中高层大气物理学第二章Earthsradiation地球的辐射.ppt

LOGO PHYSICS OF THE MIDDLE AND UPPER ATMOSPHERE中高层大气物理学Earth’s Radiation 2011 Earth’s Energy Cycle Earth’s Radiation The Earth radiates heat in a much longer wavelength regime, namely in the infrared. 5 μ m to 60 μ m The Earth, has an average global temperature of 288 K. According to the Wien displacement rule the wavelength for maximum radiation of Earth is λm = 10μm. Greenhouse Effect The radiation from the Sun absorbed by the Earth is α is the albedo or reflection coefficient (≈ 0.3) and Ee is the solar constant According to the Stephan-Boltzmann law, the Earth as a black body will radiate a total energy per unit time given by For thermal equilibrium QSe = Qe about 40 K lower than the present day average global temperature. Greenhouse Effect H2O, CO2 and O3 absorb the infrared emission from ground and reradiate this heat in all directions and part of it back to Earth. Assume that the atmosphere is forming a thin layer encircling the Earth at a height h, and let this layer be transparent to the solar radiation, but opaque to the infrared radiation from the ground. The total heat radiated per unit time from the atmosphere will be If the atmosphere is only heated by the radiation from the Earth Greenhouse Effect For the Earth receiving heat from the Sun as well as from the atmosphere The greenhouse effect Ee αEe σTe4 σTa4 σTa4 Te Long-wave Radiation from the Earth Atmospheric Window, few gases in the atmosphere absorb terrestrial radiation in wavelengths between 8 μm and 12 μm. Absorptions are mainly due to H2O, CO2, O3 Radiation Outside the Atmosphere 地球表面和厚度大于100 m的云层都可以当作黑体看待。 根据基尔霍夫定律，任何物体的发射率等于它的吸收率。 大气在作为黑体发射的波长区间内是不透明的（所有的辐射都被吸收），而在不作任何发射的波长区间是透明的。 在大气的发射少于黑体发射的那一部分，也就是大气吸收率为0–1之间的部分，它只进行部分的吸收（半透明）。 -60oC 14oC * LOGO *