Abstract
The development of an axially-symmetric convective circulation generated by release of an isolated light mass of moist air in an unstable stratification has been investigated by integrating the dynamic equations numerically. The equations include eddy viscous forces and heating by condensation of water vapor. All the condensed water is assumed to remain in the system (reversible process).
Unlike the spherical shape envisaged in bubble theories, the cloud generated here developes into a tall and slender current. The top is characterized by a sharp gradient of the condensed liquid water content and the rate of ascent of the top agrees approximately with the local vertical velocity. Physical variables such as vertical velocity and excess temperature take their maximum values near the cloud top. The trunk, extending from the cloud base to a little below the top, exhibits a columnar or cylindrical shape, rather than the cone typical of a thermal in neutral surroundings. When the environment is saturated, the physical variables inside the trunk approach a steady state. The radius of the trunk does increase with time, however, but at a rate much less than the ascent of the cloud top. When the surrounding air was not saturated, stable internal gravity waves were generated together with a fast rising cloud. These waves appear to prevent physical variables inside the trunk portion of the cloud from approaching a steady state.
Finally, some comments on the differences in circulation behavior arising from differences in the geometry of motion are presented (axial vs. line symmetry), together with a brief account of the temperature changes taking place in the surroundings as the convective element rises.
