ST. ANDREW’S HIGH SCHOOL GEOGRAPHY DEPARTMENT HIGHER GEOGRAPHY
Acid rain Global warming Greenhouse gases Atmosphere in the news Hole in the ozone layer CFC’s Climate change Atmosphere INTRODUCTION Skin cancers Although considered a difficult topic, this is the most up-to-date of the basic units!
Atmosphere In this unit we will be covering the following topics: • Topic 1: Global Insolation • Topic 2: Atmospheric Circulation • Topic 3: Oceanic Circulation • Topic 4: Air Masses • Topic 5: Climatic Change
Today we are going to find out: Atmosphere • What the atmosphere is and why it is important. • What global insolation and the heat budget are. • Why variations in insolation occur.
What is the atmosphere? Originally formed as the earth cooled, the atmosphere is a blanket of gases which contains solid material, such as volcanic dust and blown soils, and is attached to earth by the force of gravity. Atmosphere
This atmosphere is a mixture of oxygen (21%), nitrogen (78%), carbon dioxide (0.037%) and other gases such as hydrogen, helium, argon, neon, krypton, xenon and ozone. It also contains water vapour. These gases are densest at the Earth's surface and get less dense with increasing height. Around 90% of the atmosphere by weight lies in the lowest 15 km (9 miles) above the surface and it is only a very thin skin of air that keeps all life on Earth alive. Atmosphere
There are five main layers in the atmosphere. Atmosphere 1) The troposphere contains approximately 75% of the atmosphere's mass, and has an average depth of about 16 km. The troposphere is is where weather systems develop.
2) The stratosphere 16-50km is dry with rising temperatures. It contains large amounts of ozone gas which protects life on earth by filtering out most of the Sun’s harmful rays. 3) Many rock fragments from space burn up in the mesosphere 50-90km (middle sphere). As it lies between the maximum altitude for aircraft and the minimum altitude for orbital spacecraft, this is the most poorly understood part of the atmosphere. Atmosphere
4) The thermosphere is directly above the mesosphere. Within this layer, ultraviolet radiation causes ionization. The thermosphere, named from the Greek (thermos) for heat, begins about 80 km above the earth and can experience temperatures of 2,500°C. Atmosphere
5) The upper limit of our atmosphere is the exosphere. The main gases within the exosphere are the lightest gases, mainly hydrogen, with some helium, carbon dioxide, and atomic oxygen. Atmosphere
Topic 1: Global Insolation Insolation: incoming solar energy Less than half the incoming solar energy actually penetrates to the surface of the earth. The rest is lost in a variety of ways. Atmosphere
The Global Heat Budget Incoming heat being absorbed by the Earth, and outgoing heat escaping the Earth in the form of radiation are both perfectly balanced. If they were not balanced, then Earth would be getting either progressively warmer, or progressively cooler with each passing year. This balance between incoming and outgoing heat is known as Earth’s heat budget. Atmosphere
As the sun’s rays pass through the atmosphere, some are reflected, some absorbed and some pass through to reach the earth’s surface. Atmosphere
Variations in Insolation Because the earth is a sphere, there are variations in the amounts of insolation received in different places. Atmosphere Both bands of solar radiation are of the same strength. The band near the north pole though has to heat a large area (D-E) due the curve of the earth. The band at the equator can concentrate its heat in a smaller area A-B AGAIN, COPY AND MEMORISE THIS DIAGRAM!
Latitudinal Variations in insolation Atmosphere
Atmosphere Radiation Budget We can also compare energy received by the earth (insolation) with energy lost by radiation (terrestrial radiation). Insolation: solar energy received by the earth. Terrestrial radiation: solar energy lost by radiation. At the equator: insolation is greater than terrestrial radiation (due to darker forest material and higher land concentration), leading to a surplus in energy. At the polar zones, insolation is weak and terrestrial radiation is high (due to lighter light-reflecting snow + lower land concentration), leading to an energy deficit.
Seasonal Insolation Atmosphere Not only does insolation vary with latitude, it also varies with season. Because of the earth’s tilt, during the northern summer the sun is overhead at the Tropic of Cancer, and the Artic regions receive insolation 24 hours per day. However, in the northern winter, the sun does not shine on the Artic, so there is no insolation at all.
Atmosphere Factors Affecting Insolation The Green House Effect
Atmosphere What were the key points for ‘Variations in Isolation’ • Albedo Affect • Equator’s surface – low reflection (high insolation) • Pole’s surface – high reflection (high terrestrial radiation) • (land cover) Earth’s tilt • Earth’s orbit around the sun • Winter solstice – polar region – no solar insolation • Tropics – yearly solar insolation • Earth is a sphere • Concentrated rays at equator • Intensity from vertical rays
Topic 2 Atmospheric Circulation Atmosphere This diagram shows how heat from the Equatorial area is transferred to the polar regions by the circulation of the atmosphere in the Northern Hemisphere.
SOLAR ENERY CELLS AND HEAT TRANSFER The 3 CELL MODEL: The Formation of a Hadley Cell Atmosphere INSOLATION Insolation in tropical areas causes warm air to rise and spread polewards, carrying heat energy. Nb; lots of new terms to learn!
NORTHERN HADLEY CELL SOUTHERN HADLEY CELL. Atmosphere Air cools and begins to fall at about 30ºN and 30ºS of Equator. Cooled air returns to the Equator. SOLAR ENERGY Heat energy is therefore transferred from the Equator to sub-tropical latitudes.
FORMATION OF THE POLAR CELL Atmosphere Intensely cold, dense air sinks at the poles, then blows as surface winds towards the Equator.
NORTHERN POLAR CELLS. SOUTHERN POLAR CELLS. Atmosphere At about 60ºN and 60 ºS, the cold polar air is warmed in contact with the earth’s surface. This warmed air rises and returns polewards, carrying heat energy. This circular motion is called the POLAR CELL.
Atmosphere FORMATION OF THE FERREL CELL Unlike the Hadley and Polar Cells, the Ferrel Cell is not driven by differences in heat energy. The Ferrel Cell is caused by friction where air is in contact with the other two cells. (The Hadley Cell drags air down at about 30ºN and S. The Polar Cell causes an uplift at about 60ºN and S. )
Atmosphere Polar Cell THE THREE CELLS TOGETHER Ferrel Cell Hadley Cell Hadley Cell Ferrel Cell Polar Cell
ASSOCIATED PRESSURE BELTS Atmosphere Rising air at the equator causes the equatorial belt of low pressure Polar high pressure Mid latitude low pressure Descending air at about 30ºN and 30ºS causes the sub-tropical belt of high pressure Sub-tropical high pressure Equatorial low pressure Rising air at about 60ºN and 60ºS causes a mid-latitude belt of low pressure Sub-tropical high pressure Descending air at the poles causes the polar high pressure areas Mid latitude low pressure Polar high pressure
ASSOCIATED SURFACE WIND PATTERNS Atmosphere Winds always blow from high pressure to low pressure. They are deflected because of the Coriolis Force which come about because of the rotation of the earth. ( see later slide) Polar high pressure Mid latitude low pressure Sub-tropical high pressure Winds in Northern Hemisphere are deflected to the right. Equatorial low pressure Winds in the southern hemisphere are deflected to the left. Sub-tropical high pressure Mid latitude low pressure These wind belts shift seasonally. (See next section) Polar high pressure
Atmosphere Answer these questions fully in sentences. • Q1. What kind of pressure has rising air? • Low pressure has rising air. • Q2. What kind of pressure has falling air? • High pressure has falling air. • Q3.Name two latitudes with rising air. • The Equator and 60 degrees N/S have rising air. • Q4.Name two latitudes with falling air. • 30 degrees N/S and the Poles have falling air.
Atmosphere • Q5. Explain the two factors that make the NE trade winds blow in the direction they do. • ( You will need to be able to do this for any of the winds in diagram 13 !) • i) Air is flowing from a high pressure area at 30 degrees north towards a low pressure area at the Equator. ii). The winds are being deflected by the Coriolis force/ effect to the right as the area is in the northern hemisphere.
Atmosphere Rossby waves and the Jet Stream Not far above our heads in the northern UK is where the Ferrel and Polar cells meet. Here is where powerful waves of turbulence occur called Rossby waves. This turbulence is mainly responsible for the series of depressions and anticyclones that happen over Britain.
What are Rossby waves and jet streams? Rossby waves are high altitude, fast moving westerly winds, which often follow an irregular path. The path that they take changes throughout seasons, as shown in the diagram below: See the website for more information on Rossby Waves and the Jet Stream.
Atmosphere THE CORIOLIS EFFECT What happens when you set off in a plane to fly to somewhere? The earth turns beneath you, and you have to keep adjusting your direction ! Watch……….
Direction of Earth-spin New direction Thirty minutes in New direction Twenty minutes in Destination has moved Destination has moved Destination has moved Ten minutes in New direction Initial direction destination start Atmosphere Got the idea? Note the runners path is curved!
Atmosphere Watch Episode 1 of ORBIT
Atmosphere Ocean Currents
Atmosphere Ocean Currents You need to know how the ocean currents work in one ocean. The Atlantic will do. You need to remember the names of the currents and the directions in which they travel. You must know whether they are hot or cold. Note how the ocean currents also obey the Coriolis Force Laws.
Atmosphere Atmosphere Atmospheric Circulation So far, we have concentrated on the circulation of the air throughout the depth of the atmosphere. Now it is time to look in detail at air movements near the earth’s surface. It is easier to understand and remember this movement if we start with the global pressure belts. In theory, the global pressure belts are perfectly balanced north and south of the Equator.
Atmosphere The Main Global Pressure Belts There is a band of Low Pressure at the equator. There are two bands of High Pressure between 300 and 400 north and south of the Equator. There are two bands of Low Pressure around 600 north and south of the Equator. There are two bands of High Pressure over the North and South Poles.
OCEAN CURRENTS and HEAT TRANSFER Water heats up and cools down very slowly. But once it has stored it, it holds on to that temperature for a long time. As currents move, they transport heat and cold around the globe.
The pattern of ocean currents is linked to the pressure belts and wind patterns. • Land masses disrupt an otherwise straight-forward water flow pattern. • Winds blowing over currents assist them in transferring heat from warm to cool areas and vice versa. • Winds deflected by the Coriolis force help to create the currents. • The nature of the current affects the land masses it flows beside. Copy this
You will need to be able to give very detailed answers to a question on this area in an assessment. CASE STUDY AREA- the ITCZ in AFRICA This case study shows the way that the movement of thewind belts between their summer and winter positions has a profound effect on the lives – indeed the very survival- of people who live in the Sahel zone of northern Africa. You will need an atlas for most of this section. Get one now.
Copy text • The ITCZ is an area where two air masses meet- it brings heavy rain to the areas it passes over. • It happens all round the world between the Equator and about 20 degrees N/S. • Its full name is the Inter Tropical Convergence Zone. It is part of the Hadley convection cells, and has the Doldrums within its boundary.
The AFRICAN ITCZ REGION The ITCZ does not stay in the same area all year round but migrates to the north and then back south again. It is this movement that matters so much to the people and animals of the area. Discuss this diagram
The trade winds ( mT air mass) come into the zone from cooler areas in the southern mid- latitudes and have travelled over oceans; they are therefore carrying a lot of moisture.This is their position in January. Once in the hotter latitudes, they are energised into huge towering cumulo-nimbus thunderclouds. These can be anything up to 10kms across, and groups of clouds can form covering 1000kms. In between the clusters are often sunny cloud-free areas. The clusters are particularly found over land, not sea.
Wet warm mT air HEAVY RAINS IN JANUARY N S Copy diagram Hot dry cT air Moves this way ‘Harmattan’ wind Coastal areas- equatorial climate Gulf of Guinea Inland areas- savanna climate type Sahara- Desert climate type
In January, the sun is overhead near the Tropic of Capricorn, in the southern hemisphere. The ITCZ zone of meeting air lies well to the south, as seen here. The rains brought by the zone are confined to the very coastal areas of Nigeria, Togo, Ghana and their neighbours. Case study area ITCZ JANUARY
Atmosphere 23.50N 23.50N Equator Equator 23.50S July The Inter Tropical Convergence Zone- The ITCZ The movement of the ITCZ and its effects on rainfall can be best understood by examining the situation in Africa. NE Trade Winds Warm, Dry Winds (cT) Warm, Dry Winds Warm, Moist Winds (mT) The ITCZ in Africa In July SE Trade Winds Warm, Moist Winds The ITCZ in Africa In January 23.50S January
Atmosphere The Changing ITCZ The ITCZ moves north and south over Africa to “follow the sun”. However, the ITCZ sticks over the land areas since the land is warmer than the sea causing lower pressure over he land than over the area. ITCZ ITCZ ITCZ July September November