Emily Maddox

Date of Award

January 2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Atmospheric Sciences

First Advisor

Gretchen Mullendore

Abstract

An idealized three-dimensional cloud-resolving model is used to investigate the sensitivity of cross-tropopause convective mass transport to tropopause definition. A ten-hour simulation is conducted to encompass the growth and decay cycle, with focus on irreversible transport above the tropopause. Six previously published tropopause definitions are evaluated. These definitions include specific values of altitude, World Meteorological Organization (WMO) temperature lapse rate, potential vorticity, stratospheric tracer concentration, static stability, and curvature of the Brunt-Vaisala Frequency. This investigation highlights the challenge of defining a tropopause during active deep convection, and demonstrates the need of clearly communicating calculation methods and threshold choices in the literature. Definitions such as potential vorticity and stratospheric tracer are shown to perform poorly when analyzing deep convection. The WMO thermal tropopause and static stability tropopause definitions perform the best, providing similar tropopause placement and quantities of irreversible mass transport.

An additional small investigation of the universality of tropopause definitions, including the WMO and static stability definitions, between the midlatitudes and tropics is performed using the Weather Research and Forecasting model. First, a thought experiment demonstrates that the WMO thermal tropopause identifies areas of similar temperature lapse rates, not necessarily similar stability, which plays an important role in mass transport. To investigate further, two case studies are analyzed to determine the tropopause placement in each region. Again, the WMO and static stability definitions provide similar placement of the tropopause in both regions.

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