SIMULATION OF THE INTENSITY AND POLARIZATION OF SKYLIGHT DURING TWILIGHT PERIOD

Monte-Carlo method is applied to simulate the intensities and degrees of polarization in twilight sky after the eruption of the El Chichon volcano and during the 1977 volcanically quiet period, respectively. The results coincide well with the observations. It is found that the significance of multiple scattering is com-pletely different in these two periods; the background concentration of stratospheric aerosols has probably increased since the 1960s. It is necessary to study the cause of the increase and its impact on climate.