On the Radiative Relaxation Time for the Hydrogen–Helium Atmosphere Estimated from Changes in the Activity Factor of Jupiter’s Hemispheres

Abstract

The subsolar point on Jupiter’s magnetosphere changes its position by an angle of approximately 26° over the orbital period of Jupiter, which induces seasonal variations in physical and optical characteristics of the planetary atmosphere. At the time close to the summer solstice for the northern hemisphere, Jupiter is in perihelion. Consequently, due to the significant orbital eccentricity, the energy influx into the atmosphere in the northern hemisphere is 21% larger than that in the southern one. This leads to the asymmetry in the meridional distribution of the reflectance of visible clouds. Analysis of the results of photometric observations of Jupiter for 1960–2019 showed that the ratio AJ = BN/BS adequately describes the activity of atmospheric processes on Jupiter, which shows periodic increases in brightness at tropical and temperate latitudes in the southern and northern regions by turn during one orbital period of Jupiter. The response of the atmosphere to changes in the irradiation by the Sun does not occur instantaneously but with some delay. The results of observations of Jupiter in the visible range in 1960–1995 and 2012–2019 show a synchronous delay of 3.4 year (τR ≈ 1.07 × 108 s) in response to the 21% change in the irradiation of different hemispheres when the planet is orbiting the Sun. In 1995–2012, the discrepancy caused by the orbital motion of the planet was observed between the behavior of AJ, the solar activity index Sn, and Jupiter’s regime of exposure to the Sun. Variations associated with the influence of solar activity are mainly induced by significant changes in the ultraviolet radiation of the Sun. These changes first affect the energetics of the upper atmosphere of Jupiter, after which they are indirectly transmitted into the troposphere, sometimes reducing the value of the relaxation constant τR to ~2.5 years. Since 2012, the behavior of the time dependence of AJ, the index of solar activity, and the irradiation regime of Jupiter due to its orbital motion have become consistent again. The periodicity in changes of the photometric characteristics of the northern and southern hemispheres of Jupiter were also restored.