  We analyze data from the final two years of the Cassini mission to retrieve
the distributions of methane, ethane, acetylene, ethylene, and benzene in
Saturn's upper stratosphere and mesosphere from stellar occultations observed
by the Ultraviolet Imaging Spectrograph (UVIS), spanning pole-to-pole. These
observations represent the first 2D snapshot with latitude and depth of
Saturn's photochemical production region around northern summer solstice. Using
UVIS occultations and CIRS limb scans, we derive temperature-pressure profiles
and atmospheric structure models for each occultation latitude. W detect a
strong meridional trend in the homopause pressure level, which ranges from
approximately 0.05 microbar around the subsolar point to around 5 microbar at
the poles, implying much weaker mixing at the poles than near the subsolar
point. This trend could be explained by upwelling at low latitudes and
downwelling at high latitudes, requiring vertical wind speeds under 2 cm/s.
Photochemical product distributions follow this trend and also show a clear
seasonal trend at pressures between 0.01 and 10 microbar, with higher
abundances in the summer hemisphere. We compare the observed distributions with
results from 1D seasonal photochemical models, with and without ion chemistry,
to explore the impact of ion chemistry. We find that ion chemistry is
particularly important for matching the observed C6H6 distribution, while its
impact on other species is less pronounced. The best agreement between the
models and the observations is obtained in the summer hemisphere. Disagreements
between model and observations in the winter hemisphere and auroral region may
be due to the lack of transport by global circulation and auroral electron and
ion precipitation in our photochemical models. Finally, we compare C2H2
profiles from UVIS occultations with CIRS limb scans, finding good agreement
where they overlap.
