Contributions of various classes of convection to rainfall in the Atlantic Ocean

Whilst the tropics comprise only 50% of the Earth's surface, 75% of the annual, global rainfall occurs there. Hence, the tropics are the latent heat engine for the general circulation of the atmosphere. In this environment, all manner of convective weather systems exist: intense and destructive tropical storms (TS), organized mesoscale convective systems (MCCs and CCCs here) and much weaker, short-lived convection (DSL). The relative importance of these differing convective weather systems to the hydrologic cycle of the Atlantic Ocean basin is considered here. An automated, satellite-based climatology and classification of these four different classes of convective weather systems is used to define system characteristics and contribution to basin-wide rainfall over an 18 month time period. It is found that short-lived thunderstorms (DSL class) are the largest contributors to the basin-wide rainfall, however their contribution represents only about half of the total diagnosed rainfall. Organized mesoscale systems contribute the balance. Hence, mesoscale organized weather systems seem to play an important rôle in the Atlantic Ocean hydrologic cycle. Due to the potentially large error bounds on the satellite rainfall climatologies used here, the results of this study are contrasted with the recent climatology of Cotton et al. (1995), which incorporates some estimates of rainfall characteristics for mesoscale systems based on numerical model simulations. Comparison of these two climatologies showed good agreement in the relative magnitudes of rainfall determined for each class of convection.