Geography 121 Weather and Climate Welcome to Today: Solar Radiation Energy Energy is the capacity to do work or produce some change. It cannot be created or destroyed, however, it can change from one form to another. As energy changes it causes work to be done. Radiation Laws Every body with a temperature above -273.12oC (0 K, - 459oF) emits electromagnetic waves The amount of energy emitted by an object is proportional to the object?s temperature Hotter objects radiate at shorter wavelengths than cooler bodies Insolation in the atmosphere Insolation (incoming solar radiation) input ? the amount of solar radiation that is received at the surface Energy as it enters the atmosphere Transmission - passage of energy through atmosphere or water Scattering - changing direction of solar radiation movement, without altering its wavelengths Reflection - like a mirror Refraction - change in frequency and direction of solar radiation Absorption - assimilation of radiation and conversion from one form to another Solar Radiation in the Atmosphere Absorption Example: Hot slide in a slide projector Gases absorb radiation to different degrees, depending on wavelengths Absorption by Atmospheric Gases Absorption (Greenhouse Effect) Without the ?greenhouse affect? working the earth would have an average temperature of 0ºF (-18ºC) not 59ºF (15ºC) And would change rapidly from day to night Reflection and Scattering Reflection Scattering Reflected light bounces back (same angle, same intensity) Scattered light (weaker rays, various different directions) Scattering Sunburn in the shade Room is lit in the absence of direct sunlight No shadows outside during diffuse radiation Scattering at large particles (Fog, Smog) - whitish or grayish sky Scattering Shorter wavelengths are scattered more efficiently Scattering Refraction When light passes from one medium to another (e.g. empty space to atmosphere) Bending of the rays, shift of directions = Refraction Refraction 4 minutes after sunset Refraction Degree of refraction (bending) depends on the wavelength (example: prism) Dispersion ? color separation The Rainbow: Refraction and Reflection Refraction and Reflection in a Droplet Each droplet disperses the full spectrum of colors Observer will only see one color from a single raindrop. The Rainbow: Refraction and Reflection Primary Rainbow Violet reaches us from the lower droplet ? red reaches us from the upper droplet Secondary Rainbow violet red red violet Secondary Rainbow Two reflections Violet from the upper droplet Red from the lower droplet Albedo Reflective quality of a surface Percentage of insolation that is reflected (Reflected light / Incoming light) * 100 High Albedo of Clouds ? Satellite pictures Bright lights in the fog Albedo and Reflection Insolation in the atmosphere Clouds, aerosols, and the atmosphere?s albedo ? clouds can have cooling affect ? reflecting incoming insolation ?cloud-albedo forcing? Insolation in the atmosphere Clouds, aerosols, and the atmosphere?s albedo ? clouds can have cooling affect ? reflecting incoming insolation ?cloud-albedo forcing? OR clouds can have warming affect ? absorbing and reemitting long wave radiation from the earth ?cloud-greenhouse forcing? Clouds and Albedo Cooling effect Heating effect Earth?s Energy Balance Energy is transferred from one place to another in three ways Conduction Molecule-to-molecule transfer Convection Energy transferred by movement Radiation Energy traveling through air or space Heat Transfer (Heat absorbed by water vapor when water evaporates) Energy Budget by Latitude Everywhere poleward of ~ 36º Lat. More energy is lost to space than received over the course of the year. The atmosphere and oceans transport the heat surplus poleward as warm air, water vapor, and warm water. This is the motivation for atmospheric and ocean circulation Insolation (Annual Average) Sonora Sahara Arabia Gobi Namib Kalahari Australia Atacama Daily Variations in Air Temperature
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