Higher Geography 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: 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.

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.

1) The troposphere contains approximately 75% of the atmosphere's mass, and has an average depth of about 16 km. The troposphere 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.

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.

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.

Topic 1: Global Insolation Insolation: incoming solar radiation (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.

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 global heat budget.

The Heat Budget (p1) COPY AND MEMORISE THIS DIAGRAM!

The Heat Budget Incoming insolation = 100% 46% absorbed at surface 6% reflected by surface 19% absorbed by atmosphere 8% reflected by atmosphere 4% absorbed by clouds 17% reflected by clouds

The Heat Budget From the diagram we can see that less than half of the insolation actually reaches the earth – only 46%. Here the energy is converted back into heat energy and it warms the ground. As the ground warms up, it radiates energy back into the atmosphere. This outgoing radiation energy is called terrestrial radiation and is long wave or infrared.

The Heat Budget The main reasons for up to 54% insolation being ‘lost’ on the way to the Earth’s surface are: 1. Scattering – This occurs when light passes through a transparent medium, which contains small obscuring particles – therefore some light is scattered.

The Heat Budget 2. Reflection – The clouds, the atmospheric gases and the earth’s surface can reflect insolation. – Most is by the clouds – but the ice and snow sheets on the earth’s surface also reflect much. – The ratio between insolation and the amount reflected is called the albedo. – Some examples are given below: SurfaceAlbedo Thin clouds (cirrus)30-40% Thicker stratus50-70% Cumulonimbus90% Dark soil10% Coniferous forest & urban areas15% Grasslands and deciduous40% Fresh snow85%

The Heat Budget 3. Absorption – The atmosphere absorbs a relatively small amount of insolation, but a great deal of terrestrial radiation. – Most of this is absorbed by CO 2 and water vapour.

Why Does Insolation Vary Across The Globe?

1.Curvature Of The Earth Because the earth is a sphere, there are variations in the amounts of insolation received in different places. Both bands of insolation are the same width – therefore the same strength – yet the band which is near the north pole has to heat a larger area while the band at the equator can concentrate it’s heat in a smaller area. This means the insolation at the Arctic Circle is stretched and therefore weaker. AGAIN, COPY AND MEMORISE THIS DIAGRAM!

Latitudinal Variations in insolation

2.Thickness Of The Atmosphere The farther from the equator, the greater the amount of atmosphere the radiation has to penetrate. Therefore more is lost through scattering, absorption, reflection etc. At the Equator the thickness of atmosphere is comparatively thinner than at the Arctic Circle. This is again due to the earth being spherical.

3.Albedo The surface of the earth also affects the heat balance. The poles have a high albedo, due to the ice caps being light/white in colour. This results in heat loss through terrestrial radiation. They reflect heat. The equatorial areas have a low albedo due to the dark green and brown of the forests. They absorb heat.

4.Tilt Of The Earth - Seasonal As the earth tilts on its axis, the angle of the suns rays changes throughout the year. The sun is directly overhead the equator at the equinoxes: this means a peak of insolation at the equator. At this time, insolation is split between the two hemispheres.

4.Tilt Of The Earth - Seasonal After March 21 st the earth tilts and the northern hemisphere moves closer to the sun. By June 21 st the sun is overhead the Tropic of Cancer. This means the northern hemisphere is receiving maximum insolation. Due to the earth’s curve, the South Pole is receiving no insolation at this time. The opposite happens at the winter solstice (Dec 21 st ), when the North Pole receives no insolation. The tropical areas always receive insolation, no matter what time of year.

4.Tilt Of The Earth - Seasonal

Others Factors Affecting Insolation The Green House Effect Create a poster summarising the following: What causes the effect What affect does it have on global insolation Implications for the world if it is allowed to continue. Group 1 Damage to the Ozone layer Group 2