Solar Radiation and Insolation Incoming solar radiation: The output of electromagnetic energy emitted from the Sun that is received by the Earth. Intensity of radiation = The rate at which energy is radiated. Y X X = wavelength Y = temperature Inverse relationship: The higher the temperature the shorter the wavelength of radiation. Insolation is the portion of the Sun’s energy that is received by the Earth. The intensity of insolation from the Sun on a specific area of Earth is dependent on a number of factors. Effects of Earth’s Atmosphere on Insolation H20 vapor, methane and CO2 can ABSORB infrared (long wave)radiation. Ozone Much of the incoming solar radiation is REFLECTED or SCATTERED back into space, into the atmosphere or to Earth. Ozone Nearly all ultraviolet (short wave) radiation is ABSORBED by ozone (O3 gas) in Earth’s upper atmosphere. Aerosols --solids and liquids in the atmosphere – ie: pollutants, dust , ice, ash, water droplets, etc.. cause this scattering of radiation. Balance of Energy from Insolation and Earth’s Surface Radiation Nearly 50% of insolation reaches Earth’s surface. Nearly 50% of insolation is absorbed or reflected by the atmosphere. The amount of energy absorbed from insolation = Earth’s surface radiation. DYNAMIC EQUILIBRIUM Insolation received by the Earth’s surface is changed to heat energy. The Earth’s radiates this heat energy back into the atmosphere. Factors Affecting Absorption and Reflection of Insolation Angle of Incidence The higher the angle of incidence = The more insolation absorbed. Sun is high in the sky The angle of incidence is the angle at which insolation strikes the Earth’s surface. The lower the angle of incidence = The more likely the insolation will be scattered or reflected. Sun is low in the sky Factors Affecting Absorption and Reflection of Insolation Surface Characteristics The texture and color of features on the Earth’s surface can affect the absorption of insolation. Rough, uneven surfaces and/or dark surfaces absorb more insolation. Light and smooth surfaces tend to reflect rather absorb insolation. Factors Affecting Absorption and Reflection of Insolation Change of State and Transpiration Insolation may cause a change in phase for water. Insolation may fuel plant growth and increase the rate of transpiration -the process whereby a plant releases water vapor into the atmosphere. In both cases, insolation is neither reflected or absorbed, but transforms into potential energy. Land vs. Water Heating Equal areas of land and water do not heat up and/or cool off at the same rate. Water heats and cools more slowly than land for a number or reasons: Water is transparent and allows a greater area for insolation to penetrate compared to a land surface. Water has a higher specific heat than the land. Convection currents in water allow for the distribution of energy absorbed through insolation over a large volume. Some of the insolation striking the water may lead to a phase change (evaporation). The energy from insolation is transformed to potential energy. The Greenhouse Effect 1. Short wave insolation that reaches the Earth’s surface is absorbed. 2. The Earth’s surface reradiates the energy absorbed from insolation. However, the energy radiated has a longer wavelength (infrared radiation). 1. 3. “Greenhouse gases” in the atmosphere (ie: CO2, H2O vapor, etc…)absorb the infrared radiation emitted from the Earth . 4. The absorption of this radiation in the atmosphere warms our planet. 3. 2. 4. The Greenhouse Effect Modern history has shown an increase in the amount of “greenhouse gases” in the atmosphere. This increase is due primarily to human activity, such as the burning of fossil fuels and emission of pollutants in to atmosphere. The increase in “greenhouse gases” has led to an increase in the amount of radiation absorbed from the Earth. This, in turn, has led to an increase in average global temperatures. Result? Melting ice caps!!