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A. Marten, R. Moreno (Obs. Paris--Meudon), H.E. Matthews (Joint Astronomy Centre, Hawaii), T. Owen (IfA, Hawaii)
Since August 1994 the IRAM--30m telescope (Pico Veleta, Spain) and the JCMT (Mauna Kea, Hawaii) have regularly performed mm/submm heterodyne observations of Jupiter to follow the evolution of molecular species like HCN, CO and CS, newly--created in the stratosphere. The main results of this long--term monitoring are reported.
Complementary high--resolution spectra were recorded at both telescopes in several transitions of HCN, CO and CS. At the limbs of the planet complex line shapes were measured since the lines exhibited a mix of absorption and emission. Global mappings of Jupiter permitted us to trace the compositional changes during several oppositions of the planet with spatial resolution ranging from 10 to 14 arc sec. Synthetic radiative calculations using physical parameters appropriate to observations have been done for direct comparison with the spectral measurements.
Persistent layers for the three molecular compounds were observed around the 0.2--mbar pressure level. Analysis of spectral signatures has contributed to study the atmospheric cooling during the first months. Significant line intensity variations were seen in longitude in May 1995 from CS spectra taken in the southern hemisphere. Subsequently, continuous spreading toward the northern hemisphere was observed for the three species. In July 1997 we found that the latitudinal dispersion was not entirely achieved.
>From all spectra obtained at different latitudes there is some evidence that the total mass abundances of HCN and CO remain fairly constant with time. The CS mass has apparently increased by a factor of 2. Inhomogeneities were derived in the stratospheric temperature field. A model of latitudinal dispersion implying eddy diffusion processes only is proposed to explain our whole set of inferred abundances. This allows us to predict spatial and temporal abundance distributions for these compounds in the future.