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The atmosphere 2 © Zanichelli editore 2015

Characteristics of the atmosphere 3 © Zanichelli editore 2015

The atmosphere is a thin layer of gas 4 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. © Zanichelli editore 2015

The structure of the atmosphere /1 5 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. © Zanichelli editore 2015

The structure of the atmosphere /2 6 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. © Zanichelli editore 2015

The composition of the troposphere 7 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. Gas Percentage in volume Nitrogen78% Oxygen20,9% Argon0,9% Carbon dioxide0,04% © Zanichelli editore 2015

Earth’s thermal balance /1 8 © Zanichelli editore 2015

Earth’s thermal balance /2 9 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. © Zanichelli editore 2015

The greenhouse effect 10 Atmospheric CO 2 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. © Zanichelli editore 2015

The ozone layer protects life 11 The ozone (O 3 ) layer in the stratosphere is formed from oxygen due to the action of UV rays. UV radiation + 3O 2 2O 3 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. © Zanichelli editore 2015

Weather 12 © Zanichelli editore 2015

Weather is a temporary condition 13 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). © Zanichelli editore 2015

Temperature 14 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. © Zanichelli editore 2015

Temperature and altitude 15 Altitude influences temperature: air temperature decreases as altitude increases, according to a parameter called temperature gradient (6 °C / 1000 m). Temperature gradient © Zanichelli editore 2015

Thermal zones 16 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. © Zanichelli editore 2015

Humidity and precipitation 17 Air humidity depends on the concentration of water vapor from the evaporation of oceans and the transpiration of plants. When its concentration passes the saturation point, humidity condenses into clouds, fog and precipitation. © Zanichelli editore 2015 Evaporation Transpiration Condensation

The atmospheric pressure 18 Atmospheric pressure = air weight / surface below it © Zanichelli editore 2015 CYCLONE ANTICYCLONE

Winds 19 Winds are masses of air that move horizontally from anticyclones to cyclones. They can be constant (trade winds), periodical (monsoons and breezes) or variable. © Zanichelli editore 2015

Global atmospheric circulation /1 20 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. © Zanichelli editore 2015

Global atmospheric circulation /2 21 © Zanichelli editore 2015

Climate is not weather 22 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. © Zanichelli editore 2015