[Eoas-seminar] Meteorology PhD Defense for Kurtis Schubeck, Thursday, August 20, 2020, 3:30 PM on zoom

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Thu Aug 6 09:17:23 EDT 2020

Meteorology Seminar

Kurtis Schubeck

PhD Meteorology Candidate

Title:  The Effect of moist physics and resolution on baroclinic wave evolution

Major Professor:  Dr. Jeff Chagnon

Date: August 20th, 2020                         Time: 3:30 PM

Location: ZOOM

The advancement of numerical weather prediction (NWP) has hastened the effort to understand how moist processes -- many of which are parameterized in NWP models -- influence cyclone structure and intensity. Despite this effort, there still remain many open questions about the actual mechanisms by which moist physical processes modify a baroclinic wave and where those mechanisms are active. Recent investigations have focused on the roles of microphysics, convection, radiation, and horizontal potential vorticity (PV) dipoles in the modification of PV in the warm conveyor belt of an extratropical cyclone. These previous studies were designed to identify localized anomalies in PV and to determine how those anomalies were generated, either through use of Lagrangian trajectories or passive tracers. While these studies have provided a detailed description of the sub-synoptic scale modification of a cyclone due to diabatic processes, they have not clarified what is the overall impact of diabatic processes on the system-wide structure and evolution of the cyclone. The purpose of this study is to determine the systematic impact of parameterized process and resolution changes on the entirety of the cyclone. To accomplish this goal, an ensemble of simulations is conducted using various parametrization and resolution configurations. Through analysis of the ensemble of simulations, the complete effects of radiation, convection, and cloud microphysics on cyclone evolution are diagnosed.
Analysis of vertical profiles of PV averaged over the effective cyclone area (ECA) demonstrate that the baroclinic wave evolution is dominated by three processes: dry dynamics, microphysics, and radiation. Including cloud microphysics without radiation results in a cyclone that grows rapidly, reaching its peak intensity the earliest before cutting off and weakening. Despite rapid deepening, these "microphysics-only" simulations produce less precipitation and latent heating over the entire lifecycle when compared to the simulations that included radiation. The simulations with radiation deepen more slowly and cut off at a later time. Despite the slower evolution of the cyclone in the simulations with radiation, all simulations with radiation result in higher eddy kinetic energy and eddy available potential energy by the end of the simulation. While the tendencies contributed directly from the radiation scheme are relatively small, the inclusion of radiation also indirectly enhances the PV anomaly from the microphysics scheme.
While diabatic heating and DPV generation from radiation are small in comparison to the microphysics scheme, the nonlinear effects of radiation on the cyclone as a whole are significant. It is concluded that radiation plays a more important role in extratropical cyclone dynamics than originally thought and that diagnosing the effects of radiation in isolation from other physical process can lead to misleading results. Finally, it is shown that the system-scale structure and evolution of the cyclone is largely insensitive to grid resolution or the partitioning of precipitation between convective and large-scale contributions.

Shel McGuire
Florida State University
Academic Program Specialist
Department of Earth, Ocean, & Atmospheric Science
1011 Academic Way, 2019 EOA Building
Tallahassee, FL 32306

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