Transcript Diapositiva 1 - ZANICHELLI.it

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The atmosphere
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Characteristics
of the atmosphere
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The atmosphere is a thin layer of gas
The atmosphere is a thin layer of gasses surrounding Earth.
It filters harmful solar radiation, distributes solar heat,
protects Earth from falling meteorites and interacts with
lithosphere, hydrosphere and biosphere.
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The structure of the atmosphere /1
The atmosphere is divided into layers with different temperature
and densities:
• troposphere (1-17 km) displays meteorological phenomena;
• stratosphere (up to 50 km) contains the ozone layer;
• mesosphere (up to 80 km);
• thermosphere (80 to 600 km);
• exosphere (beyond 600 km) is the outer layer from the
surface of Earth.
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The structure of
the atmosphere /2
99% of the air we breathe
is located in the first 32
km, and the highest
density is in the first 5-6
km from the surface of
Earth.
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The composition of the troposphere
Gas
Percentage in
volume
Nitrogen
78%
Oxygen
20,9%
Argon
0,9%
Carbon dioxide
0,04%
The troposphere is particularly
important for life. In this layer
there is mostly water vapor
(75%), and meteorological
phenomena and biogeochemical
cycles occur.
The troposphere is mostly heated
from below, by thermal radiation
from Earth.
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Earth’s thermal balance /1
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Earth’s thermal balance /2
Planet Earth absorbs only 49% of solar radiation
coming from space.
The remaining part is absorbed or reflected by the
atmosphere, which is mainly heated by long wave
radiation emitted from Earth.
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The greenhouse effect
Atmospheric CO2 and water
vapor trap part of the heat
from the Sun and reflect it
towards Earth, causing a
natural greenhouse effect.
Human activities are
increasing the greenhouse
effect due to the release of
greenhouse gases into the
atmosphere.
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The ozone layer protects life
The ozone (O3) layer in the stratosphere is formed from
oxygen due to the action of UV rays.
UV radiation + 3O2
2O3
This layer has a protective role, since it prevents UV rays
from reaching Earth and damaging living organisms.
The ozone layer can be reduced by the release of
chemicals, such as CFCs.
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Weather
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Weather is a temporary condition
Weather is the temporary situation of the atmosphere in a
certain place, determined by several factors:
• temperature;
• humidity;
• pressure;
• meteorological events (cloud cover, precipitation, winds).
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Temperature
Air temperature is influenced by:
• daily and seasonal astronomical factors (the height of
the Sun above the horizon and the day’s length);
• geographical characteristics of the territory (altitude,
presence of mountains, proximity to the sea…);
• the presence of vegetation;
• the presence of man-made structures.
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Temperature gradient
Temperature and altitude
Altitude influences
temperature:
air temperature decreases as
altitude increases, according to
a parameter called
temperature gradient
(6 °C / 1000 m).
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Thermal zones
The values of the average monthly and annual temperatures
are used to define five climate zones on Earth: one
equatorial zone, two temperate zones, two polar zones.
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Humidity and precipitation
Condensation
Transpiration
Air humidity depends
on the concentration
of water vapor from
the evaporation of
oceans and the
transpiration of plants.
Evaporation
When its concentration passes the saturation point, humidity
condenses into clouds, fog and precipitation.
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The atmospheric pressure
Atmospheric pressure = air weight / surface below it
CYCLONE
ANTICYCLONE
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Winds
Winds are masses of air that move horizontally from
anticyclones to cyclones. They can be constant (trade winds),
periodical (monsoons and breezes) or variable.
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Global atmospheric circulation /1
Atmospheric circulation is influenced by the existence
of stable areas of alternate low and high pressure.
This alternation generates three convective cells for
each hemisphere:
• the polar cell;
• the temperate cell;
• the tropical cell.
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Global atmospheric circulation /2
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Climate is not weather
Climate is the average of the meteorological conditions
of a region, calculated over a period of 30 years.
It is different from weather, which is the temporary
situation of the atmosphere in a certain place.
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