so it is not heated evenly. The Sun warms the air in the atmosphere to different temperatures in different latitudes. Places at lower latitudes experience high temperatures and humidity. Places at higher latitudes such as the Arctic and Antarctica are cold all year round because the Sun’s rays are less concentrated and more dispersed over a larger area.

 

Earth then heats the air above its surface. When air is heated it becomes less dense and rises. Cold air then rushes in to replace it, as wind. Wind is air that is moving. The cold air is heated and the cycle repeats. This happens on a global scale and is known as the global atmospheric circulation model.

 

The Sun warms the oceans and this causes the water to evaporate to a gas known as water vapour. This affects how much moisture is in the air. Water vapour rises and begins to cool later condensing to form clouds as tiny water droplets join together. When water droplets are heavy, they fall to Earth’s surface as precipitation – rain, snow, sleet or hail. Precipitation depends on the temperature of the air.

How is weather measured?

 

Weather instruments can be found in weather stations on land. The Met Office has hundreds of weather stations all over the UK. Weather instruments are also found at sea. They are found on some ships, but mainly on weather buoys designed to monitor weather and sea conditions. Weather readings are taken four times a day at weather stations across the world. Most instruments are placed in a white box called a Stevenson Screen.

 

Stevenson screens have slatted sides to allow the free passage of air and is white in colour to reflect heat radiation. This makes sure that the temperature of the air is accurate.

 

Planes, weather balloons and satellites also have weather instruments to measure the weather away from the Earth’s surface. Satellite images can show us detailed pictures of cloud cover over large areas as well as where rain is falling.

 

  • Temperature is measured using a thermometer and temperature is measured in °Celsius.
  • Air pressure is measured using a barometer. Air pressure is measured in millibars (mbs). If air pressure is rising, it means the air is sinking. If the air pressure is declining, it means the air is rising. This tells us what type of weather to expect. If air pressure is low, you can expect cloud and rainfall whereas if air pressure is high, you can expect little cloud, clearer skies and dry weather.
  • Wind speed is recorded using a anemometer. It measures how fast the wind is moving in miles per hour (mph) or miles per second (m/s).
  • Precipitation such as rain is measured using a rain gauge. It records rainfall in millimetres. There is around 3000mm of rainfall in the North West of England compared to 600mm of rainfall in the south east of England.
  • Wind direction is measured using a weather vane and is recorded using compass directions.

Why do we forecast the weather?

 

Meteorology is the study of atmospheric conditions. Most countries have a central organisation that is responsible for weather forecasting. A weather forecast is the analysis of atmospheric conditions in a given area and likely developments.

 

The UK measures, records, collects, processes and analyses weather date into weather forecasts that are communicated to the public through forms of media – TV, internet, radio or newspaper.

 

24 hour weather forecasts can be very accurate. They can tell us information about temperature, air pressure, humidity, rainfall and wind. Weather symbols are used to show the atmospheric conditions on a map. They are easy to read and plan for. Forecasts are also used to alert people to weather warnings and communicate how best to prepare or avoid disruption.

 

Weather affects people and the economy. Daily weather forecasts help us make decisions about what to wear, what to eat and where to go. Farmers need forecasts to plan what crops to grow and travel companies need to plan for bad weather. Lightning may delay flights and high temperature may cause train tracks to expand and buckle. This means trains have to go slower or be cancelled.  Weather can cause economic losses.

 

The snowfall dubbed Beast from East caused a slowdown in economic growth during the first quarter of 2018 however there are also claims that these losses were offset by the cost of energy supply and online sales.

What is the UK weather roundabout?

 

Different parts of the world experience different temperatures caused by the uneven distribution of the Sun’s rays and the movement of air. Air moves around the Earth in huge blocks called air masses. Air masses can be cold, warm, wet or dry depending on where they come from.

 

  • Arctic maritime air approached the UK in the north from the Arctic bringing wet, cold air and snow in the winter.
  • Polar continental air approaches the UK in the east from Central Europe bringing hot, dry air in the summer and cold air and snow in the winter.
  • Tropical continental air approaches the UK in the south from North Africa bringing hot, dry air and hot weather in the summer.
  • Tropical maritime air approaches the UK in the south west from the Atlantic bringing warm, moist air and clouds, rain and mild weather. This affects the weather in Manchester.
  • Returning polar maritime air approaches the UK in the west from Greenland and the Arctic via the North Atlantic. This brings moist, mild and unstable air creating clouds and rain showers.
  • Polar maritime air approaches the UK in the North West from Greenland and the Arctic Ocean bringing wet, cold air from Greenland and the Arctic Ocean. This results in showery weather.

In Manchester our weather changes so rapidly because the warm air from the Atlantic and the cold air from the North Sea meet and form low air pressure where warm air rises.

What is Air Pressure?

 

The air around and above us has weight and pushes down on Earth due to the weight of the atmosphere. This is why it’s known as air pressure. Weather is influenced by air pressure.

 

When air pressure is low (less than 1016mb) warm air above the Earth’s surface is being heated and is rising. This is known as a low air pressure system.

 

When air pressure is high, cold air high up in the atmosphere is sinking towards the Earth’s surface. This is known as a high air pressure system or an anticyclone.

 

Different pressure systems bring different weather conditions. Low air pressure happens because the air is unstable. These systems bring clouds and rainfall.

 

The air in high air pressure systems or anticyclones is stable. As cold air sinks it becomes drier and warmer, but there is no water vapour. This means clouds do not form. The weather is usually settled with clear skies and sunshine. If air pressure is high for a long time, this can lead to drought. In the winter, temperatures can drop very quickly and water vapour on the ground condenses to form fog.

What are the different types of rainfall and how do they form?

 

The sun heats the water in the oceans, and rivers and lakes. Some water evaporates to form an invisible gas called water vapour. It goes into the air and rises. When air rises, it cools. So the water vapour condenses into water droplets that join together to form clouds. Droplets join to form bigger drops. When these grow heavy enough, they fall as rain.

 

Convectional rainfall occurs when the ground is heated by the Sun, causing moisture to evaporate and rise. The air rises quickly, and the water vapour cools and condenses forming clouds – tall cumulonimbus (rain clouds). Up draughts of warm air pushes water droplets high and suspends them there. Sometime, they are carried so high they freeze and form hailstone. Eventually, large water droplets fall as heavy rain, often with thunder and lightning. This results in periods of sunshine followed by heavy showers. This type of rainfall is very common in tropical areas but also in areas such as South East England during warm sunny spells.

 

Relief rainfall forces air to rise when it meets mountains/hills. As the air rises, it cools and forms condensation. The air continues to rise and clouds form. Rain falls on the mountains. As the air sinks down the other side of the mountains, it warms up and can hold more water vapour. This area of the mountains is drier and is known as the rain shadow.

 

Frontal rainfall occurs when a warm air mass meets a cold air mass, the warm, less dense air is pushed up above the cold, dense air to create a front. The warm, less dense air cools to form clouds. The water vapour condenses into water droplets and eventually it rains. The north west of England experiences this type of rainfall air warm maritime air from across the Atlantic meets polar continental air from central Europe.

 

Clouds are made up of millions of water droplets and ice particles floating in the sky. There are different classifications of clouds. Cirrus clouds are thin and wispy. Cumulonimbus clouds are big mushroom shaped at the top. Stratus clouds are like a big blanket of cloud.

What extreme weather does the UK experience?

 

Extreme weather is a weather event significantly different to the average or usual weather patterns. Extreme weather can last for a day or a short period of time. Examples of extreme weather include heatwaves, droughts, heavy rain and storms, heavy snowfall or strong winds.

 

The Beast from the East is a phrase used to describe cold wintery conditions in the UK resulting from the polar continental air mass. Ordinarily the jet stream from Mexico to the UK keeps the UK mild during the winter by bringing warm air across the Atlantic. However, stratospheric warming disturbed the jet stream changing the direction of winds from west to east to east to west, allowing cold wind from Russia to travel across the European continent as far as the UK. This happened between February and March 2018.

 

When the cold air left Siberia and Russia is around -50°C but it was just below freezing when it reached the UK. The air mass picked up water over the North Sea causes widespread snowfall across much of the country.

 

The severe winter weather brought widespread impacts.

  • On 28 February a man died after falling into a frozen lake in a London park.
  • There was severe travel disruption with roads closed, numerous road traffic collisions and cars were stranded overnight on many roads in both Scotland and England, for example the A31 in Hampshire and M80 in Scotland.
  • Rail series were cancelled and air transport was severely disrupted, for example Glasgow airport closed on 28 February.
  • Thousands of schools across England, Wales and Scotland were closed.
  • Many areas suffered power cuts.
  • Isolated communities and farms across the North Pennines received supplies by helicopter.

What is climate?

 

Climate is the average atmospheric or weather conditions over a long period of time, usually 30 years. Components of climate include how hot, cold, windy, wet or dry a place is. Climate is different to weather because it is measured over a longer period of time. Weather is the day to day conditions of the atmosphere, such as temperature and presence of rain, clouds and sunshine.

 

The UK has a mild climate. It is in the temperate climate zone and the sea affects the weather. In general, this means that Britain gets cool, wet winters and warm, wet summers. 

What factors affect climate?

 

The main factor that affects climate is latitude. Latitude means the distance north or south from the equator. The further you go from the equator, the cooler it gets. That’s because the earth is curved and so temperature is not distributed evenly. The Sun’s rays are more dispersed at the poles and cover a larger areas, so it is colder.

 

Prevailing winds are the dominant (main) wind direction in an area. The temperature of the wind and the amount of rainfall partly depend on where the air has come from. In the UK, the prevailing wind is from the south west. It brings water vapour from the Atlantic Ocean which results in more rainfall.

 

The sea is cooler than the land in the summer, and warmer in the winter. Sea breeze keeps the coast cool in the summer and warm in winter. Manchester is 36 miles inland from the coast.

 

An ocean current is the continuous movement of water from one place to another. There are warm and cold ocean currents and they can affect the climate of coastal areas. In Britain, a warm ocean current called the North Atlantic Drift keeps us warmer and wetter in the west of the UK than places in continental Europe.

 

The higher you are above sea level (altitude), the cooler it gets. The temperature falls by about 1 degree Celsius for every 100 metres in altitude. This explains why Scotland is colder than the south of the UK.

What are tornadoes and how do they form?

 

A tornado is a mobile (moving) column of rapidly rotating air which extends, usually, from a cumulonimbus (thunderstorm) cloud to the ground. They produce some of the fastest moving winds in the world with wind speeds in excess of 200mph.

 

Tornadoes commonly occur in spring in an area of the Mid-West of the USA known as “Tornado Alley”. This is due to the continental air mass in this area being very stable and the sun’s energy being very strong in these areas.

 

The UK experiences between 30 and 50 tornadoes every year. Although they are generally less violent than in the USA, they still produce wind speeds up to 145 mph.

  • Certain conditions are needed for tornadoes to form; particularly intense heat and stable air masses.
  • As the ground temperature increases, moist air heats and starts to rise (like convectional rain)
  • The warm wet air rises to meet cold dry air and forces through into the cold layer. A thunder cloud (or supercell) begins to form.
  • A thunderstorm develops quickly, there may be rain, thunder and lightning.
  • The upward movement (updraught) of air becomes faster and winds from different directions start to rotate.
  • Finally a funnel drops out of the cloud to the ground creating a vortex of winds which can be hundreds of metres wide.

Tornadoes cause most of their damage by the speed at which they spin, not the speed they move along the ground.

 

The damage they cause is measure using the Enhanced Fujita Scale. (EF).

The enhanced Fujita Scale is rated from 0 to 5 (zero being the least destructive, 5 causing almost total destruction to an area).