Components of infrared net radiation in a mountain valley

Abstract

The infrared components of the surface radiation budget in a mountain valley have been investigated theoretically. Calculations were based on a set of winter and summer atmospheric soundings specifying temperature and moisture content and for two valley models including a linear valley model and a circularly symmetric valley model. Radiance and irradiance calculations are compared with similar calculations for flat terrain. Downward irradiances at the valley center were shown to be higher than for flat terrain and were due to radiation from the valley sidewalls. The largest effect was obtained for a dry winter atmosphere with the sidewalls warmer than the valley bottom. Downward irradiance was increased by 16% over the flat terrain case and the net irradiance at the valley center was decreased by 24% which would lead to a decreased surface cooling. Calculations were made for five spectral intervals including the 6.5 micron water band (4.4 - 7 .8μ), the water vapor continuum or atmospheric window (7. 8 - 13. 4μ), the 15 micron carbon dioxide band (13. 4 - 16. 3μ), a small window (16. 3 - 20. 2μ), and the rotational water bands (20. 2 - 48. 8μ). Only the two bands described as windows contribute significantly to the changes in downward irradiance. The remaining three spectral intervals are nearly opaque to transmission of radiation from the valley sidewalls to the valley center.