Grainger College of Engineering Seminars & Speakers

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PhD Final Defense – Sean Matus

Event Type
Conference/Workshop
Sponsor
Civil and Environmental Engineering
Location
Natural History Building, Room 2083
Date
Nov 8, 2024   1:00 pm  
Views
16
Originating Calendar
CEE Seminars and Conferences

Investigating the Role of the Land Surface in Modulating the Great Plains Low-Level Jet

Advisor: Professor Francina Dominguez

Abstract

The warm season in the United States Great Plains (GP) is characterized by frequent nocturnal

low-level jets (LLJs). The GPLLJ serves as a major mechanism of atmospheric moisture transport,

contributing to severe weather and precipitation in the region. Additionally, the nocturnal wind

maxima of GPLLJs are a resource for wind energy production throughout the GP. These

hydrometeorological and socioeconomic implications motivate a better understanding of the

GPLLJ to improve predictability. It is accepted that a combination of atmospheric and land surface

forcing modulates GPLLJ diurnal variability. Previous studies have examined the diurnal variability

of soil moisture associated with GPLLJs, this is the first analysis at the subseasonal timescale.

This thesis is the first documented evidence of a subseasonal timescale embedded within GPLLJ

intensity that covaries with soil moisture over the U.S. Great Plains. I show that, due to the

memory of the land surface, longer time scale variability associated with surface moisture affects

GPLLJ intensity through a chain of land-atmosphere processes. Through a combined

observational and statistical framework, this dissertation addresses the following questions on

subseasonal GPLLJ variability:

1. What are the land and atmosphere conditions, at the diurnal, synoptic/pentad, and

subseasonal timescales, antecedent to extreme GPLLJ events?

2. What physical mechanisms lead to stronger GPLLJ when dry soil moisture anomalies

prevail over the southern Great Plains?

3. Can the temporal scales embedded within GPLLJ variability be disentangled to extract the

subseasonal variability and link to soil moisture variability?

The work starts with the first documented study of antecedent, subseasonal soil moisture

anomalies associated with GPLLJs. We then present mechanistic evidence of how dry soil

moisture anomalies can contribute to stronger GPLLJs. Our findings suggest that subseasonal

dry soil moisture anomalies modulate GPLLJ intensity through warmer near surface

temperatures, deepening of the planetary boundary layer, and stronger ageostrophic winds at

sunset, all leading to nocturnal supergeostrophic winds through the Blackadar inertial oscillation.

We lastly disentangle the different timescales of variability of GPLLJ to extract the land surfacedriven

subseasonal timescale embedded within GPLLJ variability with Multichannel Singular

Spectrum Analysis. Our findings show that reconstructing the GPLLJ without the subseasonal

variability, which is strongly linked to soil moisture, leads to underestimated wind speeds during

dry periods and overestimated during wet. These findings quantitatively demonstrate how the land

surface plays an important role in modulating GPLLJ intensity which can have major implications

for improving subseasonal predictability of GPLLJ activity, and subsequent energy production and

precipitation.

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