Current Issue

24 September 1986, Volume 5 Issue 3   
  • A NUMERICAL EXPERIMENTAL STUDY ON THE TRANSFER OF SOLAR RADIATION IN CLOUDY ATMOSPHERE
  • Li Yinhai;Zhong Qiang
  • 1986 Vol. 5 (3): 211-225. 
  • Abstract ( ) PDF (1047KB) ( )
  • Based on the radiation model of two-stream approximation(Hense et al. 1982) this paper has investigated the effect of cloud on the solar radiation budget of the earth-atmosphere system and the heating rate of the atmosphere. The reflection and absorption of the clouds having various optical depth is discussed. This model has also been applied for the Plateau Model Atmosphere to investigate the effect of cloud on the solar radiation budget over the Plateau area. The absorption of cloud droplets and aerosol is included in the computation. The vertical distributions of the aerosol attenuation coefficients are adopted in two types, corresponding to visibility of 23km and 8km, respectively. It is shown that the heating rates of the cloud layer having optical depth 10-100 can reach 7-8℃/day. The absorption of cloud droplets and aerosol is an important mechanism for increasing heating rate in cloud layer. The cover of cloud layer has a great influence upon the neatiog rate near earth's surface. The reflectance of the cloud having various optical depth can vary within the range 0.24-0.90 coinciding with observation results basically. The absorptance of the cloud can vary within the range 0.07-0.25.Aircraft observations reveal that the absorptance of the cloud can reach 0.30-0.40. The mechanism responsible for this large absorption remains to be studied in depth. The ratio of the global radiation at the earth's surface in cloudy sky to that in clear sky(Q c/Q 0) is determined mainly by the cloud optical depth (corresponding to cloud optical depth increasing from 1 to 100 the ratio Q c/Q 0 decreases from 80% to 10%) and secondly by the solar zenith. The ratio Q c/Q 0 is much less influenced by the aerosol, surface altitude and cloud altitude and therefore is a adoptable parameter representing the influence of the cloud on the global radiation at the earth's surface.