Comparative Study of the Molecular Absorption Bands Behavior on Jupiter Before and at the Southern Equatorial Belt Disappearance

Introduction: The disappearance of dark Southern Equatorial Belt (SEB) in 2010 is not exclusive but very rare event on Jupiter. Preceding cases of the SEB disappearance or very low contrast took place in 1989 and yet no less 8 times during the last century : in 1952, 1949, 1943, 1940-1941, 1936-1937, 1927-1928, 1926 according [1,2]. In 1904 the NEB disappeared, if the orientation of two pictures for that time in [1] is right. It is evident that these changes are connected with more or less intensive vertical atmospheric circulation at low latitudes. Now we have an opportunity to search probable changes in the cloud structure from the study of the molecular absorption bands measurements on Jupiter’s disk and to compare them for SEB and NEB during “usual” and “unusual” state of the SEB region. The observations: Spectral observations of Jupiter on the observatory of Fessenkov Astrophysical Institute are fulfilling regularly during each season of this planet visibility [3]. There were 14 observational nights in June-October 2009 and 18 nights in JulyDecember 2010. For these observations 24-inch telescope and diffraction spectrograph SGS with CCDcamera ST-7XE were used. The spectra of central meridian of Jupiter have been recorded as well as special scanning of Jupiter’s disk was done by consequent records of zonal spectra at the slit oriented in parallel to Jovian equator. In general more 7800 spectrograms have been obtained and their processing is continued. But some conclusions may be done from preliminary analysis of the processing results. The analysis includes a number of the methane absorption bands in the range 580-900 nm and separately the ammonia band centered at 787 nm This band was measured from the Jupiter and Saturn spectra ratio to exclude metane absorption in this range. The spectra of Ganymede vere recorded also to exclude the telluric H2O absorption influence in the CH4 band 725 nm. Data processing: The profiles of the absorption bands were plotted and the equivalent widths and central depths of bands were calculated for all points of Jovian central meridian or for separate belts at low and temperate latitudes. Main view was directed on the comparison of the data for SEB and NEB in 2009 and 2010 to find probable and noticeable distinctions. Figures 1-2 illustrate the meridianal variations of the methane absorption for moderate bands CH4 619 and 725 nm. There are some small latitudinal differences which show an icrease of absorption in 725 nm within SEB and NEB although these differences are no more +/-3-5 per cent as well as for all temperate and low latitudes. The variations of the CH4 619 nm band are more and reach about 10 per cent. This band is formed significantly deeper in the cloud layers and its behavior is more irregular on Jupiter’s disk.