Location
Off Campus : via WebEx
Date & Time
October 30, 2020, 11:00 am – 1:00 pm
Description
ADVISOR: Dr. Belay Demoz
TITLE: Investigating of the Role of Boundary Layer Convergence on Elevated Convection and Transport Dynamics in the Southern Great Plains During the Warm Season
ABSTRACT: The planetary boundary layer (PBL) is a turbulent, well-mixed layer in the lower troposphere which plays an essential role in mesoscale dynamic processes and the transport of chemical species, aerosols, and water vapor. For decades, forecasting skill for afternoon thunderstorms driven by synoptic scale forcings and high values of convective available potential energy (CAPE) have steadily improved, while skill in predicting nocturnal thunderstorms driven by more nuanced forcings such as bore waves and converging boundaries in the PBL have not made appreciable advances. In the Southern Great Plains (SGP) where agriculture is a vital component of the economy and precipitation has a direct impact on soil fertility, forecast accuracy is critical both from an economic and public safety perspective.
Convergent PBL boundaries have been simulated in previous research, although these studies rely on assumptions including linearity, hydrostaticity, and two-dimensionality which do not always prove to be useful, particularly when gravity waves are present. Additionally, few real nocturnal convection cases are documented in the literature. This research aims to fill theoretical gaps which simulations are unable to resolve using ground-based remote sensing observations from three field campaigns: 1997 IOP, PECAN, and SCOAPE.
Observations from the 1997 IOP field campaign in the SGP reveal a unique boundary layer convergence with nearly vertical lifting of water vapor and symmetric divergence aloft. This structure, which we refer to as “symmetric convergence” leads to transport of water vapor over the preceding environmental air mass, a tendency not discussed in previous research. Ground-based remote sensing instruments including a Radar Wind Profiler, Raman Lidar, Atmospheric Emitted Radiance Interferometer (AERI), Microwave Radiometer, and Meteorological Towers collected observations including wind magnitude and direction, water vapor mixing ratio, and temperature from multiple perspectives as the symmetric convergent boundary passed over the research site. From these observations we will show evidence and propose to establish theories of symmetric convergence. This work will also use observations to derive dynamic quantities and extend current theories involving vorticity ventilation and cross-sectional CAPE in terms of elevated convection. Comparisons between observations and model simulations of this event will allow us to determine the extent to which convergence theories hold true in the environment. The PECAN field campaign collected similar observations of elevated convection initiated by converging boundaries and bore waves over the SGP. Case studies of these events, some of which led to convection, and others which failed to trigger convection will be similarly evaluated in order identify ideal conditions for elevated convection to occur. SCOAPE observations, which contain observations of chemical concentrations in the atmosphere will be used to characterize PBL convergence from the perspective of transport dynamics.
The importance of improving understanding of PBL convergent boundaries has implications for convective weather forecasting and applications of chemical transport. We provide a unique perspective of the PBL during such events with the merging of observations, theory, and modelling to enhance our field’s knowledge of dynamics at work in the boundary layer.
Proposal will be held using WebEx.
TITLE: Investigating of the Role of Boundary Layer Convergence on Elevated Convection and Transport Dynamics in the Southern Great Plains During the Warm Season
ABSTRACT: The planetary boundary layer (PBL) is a turbulent, well-mixed layer in the lower troposphere which plays an essential role in mesoscale dynamic processes and the transport of chemical species, aerosols, and water vapor. For decades, forecasting skill for afternoon thunderstorms driven by synoptic scale forcings and high values of convective available potential energy (CAPE) have steadily improved, while skill in predicting nocturnal thunderstorms driven by more nuanced forcings such as bore waves and converging boundaries in the PBL have not made appreciable advances. In the Southern Great Plains (SGP) where agriculture is a vital component of the economy and precipitation has a direct impact on soil fertility, forecast accuracy is critical both from an economic and public safety perspective.
Convergent PBL boundaries have been simulated in previous research, although these studies rely on assumptions including linearity, hydrostaticity, and two-dimensionality which do not always prove to be useful, particularly when gravity waves are present. Additionally, few real nocturnal convection cases are documented in the literature. This research aims to fill theoretical gaps which simulations are unable to resolve using ground-based remote sensing observations from three field campaigns: 1997 IOP, PECAN, and SCOAPE.
Observations from the 1997 IOP field campaign in the SGP reveal a unique boundary layer convergence with nearly vertical lifting of water vapor and symmetric divergence aloft. This structure, which we refer to as “symmetric convergence” leads to transport of water vapor over the preceding environmental air mass, a tendency not discussed in previous research. Ground-based remote sensing instruments including a Radar Wind Profiler, Raman Lidar, Atmospheric Emitted Radiance Interferometer (AERI), Microwave Radiometer, and Meteorological Towers collected observations including wind magnitude and direction, water vapor mixing ratio, and temperature from multiple perspectives as the symmetric convergent boundary passed over the research site. From these observations we will show evidence and propose to establish theories of symmetric convergence. This work will also use observations to derive dynamic quantities and extend current theories involving vorticity ventilation and cross-sectional CAPE in terms of elevated convection. Comparisons between observations and model simulations of this event will allow us to determine the extent to which convergence theories hold true in the environment. The PECAN field campaign collected similar observations of elevated convection initiated by converging boundaries and bore waves over the SGP. Case studies of these events, some of which led to convection, and others which failed to trigger convection will be similarly evaluated in order identify ideal conditions for elevated convection to occur. SCOAPE observations, which contain observations of chemical concentrations in the atmosphere will be used to characterize PBL convergence from the perspective of transport dynamics.
The importance of improving understanding of PBL convergent boundaries has implications for convective weather forecasting and applications of chemical transport. We provide a unique perspective of the PBL during such events with the merging of observations, theory, and modelling to enhance our field’s knowledge of dynamics at work in the boundary layer.
Proposal will be held using WebEx.
