Variations of longwave downwelling irradiance (LDI) due to different atmospheric factors in Moscow

We present the results of continuous longwave downwelling irradiance (LDI) monitoring in Moscow from April 2008 to March 2012, which has been in operation at the Meteorological Observatory of Moscow State University (MSU MO). The measurements are carried out within wavelength range 3.5-50 μm using a precision infrared radiometer (PIR) which is regularly calibrated against international standards and tested in the Physical Meteorological Observatory in Davos (Switzerland) with accuracy comparable to the BSRN measurements (2-4 W/m2). According to these measurements the impact of various atmospheric factors on LDI has been assessed. For clear sky conditions we estimated the effects of temperature T and water vapor content W (cm). Water vapor content was evaluated from Cimel sunphotometer data (AERONET) in the 940 nm channel. A simple equation is proposed to retrieve the LDI in the absence of cloudiness and aerosol optical thickness at 500 nm (AOT500) less than 0.7 which has been compared with the results of ...