5. a) Write out an equation describing the intensity of infrared radiation propagating upward through a planetary atmosphere. Explain each term. (10 marks) b) Draw graphs of the height variation in the intensity of infrared radiation propagating upward through an atmosphere where 1) the atmosphere is colder than the surface ii) the atmosphere is warmer than the surface Explain using the equation of part (a). (10 marks) c) The spectra of intensity of infrared radiation measured from orbit above the Sahara Desert Antarctica are shown in Figures la and 1b. Explain why there is a relative minimum for wavelengths in the range 13 - 17 m above the Sahara Desert, but there is a relative maximum for the same wavelengths above Antarctica. (10 marks) Www 15112 (a) Sahara Desert 19 LOW 300 10000 od 10000000000000 Wovember 20111411 11 Ace Sheet Figure 1. Spectra of infrared radiation intensity mca ired from an orbiting satellite above (a) the Sahara Desert (no clouds) and (b) Antarctica (no clouds). Plank function curves at various temperatures are shown (dashed lines) for comparison. Wavelength lami 11 10 9 8 7 20 18 15 14 13 12 25 200 (a) Sahara Desert 150 Radiance ImWm srcm' 100 with 50 0 400 500 500 700 300 900 1000 1100 1200 1300 1400 1500 1500 Wavenumber cm) Wavelength (um 15 14 13 12 31 10 9 25 50 2018 9 45 (b) Antarctic Ice Sheet 40 30 25 20 Radiance ImW/srcm' o 400 500 600 700 300 1500-1600 900 1000 1100 1200 1300 1400 Waverumber com