Doctor of Philosophy

dissertationNumerical studies of sea and lake breezes are reviewed and gaps in our current understanding of these thermally-driven circulations are discussed. A numerical sensitivity study is conducted using large-eddy simulations to determine the dependence of sea- and lake-breeze speed and length scales to variations in the land-surface sensible heat flux, offshore background wind, initial atmospheric stability, and lake diameter. This study is the first to test the dependence of sea- and lake-breeze characteristics to variations in these geophysical variables using a three-dimensional large-eddy simulation capable of explicitly resolving boundary-layer turbulence and vertical motion near the sea-breeze front. This study provides new understanding on the sensitivity of sea and lake breezes to variations in the land-surface sensible heat flux, opposing background wind, and lake diameter as well as the complex interactions that occur among these geophysical variables. For the first time, the daytime life cycle of sea and lake breezes in the presence of variations in these variables is simulated, in contrast to many earlier studies that focused primarily on the mature midafternoon sea-breeze circulation. Significant spatial variability in the intensity and vertical structure of lake and sea breezes is noted in the large-eddy simulations. The critical value of an opposing wind at which a sea or lake breeze is destroyed by synoptic-scale pressure gradients is approximately 20% lower in this study than that documented in earlier numerical studies. The depth of sea and lake breezes has also been found to be highly sensitive to the magnitude of the opposing background wind. Finally, the results of this study show that lake breezes for small and medium-sized lakes evolve much differently than sea breezes during the afternoon due to a limited quantity of cool air over the lake

Idealized large-eddy simulations of sea and lake breezes: sensitivity to lake diameter, heat flux and stability

ManuscriptIdealized large-eddy simulations of lake and sea breezes are conducted to deter mine the sensitivity of these thermally-driven circulations to variations in the land-surface sensible heat flux and initial atmospheric stability. The lake-breeze and sea-breeze metrics of horizontal wind speed, horizontal extent, and depth are assessed. Modelled asymmetries about the coastline in the horizontal extent of the low-level onshore flow are found to vary as a function of the heat flux and stability. Small lake breezes develop similarly to sea breezes in the morning, but have a significantly weaker horizontal wind speed component and a smaller horizontal extent than sea breezes in the afternoon

Summer Ozone Concentrations in the Vicinity of the Great Salt Lake

Residents near the Great Salt Lake in northern Utah, USA have been exposed to ozone levels during recent summers exceeding the current United States National Ambient Air Quality Standard. Accurately forecasting those exceedances has been difficult as a result of the complex meteorological and photochemical processes fostering them. To help improve such forecasts, a low-cost field study was conducted during summer 2015 to provide comprehensive observations of boundary-layer ozone concentrations in the context of the prevailing meteorological conditions. A network of surface ozone sensors was supplemented by sensors mounted on vehicles, a public transit light-rail car, news helicopter, tethered sonde, and unmanned aerial vehicle. The temporal and spatial evolution of boundary-layer ozone concentrations were compared with the prevailing regional and local meteorological conditions on the basis of gridded operational analyses, surface weather stations, and additional sensors deployed for the field study. High ozone concentrations during June 2015 resulted primarily from local processes while smoke transported from distant wildfires contributed to elevated ozone concentrations during August. The Great Salt Lake influenced ozone concentrations along the Wasatch Front through several mechanisms, most importantly its impact on local wind circulations. The highest ozone concentrations were often found in a narrow zone between the Great Salt Lake and the urban regions to its south and east. Observations from multiple fixed site and mobile platforms during 18–19 August illustrate the complex variations in ozone concentrations as a function of elevation at the surface as well as vertically through the deep boundary layer

Quantifying Methane Emissions in the Uintah Basin During Wintertime Stagnation Episodes

This study presents a meteorologically-based methodology for quantifying basin-scale methane (CH4) emissions in Utah’s Uintah Basin, which is home to over 9,000 active and producing oil and natural gas wells. Previous studies in oil and gas producing regions have often relied on intensive aircraft campaigns to estimate methane emissions. However, the high cost of airborne campaigns prevents their frequent undertaking, thus providing only daytime snapshots of emissions rather than more temporally-representative estimates over multiple days. Providing estimates of CH4 emissions from oil and natural gas production regions across the United States is important to inform leakage rates and emission mitigation efforts in order to curb the potential impacts of these emissions on global climate change and local air quality assessments. Here we introduce the Basin-constrained Emissions Estimate (BEE) method, which utilizes the confining topography of a basin and known depth of a pollution layer during multi-day wintertime cold-air pool episodes to relate point observations of CH4 to basin-scale CH4 emission rates. This study utilizes ground-based CH4 observations from three fixed sites to calculate daily increases in CH4, a laser ceilometer to estimate pollution layer depth, and a Lagrangian transport model to assess the spatial representativity of surface observations. BEE was applied to two cold-air pool episodes during the winter of 2015–2016 and yielded CH4 emission estimates between 44.60 +/– 9.66 × 103 and 61.82 +/– 19.76 × 103 kg CH4 hr–1, which are similar to the estimates proposed by previous studies performed in the Uintah Basin. The techniques used in this study could potentially be utilized in other deep basins worldwide

Meteorological Drivers of Permian Basin Methane Anomalies Derived from TROPOMI

The launch of the TROPOspheric Monitoring Instrument (TROPOMI) on the Sentinel-5 Precursor (S-5P) satellite has revolutionized pollution observations from space. The purpose of this study was to link spatiotemporal variations in TROPOMI methane (CH4) columns to meteorological flow patterns over the Permian Basin, the largest oil and second-largest natural gas producing region in the United States. Over a two-year period (1 December 2018–1 December 2020), the largest average CH4 enhancements were observed near and to the north and west of the primary emission regions. Four case study periods—two with moderate westerly winds associated with passing weather disturbances (8–15 March 2019 and 1 April–10 May 2019) and two other periods dominated by high pressure and low wind speeds (16–23 March 2019 and 24 September–9 October 2020)—were analyzed to better understand meteorological drivers of the variability in CH4. Meteorological observations and analyses combined with TROPOMI observations suggest that weakened transport out of the Basin during low wind speed periods contributes to CH4 enhancements throughout the Basin, while valley and slope flows may explain the observed western expansion of the Permian Basin CH4 anomaly

Remote Sensing of the Surface Temperature of the Great Salt Lake

Utah’s Great Salt Lake has been an object of observation since the advent of satellite meteorology. However, no comprehensive study of the lake’s temperature has previously been conducted on the basis of remote sensing. Several years of satellite-derived daily lake surface temperature measurements from the Advanced Very High Resolution Radiometer (AVHRR) have been processed at the University of Utah. In addition, lake temperature imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) have also been examined and validated against the AVHRR retrievals. The thermal characteristics of the lake vary on diurnal, weekly, monthly and inter-annual time scales. Thermal patterns related to river inflow, thermal fronts, gyres and variable mixing of the lake have been documented from satellite imagery. In addition, remote sensing of the Great Salt Lake gives insight into spatial variations in lake salinity and turbidity. More information is available at http://www.met.utah.edu/research/saltlake

Observational and Numerical Study of the Great Salt Lake Breeze

Lake and land breezes modulate pollutant transport and concentration, surface evaporation rates, temperature, wind speed, and precipitation in many populated regions of the world. Utah\u27s Great Salt Lake (GSL) is ideally suited for the investigation of these mesoscale circulations in arid environments. A multifaceted observational and modeling study is underway to better understand the sensitivity of the GSL lake breeze to variations in the atmospheric and surface state. While the body of theoretical, observational, and numerical studies related to lake and sea breeze systems and associated air quality issues is extensive, most theoretical modeling of lake and sea breezes has been two-dimensional. With the recent increase in computational power, this study will systematically revisit the impact of a number of important forcing mechanisms (for example, lake width, background wind, stability, and surface heat flux) on the lake breeze using the weather research and forecasting (WRF) model run as a fully three-dimensional large eddy simulation. An array of surface weather and air quality stations, radiosonde profiles, and high resolution surface temperature data from the Moderate Resolution Imaging Spectroradiometer and Advanced Spaceborne Thermal Emission and Reflection Radiometer will be used to initialize and validate model simulations. Initial modeling results will be presented and an undergraduate student field project funded by the National Science Foundation will be discussed

Evaluation of the Multi-Scale Ultra-High Resolution (MUR) Analysis of Lake Surface Temperature

Obtaining accurate and timely lake surface water temperature (LSWT) analyses from satellite remains difficult. Data gaps, cloud contamination, variations in atmospheric profiles of temperature and moisture, and a lack of in situ observations provide challenges for satellite-derived LSWT for climatological analysis or input into geophysical models. In this study, the Multi-scale Ultra-high Resolution (MUR) analysis of LSWT is evaluated between 2007 and 2015 over a small (Lake Oneida), medium (Lake Okeechobee), and large (Lake Michigan) lake. The advantages of the MUR LSWT analyses include daily consistency, high-resolution (~1 km), near-real time production, and multi-platform data synthesis. The MUR LSWT versus in situ measurements for Lake Michigan (Lake Okeechobee) have an overall bias (MUR LSWT-in situ) of −0.20 °C (0.31 °C) and a RMSE of 0.86 °C (0.91 °C). The MUR LSWT versus in situ measurements for Lake Oneida have overall large biases (−1.74 °C) and RMSE (3.42°C) due to a lack of available satellite imagery over the lake, but performs better during the less cloudy 15 July–30 September period. The results of this study highlight the importance of calculating validation statistics on a seasonal and annual basis for evaluating satellite-derived LSWT