Bursting events in the stable atmospheric boundary layer
Phillipson, Julie Ann
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Though recent experiments and field projects regarding the characteristics of the boundary layer have been conducted, there is still an overall lack of understanding about the mechanics of the stable boundary layer, whether it is transitionally stable, such as the nocturnal stable boundary layer in mid-latitudes, or persistently stable, such as the boundary layer in Polar Regions. ISCAT-00 is one such field project conducted in Antarctica, where an instrumented tower was used to record wind speed and temperature information, from which heat and momentum flux transfers can be discerned. Understanding of boundary layer processes is especially important for the stable layer since despite its stable nature, sporadic bursts of turbulence have been observed to occur, indicated by data collected from the ISCAT-00 campaign. These bursts, though short-lived, are responsible for most of the heat and momentum transfer that occurs within the otherwise stable layer. Since these bursts of turbulence disrupt the stable layer, they can not only pose problems for air quality forecasts, but they can also inhibit the performance of wind turbines. Transient loading from these bursting events as rotor blades pass through patches of organized, coherent turbulence can shorten the life span of a wind turbine by 5 to 10 years. However, despite the noted occurrence of turbulence bursting in the stable layer there is still very little known about its origins, causes, or basic properties. In order to explore the characteristics of turbulent bursting events in the stable layer, two methodologies are applied to analyze data obtained from the ISCAT00 campaign. The first methodology applied to discern the occurrence of turbulent bursting is one created by Nakamura & Mahrt (2005). The second methodology is a newly developed adaptive threshold methodology, which is much more robust, and removes much of the subjectivity of other turbulence bursting identification methods. The adaptive technique allows for the reduction of subjectivity in the data analysis phase, and is therefore felt to be more accurate. Also, spectral characteristics of polar turbulence are explored, and are found to have similar properties to spectra observed in mid-latitudes. This research focuses primarily on different methods, both old and newly developed that can help to further understanding about turbulence in the stable boundary layer and the corresponding heat and moisture flux properties.