Master of Science

thesisFlashes in the anvil and stratiform regions of storms are identified and their statistics are analyzed from Tropical Rainfall Measuring Mission (TRMM) observations between 1998 and 2009. In total, ~5% of all lightning flashes are observed in either the anvil or stratiform region. Global distributions and seasonal and diurnal variations of these flashes are discussed. Electric Charging Regions (ECRs) are identified by grouping areas with 30 dBZ radar echo at 6 km from TRMM Precipitation Radar (PR) observations. Then, flashes in the anvil and stratiform regions are associated to their nearest ECRs. About ~15% of all ECRs near lightning have been found to be associated with at least one stratiform or anvil lightning flash. The relationships between these flashes and their nearest ECRs are discussed. To validate the results from TRMM observations, ground-based observations from the Tropical Warm Pool International Cloud Experiment (TWP-ICE) are analyzed. Based on the results of both data sets, flashes in the anvil region are found to often occur near the edges of convective cells within single cell systems, and many of them occur in relatively early stages of convection. Stratiform flashes, on the other hand, are more common as convective systems weaken, and many of them occur within multicellular systems

Doctor of Philosophy

dissertationThe optical properties of lightning observed by the Lightning Imaging Sensor (LIS) aboard the Tropical Rainfall Measuring Mission (TRMM) satellite between 1998 and 2010 are described and examined in the context of how they interrelate, when and where they occur globally, the nature of the cloud environment they illuminate, and the properties of the parent thunderstorm. Daytime (nighttime) flashes that occur over the open ocean are shown to be 31.7% (39.8%) larger and 55.2% (75.1%) brighter than flashes over land. Three factors are proposed that determine the size of the illuminated region: the brightness of the flash, the scattering properties of the cloud medium, and the structure of the electrical breakdown. Some of these results are explored using a Monte-Carlo radiative transfer model. The properties of TRMM Radar Precipitation Features (RPFs) that produce exceptionally large, long-lasting, and optically bright lightning flashes are compared to typical storms. RPFs over land with exceptionally large lightning flashes are up to three times larger than typical RPF thunderstorms and are considerably stronger. Coastal and oceanic RPFs with exceptionally large lightning flashes, as well as RPFs with exceptionally long lasting or bright flashes are also considerably larger and stronger than typical thunderstorms. Finally, high-altitude aircraft passive microwave and electric field observations taken by the NASA ER-2 over the course of multiple field campaigns are used to examine relationships between the properties of electrified clouds and above-cloud electric fields. A retrieval algorithm is created that is capable of estimating above-cloud electric fields from 85 GHz or 37 GHz passive microwave observations. The 37 GHz estimates are only valid over land since the ocean surface appears "cold" at 37 GHz and can reproduce the observed electric fields to within a factor of two 60% of the time. By comparison, the 85 GHz estimates fall within a factor of two of observations more than 70% of the time over land, but the 85 GHz routine is valid for both land and ocean cases. Individual cases are examined, and methods for improving the routine before applying it to satellite observations to study the Global Electric Circuit are discussed

A mixed-model moving-average approach to geostatistical modeling in stream networks

Spatial autocorrelation is an intrinsic characteristic in freshwater stream environments where nested watersheds and flow connectivity may produce patterns that are not captured by Euclidean distance. Yet, many common autocovariance functions used in geostatistical models are statistically invalid when Euclidean distance is replaced with hydrologic distance. We use simple worked examples to illustrate a recently developed moving-average approach used to construct two types of valid autocovariance models that are based on hydrologic distances. These models were designed to represent the spatial configuration, longitudinal connectivity, discharge, and flow direction in a stream network. They also exhibit a different covariance structure than Euclidean models and represent a true difference in the way that spatial relationships are represented. Nevertheless, the multi-scale complexities of stream environments may not be fully captured using a model based on one covariance structure. We advocate using a variance component approach, which allows a mixture of autocovariance models (Euclidean and stream models) to be incorporated into a single geostatistical model. As an example, we fit and compare ‘‘mixed models,’’ based on multiple covariance structures, for a biological indicator. The mixed model proves to be a flexible approach because many sources of information can be incorporated into a single model

William (Bill) Peterson's contributions to ocean science, management, and policy

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Schwing, F. B., Sissenwine, M. J., Batchelder, H., Dam, H. G., Gomez-Gutierrez, J., Keister, J. E., Liu, H., & Peterson, J. O. William (Bill) Peterson's contributions to ocean science, management, and policy. Progress in Oceanography, 182, (2020): 102241, doi:10.1016/j.pocean.2019.102241.In addition to being an esteemed marine ecologist and oceanographer, William T. (Bill) Peterson was a dedicated public servant, a leader in the ocean science community, and a mentor to a generation of scientists. Bill recognized the importance of applied science and the need for integrated “big science” programs to advance our understanding of ecosystems and to guide their management. As the first US GLOBEC program manager, he was pivotal in transitioning the concept of understanding how climate change impacts marine ecosystems to an operational national research program. The scientific insight and knowledge generated by US GLOBEC informed and advanced the ecosystem-based management approaches now being implemented for fishery management in the US. Bill held significant leadership roles in numerous international efforts to understand global and regional ecological processes, and organized and chaired a number of influential scientific conferences and their proceedings. He was passionate about working with and training young researchers. Bill’s academic affiliations, notably at Stony Brook and Oregon State Universities, enabled him to advise, train, and mentor a host of students, post-doctoral researchers, and laboratory technicians. Under his collegial guidance they became critical independent thinkers and diligent investigators. His former students and colleagues carry on Bill Peterson’s legacy of research that helps us understand marine ecosystems and informs more effective resource stewardship and conservation

A Survey of Pressure Vessel Code Compliance for Superconducting RF Cryomodules

Superconducting radio frequency (SRF) cavities made from niobium and cooled with liquid helium are becoming key components of many particle accelerators. The helium vessels surrounding the RF cavities, portions of the niobium cavities themselves, and also possibly the vacuum vessels containing these assemblies, generally fall under the scope of local and national pressure vessel codes. In the U.S., Department of Energy rules require national laboratories to follow national consensus pressure vessel standards or to show "a level of safety greater than or equal to" that of the applicable standard. Thus, while used for its superconducting properties, niobium ends up being treated as a low-temperature pressure vessel material. Niobium material is not a code listed material and therefore requires the designer to understand the mechanical properties for material used in each pressure vessel fabrication; compliance with pressure vessel codes therefore becomes a problem. This report summarizes the approaches that various institutions have taken in order to bring superconducting RF cryomodules into compliance with pressure vessel codes.Comment: 7 p

Global rural temperature trends

Using rural/urban land surface classifications derived from maps and satellite observed nighttime surface lights, global mean land surface air temperature time series were created using data from all weather observing stations in a global temperature data base and from rural stations only. The global rural temperature time series and trends are very similar to those derived from the full data set. Therefore, the well-known global temperature time series from in situ stations is not significantly impacted by urban warming

Bayesian spatio-temporal models for stream networks

Spatio-temporal models are widely used in many research areas including ecology. The recent proliferation of the use of in-situ sensors in streams and rivers supports space-time water quality modelling and monitoring in near real-time. In this paper, we introduce a new family of dynamic spatio-temporal models, in which spatial dependence is established based on stream distance and temporal autocorrelation is incorporated using vector autoregression approaches. We propose several variations of these novel models using a Bayesian framework. Our results show that our proposed models perform well using spatio-temporal data collected from real stream networks, particularly in terms of out-of-sample RMSPE. This is illustrated considering a case study of water temperature data in the northwestern United States.Comment: 26 pages, 10 fig