  Super Earths and mini Neptunes likely have a wide range of atmospheric
compositions, ranging from low-molecular mass atmospheres of H2 to higher
molecular atmospheres of water, CO2, N2, or other species. Here, we
systematically investigate the effects of atmospheric bulk compositions on
temperature and wind distributions for tidally locked sub-Jupiter-sized
planets, using an idealized 3D general circulation model (GCM). The bulk
composition effects are characterized in the framework of two independent
variables: molecular weight and molar heat capacity. The effect of molecular
weight dominates. As the molecular weight increases, the atmosphere tends to
have a larger day-night temperature contrast, a smaller eastward phase shift in
the thermal phase curve and a smaller zonal wind speed. The width of the
equatorial super-rotating jet also becomes narrower and the "jet core" region,
where the zonal-mean jet speed maximizes, moves to a greater pressure level.
The zonal-mean zonal wind is more prone to exhibit a latitudinally alternating
pattern in a higher-molecular-weight atmosphere. We also present analytical
theories that quantitatively explain the above trends and shed light on the
underlying dynamical mechanisms. Those trends might be used to indirectly
determine the atmospheric compositions on tidally locked sub-Jupiter-sized
planets. The effects of the molar heat capacity are generally small. But if the
vertical temperature profile is close to adiabatic, molar heat capacity will
play a significant role in controlling the transition from a divergent flow in
the upper atmosphere to a jet-dominated flow in the lower atmosphere.
