  The steady and transient response of "dynamically" dry and moist atmospheres
to uniform sea-surface temperature (SST) is studied. Specifically, the latent
heat (Lv) of water vapor is varied, so that for small Lv, water substance is
essentially a passive tracer from a dynamical point of view. Despite the lack
of SST gradients, a general circulation with Hadley and Ferrel cells is
observed for relatively stronger moist coupling. Organized precipitation
patterns via equatorial waves appear to play a significant role in tropical
ascent, and along with the equatorial deformation radius, the Hadley cell width
increases with coupling strength. An abrupt switch to a much shallower tropical
cell is noted when the system becomes completely passive. In all cases, the
Hadley cell is thermally indirect and is influenced by eddy fluxes which are
strong in the upper and lower troposphere. Moist static energy is transported
equatorward in the tropics and a larger amount is directed poleward in the
midlatitudes. Transient extratropical activity is seen in the form of intense
warm-core vortices for strong coupling, and these systems become weaker and
smaller as Lv decreases. The drift of these moist vortices results in the
observed poleward energy transport in the midlatitudes. In the tropics,
intraseasonal variability is dominant and systematically shifts to longer time
periods with stronger coupling. In fact, large-scale, low-frequency Kelvin
waves and MJO-like modes disappear as water vapor becomes passive in nature.
Finally, extreme rainfall events associated with cyclonic storms vanish as
water vapor becomes dynamically inactive. Tropospheric heating due to a
saturation of the outgoing longwave radiation results in an increase in the
stability of the atmosphere for strong coupling, and provides a plausible
physical mechanism for interpreting the behavior of precipitation.
