  Moist processes are among the most important drivers of atmospheric
dynamics,and scale analysis and asymptotics are cornerstones of theoretical
meteorology. Accounting for moist processes in systematic scale analyses
therefore seems of considerable importance for the field. Klein & Majda (TCFD,
20, 525--552, (2006)) proposed a scaling regime for the incorporation of moist
bulk microphysics closures in multiscale asymptotic analyses of tropical deep
convection. This regime is refined here to allow for mixtures of ideal gases
and to establish consistency with a more general multiple scales modelling
framework for atmospheric flows. Deep narrow updrafts, so-called "hot towers",
constitute principal building blocks of larger scale storm systems. They are
analysed here in a sample application of the new scaling regime. A single
quasi-onedimensional columnar cloud is considered on the vertical advective (or
tower life cycle) time scale. The refined asymptotic scaling regime is
essential for this example as it reveals a new mechanism for the
self-sustainance of such updrafts. Even for strongly positive convectively
available potential energy (CAPE), a vertical balance of buoyancy forces is
found in the presence of precipitation. This balance induces a diagnostic
equation for the vertical velocity and it is responsible for the generation of
self-sustained balanced updrafts. The time dependent updraft structure is
encoded in a Hamilton-Jacobi equation for the precipitation mixing ratio.
Numerical solutions of this equation suggest that the self-sustained updrafts
may strongly enhance hot tower life cycles.
