Some Characteristic Features of Latitudinal Variations in Methane and Ammonia Absorption on Jupiter

Abstract

This paper examines the latitudinal variations in the intensity of methane and ammonia absorption bands in the near IR region of the spectrum (600–950 nm), such as CH₄ (619, 703, 727, 780, 861, 889 nm) and NH₃ (645, 790 nm). The results are presented as variations in the profiles of each of the absorption bands, their residual intensities, central depths and equivalent widths both in values obtained directly during the processing of spectrograms and in relation to the reference detail, as well as in relation to each other. The shallowest methane band at 703 nm and the deepest methane band at 886 nm give almost mirror-opposite values of absorption change along Jupiter’s central meridian. The extreme absorption values (maximum for 703 nm and minimum for 890 nm) coincide and fall on the boundary of the Equatorial Zone (EZ) and the Northern Equatorial Belt (NEB) at a relative distance of the radius of the planet’s disk r/R = 0.07. The remaining absorption bands of methane, as their intensity changes, occupy an intermediate position. As in previous years, a clearly expressed local decrease in the intensity of the NH₃ absorption bands is observed and especially centered at 787 nm at the boundary between the Equatorial Zone (EZ) and the North Equatorial Belt (NEB) compared to other regions of the central meridian. The decrease in absorption in this band begins almost from the equator, and its maximum occurs at the planetographic latitude of 10° N, then the absorption increases again, approaching the latitude of 20° N. The NH₃ absorption band at a wavelength of 645 nm also shows a decrease at low latitudes in the northern hemisphere. In the temperate latitudes of the Northern Hemisphere, absorption in this band is systematically lower than in the Southern Hemisphere. A comparison of the authors’ observations with data in the IR region and in the radio range is given, which show that the closest relationship between the brightness temperature and the absorption depth at 890 nm is observed in the upper stratosphere, in the latitude range of ±60°. Good agreement is also observed between the results of our estimates of the meridional absorption variations in the ammonia bands at 645 and 787 nm and the brightness temperature measurements performed at the VLA in the millimeter thermal emission range at frequencies of 8–12 GHz. The data for the 787-nm band in the wake region of the Great Red Spot are in particularly good agreement.