Determination of Best Tropopause Definition for Convective Transport

An idealized three-dimensional cloud–resolving model is used to investigate the sensitivity of cross–tropopause convective mass transport to tropopause definition. A simulation is conducted to encompass the growth and decay cycle of a supercell thunderstorm, with focus on irreversible transport above the tropopause. Five previously published tropopause definitions are evaluated: World Meteorological Organization (WMO) temperature lapse rate, potential vorticity, static stability, vertical curvature of the Brunt Vaisala frequency, and stratospheric tracer concentration. By analyzing the behavior of different definitions both during and after active convection, we are able to define “best” choices for tropopause definition as those which return to a state most closely matching the pre–convective environment. Potential vorticity and stratospheric tracer are shown to perform poorly when analyzing deep convection. The WMO thermal tropopause and static stability definitions are found to perform the best, providing similar tropopause placement and quantities of irreversible mass transport. This investigation highlights the challenges of defining a tropopause in the vicinity of deep convection, and demonstrates the need to clearly communicate calculation methods and threshold choices in the literature.