  General circulation models are a useful tool in understanding the three
dimensional structure of hot Jupiter and sub-Neptune atmospheres; however,
understanding the validity of the results from these simulations requires an
understanding the artificial dissipation required for numerical stability. In
this paper, we investigate the impact of the longitudinal filter and vertical
``sponge'' used in the Met Office's {\sc Unified Model} when simulating gaseous
exoplanets. We demonstrate that excessive dissipation can result in
counter-rotating jets and a catastrophic failure to conserve angular momentum.
Once the dissipation is reduced to a level where a super-rotating jet forms,
however, the jet and thermal structure are relatively insensitive to the
dissipation, except in the nightside gyres where temperatures can vary by $\sim
100\,\mathrm{K}$. We do find, however, that flattening the latitudinal profile
of the longitudinal filtering alters the results more than a reduction in the
strength of the filtering itself. We also show that even in situations where
the temperatures are relatively insensitive to the dissipation, the vertical
velocities can still vary with the dissipation, potentially impacting physical
processes that depend on the local vertical transport.
