T. Fouchet 1, E. Lellouch 2, P. Drossart 1, H. Feuchtgruber 2, Th. Encrenaz 1, J. Crovisier 3, B. Bézard 1, & Th. de Graauw 4
1 DESPA, Observatoire de Paris, Meudon, France
2 Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany
3 ARPÈGES, Observatoire de Paris, Meudon, France
4 SRON, Groningen, The Netherlands
The methane photochemistry plays a major role in the stratosphere
of Jupiter. Its various photochemical products, like 
and
,
are optically active below 2000Å
where they absorb solar energy, and in the infrared where they act
as stratospheric coolers. The knowledge of their vertical distributions
is also a unique opportunity to retrieve the dynamical
state of the stratosphere: heavy hydrocarbons are produced around the
bar levela dn their downward transport is, to the first
order, directly proportional to the eddy diffusion coefficient, which
is essentially a free parameter in photochemical models.
Here we will present interpretation of the ISO/SWS grating observations
between 3 and 16
and their implications for our understanding
of the jovian stratospheric phtochemistry. The stratospheric temperature
profile is retrieved from the observation of the 
band (7.7 )
of methane. The vertical distribution of and
is deduced from respectively observations of the
(12.5 )
(13.7 )
bands. The
stratospheric eddy diffusion coefficient is determined from a first
simple photochemical analysis. Other hydrocarbons
and
are not detected but we derive upper limits of these constituents useful
for photochemical models.
The methane vertical distribution is itself poorly constrained in the
upper stratosphere (
). It is governed by the pressure
of the homopause - the level where the turbulent diffusion equals the
molecular diffusion - which is not known better than by an order of
magnitude. ISO/SWS observations of the 
band (3.3 )
of methane, seen for the first time in emission, will improve our
knowledge on this important question. The emission process in this band
is not thermal emission but fluorescence. Fluorescence occurs mainly
above the 5
level. the emitted flux is directly related to
the column density of methane above that level, and therefore to the
homopause pressure. Modelization of the ISO/SWS spectrum and a new constraint
on the methane vertical distribution are presented.
The ISO/SWS data set on Jupiter allows us a better understanding of the photochemistry and the dynamics taking place in the stratosphere of the giant planet.