ENERGY TRANSFER IN THE ATMOSPHERE:
Atmosphere surrounds the earth made up of different layers of gases such as Argon, Oxygen, Nitrogen, Exophere, Thermosphere, Mesophere, Stratosphere, Toposphere
The energy that drives the climate system comes from the Sun. When the Sun's energy reaches the Earth it is partially absorbed in different parts of the climate system. The absorbed energy is converted back to heat, which causes the Earth to warm up and makes it habitable. Solar radiation absorption is uneven in both space and time and this gives rise to the intricate pattern and seasonal variation of our climate. To understand the complex patterns of Earth's radiative heating we begin by exploring the relationship between Earth and the Sun throughout the year, learn about the physical laws governing radiative heat transfer, develop the concept of radiative balance, and explore the implications of all these for the Earth as a whole. We examine the relationship between solar radiation and the Earth's temperature, and study the role of the atmosphere and its constituents in that interaction, to develop an understanding of the topics such as the "seasonal cycle" and the "greenhouse effect".
The Sun and its energy.
The Sun is the star located at the center of our planetary system. It is composed mainly of hydrogen and helium. In the Sun's interior, a thermonuclear fusion reaction converts the hydrogen into helium releasing huge amounts of energy. The energy created by the fusion reaction is converted into thermal energy (heat) and raises the temperature of the Sun to levels that are about twenty times larger that of the Earth's surface. The solar heat energy travels through space in the form of electromagnetic waves enabling the transfer of heat through a process known as radiation.
Solar radiation occurs over a wide range of wavelengths. However, the energy of solar radiation is not divided evenly over all wavelengths but is rather sharply centered on the wavelength band of 0.2-2 micrometers (μm=one millionth of a meter).
The physics of radiative heat transfer.
Before proceeding to investigate the effect of solar radiation on Earth we should take a moment to review the physical laws governing the transfer of energy through radiation. In particular we should understand the following points:
The radiative heat transfer process is independent of the presence of matter. It can move heat even through empty space.
All bodies emit radiation and the wavelength (or frequency) and energy characteristics (or spectrum) of that radiation are determined solely by the body's temperature.
The energy flux drops as the square of distance from the radiating body.
Radiation goes through a transformation when it encounters other objects (solid, gas or liquid). That transformation depends on the physical properties of that object and it is through this transformation that radiation can transfer heat from the emitting body to the other objects.
Radiation transfer from Sun to Earth.
Properties of Solar radiation: The Sun is located at the center of our Solar System, at a distance of about 150 x 106 kilometers from Earth. With a surface temperature of 5780 K (degrees Kelvin = degrees C + 273.15), the energy flux at the surface of the Sun is approximately 63 x 106 W/m2. This radiative flux maximizes at a wavelength of about 0.5 μm.
Solar radiation on Earth: As the Sun's energy spreads through space its spectral characteristics do not change because space contains almost no interfering matter. However the energy flux drops monotonically as the square of the distance from the Sun. Thus, when the radiation reaches the outer limit of the Earth's atmosphere, several hundred kilometers over the Earth's surface, the radiative flux is approximately 1360 W/m2.
