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Challenge of the Challenge of the Weather and ClimateWeather and Climate

Weather Vs ClimateWeather Vs Climate

Weather is the day to day interaction of Weather is the day to day interaction of the atmosphere.the atmosphere.

Climate is the weather over a period of Climate is the weather over a period of years, often 30 year periods.years, often 30 year periods.

Factors affecting climateFactors affecting climate

Latitude or distance from the Latitude or distance from the equatorequator

Temperatures drop the further an area is from the equator. Due to the curvature of the earth. In areas closer to the poles, sunlight has a larger area of atmosphere to pass through and the sun is at a lower angle in the sky. As a result, more energy is lost and temperatures are cooler.

In addition, the presence of ice and snow nearer the poles causes a higher albedo. This means that more solar energy is reflected, also contributing to the cold.

Air MassesAir Masses

Different Air Mass = Different Air Mass = different weatherdifferent weatherThe main air masses that affect Britain are The main air masses that affect Britain are those that form over the Mid-Atlantic but those that form over the Mid-Atlantic but there are several other air masses that bring there are several other air masses that bring particular weather conditions. particular weather conditions.

The air masses are defined according to The air masses are defined according to where they originated and their course of where they originated and their course of travel. travel.

For example air from Arctic regions is For example air from Arctic regions is classified as classified as Arctic maritimeArctic maritime as it originates as it originates in the Arctic and travels across the North Sea. in the Arctic and travels across the North Sea.

Another example is Another example is Tropical maritimeTropical maritime air which originates near the Gulf of air which originates near the Gulf of Mexico and travels across the warm Mexico and travels across the warm Atlantic Ocean before arriving in Britain. Atlantic Ocean before arriving in Britain.

Other air masses include the Polar Other air masses include the Polar maritime, Polar continental and Tropical maritime, Polar continental and Tropical continental.continental.

Ocean CurrentsOcean Currents

A warm ocean current called the North A warm ocean current called the North Atlantic drift is a major driving force, Atlantic drift is a major driving force, especially in the winter giving us milder especially in the winter giving us milder temperatures than places with the same temperatures than places with the same latitude eg. Moscow.latitude eg. Moscow.

North Atlantic DriftNorth Atlantic Drift

Prevailing WindsPrevailing Winds

The prevailing wind is the most frequent wind The prevailing wind is the most frequent wind direction a location experiences. direction a location experiences.

In Britain the prevailing wind is from the In Britain the prevailing wind is from the southwest, which brings warm, moist air from southwest, which brings warm, moist air from the Atlantic Ocean. the Atlantic Ocean.

This contributes to the frequent rainfall. When This contributes to the frequent rainfall. When prevailing winds blow over land areas, it can prevailing winds blow over land areas, it can contribute to creating desert climates.contribute to creating desert climates.

Maritime InfluenceMaritime Influence

Britain has a Britain has a maritime climatemaritime climate. A warm ocean . A warm ocean current called the current called the North Atlantic DriftNorth Atlantic Drift keeps keeps Britain warmer and wetter than places in Britain warmer and wetter than places in continental Europe.continental Europe.

The sea affects the Uk climate. We live on an The sea affects the Uk climate. We live on an island, so the air above us tends to be humid island, so the air above us tends to be humid (with water). This explains the mainly cloudy (with water). This explains the mainly cloudy weather with large amounts of rainfall.weather with large amounts of rainfall.

Continentality (distance Continentality (distance from the sea)from the sea)

Oceans heat up and cool down much more Oceans heat up and cool down much more slowly than land. slowly than land.

This means that coastal locations tend to be This means that coastal locations tend to be cooler in summer and warmer in winter than cooler in summer and warmer in winter than places inland at the same latitude and altitude. places inland at the same latitude and altitude.

Derry, for example, is at a similar latitude to Derry, for example, is at a similar latitude to Moscow, but is much milder. Moscow, but is much milder.

AltitudeAltitude

Locations at a higher altitude have colder Locations at a higher altitude have colder temperatures. Temperature usually decreases temperatures. Temperature usually decreases by 1° C for every 100m in altitude.by 1° C for every 100m in altitude.

If it is 20 degrees at the bottom of the If it is 20 degrees at the bottom of the mountain, with the mountain 1000m high, then mountain, with the mountain 1000m high, then it will be 10 degrees at the top. it will be 10 degrees at the top.

Air is forced to rise up over upland areas giving Air is forced to rise up over upland areas giving them higher amounts of precipitation.them higher amounts of precipitation.

Types of RainfallTypes of Rainfall

There are 3 types:There are 3 types:

1.1. ConvectionalConvectional

2.2. ReliefRelief

3.3. Frontal (Depressions)Frontal (Depressions)

Stage 1.Stage 1.The sun heats the ground and warm air rises. The sun heats the ground and warm air rises.

Stage 2Stage 2

As the air rises it cools and water vapour condenses to form As the air rises it cools and water vapour condenses to form clouds.clouds.

Stage 3.Stage 3.

When the condensation point is reached large cumulonimbus When the condensation point is reached large cumulonimbus clouds are formed. clouds are formed.

Stage 4. Stage 4.

Heavy rain storms occur. These usually include thunder and Heavy rain storms occur. These usually include thunder and lightening due to the electrical charge created by unstable lightening due to the electrical charge created by unstable conditions. conditions.

Stage 1.Stage 1.Warm wet air is forced to rise over high land. Warm wet air is forced to rise over high land.

Stage 2.Stage 2.As the air rises it cools and condenses. Clouds As the air rises it cools and condenses. Clouds form and precipitation occurs. form and precipitation occurs.

Stage 3.Stage 3.The drier air descends and warms. The drier air descends and warms.

Stage 4.Stage 4.Any moisure in the air (e.g. cloud) evaporates. Any moisure in the air (e.g. cloud) evaporates.

Stage 1.Stage 1.An area of warm air meets and area of cold air. An area of warm air meets and area of cold air.

Stage 2.Stage 2.The warm air is forced over the cold air.The warm air is forced over the cold air.

Stage 3.Stage 3.Where the air meets the warm air is cooled and Where the air meets the warm air is cooled and water vapour condenses. water vapour condenses.

Stage 4.Stage 4.Clouds form and precipitation occurs.Clouds form and precipitation occurs.

What is pressure?What is pressure?

Pressure is the Pressure is the weight of air pressing weight of air pressing down on the earth's surfacedown on the earth's surface. Pressure . Pressure varies from place to place and results in varies from place to place and results in pressure systems. pressure systems.

Isobars and frontsIsobars and fronts

Isobars are lines on a weather map Isobars are lines on a weather map joining together places of equal joining together places of equal atmospheric pressureatmospheric pressure..

On the map the isobar marked 1004 On the map the isobar marked 1004 represents an area of high pressure, represents an area of high pressure, while the isobar marked 976 represents while the isobar marked 976 represents an area of low pressure. an area of low pressure.

Note that: The numbers measure the atmospheric pressure in

millibars.

Usually isobars are drawn at intervals of two or four millibars (one thousandth of a bar).

The closer the isobars are together the windier it is.

If the lowest number is in the middle circle this is a low pressure or depression. Often low pressures mean wet and windy weather.

If the highest number is in the middle circle, this is a high pressure or anticyclone. Often high pressures mean dry, sunny weather.

Air pressure tends to range from 890mb (a hurricane) to 1060mb (an anticyclone).

Synoptic chartsSynoptic charts

3 types of front3 types of front

Note the three different kinds of front shown on the map - a cold front, a Note the three different kinds of front shown on the map - a cold front, a warm front and an occluded front.warm front and an occluded front.

Fronts occur where two different Fronts occur where two different air massesair masses meet. meet.

Occluded fronts occur at the point where a cold front takes over a Occluded fronts occur at the point where a cold front takes over a warm front or vice versa. If a cold front undercuts a warm front it is warm front or vice versa. If a cold front undercuts a warm front it is known as a cold occlusion and if the cold front rises over the warm known as a cold occlusion and if the cold front rises over the warm front it is called a warm occlusion. Occluded fronts bring front it is called a warm occlusion. Occluded fronts bring changeable weather conditions.changeable weather conditions.

On a synoptic chart occluded fronts are represented by semi-circles On a synoptic chart occluded fronts are represented by semi-circles and triangles positioned next to each other. The triangles are in blue and triangles positioned next to each other. The triangles are in blue and the semicircles are in red, or both are purple (mixing both red and the semicircles are in red, or both are purple (mixing both red and blue colours together).and blue colours together).

Warm FrontWarm Front

Warm fronts are formed when warm air rises over a Warm fronts are formed when warm air rises over a mass of cold air. As the air lifts into regions of mass of cold air. As the air lifts into regions of lower pressure, it expands, cools and condenses lower pressure, it expands, cools and condenses the water vapour as wide, flat sheets of cloud.the water vapour as wide, flat sheets of cloud.

Warm fronts are shown on Warm fronts are shown on synoptic chartssynoptic charts by a by a solid line with semicircles pointing towards the solid line with semicircles pointing towards the colder air and in the direction of movement. On colder air and in the direction of movement. On coloured weather maps, a warm front is drawn with coloured weather maps, a warm front is drawn with a solid red line with red semicircles.a solid red line with red semicircles.

Cold FrontCold Front

Cold fronts are usually associated with Cold fronts are usually associated with depressionsdepressions. .

A cold front is the transition zone where a A cold front is the transition zone where a cold air mass is replacing the warmer air cold air mass is replacing the warmer air mass. mass.

The cold air is following the warm air and The cold air is following the warm air and gradually moves underneath the warmer air. gradually moves underneath the warmer air. When the warm air is pushed upwards it will When the warm air is pushed upwards it will rain heavily. rain heavily.

Weather with a cold front Weather with a cold front passing overpassing over

Often more rain will fall in the few Often more rain will fall in the few minutes the cold front passes than it minutes the cold front passes than it will during the whole passage of a will during the whole passage of a warm front. As the cold front passes, warm front. As the cold front passes, the clouds roll by and the air the clouds roll by and the air temperature is cooler.temperature is cooler.

Cold fronts are shown on synoptic Cold fronts are shown on synoptic charts by a solid line with triangles charts by a solid line with triangles along the front pointing towards the along the front pointing towards the warmer air and in the direction of warmer air and in the direction of movement. On coloured weather movement. On coloured weather maps, a cold front is drawn with a maps, a cold front is drawn with a solid blue line with blue triangles.solid blue line with blue triangles.

Occluded FrontsOccluded Fronts

Occluded fronts occur at the point Occluded fronts occur at the point where a cold front takes over a warm where a cold front takes over a warm front or vice versa. If a cold front front or vice versa. If a cold front undercuts a warm front it is known as undercuts a warm front it is known as a cold occlusion and if the cold front a cold occlusion and if the cold front rises over the warm front it is called a rises over the warm front it is called a warm occlusion. Occluded fronts warm occlusion. Occluded fronts bring changeable weather conditions.bring changeable weather conditions.

On a synoptic chart occluded fronts On a synoptic chart occluded fronts are represented by semi-circles and are represented by semi-circles and triangles positioned next to each triangles positioned next to each other. The triangles are in blue and the other. The triangles are in blue and the semicircles are in red, or both are semicircles are in red, or both are purple (mixing both red and blue purple (mixing both red and blue colours together).colours together).

DepressionsDepressions

      

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Depressions are areas of low Depressions are areas of low atmospheric pressureatmospheric pressure which produce which produce cloudy, rainy and windy weather. cloudy, rainy and windy weather.

These low-pressure systems often begin These low-pressure systems often begin in the Atlantic, moving eastwards towards in the Atlantic, moving eastwards towards the UK. They are responsible for the UK's the UK. They are responsible for the UK's changeable weather.changeable weather.

Warm FrontWarm Front

At the Warm FrontAt the Warm Front

At the warm front, lighter, warmer air from At the warm front, lighter, warmer air from the south (the south (tropical maritime airtropical maritime air) meets ) meets cooler air from the north (cooler air from the north (polar maritime airpolar maritime air) ) and rises gradually over it. and rises gradually over it.

As the warm air slowly rises it cools, its As the warm air slowly rises it cools, its water content condenses and clouds form water content condenses and clouds form ((nimbostratusnimbostratus then then altostratusaltostratus). The result ). The result is steady rain, later giving way to drizzle is steady rain, later giving way to drizzle and finally clearer skies with high and finally clearer skies with high cirruscirrus clouds. clouds.

In the Warm sectorIn the Warm sector

Behind the warm front is an area of Behind the warm front is an area of warm, rising air and low pressure - the warm, rising air and low pressure - the centre of the low-pressure system. As centre of the low-pressure system. As this part of the depression passes this part of the depression passes over, there may be a short period of over, there may be a short period of clear, dry weatherclear, dry weather

Cold FrontCold Front

At the Cold FrontAt the Cold Front

However, at the trailing cold front, heavier, cooler However, at the trailing cold front, heavier, cooler air meets the warm air at the centre of the air meets the warm air at the centre of the depression, undercutting it and forcing it steeply depression, undercutting it and forcing it steeply upwards. Quickly moving air masses produce high upwards. Quickly moving air masses produce high winds and cooler temperatures... winds and cooler temperatures...

As the rapidly rising warm air cools, its water As the rapidly rising warm air cools, its water condenses and clouds form (condenses and clouds form (cumulonimbuscumulonimbus, then , then cumuluscumulus). The result is heavy rain or ). The result is heavy rain or thunderstorms, giving way to showers and finally thunderstorms, giving way to showers and finally to clear skies as the cold front moves away to clear skies as the cold front moves away eastwards.eastwards.

Occluded Front - DepressionOccluded Front - Depression

AnticyclonesAnticyclonesAnticyclones are the opposite of depressions – they are an area of high atmospheric pressure where the air is sinking.

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

AnticyclonesAnticyclones

What type of weather do What type of weather do Anticyclones bring?Anticyclones bring?

The absence of fronts means winds may be very light.

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

Summer Vs WinterSummer Vs Winter

In summer, anticyclones bring dry, hot weather. In winter, clear skies may bring cold nights and frost.

In cold conditions, anticyclones may also bring fog and mist. This is because the cold forces moisture in the air to condense at low altitudes.