On the Atmospheric Infrared Continuum

Abstract

were confirmed and extended to include the region 4 -12 p.Unexpectedly high absorption was observed in this latter region.(ii) These results inspired a reexamination of all available previous work, from which it was concluded that the extinction arises from two separate effects with different frequency and temperature dependence.They are i) a foreignbroadened component, roughly proportional to the foreign gas pressure and probably positively temperature dependent (0.5 to 1% per °C); and ii) a self-broadened component roughly proportional to partial vapour pressure and with a strong negative temperature dependence (2% per °C at 30°C).On the basis of several assumed line shapes, the accumulated wings of lines in the 50 la rotation band were computed at several points in the range 12 -40 p; the Lorentz shape gave a very good fit (1. 10%) to the foreign-broadened component, but none gave a satisfactory fit to the selfbroadened component. *The 15 11 CO2 band was found to give no detectable absorption (< 1% for 43 atm -cm of CO 2' the equivalent of 1.4 km of air at sea level) outside the range 12.7 to 17.8 11.The horizontal path experiment has already been reported in a joint paper with F. Saiedy and P. A. Sheppard, entitled 'On the Atmospheric Infrared Continuum', J.O.S.A. 51, 466 (1963); a copy is attached to this thesis.During this research a further paper, on the related topic of terrestrial heat balance, entitled 'Heat-balance measurements from an earth satellite -an analysis of possibilities' was published in Quart. J. Roy. Met. Soc., 87, 231 (1961); a copy is attached. 11.13 See Addendum for amended version. ,Chapter 1?1. IntroductionThe existence of a continuous absorption throughout the atmospheric infrared window between 8 and 13 microns has been knoinfor a long time, Elsasser (1938) probably being the first to draw attention to it. It has been observed many times since by all workers in the study of atmospheric radiation, both in transmission observations using the sun and artificial sources, and in emission studies from ground and space 2.iii) Since the advent of artificial earth satellites, several infrared emission experiments have been proposed, or in some cases already been carried out, to determine the earth's surface temperature distribution, cloud top height, ozone and carbon dioxide distribution, and temperature structure in the upper atmosphere.All of these, except possibly the last, require correction to some extent for the continuum.Much discussion has centred on the question of the origin of the continuum absorption; there is no doubt that it is largely due to wcter vapour, but the role of aerosol is less certain. That it is necessary to appeal to something other than water vapour appears to be due to the fact that measurements of continuum absorption by different workers do not seem to be consistent when compared on the basis of the existing picture of the water vapour continuum alone. Whilst it is not disputed that aerosol absorption in the 8 -13j. region can be significant under extremel...

Infrared Absorption by H2O and N2O

“…The line parameters have a combined experimental-theoretical ^asis. Transmission spectra calculated on the basis of these parameters generally agree we 1 .! with experimental results when averaged over intervals several cm" 1 wiJe in regions where most of the absorption arises from lines centered within 20 or 30 cm"…”

“…These wi occur in a region containing many t^O lines of medium intensity between approximate!/ 1840 and 1990 cm" 1 .…”

A Numerical Study of the Formation and the Dissipation of Radiation Fogs

“…The values of the coefficients k1 and k2 are adopted as k1=0.1 (cm2 g-1 atm-1) and k2=10.0 (cm2 g-1 atm-1), respectively, from experimental data by Bignell et al (1963) and Burch (1970).…”

A P3-approximation Method as Applied to Foggy and Cloudy Atmospheres

“…(15). In the window region Similarly, the net (downward) flux of the infrared radiation is given by where P is the atmospheric pressure, e is the water vapor pressure, and the values of the coefficients k1 and k2 are assumed to be 0.1 cm2 g-1 atm-1 and 10 cm2 g-1 atm-1 from measurements by Burch (1970) and Bignell et al (1963), respectively. For brevity sake we assume again that the fog layer can be regarded as a single homogeneous layer.…”