Massive Parameter Sweep Experiment on Convective Cloud Environment: Changes in Rainfall Characteristics in Moisture–Instability–Shear Space

This study aimed to generalize the understanding of the dependence of convective clouds on the environment. We conducted a massive parameter sweep experiment on convective cloud environments using the warm bubble method with 15600 different profiles to examine how the rainfall characteristics of convective clouds change in response to environmental changes. The experiment showed that an increase in the conditional instability resulted in a significant increase in the total rainfall amount by several orders of magnitude, even when the precipitable water was almost identical. Vertical wind shear either enhanced or suppressed convective rainfall, depending on the degree of conditional instability. The threshold of conditional instability at which the effect of vertical shear switched from suppression to enhancement lowered as the magnitude of vertical shear increased. Regarding the depth of the shear layer, the effect of vertical shear became more significant as the depth increased from 3 km to 6 km. The drastic change in the rainfall amount reflects a shift in the mode of convective cloud development. When the conditional instability was large, vertical shear changed the convective cloud development from the “decay mode” to the “growth mode” in some environments, resulting in a significant increase in the rainfall amount.