Polar Stratospheric Clouds (PSCs) are composed of H₂SO₄/HNO₃/H₂O aerosols called supercooled ternary solution (STS), solid nitric acid trihydrate (NAT) particles and ice particles. These clouds require the low temperatures found in the polar regions of the lower stratosphere to occur. PSCs are important due to the critical role they play in the destruction of ozone over the poles. The role of PSCs in ozone destruction has been understood since the 1980’s however the mechanisms involved in PSC formation, particularly NAT formation, is still not well understood. Typically formation of PSCs in climate models is handled by using a temperature threshold as a proxy. A commonly used threshold is the equilibrium temperature for the existence of NAT, TNAT ; however when the area with temperatures below TNAT are compared with observations of PSC it is found that this measure significantly over-estimates the abundance of PSC. This research uses back trajectories stemming from the site of PSC observations to investigate the effect that the temperature history has on PSC formation. The trajectories are calculated using a simple Lagrangian model on an isentropic surface. The observational PSC data is obtained from the CALIOP (Cloud Aerosol Lidar with Orthogonal Polarization) instrument, which is from the CALIPSO (Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations) mission launched in 2006. The CALIOP data used in this research is taken from the June to September period from the years 2007-10 and for latitudes between -55° and -82°S, and totals in excess of 7 million individual measurement profiles, a four day back trajectory is calculated for each observation along the 450 K isentropic level. Temperature and wind data is from the MERRA (Modern Era Retrospective-analysis for Research and Applications) reanalysis and H₂O and HNO₃ concentrations (required for calculating equilibrium temperatures) are from Earth Observing System (EOS) Aura Microwave Limb Sounder (MLS) version 3.3. It was found that different PSC types had different characteristics in their temperature histories. The mean temperature history associated with ice observations cooled by around 3 K over the previous 24 hours to slightly below the water ice frost point at the time of observation. However, in trajectories associated with the presence of NAT the temperature has on average stayed 4-5 K below TNAT for the entire four days of the trajectory. Based on these findings and theories of PSC formation, a system for predicting PSC occurrence based on the temperature histories is proposed. This system provides a better approximation for the total extent of PSC occurrence than the TNAT threshold. The average area covered by PSC on the 450 K level over the period examined as observed by CALIOP was 7.6 million km² while the area predicted by the temperature histories was 8.6 million km² as compared to 20.4 million km² with temperatures below TNAT. The average geographical coverage of the different PSC types is reasonably well replicated by the temperature history classification; however, the ability to discriminate between different PSC types based on individual temperature histories is somewhat limited.

No description available.

Arctic surface air temperatures have been warming at twice the global rate, making it one of the most susceptible regions to current climate change. Effects on cold-adapted aquatic species, such as the culturally and ecologically important Arctic charr (Salvelinus alpinus), are difficult to anticipate and may vary depending on site-specific attributes. Temperature has a direct influence on aspects of species’ fitness, including growth, reproduction and, ultimately, survival. Previous research on temperature-growth patterns in Arctic charr has yielded variable results, particularly for studies observing these patterns in the wild. Two field-based studies are presented in this thesis, in an attempt to better understand temperature-growth patterns for wild populations of Arctic charr. In the first study, individual measurements of annual, or within-season growth were determined from tag-recaptured Arctic charr and examined in relation to summer sea surface temperatures and within-season capture timing in the Ungava and Labrador regions of eastern Canada. Differences in among-year growth were significant for Ungava Bay Arctic charr, with growth being positively correlated with temperature. Growth of Labrador Arctic charr did not vary significantly among years. Regional comparisons demonstrated that Ungava Arctic charr had significantly higher annual growth rates, with differences among years in all regions being positively correlated with temperature. Within-season growth rates of Labrador Arctic charr peaked in June, declined toward August, and were negatively correlated with the length of time spent at sea and mean experienced sea surface temperatures. A quadratic model relating growth rate to temperature best explained the pattern of within-season growth. The higher annual growth of Ungava Bay Arctic charr was attributed to the high sea surface temperatures experienced in 2010-11 and the localized differences in nearshore productivity as compared to Labrador. Results suggest that increases in water temperature may have profound consequences for Arctic charr growth in the Canadian sub-Arctic, depending on the responses of local marine productivity to those same temperature increases. In the second study, oxygen stable isotope temperature reconstruction methods were used to estimate mean experienced summer temperatures from growth zones within individual otoliths of Arctic charr sampled from contrasting lake environments. For either lake, otolith-estimated temperatures were not significantly related to back-calculated growth. Significant negative effects on back-calculated growth were observed due to increasing air temperatures in the smaller lake, owing to warmer surface waters and a limited amount of preferred cool-water habitat available. A similar relationship was not observed in the larger lake, indicating that the cooler, deeper lake provides ample preferred cool-water habitat for Arctic charr despite climate warming. In addition, young-of-the-year temperatures negatively related to zone 2 growth for the smaller lake, whereas no significant correlation was found for the larger lake. Results here provide evidence for differing climate-influenced growth outcomes depending on the site-specific fish density: preferred thermal habitat volume ratio as dictated by local attributes including lake morphometry, upstream catchment area and life-history strategy. Conclusions from this thesis include the increased need for detailed site- and population-specific assessments of the impacts of increasing temperatures on Arctic charr growth. Better understanding of the drivers of temperature-growth relationships in wild Arctic charr populations will facilitate more accurate stock forecasts with the overall goal of sustaining exploited Arctic charr populations as the climate warms and becomes increasingly variable.

No description available.

Apparatus to measure the thermal conductivity of YBa(_2)Cu(_3)O(_7-δ) at temperatures between 20K and 120K has been designed and constructed. The thermal conductivity is measured using a longitudinal steady state heat flow technique. Thermal conductivity measurements have been performed upon a sample of YBa(_2)Cu(_3)O(_7-δ) which has been subjected to a series of heat treatments in order to remove oxygen from the material. The measurements show conclusively that the thermal conductivity of YBa(_2)Cu(_3)O(_7-δ) is very strongly influenced by the oxygen content of the material. A reduction of the oxygen content of the material results in a substantial lowering of the thermal conductivity. To explain this result, a quantitative model has been constructed; the model demonstrates that consideration of the changes in phonon interactions alone cannot account for the differences in the behaviour of the thermal conductivity of YBa(_2)Cu(_3)O(_6) and YBa(_2)Cu(_3)O(_7). In addition; the model, shows that there must be a significant carrier contribution to the thermal conductivity in both the normal and superconducting states. A physical process has been proposed which provides the required large carrier contribution below T(_c). Further studies have been performed on a series of samples of YBa(_2)Cu(_3)O(_7-δ) which were sintered at slightly different temperatures. Qualitative analysis of the physical properties, of these samples has been performed.

The plasma membrane, which separates intracellular contents from extra cellular milieu, consists of a lipid bilayer comprising mainly phospholipids and cholesterol together with various functional proteins, which control the interaction of the cell with its environment. Cells are killed at elevated temperatures and previous work suggests that the plasma membrane may be a primary target in this hyperthermic cell death. The present study set out to test this hypothesis using a rat liver tumour cell hue (Hepatoma Tissue Culture cells). Several different experimental approaches were adopted. Supplementation of these cells with linoleic acid (18 : 2) for a 36 hour period increased the thermal sensitivity of cells at 43 C, though increased sensitivity was not evident at other times. Plasma membrane-enriched fractions were obtained from control cells and from cells supplemented with linoleic acid for a 36 hour period, then lipids were extracted and characterised. Whilst there was little difference in the cholesterol : phospholipid ratio, the phospholipid fatty acid composition of membranes from supplemented cells showed elevated levels of 18 : 2 and decreased levels of oleic acid (18 : 1) relative to control cell membranes. DPH fluorescence polarisation studies indicated that plasma membranes from supplemented cells were less 'ordered' than control membranes. Alkaline phosphodiesterase I, a plasma membrane-bound enzyme, appeared to be more thermolabile in supplemented cells suggesting that plasma membrane 'fluidity' may be an important factor in determining the thermal sensitivity of this membrane-bound enzyme. Hyperthermic cell death was potentiated by the presence of local anaesthetics, two of which, dibucaine and tetracaine, also produced less 'ordered' membranes. Morphological studies conducted on cells in the presence and absence of local anaesthetic at elevated temperatures indicated changes in cellular surface morphology on heating which were accelerated in the presence of the anaesthetic. The intermediate filament network of these cells did not appear to be a primary target of hyperthermic treatment. These studies suggest that the lipid composition and physical state of the plasma membrane are critical features involved in the expression of cell death, possibly through a modulation of membrane protein thermal sensitivity.

Thermal mapping, the measurement of road surface temperatures (RSTs) with an infra-red thermometer (IRT) mounted in a moving vehicle, seeks to identify a 'characteristic and repeatable' thermal fingerprint (temperature profile) for any stretch of road. A number of uses have been suggested for the process, including ice detection sensor network design and identifying stretches of road for selective gritting, with potential financial and environmental benefits due to reduced salt usage. The project 'Thermal Mapping for a Highway Gritting Network' has resulted in the most extensive survey yet undertaken. The aims were to investigate the reliability/repeatability of fingerprints and establish confidence limits. Comprehensive mapping of Sheffield roads took place during winters 1988/89- 1991/92. Significant errors (+/-3°C) in RST readings were identified after the first winter. Laboratory and road tests confirmed errors were produced due to warming/cooling of the IRT. Operating the IRT in a temperature control box eliminated these errors. Seven Sheffield routes were mapped during winters 89/90 and 90/91 with route 1 fingerprints (100) used for most of the analysis. The main factors affecting the variation in RSTs were confirmed as altitude and land-use with localised peaks occurring under bridges and by trees and tall buildings. The occurrence of cold air drainage on clear/calm (extreme') nights resulted in 'low' RSTs at relatively low altitudes. Differences were identified between what should have been identical extreme fingerprints. These were related to variations in the behaviour of cold air drainage. rom night to night and variations in wind direction/speed interacting with local relief. Confidence limits for extreme fingerprints and maps, taking into account possible errors in mapping and differences between fingerprints, were +/-20C and +/- 2.5°C respectively. With important decisions concerning gritting made when RSTs are +/-5°C confidence limits of this magnitude have important implications for thermal mapping. Future use should be restricted to sensor network design and assessment/re-design of gritting network.

No description available.

The impacts of extreme temperatures on human health and morbidity have been well documented in many studies. In literature, changes in the trends of extreme temperatures have been studied using percentiles, indicators and climate modeling. The aim of this study is to determine if the trend exhibited in the literature of statistically significant increases in extreme minimum temperatures, is also exhibited in the Greater Toronto Area during the 1971 to 2000 timeframe. A methodological approach using counts is the basis for the analysis. Statistical significance is determined through the use of Spearman’s Rank, Kendal-Tau and T-tests. A total of five stations are analysed, three being urban and two representing the surrounding suburban areas. The results indicate that statistically significant decline in extreme minimum temperature counts have occurred. In agreement with the literature, statistically significant increases in extreme maximum temperature counts can not be determined.

The impacts of extreme temperatures on human health and morbidity have been well documented in many studies. In literature, changes in the trends of extreme temperatures have been studied using percentiles, indicators and climate modeling. The aim of this study is to determine if the trend exhibited in the literature of statistically significant increases in extreme minimum temperatures, is also exhibited in the Greater Toronto Area during the 1971 to 2000 timeframe. A methodological approach using counts is the basis for the analysis. Statistical significance is determined through the use of Spearman’s Rank, Kendal-Tau and T-tests. A total of five stations are analysed, three being urban and two representing the surrounding suburban areas. The results indicate that statistically significant decline in extreme minimum temperature counts have occurred. In agreement with the literature, statistically significant increases in extreme maximum temperature counts can not be determined.