Influence of solar activity on seasonal variations of methane absorption in the atmosphere of Saturn

Abstract

Seasonal variations of methane absorption distribution over the disk of Saturn at the levels of visible clouds and an overcloud haze have been found from the results of observations in the period from 1965 to 2011. The meridional behavior of the methane absorption at the equinox moments in 1966 and 1995 is opposite in phase to the analogous data obtained at the equinox in 1980. During the equinox in 2009, no difference in the methane absorption (expected to be analogous to that in 1980) between the southern and northern hemispheres at the mid latitudes of Saturn were observed, though all of the physical and orbital characteristics of Saturn at the equinox moments in 1966 and 1980, as well as in 1995 and 2009, are practically the same. Several years before the equinoxes in 1966, 1980, and 1995, the solar activity was rather high, while the Sun was in its minimum activity before the 2009 equinox. As has been shown, the dynamic time scale in the mid troposphere of Saturn may be of several dozens of hours if the condensation and convection are accounted for. In this case, large changes of the insolation in the UV spectral range may yield substantial short-term dynamical changes. At the equinox in 2009, convection in the atmosphere of Saturn was as low as possible; because of this, the deep cloud layers in the winter northern hemisphere remained “frozen” after the emersion from the rings’ shadow, while there were practically no active processes on the Sun. Due to this, the low-active cloud layer that had been shadowed before by the rings remained at the same level below the tropopause. This allowed a thick overcloud layer of gaseous methane and ammonia to be easily detected. Because of this, in the low-active hemisphere, where there had been winter before, the methane absorption remained practically the same and equal to the absorption in the hemisphere, where there had been summer before.