中高层大气物理学Hydrostaticbarometricequation静液压气压方程.ppt

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 Absorption by 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 Radiative Transfer Calculation Assumptions: Monochromatic (single wavelength) radiation The atmosphere consists of a single absorbing species, which decreases exponentially with altitude of a const H. The atmosphere is horizontally stratified. I(λ,z), incoming solar radiation at wavelength at altitude z σ (λ), wavelength-dependent absorption cross section ?(z) ?(s) z ? I(λ,z) ds Maximum Absorption Height The absorption (σ .n.I) must reach a maximum at some altitude (z). ?(z) ?(s) z ? I(λ,z) ds Maximum Absorption Height For an atmosphere in hydrostatic equilibrium ?(z) ?(s) z ? I(λ,z) ds Maximum Absorption Height Finally we get Atmosphere with const H N Integrate from infinity (source of the radiation) Optical depth The intensity of the radiation decreases to 1/e at the height of maximum absorption. Optical depth, ? At maximum absorption height, ?m=1 dimensionless Altitude n I dI/dz σ (Cross Section) ?m=1 The smaller is the cross section of certain wavelength interaction with gas particles, the deeper can it penetrate into the atmosphere. Altitude n I dI/dz Maximum rate/height Rate The ratio σi/σa = ηi is called the ionization efficiency The production at maximum can never be larger than for an overhead Sun. Height Constant scale height The height of the maximum ion production deceases as the zenith angle decreases. Absorption rate In an isothermal atmosphere Independently of the zenith angle the ionization prof