Influence of atmospheric parameters on downward longwave radiation and features of its regime in Moscow

Measurement results of downward longwave radiation (DLR) in a wavelength range of 3.5–50 μm are considered which have been obtained with the use of a precision IR radiometer (Eppley pyrgeometer) of the PIR model at the Meteorological Observatory of Moscow State University in 2008–2010. The influence of air temperature and atmospheric moisture content on the DLR values has been analyzed; correlations between DLR and the above parameters have been found. The effect of clouds on DLR has been estimated: DLR increases by about 30% in daytime and by 25% in nighttime under overcast low clouds. The annual average DLR in Moscow is 305 W/m2, with a minimum in December–March and a maximum in July–August. Variations in DLR throughout a year can exceed 250 W/m2. The daily average amplitude is 18–33 W/m2 in summer and 6–13 W/m2 in winter. An increase in DLR by about 40 W/m2 is noted under conditions of haze from forest and peat-bog fires and an aerosol optical depth of about 4 at a wavelength of 500 nm.