2.  

The default values in ModTran (link in Canvas Pages) represent the mixing ratios of gases in today's atmosphere. Which one contributes the most to reducing the Earthlight shining into space (i.e. when looking down from 70km)? Use the 1976 US Standard Atmosphere. Turn off individual gases by setting their concentration or scale factor to zero. Don't forget to reset the values back to their default when you check the next gas. Default values are in the hints, or you can do a reload of the website (don't forget to change the locality back to the US after reloading the website!) The default parameters are 400ppm CO2; 1.7ppm CH4; 28ppb tropospheric O3; Stratospheric Ozone scale = 1 Ground Temperature Offset = 0 C; hold water vapor as a constant pressure (not constant relative humidity) ; water vapor scale = 1 Locality: Tropical Atmosphere with No Clouds or Rain The sensor is looking down from an altitude of 70km. The default is to not save the data. Carbon Dioxide (CO2) Methane (CH4) Trop. Ozone (O3) Strat. Ozone (O3) Water Vapor (HOv)