Dissertation

Climate Change and the Sea Breeze in the North Carolina Coast

Luchetti, Nicholas Thomas

2016

Overview

Forecasting SB genesis and evolution is often a difficult task for coastal meteorologists. This is especially the case when attempting to forecast SB-induced precipitation, as not every SB front induces rainfall. The two primary objectives in this thesis were to 1) study why some SB fronts induce precipitation while others do not, and 2) to explore the effects of a future warmer climate on SB evolution. To explore these objectives, a SB climatology for 2009–2012 along the NC coast was constructed using radar and reanalysis datasets. Additionally, current and future climate SB simulations were produced using the Weather Research and Forecasting (WRF) model. Future climate WRF simulations utilized the pseudo-global warming (PGW) approach, which involves rerunning current climate SB simulations using modified thermodynamic initial conditions that represent a warmer, late 21st century climate. The 88 SB events that were detected between 2009–2012 were nearly evenly distributed into SB dry (53%) and SB wet (47%) events. Significant differences in kinematic and thermodynamic conditions were present during SB dry and wet events. On average, SB dry events occurred under stronger synoptic-scale winds (6.00 ± 2.36 m/s), while SB wet events occurred under lighter synoptic-scale winds (4.02 ± 2.16 m/s). Moreover, most (85%) SB events occur during offshore (53%) or parallel (22%) flow. However, as is the case throughout the literature, the maximization of SB fronts during offshore synoptic flow is sensitive to the synoptic wind speed. SB events that occurred under offshore synoptic-scale flow in the 0 to 4–6 m/s range were more likely to be categorized as SB wet events, while SB events that occurred under offshore synoptic-scale flow above 0 to 4–6 m/s were more likely to be categorized as SB dry events, results similar to those seen in the literature. In terms of thermodynamic controls, results from this climatology show that the atmosphere has larger values of CAPE and lower values of CIN and is therefore more conducive to deep convection on SB wet than on SB dry event days. This study suggests that favorable conditions for the formation of precipitation along the SB include enhanced early morning instability, minimal stable air aloft, and synoptic-scale offshore wind flow with speeds between 0 and 4-6 m/s throughout the duration of the event. Seven of the observed SB precipitation events were simulated in WRF under current climate conditions and repeated for future climate conditions under the RCP 4.5 and RCP 8.5 scenarios. Under current climate conditions WRF performed well in simulating the horizontal extent and late day veering/backing of the SB front, as well as the timing of initiation and peak SB-induced precipitation. However, it struggled to simulate the inland penetration distance of the SB front, as well as the spatial distribution and total accumulation of precipitation along the SB front. Under future climate conditions the evolution of WRF simulated SB fronts was altered resulting in some future SB fronts that induced more precipitation, while other future SB fronts induced less precipitation when compared to the current climate WRF simulations. Additionally, under future climate conditions the inland penetration timing and distance was altered for all of these SB cases when compared to the current climate WRF simulations. In both the current and future climate simulations the synoptic-dynamic shifts in the atmospheric flow appear to have more of an influence on SB evolution and associated precipitation than enhanced temperatures, moisture content, and instability. Subtle shifts in the synoptic-scale wind direction and speeds along the coast, associated with a westward migration of the North Atlantic Subtropical High’s western ridge, had considerable influence on the amount and spatial distribution of future climate SB-induced precipitation. From a climatological perspective, the results herein suggest that understanding the effects of climate change on mesoscale precipitation patterns is a very complex task. From a forecasting perspective, the results presented herein suggest that subtle kinematic and thermodynamic shifts in the atmosphere will influence NC SB evolution in both the current and future climate.

• Publisher: ProQuest Dissertations & Theses
• Subject: Atmospheric sciences / Climate Change / Geography / Meteorology
• ISBN: 9781369230307, 1369230303