Accurate representation of bores in forecast models is a challenge. This challenge is
of considerable interest to both the operational and the research communities because
bores are capable of producing vertical displacements of air sufficient for initiating
convection. While the research presented here does not offer improvements to forecast
models, it lays a foundation for future numerical studies focused on the life cycle
of nocturnal thunderstorms and the development of forecast tools designed to predict
the onset of bore-initiated convection. Although the current research may be relevant
to similar nocturnal convection systems in other regions of the world, the scope of
this research is limited to the Southern Great Plains of the United States, where the
forecast skill for nocturnal thunderstorms is relatively poor.
The datasets for the current study are predominantly from two field projects over
the Great Plains. The first dataset is from the International H20 Project (IHOP_2002),
and the dataset is used to characterize the origin of radar fine lines in reflectivity as
density currents, bores or other nocturnal phenomena. Subsequently, the frequency
of bores observed in IHOP_2002 data is compared with a statistical model applied
to hydraulic theory. The longevity of the observed bores and their preferred direction
is compared with environmental winds and wave ducting properties using linear
wave theory. Next, using the Plains Elevated Convection At Night (PECAN) dataset,
a method for forecasting the generation of a bore and subsequent bore-initiated convection
is proposed and tested on a 3 June 2015 case study. Two techniques based on
hydraulic and linear wave theory are used as part of the method to forecast the vertical
displacement of parcels.
The results indicate that density currents often generated bores in the nocturnal environment observed during IHOP_2002. This result is consistent with hydraulic
theory which characterizes the interaction between a density current and the observed
environment as partially blocked, leading to the generation of a bore. Of the parameters
used to evaluate the flow regime, the inversion properties had the most influence
over changes in the flow regime with time. Once a bore developed, the maintenance
of a wave duct is diagnosed with a two-layer model based on the Scorer parameter.
The curvature of the horizontal wind with height is a component of the Scorer parameter
and the curvature associated with the nocturnal low level jet was found to be the
primary mechanism for maintaining a wave duct.
Convective instability parameters calculated from pre- and post-bore environment
soundings are compared to gauge if a bore would initiate convection. The post bore
soundings are generated with one of two techniques that mimic the parcel displacement
through a bore. The technique based on hydraulic theory overestimates the displacement
while the technique based on linear wave theory severely underestimates
the displacement. These findings are part of a new line of investigation into the development
of reliable tools to predict bore-initiated and bore-maintained convection
