Idealised convection in pure steam atmospheres

Atmospheres with a significant mass fraction of condensable gases may not be uncommon among terrestrial or sub-Neptune exoplanets. A wide variety of important planetary climate problems involve understanding of dynamical properties of condensible-rich atmospheres. Recent theoretical advances have shown that non-dilute dynamics, either in large or local scales, differs in fundamental ways from that in the dilute conditions. We further examine the properties of small-scale moist convection in non-dilute atmospheres using numerical simulations. Here we start with an extreme case of pure steam atmospheres using an idealized, fully compressible, non-hydrostatic model, with parameterized instantaneous condensation, rainout, and evaporation. Our preliminary results show that, in agreement with previous theory, pure steam atmospheres cease convective buoyancy due to the stringent relation between temperature and pressure. There seems to be a lack of hurricanes in such worlds even when rotation is included. We will discuss further situations wherein very simple clouds are included or a high supersaturation ratio is allowed. Implications for convective parameterization in global models will be also discussed.