  Jupiter's tropospheric composition and cloud structure are studied using
Cassini VIMS 4.5-5.1 {\mu}m thermal emission spectra from the 2000-2001 flyby.
We make use of both nadir and limb darkening observations on the planet's
nightside, and compare these with dayside observations. Although there is
significant spatial variability in the 5-{\mu}m brightness temperatures, the
shape of the spectra remain very similar across the planet, suggesting the
presence of a spectrally-flat, spatially inhomogeneous cloud deck. We find that
a simple cloud model consisting of a single, compact cloud is able to reproduce
both nightside and dayside spectra, subject to the following constraints: (i)
the cloud base is located at pressures of 1.2 bar or lower; (ii) the cloud
particles are highly scattering; (iii) the cloud is sufficiently spectrally
flat. Using this cloud model, we search for global variability in the cloud
opacity and the phosphine deep volume mixing ratio. We find that the vast
majority of the 5-{\mu}m inhomogeneity can be accounted for by variations in
the thickness of the cloud decks, with huge differences between the cloudy
zones and the relatively cloud-free belts. The relatively low spectral
resolution of VIMS limits reliable retrievals of gaseous species, but some
evidence is found for an enhancement in the abundance of phosphine at high
latitudes.
