Elizabeth Smith-Defense-November 26

The Great Plains Nocturnal Low-Level Jet: Spatial and Temporal Evolution


November 26, 2018 - 2:30 pm


November 26, 2018 - 3:30 pm


120 David L. Boren Blvd. Room 1313, Norman, OK 73072   View map

The Great Plains Nocturnal Low-Level Jet: Spatial and Temporal Evolution

The nocturnal low-level jet is a maximum in the vertical wind profile often occurring in
the lowest 1-km during the overnight hours in the Great Plains of the United States. This
wind maximum has many implications including wind energy impacts, aviation hazards,
and convection and precipitation forecasting. In broad terms, this dissertation set out to
expand the current understanding the mechanisms leading to the development of NLLJs in
the Great Plains. Using high resolution observations and numerical simulations together,
this dissertation documents, describes, and analyzes spatial and temporal characteristics of
the Great Plains nocturnal low-level jet (NLLJ).
The first part of the dissertation focused on identifying the optimal configuration in
which to run the Weather Research and Forecasting (WRF) model for NLLJ studies. Hori-
zontal spacing finer than 4-km did not offer enough improvement to the resulting simulation
to justify computational expense. Using finer vertical spacing did improve simulations of
NLLJ cases. Sensitivity to planetary boundary layer parameterization scheme was gener-
ally small. Based on the conducted sensitivity tests, the optimal WRF model configuration
for NLLJ studies was identified as based on a grid with 4-km horizontal spacing, 40-m
vertical constant spacing, and employing the Quasi-Normal Scale Elimination planetary
boundary layer parameterization scheme.
Next, data were collected during three Plains Elevated Convection at Night (PECAN)
field campaign NLLJ cases and used alongside optimally configured simulations to identify
and describe the spatial and temporal characteristics of Great Plains NLLJs. This analysis
showed that the NLLJ is heterogeneous with respect to depth, wind speed, and wind direc-
tion. Additionally, the spatially heterogeneous NLLJ was shown to be moving across the
slope of the Great Plains through the night. As such, the spatial and temporal character-
istics of the nocturnal low-level jet are inherently connected and should not be considered

This spatial-temporal evolution of the NLLJ has multiple implications for our un-
derstanding of local NLLJ features. The typical spatial and temporal evolution of the
NLLJ was described using PECAN observed cases. A set of fourteen cases (including
both PECAN and Lower Atmospheric Boundary Layer Experiment, LABLE, cases) were
used to document and describe features of this evolution. Two buoyancy-related driving
mechanisms were investigated to explain the spatial-temporal variability of the nocturnal
low-level jet. The consideration of this motion and spatial heterogeneity of the nocturnal
low-level jet showed that sudden changes in the nocturnal boundary layer structure could
be induced by the advection of spatial jet characteristics rather than local effects.