The Influence of Moisture on the Development of Tropical Deep Convection in High Resolution Simulations

A key variable in modulating convection and its interaction with the environment is the amount of moisture available to a developing storm. To a first order the relationship between moisture and convection is clear, as increased water vapor leads directly to an increase in buoyancy. Observations have consistently supported this basic premise, showing strong dependence of convective rain rates on tropospheric moisture content. Moister convective inflow, whether from the boundary layer or a deeper layer through the lower free troposphere, is linked with stronger and more active convection. Deep convection can be sensitive to moisture in the mid-troposphere due to mixing, or due to its role in forming downdrafts that can help sustain an organized system.

We set out to gain further insight into the varying sensitivities of tropical deep convection to moisture. This is accomplished using a cloud resolving model to produce an ensemble of idealized simulations with small variations on the initial conditions. In general when an environment has more low-level moisture available, storms will have enhanced buoyancy and updraft speeds, and larger extremes in precipitation rates. We use this idealized framework, perturbing relative humidity in specific layers of the troposphere, and can thus begin to disentangle the contributions of water vapor at different heights to the formation, maintenance and organization of tropical deep convective clouds.