The Restless Atmosphere Weather
The Atmosphere • The atmosphere is a blanket of gases surrounding the earth. • It is made up of a mixture of different gases.
Solar Energy – Energy from the Sun • The sun provides us with heat and light. • However, not all of the sun’s energy reaches our planet. • 50% of the sun’s energy reaches planet earth. • 25% is deflected back into space by dust and clouds in the atmosphere. • 25% is absorbed as it passes through the atmosphere.
Latitude • Latitude means distance North or South of the equator. • It is measured in degrees. • In general, the further a place is away from the equator, the colder it will be. • There are 3 reasons for this.
Latitude 1. We know the sun’s energy is absorbed as it passes through the atmosphere. Well, at the poles the atmosphere is thicker than at the equator. Therefore, less heat gets through to the polar regions. 2. At the equator the sun shines directly overhead. This means the heat is concentrated on a small area and so this area becomes hot. 3. At the poles the sun’s energy is slanted and it is spread over the curved surface of the earth. This means it has to heat up a larger area and so this area does not heat up as much. In summary, less heat gets through to the poles. It has to heat up a large area. Lots of heat gets through to the equator. It has to heat up a smaller area.
Wind • Wind is moving air. • Air moves from High pressure areas to Low Pressure areas.
Winds and Air Pressure • Air moves from High Pressure areas to Low Pressure areas. • Some places on the earth have high pressure and some have low pressure. But why? • Warm air rises leaving areas of low pressure. • Cold air descends creating areas of high pressure.
High and Low Pressure Areas • If we apply this principle to the earth we see that some places on the earth’s surface will have high pressure and other areas will have low pressure. • These areas of different pressure create wind.
Global Wind Patterns • We now know that winds travel from HP areas to LP areas. • This creates a regular pattern of the different winds on the earth.
Global Winds and the Coriolis Effect • The earth is spinning on its axis. • Because of this the winds are deflected at an angle. • They are deflected to the right in the Northern hemisphere, and to the left in the southern hemisphere. • This is called the Coriolis Effect.
Air Masses • An air mass is a body of air with its own temperature, pressure, and humidity level. • Air masses can effect the weather of the countries they pass over. • Many different air masses meet over Ireland so our weather changes a lot. There are 4 different air masses which effect Ireland’s weather. • 1. Polar Air Masses • 2. Continental Air Masses • 3. Tropical Air Masses • 4. Maritime Air Masses
Fronts • When two air masses meet they do not mix very well because of their different temperature, pressure and humidity. • Where the two air masses meet is called a Front. • We will look at two types of Fronts, a Cold Front and a Warm Front.
Cold Fronts • A Cold Front occurs when cold air moves in towards warm air. • The cold air forces the light warm air to rise. • As the warm air rises it cools and condensation occurs. • Clouds are formed and this leads to heavy rainfall.
Warm Fronts • A Warm Front develops when warm air moves in towards cold air. • The warm light air rises up over the cold air. • As it rises it cools and condensation occurs. • Clouds are formed and this leads to rainfall.
Depressions • A Depression is an area of Low Atmospheric Pressure. • Depressions are also known as Cyclones. • Depression often pass over Ireland. • Depressions bring wet and windy weather. This is why we receive lots of rain.
Anticyclones • An anticyclone is an area of high pressure. • Anticyclones bring clear sunny weather. • There are few clouds and a gentle breeze.
The Water Cycle • Water is a Renewable Resource. • When rain falls, the water is recycled and eventually goes back to the clouds to fall as rain again. • This is called the water cycle. • There are 4 stages in the Water Cycle. • Evaporation • Condensation • Precipitation • Run-Off
Clouds • Clouds are made when water vapour condenses into tiny droplets. • There are many different types of clouds. • The most common types of clouds are; • Cirrus Clouds • Cumulus Clouds • Stratus Clouds
Rainfall • Precipitation means hail, rain, sleet or snow. • Rain is the most common type of precipitation. • Rain occurs when warm air is forced to rise. As the warm air rises it cools. Cold air cannot hold as much water vapour as warm air, so condensation occurs. Clouds are formed and rain occurs. • There are 3 different types of rain, because there are 3 different reasons why warm air is forced to rise. • Relief rainfall • Frontal (cyclonic) rainfall • Convectional rainfall
Relief Rainfall • Relief rainfall occurs when; • Warm moist air moves in from the sea. • It hits a mountain range at the coast and is forced to rise. • It cools as it rises. • Condensation occurs, clouds form and it starts to rain.
Frontal Rainfall • Frontal rainfall occurs when; • Warm and cold air masses meet at a Front • The warm air mass moves up over the cold air mass. • The warm air cools and condensation takes place. • Stratus clouds form and rain occurs.
Convectional Rainfall • Convectional rain occurs when; • The sun shines on the land and heats up the air above it. • The heated air rises quickly. • As it rises it cools and condensation occurs. • Cumulus clouds are formed and heavy rain occurs.
The Weather • When we talk about the weather we usually talk about the following things. • Temperature • Precipitation (rain etc) • Sunshine • Wind speed • Wind direction • Atmospheric pressure • Humidity All of these different aspects of the weather can be measured. There are different weather instruments to measure each thing. These instruments are usually in a weather station.
Temperature • Temperature is measured using a Thermometer. • It is measured in degrees Celsius (°C). • Lines on a weather map showing areas of equal temperature are called Isotherms.
Temperature • You need to know how to calculate the; 1. Mean Temperature 2. Temperature Range Mean Temperature: Add all the monthly temperatures, then divide by 12. Temperature Range: Take the lowest temperature away from the highest temperature.
Precipitation • Precipitation is measured using a Rain Gauge. • It is measured in millimetres. • Lines on a map showing areas of equal precipitation are called Isohyets.
Sunshine • Sunshine is measured using a Campbell Stokes sunshine recorder. • Sunshine is measured in Hours per day. • Lines on a weather map showing areas of equal sunshine are called Isohels.
Wind • We can measure 3 things about the wind. • Wind Speed – Using an Anemometer. • Wind Direction – Using a Wind Vane. • Wind Strength – Using the Beaufort Scale
The Beaufort Scale • The Beaufort Scale describes the effect the wind has on the landscape. • Wind strength is divided into 12 forces. • The Beaufort Scale was invented by an Irishman.
Atmospheric Pressure • Atmospheric pressure is measured using a Barometer. • It is measured in millibars. • Lines on a weather map showing areas of equal pressure are called Isobars.
Humidity • Humidity is measured using a Hygrometer. • A common type of hygrometer is a wet and dry bulb thermometer. • It is expressed as a %. 100% is the maximum.