Meteorology,Geography Department East China Normal University Shu Jiong,The Earths Global Energy Balance, Solar radiation is the driving power source for wind, waves, weather, rivers, and ocean currents. The earths energy balance, which includes land and ocean surfaces and the atmosphere, controls the seasonal and daily changes in the earths surface temperature.,Electromagnetic Radiation, Wavelength describes the distance separating one wave crest from the next crest. The unit to measure wavelength is the micrometer. Radiant energy can exist at any wavelength.,Radiation and Temperature, There is an inverse relationship between the radiation that an object emits and the temperature of the object. Hot objects radiate more energy, and at shorter wavelengths, than cooler objects.,Solar radiation, The Sun is a ball of constantly churning gases that are heated by continuous nuclear reactions. It has a surface temperature of about 6000oC. Like all objects, it emits energy in the form of electromagnetic radiation.,electromagnetic spectrum,Shortwave radiation Ultraviolet radiation (0.2 to 0.4 m) Visible light radiation(0.4 to 0.7m) Shortwave infrared radiation (0.7 to 3m) Longwave radiation Thermal infrared wavelengths (3m),Characteristics of solar energy, The sun does not emit all wavelengths of radiation equally The intensity of solar energy is strongest in visible wavelengths,Longwave radiation from the Earth, The earths surface and atmosphere are much colder than the suns surface,so the energy from the Earth has longer wavelength,The global radiation balance, The earth constantly absorbs solar shortwave radiation and emits longwave radiation. The sun provides a nearly constant flow of shortwave radiation toward earth. The atmosphere, land, and ocean also emit energy in the form of longwave radiation.,Figure 1 Global Energy Balance,Insolation over the Globe, Insolation(incoming solar radiation) depends on the angle of the sun above the horizon.,The Path of the Sun in the Sky,The suns path in the sky changes greatly in position and height above horizon from summer to winter. At equinox, the sun rises directly to the east and sets directly to the west. The noon sun is positioned at an angle of 50o above the horizon in the southern sky., The sun is above the horizon for exactly 12 hours. At noon it will be 73.5o above the horizon. The sun is above the horizon for about 15 hour,Daily Insolation Through the Year, Daily insolation depends on two factors: the angle at which the suns rays strike the earth the length of time of exposure to the rays the equator has two periods of maximum daily insolation, these periods occur near the equinoxes., There are also two minimum periods near the solstices, when the subsolar point moves farthest north and south from the equator. All latitudes between the tropic of cancer 23.5oN and the tropic of Capricorn 23.5oS have two maximum and minimum values . Seasonal pattern of daily insolation is directly related to latitude.,Annual Insolation by Latitude, Annual insolation varies smoothly from the equator to the pole The annual insolation value at the pole is about 40% of the value at the equator. The tilting of the earths axis redistributes a significant portion of the earths insolation from the equatorial regions toward the poles.,World Latitude Zones, The equatorial zone encompasses the equator and covers the latitude belt roughly 10oN to 10oS Spanning the tropics of cancer and Capricorn are the tropical zones, ranging from latitudes 10o to 25o north and south, Moving toward the poles from each of the tropical zones are transitional regions called the subtropical zones, ranging from latitudes 25o to 35o north and south The midlatitude zones lie between 35o and 55o latitudes in the northern and southern hemispheres, Bordering the midlatitude zones on the poleward side are the subarctic zone and subantarctic zone, 55o to 60o north and south latitudes Astride the arctic and Antarctic circles from latitudes 60o to 75o N and S lie the arctic and Antarctic zones The polar zones, north and south, are circular areas between about 75o latitude and the poles,Composition of the Atmosphere, The earths atmosphere consists of air-a mixture of various gases surrounding the earth to a height of many kilometers. Almost all the atmosphere 97% lies within 30km of the earths surface.,The upper limit of the atmosphere is at a height of approximately 10,000km above the earths surface, a distance approaching the diameter of the earth itself., Pure, dry air consists largely of nitrogen, about 78% by volume, and oxygen, about 21%. Other gases account for the remaining 1% Water vapor is an important component of the atmosphere that varies in concentration from place to place and time to time,Ozone in the Upper Atmosphere, Ozone (O3) is found mostly in the upper part of the atmosphere, in a layer termed the stratosphere. O