中高层大气物理学第二章absortion吸收.pptVIP

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中高层大气物理学第二章absortion吸收.ppt

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中高层大气物理学第二章absortion吸收

LOGO PHYSICS OF THE MIDDLE AND UPPER ATMOSPHERE中高层大气物理学Absorption 2011 Optical Depth 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 profile will maintain its form Chapman Production Profile For very large x (x ? 0 or z ? zm,0) the profile takes the form The profile decays by altitude as the density of the target atmosphere above the maximum. For very small x (x ? 0 or z ? zm,0) the profile takes the form The profile decreases very rapidly with height below the altitude of peak production. Ionization Rates Profile Applications Absorption Heating rate Dissociation rate Ionization rate Atmospheric Absorption Processes Ionization O2 + h? ? O2+ + e*, … Dissociation N2 + h? ? N + N, … Excitation O + h? ? O* O*? O + h?’ radiation O* + X ? O + X deactivation Dissociative ionization – excitation N2 + h? ? N+* + N + e, … Potential Energy of Biatmoic Molecule Dissociation/Ionization Potential The different constituents in the atmosphere have different ionization and dissociation potentials. X-ray region (0.1-17nm) and EUV region (17-175nm) are especially significant to the ionization process. Species Dissociation (?) Dissociation (eV) Ionization (?) Ionization (eV) H He O O2 N2 NO 2423.7 1270.4 1910.0 5.11 9.76 6.49 911.75 504.27 910.44 1027.8 796 1340 13.6 24.58 13.62 12.06 15.57 9.25 Cross Section of O λi=911A Cross Section of N2 λd=1270A λi=796A Cross Section of O2 λd=2422A λi=1026A Penetration of Solar Radiation Typical ionization cross-section