A cloud resolving model investigation into the dynamics and microphysics of hot towers

Cloud resolving model simulations run over a large domain are used to understand the mechanisms that drive the deepest of tropical convective cores upward to the tropical tropopause. These cores, known as “hot towers”, are critically important units in the climate system, since they are responsible for much of the energy transport from lower to higher latitudes within the Hadley circulation. Convective elements that qualify as hot towers are examined; these towers often exhibit non-negligible dry air entrainment in the middle to upper troposphere. Their ascent to the tropical tropopause would therefore seem to be paradoxical, apart from evidence that thermodynamical or microphysical processes are somehow enhancing convective buoyancy. This study identifies some of the dominant physical modes responsible for hot tower ascent to the tropical tropopause. This will be achieved through analysis of a large domain, long duration cloud-resolving simulation that accurately represents the tropical environment and captures many hot towers.

Physical processes within hot tower cores are assessed along ascending parcel trajectories. The starting locations of the parcels are chosen systematically, and parcels are advected through use an interpolated wind field. This interpolation occurs in both 3-D space and time using non-linear functions derived from localized wind field gradients. When parcels conserve thermodynamic scalars such as ice-liquid water potential temperature or equivalent potential temperature along portions of their ascent, understanding is gained into the underlying microphysics at the levels at which conservation occurs. Latent heat budgets and other microphysical characteristics are also constructed along the ascending trajectories. These results are quantified and presented in this study.