No description available.

No description available.

This thesis investigates causal mechanisms and predictability of North Pacific decadal variability in the 1980s and early 1990s. Observations and proposed mechanisms of North Pacific decadal variability are reviewed. A significant warming of central North Pacific Ocean surface and subsurface was identified and shown to be predictable up to six years lead-time in the United Kingdom Meteorological Office Decadal Prediction System (DePreSys). The possible role of the April 1982 El Chich6n volcanic eruption in North Pacific Ocean cooling prior to the warming is investigated using climate model experiments. El Chich6n significantly weakens the East Asian Summer Monsoon and enhances the East Asian Winter Monsoon through modification of the land-ocean temperature contrast between East Asia and the western North Pacific. East Asian Monsoon changes cool the western North Pacific for up to three years through enhancement of cloudiness in summer and latent heat flux in winter. The resulting cooling enhances the magnitude and persistence of central North Pacific Ocean cooling. North Pacific atmospheric variability during the late 1980s and early 1990s was persistently anticyclonic and equivalent barotropic. A sensitivity experiment finds anomalous turbulent surface heat and momentum fluxes, resulting from anomalous anticyclonic atmospheric conditions, force the central North Pacific Ocean warming. This warming is related to a poleward displacement of the subtropical gyre resulting from anomalous Ekman pumping. A sensitivity experiment investigates the role of North Pacific, North Atlantic and Tropical sea surface temperatures as the predictability source of persistent anticyclonic tropospheric conditions over the North Pacific. Winter 1988/89 anticyclonic conditions are the result of a concurrent La Nina. A multi-year anticyclonic persistence mechanism is not identified. Recommendations for future investigations of the late 1980s and early 1990s warming, the East Asian Monsoon volcanic eruption response, and decadal climate prediction are presented.

No description available.

No description available.

No description available.

No description available.

No description available.

Population growth and predicted global climate change are applying new, and increasing, pressure to mountain environments, but the consequences of these changes upon the biodiverse and vulnerable Tropical Andean ecosystems are poorly understood. This thesis explores past human-climate-ecosystem interactions using multi-proxy palaeolimnological investigations (fossil pollen, spore, charcoal and Chironomidae (midges); elemental abundance, colour spectra and magnetic susceptibility) of two sites in the eastern Bolivian Andes (Lake Challacaba and Laguna Khomer Kocha Upper) over the last c. 18,000 years. During the deglaciation and Holocene, ecosystems were exposed to varying climatic stress levels, and pressures imposed by the development of human cultures. Examination of preserved ecological assemblages, including the first assessment of subfossil central Andean Chironomidae, reveals ecosystem sensitivity to changes in temperature, moisture, fire regime, lake level, nutrients and salinity. Charcoal analysis from Laguna Khomer Kotcha Upper reveals changes in burning at c. 14,500, 10,100 and 6,400 cal yr BP. Concomitant palynological shifts shows climatically controlled fire regime was a transformative agent of Andean vegetation, particularly for the threatened, high elevation, Polylepis woodlands. Pollen and geochemical data from Lake Challacaba indicate two periods of aridity (c. 4,000-3,370 and 2,190-1,020 cal yr BP), these broadly correlated to El Nino/Southern Oscillation variations. Increased Sporormiella abundance after c. 1,340 cal yr BP indicate changes in trade-route use and agricultural practices; demonstrating human adaptation to environmental change and interconnectivity to Tiwanaku and Inca civilizations. The long-term response of the terrestrial and aquatic ecosystems, reconstructed from these lakes, has provided insights into how Tropical Andean ecosystems may respond to future changes in temperature, precipitation and human interference. The palaeoenvironmental data has implications for conservation management; it indicates that spatial and temporal variations in site sensitivity, exposure and resilience should be assessed, and that planting strategies should mimic the present day natural patchy distribution of Polylepis woodlands.

The vertical profile of diabatic heating associated with convection is vitally important to the largescale tropical circulation. Systematic errors in diabatic heating distributions in models are considered to be a primary cause in their errors in representing the large-scale mean circulation and tropical variability in the Tropics. Much attention has been given to the vertical heating structure of the Madden-Julian Oscillation (MJO) in recent years to understand the fundamental physics of the MJO and why many general circulation models struggle to simulate a robust MJO. In this thesis, estimates of vertical diabatic heating structures from reanalysis datasets and Tropical Rainfall Measuring Mission (TRMM) latent heating algorithms are used to understand how variations in the detailed structure of the heating influence the structure in the dynamical response in the Tropics. As pan of this study, the role of the vertical structure of the heating of the MJO to the dynamical response is investigated by integrating a primitive equations model with vertical anomalous diabatic heating structures associated with the MJO. In particular, the role of a vertical tilt in the heating, which has been identified in three reanalysis datasets. is investigated in relation to the moisture convergence and energetics. An eastward phase shift of the moisture convergence of approximately 1 day directly associated with the vertical anomalous heating structure of the MJO was found for each of the reanalysis heatings. As a consequence of this phase shift, a surplus of moisture convergence over the anomalous heating was generated in regions ahead of the MIO convection centre indicating a pre-moistening of tlle atmosphere prior to deep convection. It was demonstrated that both a leading mid to shallow congestus heating and a lagging stratiform heating relative to the main MJO convection were important in contributing to the phase shift in the moisture convergence. Both these vertical heating structures may therefore be critical to the maintenance of the MJO through the warm pool region. The response to the two the heatings from the TRMM products showed no phase shift in the moisture convergence relating to the vertical heating structure of the MJO. This was due to no observable vertical tilt in the heating structure. There is increased generation of eddy entropic potential energy and conversion of that energy into eddy kinetic energy through the MJO cycle associated with the vertical anomalous heating structure of the MIO. This was related to stronger heating in the mid-troposphere generating stronger eddy potential energy (EPE) between 600 and 400 hPa, which exceeded the rcduction in generation of EPE in the planetary boundary layer (PBL).