Time-evolution of Mass Transport in a Supercell Storm

Deep convection is the primary mechanism for transporting chemical constituents from the planetary boundary layer up through the free troposphere and depositing these chemicals into the upper troposphere and lower stratosphere region. Although deep convection is recognized as important in transport, little is known about how transport varies, in both altitude and magnitude, over the lifetime of the storm. Previous analysis of an observed supercell demonstrated a large amount of variability when examining the level of maximum detrainment, or the level at which the maximum amount of mass is detrained from the updrafts. A cloud-resolving model was used to simulate the observed storm, showing a strengthening of the updraft as the storm transitioned to a rapid right-moving cell. The updraft core (w > 30 ms-1) increased in both altitude and magnitude, and the detrainment increased in magnitude while the level of detrainment increased in altitude.

The modeled storm included a passive boundary layer tracer, but irreversible mass transport in the updraft column is difficult to define due to negatively buoyant air in the overshooting storm tops. By assuming the downstream plume of lofted boundary layer air is representative of irreversible mass transport, the transport evolution derived from tracers and from vertical momentum divergence can be compared. For both methods, the maximum detrainment levels were located around 9 km near the mature stage of the storm and rapidly increased to ~ 11 km as the storm increased in strength and made its right turn. By analyzing the forcing terms of the vertical velocity tendency equation and comparing these terms to the evolution of the tracer plume, we gain further insight into the relationships between deep convective mass transport and the updraft evolution. Preliminary results from the forcing term analysis will be presented, and implications for transport parameterizations will be discussed.