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Abstract A preliminary morphology of convective systems observed in the vicinity of Darwin, Australia is presented. Several types of tropical convection during monsoonal and break‐season flow are identified using specific examples and compared with a range of systems observed worldwide in the general context of the bulk Richardson number. A significant spectrum of convective activity ranging from low shear and low Convective Available Potential Energy (CAPE), to high shear and moderate to high CAPE, typical of mid‐latitude severe storms, is identified. Significant differences between monsoonal flow and break‐season systems are apparent. the formation of convective lines perpendicular to the low‐level shear and the apparent balance between advancing shallow cold pools and the shear are ubiquitous features. Convective‐scale downdraughts and mesoscale descent appear to be responsible for redistribution of 700 mb momentum to the planetary boundary layer (PEL). The motion of the break‐season squall lines appears to result from an equilibrium between the cold pool and the undisturbed environmental PEL flow. Deviations from this balance are hypothesized, to result in the observed ‘propagating’ and ‘non‐propagating’ or slow‐moving modes. Examples of these modes are given, showing the classical continuous development of new cells in a balanced state along the leading edge of long‐lived squalls and, in the propagating case, the discontinuous development of new cells on the cold pool ahead of the squall.
Keenan et al. (Wed,) studied this question.