Mesoscale dynamics and boundary-layer structure in topographically forced low-level jets

Two types of mesoscale wind-speed jet and their effects on boundary-layer structure were studied. The first is a coastal jet off the northern California coast, and the second is a katabatic jet over Vatnajökull, Iceland. Coastal regions are highly populated, and studies of coastal meteorology are of general interest for environmental protection, fishing industry, and for air and sea transportation. Not so many people live in direct contact with glaciers but properties of katabatic flows are important for understanding glacier response to climatic changes. Hence, the two jets can potentially influence a vast number of people. Flow response to terrain forcing, transient behavior in time and space, and adherence to simplified theoretical models were examined. The turbulence structure in these stably stratified boundary layers was also investigated. Numerical modeling is the main tool in this thesis; observations are used primarily to ensure a realistic model behavior. Simple shallow-water theory provides a useful framework for analyzing high-velocity flows along mountainous coastlines, but for an unexpected reason. Waves are trapped in the inversion by the curvature of the wind-speed profile, rather than by an infinite stability in the inversion separating two neutral layers, as assumed in the theory. In the absence of blocking terrain, observations of steady-state supercritical flows are not likely, due to the diurnal variation of flow criticality. In many simplified models, non-local processes are neglected. In the flows studied here, we showed that this is not always a valid approximation. Discrepancies between simulated katabatic flow and that predicted by an analytical model are hypothesized to be due to non-local effects, such as surface inhomogeneity and slope geometry, neglected in the theory. On a different scale, a reason for variations in the shape of local similarity scaling functions between studies is suggested to be differences in non-local contributions to the velocity variance budgets.

Bovine Teeth in Age Assessment, from Medieval Cattle to Belgian Blue : Methodology, Possibilities and Limitations

The overall aim of the present thesis was to develop and characterise an age assessment method based on incremental lines in dental cementum using contemporary bovine teeth and teeth from archaeological faunal assemblages. The investigations also included two other age assessment methods: tooth wear pattern and macroscopic dental measurements. The first permanent mandibular molar and lower jaws from 70 contemporary cattle of known age and 170 archaeological molar sets from ten different Swedish archaeological sites were used. The following conclusions were drawn: • The number of incremental lines in the dental cementum varied between different parts of the tooth root as well as within one and the same individual. The results from contemporary cattle of known age showed a strong relationship between age and incremental lines in the cementum of the distal part of the mesial root (R2=65.5%) and the known ages of the animals. • With the “best” model variation in age could be explained to 65.5% (R2) by the number of incremental lines. Thus, the remaining age variation (approximately 35%) could not be explained by these lines. Other factors than must thus be responsible. However, with the exception of calves born the present material did not reveal any such significant relationship. • The results from cattle of known age indicate that the method of assessing age on the basis of cemental incremental lines is more reliable than other methods such as tooth wear or tooth measurements. However, by combining counting incremental lines and one variable assessing tooth dimension (tooth height) a slightly stronger relationship could be obtained (R2=74.5%). The results from age assessment of the medieval and post-Reformation cattle emphasize the importance of supplementing any age estimation of archaeological assemblages based on dental indicators with characteristics for the particular assessment model. Furthermore, conclusions based on age assessment with such models can not be drawn with any more detailed time scale than about 2 years leaving at best only 25% (R2) of factors influencing the dental indicator(s) utilized in the model unexplained. The accuracy of the age assessment required by the particular historical context in which the archaeological remains are found should thus decide what level of accuracy should be chosen.