On the exact solution of the mixed-spin Ising chain with axial and rhombic zero-field splitting parameters

Ground-state phase diagram of the mixed spin-$1/2$ and spin-$1$ Ising chain with axial and rhombic zero-field splitting parameters is exactly calculated within the framework of the transfer-matrix method. It is shown that the rhombic zero-field splitting parameter prefers the magnetically ordered phase instead of the disordered phase.Comment: 5 pages, 2 figure

Understanding the Features and Mechanisms of the Great Plains Low-Level Jet in CMIP5 Models

The Great Plains low-level jet (GPLLJ) is an important driver of precipitation and severe weather outbreaks over the U.S. Great Plains during the spring and summer. Therefore, it is extremely important that features of the GPLLJ, including its atmospheric and oceanic mechanisms, are understood and simulated accurately by global climate models so Great Plains precipitation can be predicted reliably in the future. This study examines the features of the GPLLJ and the mechanisms relating it to the El Niño Southern Oscillation (ENSO) in reanalyzes and global climate models, to aid near- and long-term predictions and projections of Great Plains weather and climate. Sea surface temperature data, four reanalyzes, and an ensemble of 42 historical simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are used. This makes this study the first of its kind to examine the ability of the entire suite of CMIP5 models to represent the observed features of the GPLLJ and its relationship with ENSO. Biases in the CMIP5 model simulation of the climatology of the GPLLJ are identified, including a GPLLJ that is too weak, extends too late in the summer, and peaks too low in the troposphere. Noting these biases, the accuracy of the ENSO - GPLLJ relationship in the CMIP5 models is investigated. As in previous studies, observations and reanalysis show that winter ENSO has a significant negative correlation with the GPLLJ in the following spring and a significant positive correlation with the GPLLJ in the following summer. This study illustrates that the influence of ENSO on the GPLLJ is mainly on the frequency, not intensity, of GPLLJ events in the spring, while both the frequency and intensity of GPLLJ events are affected in the summer. However, although the majority of CMIP5 historical simulations (82 out of 131 ensemble members) exhibit the observed significant negative ENSO - GPLLJ correlations in the spring, nearly all of them (129 out of 131 ensemble members) fail to simulate the significant positive correlation in the summer. The ability of the models to simulate the ENSO - GPLLJ relationship is attributed to the strength of simulated ENSO events and the associated effects on geopotential heights and atmospheric circulation. These results have implications for the predictability of climate in the Great Plains and suggest that the variability of the GPLLJ will not be reliably captured in future climate simulations if the magnitude of ENSO events and their impacts are not well represented

The association between watershed characteristics and mercury concentrations in fish of Northern Ontario lakes

Many landscape, limnological, and ecological factors synergistically affect the mercury cycle and subsequently influence total mercury (THg) concentrations in fish. In Chapter 1, the associations between watershed and lake scale characteristics with THg in piscivorous fish are examined. ArcGIS was used to delineate the waterbody catchment area and extract waterbody catchment characteristics for 243 of northern Ontario’s lakes. Walleye (Sander vitreus, n= 121 lakes), lake trout (Salvelinus namaycush, n= 60 lakes), brook trout (Salvelinus fontinalis, n= 18 lakes), northern pike (Esox lucius, n =107 lakes), and smallmouth bass (Micropterus dolomieu, n = 37 lakes) were standardized to the mean length of the populations by using power-series regressions. Multivariate analysis (non-metric multidimensional scaling) and univariate analysis were used to determine the associations between total mercury concentrations in fish and watershed scale and lake scale variables. Watershed and lake chemistry characteristics poorly described the variability in THg concentrations. Forest harvesting and natural disturbance were not associated with fish mercury concentrations. In Chapter 2, the relationship between walleye (Sander vitreus) growth rates and mercury concentrations was evaluated. The von Bertalanffy growth model was used to standardize the age of walleye to the mean total length. Walleye populations with slower growth rates had higher THg concentrations (r2=0.333, p< 0.001), suggestive of growth efficiency. Moreover, abundance of walleyes was associated with the growth rate (r2 =0.136, p<0.0001). Concentrations of THg in piscivorous fish are attributed to physical, chemical, and ecological characteristics of lakes. It is likely that lake ecology exerts the strongest influence on high mercury concentrations in piscivorous species, masking the effect from from watershed disturbance