Abstract
Wave-CISK (conditional instability of second kind) with conditional heating on a rotating sphere is investigated using a global spectral model. With certain initial conditions, an eastward-propagating wavenumber-one mode with a single ascending region is obtained. With more general initial conditions, however, more than one convection events, of nearly equal strength and separated at nearly equal intervals, coxist and interact very little with each other. This happens when the radius for a convection event to affect other such events, which is inversely proportional to the growth rate, is much smaller than the circumference of the earth. In additional to the eastward propagating modes, a westward-propagating mode is also found, whose flow field is dominated by gravity wave response to the cumulus heating.
The above results indicate that the wave-CISK with conditional heating does not always select the eastward-propagating wavenumber-one mode. An alternative mechanism that leads to the selectivity of the wavenumber-one mode is suggested.
