No description available.

No description available.

No description available.

A mean sea level (MSL) and 500 hPa height field synoptic climatology of ozone is developed for the Montreal region over the period 1980-1992 using the Kirchhofer computer-assisted map-pattern technique. Synoptic class air quality signatures are examined on an annual, seasonal and interannual basis. Residual cumulative dose analysis confirms that the "Back of the High" synoptic types are responsible for above average ozone concentrations in the summer months. In contrast, during the winter, the stable conditions and cold temperatures associated with these same synoptic types promote ozone scavenging and below average ozone concentrations. Above average winter ozone levels are associated with cyclonic synoptic types, possibly as a result of stratospheric ozone intrusion. Synoptic sequencing confirms the importance in stability in upper level features (particularly an upper level trough to the northeast of Montreal) and stagnation of surface features (primarily the "Back of the High") for the development of elevated ozone concentrations in Montreal. Finally, a declimatizing technique is evaluated as a means of removing the synoptic signal from the ozone time series. Results of this study are in broad agreement with similar investigations elsewhere in northeastern North America.

The spring freshet is the dominant annual hydrologic event occurring on largely nival Arctic river systems. It provides the greatest proportion of freshwater influx to the Arctic Ocean, amongst all other atmospheric input sources. To assess whether any shift in the seasonality of spring freshets has occurred, and how climatic drivers and flow regulation govern trends in sub-basin freshets and their contribution to outlet flow, a temporal and spatial analysis of 106 hydrometric stations located across four major Arctic-draining river systems is performed to extract information regarding the timing, magnitude and volume of the spring freshet of the four largest Arctic-draining rivers; namely, the Mackenzie River in Canada, and the Ob, Yenisei and Lena rivers in Eurasia. Total annual freshwater influx to the Arctic Ocean from these basins increased by 14% during 1980-2009. Despite freshet volume displaying a net increase, its proportional contribution to annual flow has decreased. In fact, rising winter, spring and fall discharge proportions, combined with lower peak freshet magnitudes, potentially increased freshet durations, and lower summer proportions indicate a shift towards flatter, more gradual annual hydrographs with earlier pulse onsets. Discharge assessed on a sub-basin level during 1962-2000 and 1980-2000 reveals regional differences in trends, with higher-relief drainage areas displaying the strongest trends. Sub-basin trends generally agree with those at the outlets, particularly in sub-basins without upstream flow regulation. Flow regulation has had a greater impact on observed trends in freshet volume compared to peak freshet magnitude. Timing measures are found to be strongly linked to spring temperatures. Volume relationships are also apparent with winter precipitation, however, these are less distinct. Moreover, flow regulation appears to suppress climatic drivers of freshet volume but has a lesser effect on timing measures. Significant relationships are found with several major atmospheric and oceanic teleconnections indices. This study provides valuable information regarding the dominant controls of freshet generation, whilst highlighting potential impacts of freshet variability on the freshwater balance of the Arctic Ocean. / Graduate / 0388 / 0368 / roxannea@uvic.ca

No description available.

Coupled atmosphere-ocean general circulation models are the simplest models which are capable of simulating both the variability which occurs within each component of the climate system, and the variability which arises from the interactions between them. Only recently has it become computationally feasible to use coupled general circulation models to study climate variability and change on timescales of O(104) years and longer. Flux adjustments are often employed to maintain a control climate that is both stable and realistic; however, the magnitude of the adjustments represents a source of concern. This study employs the CSIRO Mk3L climate system model, a low-resolution coupled atmosphere-sea ice-ocean general circulation model. The atmospheric and oceanic components are spun up independently; the resulting atmospheric simulation is realistic, while the deep ocean is too cold, too fresh and too buoyant. The spin-up runs provide the initial conditions for the coupled model, which is used to conduct a 1400-year control simulation for pre-industrial conditions. After some initial adjustment, the simulated climate experiences minimal drift. The dominant mode of internal variability is found to exhibit the same spatial structure and correlations as the observed El Ni˜no-Southern Oscillation phenomenon. The ability of Mk3L to simulate the climate of the mid-Holocene is evaluated. It correctly simulates increased summer temperatures at northern mid-latitudes, and cooling in the tropics. However, it is unable to capture some of the regional-scale features of the mid-Holocene climate, with the precipitation over northern Africa being deficient. The model simulates a 13% reduction in the strength of El Ni˜no, a much smaller decrease than that implied by the palaeoclimate record. A 1400-year transient simulation is then conducted, in which the atmospheric CO2 concentration is stabilised at three times the pre-industrial value. The transient simulation exhibits a reduction in the rate of North Atlantic Deep Water formation, followed by its gradual recovery, and a cessation of Antarctic Bottom Water formation. The global-mean surface air temperature warms 2.7◦C upon a trebling of CO2, and 5.3◦C by the end of the simulation. A number of modifications to the spin-up procedure for the ocean model are evaluated. A phase shift in the prescribed sea surface temperatures and salinities is found to reduce the phase lag between the model and observations, and to lead to a reduction in the magnitude of the diagnosed flux adjustments. When this spin-up run is used to initialise the coupled model, the reduced flux adjustments are found to have negligible impact upon the nature of the internal variability. While the flux adjustments are not found to have any direct influence upon the response of the model to external forcing, they are found to have an indirect influence via their effect upon the rate of drift within the control simulation. An iterative spin-up technique is also developed, whereby the response of the ocean model is used to derive a set of effective surface tracers. These result in a much more realistic vertical density profile within the ocean. The coupled model exhibits slightly increased internal variability, with reduced convection within the ocean. There is a slightly greater surface warming in response to an increase in the atmospheric CO2 concentration, with the reduced convection resulting in slower penetration of the surface warming to depth.

Thesis (M.S.)--University of Nevada, Reno, 2007. / "August, 2007." Includes bibliographical references (leaves 143-147). Online version available on the World Wide Web.

Thesis (doctoral)--Universität, Rostock, 2005. / Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 1993. / Vita. Includes bibliographical references (leaves [184]-201).