The Atmosphere: Energy Transfer & Properties Weather Unit Science 10

Weather & Climate Weather can be defined as the physical conditions of the atmosphere at a specific time and place. Climate refers to average weather conditions over an extended period of time.

Components of Weather When we discuss weather it includes descriptions of temperature, precipitation, atmospheric pressure, humidity, wind speed and direction, and sky cover. All of these components are a result of what happens to the Sun’s energy when it enters the Earth’s atmosphere.

The Biosphere Energy from the sun interacts with the Earth's biosphere; the layer of air, land and water near the Earth’s surface where all life exists. The biosphere is composed of three different parts; the atmosphere (air), the lithosphere (land), and the hydrosphere (water).

Absorption of Energy and the Biosphere If the biosphere absorbed all the energy from the sun, life on earth would not be possible. Instead, the Earth maintains an energy budget by absorbing and reflecting a balanced amount of solar energy (the energy generated and given off by the sun).

Solar Energy Solar energy travels through a process known as radiation, a mechanism of heat transfer in which atoms or molecules give off energy as electromagnetic waves. The waves are carried through space and the atmosphere and do not release any energy until they come in contact with some form of matter (ground, water or air).

Wavelengths of Solar Energy While solar energy consists of seven different types of wavelengths, the majority of those that reach the Earth are in the form of visible light, infrared and ultraviolet wavelengths.

Visible Light Visible light travels through the atmosphere unchanged and is either reflected or absorbed by the Earth’s surface depending on the color and properties of the surface it strikes. The absorbed solar energy warms the surface and then the surface gives off energy in the form of infrared radiation.

Infrared Radiation from the Surface The atmosphere can absorb the infrared radiation given off by the ground and this warms the air. Some of the infrared radiation is passed back into space while some of it is trapped in our atmosphere by gasses such as carbon dioxide, water vapour and methane.

Earth’s Energy Budget The Earth maintains a balance between the energy it absorbs from the sun and the energy it radiates back into space. This is called the Earth’s energy budget and it is essential in sustaining Earth’s biosphere. How do you think we are doing maintaining Earth's energy balance in the 21 st century?

Solar Energy Budget Incoming Solar Radiation 49% absorbed by land 42% absorbed, reflected & scattered by clouds, gases and aerosols in atmosphere 9% is reflected by Earth’s surface Outgoing Radiation 69% is emitted as long- wave radiation 31% is emitted as outgoing solar radiation reflected by the surface, clouds and aerosols.

Factors Affecting Absorption of Energy The amount of energy a surface will absorb is affected by its color. Darker surfaces will absorb more energy while lighter surfaces will reflect energy. How much energy a substance reflects is known as its albedo. The albedo of a surface can change with the seasons. For example an open field covered with snow in the winter will have a higher albedo than in the summer.

Factors Affecting Absorption of Energy The type of substance will also influence its albedo. Water is an excellent heat sink which means it can absorb and retain a larger quantity of energy than most other substances before changing state. This is because water has a high specific heat capacity (much higher than air or land)

Water and Weather Due to the high specific heat capacity of water, it has a big influence on weather. Areas near large bodies of water will tend to have cooler summers and warmer winters than inland locations.

Greenhouse Gases as Heat Sinks Greenhouse gases such as carbon dioxide, methane and water vapour act as a heat sink because they absorb outgoing radiant energy and reflect it back in all directions. This is why the Earth does not completely cool at night and they cause the troposphere (where weather occurs) to retain more heat.