Download Resource Material – Weather and Climate

Class VI
PBL Weather and Climate
Reading Material
Atmosphere; Composition and Structure
INTRODUCTION
The Earth is the only known planet on which life exists. The present condition and properties of the Earth’s
atmosphere support life. But, what is atmosphere? Atmosphere is a thin gaseous layer surrounding the
Earth. It is very thin when compared to the size of the Earth and contains a mixture of gases, yet, this thin
layer has its own influences on various processes that take place on Earth.
The atmosphere is special because it contains life-sustaining oxygen in large quantities (about 21% by
volume). In fact, it took millions of years and a wide range of different processes in order to reach its
present condition .
The atmosphere constantly exchanges energy and matter with other components of the Earth – the
lithosphere, hydrosphere and biosphere. Our atmosphere extends from a few meters below the Earth’s
surface to a height of about 60,000 km. However, about 90% of the atmosphere is within the first few
kilometres from the ground. This means that most of the mass of the atmosphere is near planetary
surface as the gravity pulls the atmosphere towards the Earth’s centre.
THE IMPORTANCE OF ATMOSPHERE
Our atmosphere is very important for sustaining life on Earth, containing life-supporting oxygen in large
quantities. A constant concentration of oxygen is maintained through the oxygen cycle. The oxygen cycle
does not take place in isolation but it takes place along with other bio-geo chemical cycles. These cycles
connect the atmosphere with the hydrosphere (water on Earth), lithosphere (land on Earth) and biosphere
(life on Earth). The atmosphere does not function by itself, but it functions in conformity with other
spheres on Earth.
Our atmosphere is the transparent layer through which, life-sustaining solar radiation passes and reaches
the Earth’s surface. Solar radiation is the only source of energy for photosynthesis to take place on Earth
supporting plant life and therefore all other forms of life.
COMPOSITION OF THE ATMOSPHERE
The Earth’s lower atmosphere is a mixture of many gases called air. The two main gases in air are nitrogen
and oxygen. Together, they form about 99 per cent of dry air by volume. The remaining 1 per cent is
mostly argon and carbon dioxide. The atmosphere also contains tiny amounts of helium, hydrogen, neon,
ozone, krypton, and other gases.
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Nitrogen- 78%
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Oxygen- 21%
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Argon- almost 1%
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Carbon Dioxide- .03%
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All Other Gases- .01%
Gas molecules at the bottom of the atmosphere are squeezed together by the gases above them. As a
result, 99 per cent of the atmosphere’s weight is found within about 32 kilometres of Earth’s surface. Half
the atmosphere’s weight is within 5.5 kilometres.
Air always contains some water vapour. Water vapour enters the air by evaporation from the oceans and
from water or plants on land. The amount of water vapour varies with location, season, and time of day.
Most of the water vapour is near the surface, and the percentage decreases with height.
Dust, another part of air, includes tiny grains of rock, dirt, pollen, salt crystals from sea spray, soot from
fires, chemicals from factories, and bacteria. Dust helps form fog and rain. Water vapour condenses
around some dust grains, forming tiny water droplets.
Incoming Solar Radiation and Ozone Layer
When solar radiation passes through the atmosphere, harmful ultra violet radiation gets “absorbed” by
the ozone layer, which is also a part of our atmosphere. The ozone layer prevents about 95% of harmful
ultra-violet radiation from reaching the Earth’s surface. When solar radiation passes through the
troposphere (the lowest layer of the a atmosphere) part of the radiation is reflected back by clouds,
scattered by atmospheric constituents (thereby reducing visibility) absorbed by atmospheric constituents
and the remainder reach the Earth’s surface (land or water).
Outgoing Backward Radiation and the Greenhouse Effect
The heated Earth emits energy in the form of infrared radiation at night and this radiation is absorbed by
carbon dioxide, water and a few other gases. This process results in the “greenhouse effect”. Thus, the
atmosphere is kept warm during night; otherwise it would become extremely cold and intolerable for
living organisms.
Weather Patterns
The Earth is not heated by solar radiation uniformly due to its inclination. As a result, different weather
patterns exist across the Earth at any one time. In order to compensate for these differences, air circulates
which results in winds. Winds can be of a global scale as well as on a local scale. They can be responsible
for disastrous storms like cyclones, dust storms, and tornadoes etc. These wind currents also influence
water currents in the oceans which in turn also affect wind currents. Consequently, understanding the
atmosphere and its functions and behaviour is quite complex. Because of all these processes, the
atmosphere is very dynamic.
STRUCTURE OF THE ATMOSPHERE
Scientists divide the atmosphere into four layers based on temperature changes.
The Troposphere
The layer closest to the Earth is called the troposphere. The troposphere starts at the Earth’s surface. Its
thickness depends on the latitude. At the equator the troposphere is about 18 kilometres thick; at the
poles it is only about 8 kilometres thick. The gases of the troposphere are essential to life on Earth. The
Earth’s weather occurs in the troposphere. Temperatures gradually decrease with altitude in the
troposphere. The top of the troposphere is called the tropopause. There, the decrease in temperature
stops. At the poles, the tropopause temperature is about -55 degrees Celsius.
Stratosphere
The second layer is the stratosphere. It reaches from the tropopause to a height of about 50 kilometres
from the Earth. The stratosphere is clear and dry. It has strong, steady winds and only few weather
changes. Because of its steady weather conditions, jet aircraft fly in the stratosphere. The lower part of
the stratosphere is as cold as the tropopause, then it warms up steadily to its top, at the stratopause. The
absorption of sunlight by ozone is what makes the stratosphere’s temperatures increase with height. The
ozonosphere is therefore located in the stratosphere.
Mesosphere and Thermosphere
The third and fourth layers are the mesosphere, in which temperatures drop again, and the thermosphere,
in which temperatures rise again. The top of the thermosphere is around 500 kilometres from the Earth.
In the thermosphere, nitrogen and oxygen atoms absorb solar energy, causing the temperature to rise.
Ionosphere
At heights between about 65 and 500 kilometres above the Earth, the air is highly ionised. The ions are
formed when ultraviolet rays from the sun knock electrons off oxygen atoms. This part of the atmosphere
is called the ionosphere. It stretches from the lower mesosphere to the top of the thermosphere. The ions
and electrons are concentrated in layers at four different levels. Each layer reflects radio waves of
different wavelengths. The ionosphere therefore reflects radio waves back to Earth which greatly
increases the area in which they can be received. The ionosphere does not reflect the waves used to
transmit television. These waves, however, can be picked up and re-broadcast by special satellites orbiting
high above the Earth. The ionosphere is affected by solar events. Eruptions on the sun send out large
amounts of short-wave radiation which disrupts radio communication.
The Auroras
Solar eruptions also send out ionised particles. Since they are electrically charged, these particles are
deflected by the Earth’s magnetic field to the North and South Poles. At the poles, the ionised particles
interact with air molecules to form auroras, coloured displays of light in the night time sky.
The Project
Introduction:
The reading material talks about the major components of the atmosphere and their classification in
layers based upon thermal changes. The basic information about Auroras and incoming and outgoing solar
radiation has also been given and in the end the importance of atmosphere for land and people has been
explained in detail.
The Task:
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The teacher will make groups and the students will be provided with a graph paper. They will plot
the temperature of different layers accordingly after reading the material carefully. They will label
the layers as well. Show temperatures in degree centigrade on the X axis and altitude in km above
sea level on Y axis.
They will scan the graph paper and add that to the power point presentation or they can straight
away plot the graph on excel and paste it on power point slide.
They can make an OHT in case they opt to use OHP for presentation.
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Separate the boundaries between each layer.
Mark the general location of the ozone layer.
Mark the ionosphere to know which layer has the ionization.
Find out more than what is written in the reading material about the formation of Auroras.
Find photographs of Auroras.
Find an appropriate video of either of the auroras, not more than 6 minutes duration.
Prove that the Earth’s atmosphere is important for the land and people by comparing it with
Venus and Mars.
Number of Periods:
Four (4) periods are required to carry out this project.
Success Criteria:
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The duration of power point presentation or OHT will not be more than 10 minutes.
The presentation will include slides beginning with the details of members of group to references
in this order
 Main topic
 Group details
 Introduction (what is the task)
 Materials used
 Video link
 Conclusion
 References (for materials used)
Every group member has to present a part in front of the audience
Slides should be relevant to the topic
Slides should not be overwhelmingly colourful or contain too much information
Suggestions:
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Information can be gathered from multiple sources such as different websites of SUPARCO, NASA,
HAARP, encyclopedia etc.
Students can use different sources which may include facts and figures, tables, charts, diagrams
Library period can be integrated with this project.