El Ni??o-Southern Oscillation (ENSO) is the most important coupled ocean-atmospheric phenomenon to cause global climate variability on interannual time scales. Efforts to understand recent, apparently anomalous ENSO behaviour are hampered by the lack of long, high-quality climate records. While instrumental data generally covers the past 150 years, record length is insufficient for the assessment of past changes in the frequency, magnitude, and duration of ENSO. Here, multiproxy networks of high-resolution tree-ring, coral, ice and documentary records derived from eastern and western Pacific ENSO ???centres of action??? are analysed (A.D. 1525-2002). Considerable improvements in ENSO reconstruction are achieved from expanding the use of records from the western Pacific. In particular, ~500 years of a continuous 3,722 year ENSO sensitive tree-ring record from New Zealand is introduced. Although extreme ENSO events are seen throughout a 478-year discrete event analysis, 43% of extreme, 20% of very strong and 28% of all protracted ENSO events occur within the 20th century. Principal component analysis was used to extend instrumental records of the Southern Oscillation Index (SOI) Ni??o 3.4 Sea Surface Temperature (Ni??o 3.4 SST) and a newly developed coupled ocean-atmospheric ENSO index (CEI) by 347 years. Significantly, of the three indices reconstructed here, CEI reconstructions were largely found to be the best predictors of ENSO. The results suggest that ENSO may be more effectively characterised using a coupled ocean-atmosphere index, particularly for December-May periods. Compared to the pre-instrumental period, the late 19th and early 20th centuries indicate a clear trend toward increased ENSO variability over the past 150 years. Significantly, spectral analysis of reconstructed indices reveals a marked change in the frequency and intensity of ENSO beginning ~A.D. 1850, coinciding with the end of the Little Ice Age and the boom in global industrialisation. This suggests that ENSO may operate differently under natural (pre-industrial) and anthropogenically influenced background states. This study asserts that recent ENSO variability appears anomalous in the context of the past five centuries. Given the considerable socio-economic impacts of ENSO events, future investigation into the implications an increasingly anthropogenically-warmed world may have on ENSO is vital.

El Ni??o-Southern Oscillation (ENSO) is the most important coupled ocean-atmospheric phenomenon to cause global climate variability on interannual time scales. Efforts to understand recent, apparently anomalous ENSO behaviour are hampered by the lack of long, high-quality climate records. While instrumental data generally covers the past 150 years, record length is insufficient for the assessment of past changes in the frequency, magnitude, and duration of ENSO. Here, multiproxy networks of high-resolution tree-ring, coral, ice and documentary records derived from eastern and western Pacific ENSO ???centres of action??? are analysed (A.D. 1525-2002). Considerable improvements in ENSO reconstruction are achieved from expanding the use of records from the western Pacific. In particular, ~500 years of a continuous 3,722 year ENSO sensitive tree-ring record from New Zealand is introduced. Although extreme ENSO events are seen throughout a 478-year discrete event analysis, 43% of extreme, 20% of very strong and 28% of all protracted ENSO events occur within the 20th century. Principal component analysis was used to extend instrumental records of the Southern Oscillation Index (SOI) Ni??o 3.4 Sea Surface Temperature (Ni??o 3.4 SST) and a newly developed coupled ocean-atmospheric ENSO index (CEI) by 347 years. Significantly, of the three indices reconstructed here, CEI reconstructions were largely found to be the best predictors of ENSO. The results suggest that ENSO may be more effectively characterised using a coupled ocean-atmosphere index, particularly for December-May periods. Compared to the pre-instrumental period, the late 19th and early 20th centuries indicate a clear trend toward increased ENSO variability over the past 150 years. Significantly, spectral analysis of reconstructed indices reveals a marked change in the frequency and intensity of ENSO beginning ~A.D. 1850, coinciding with the end of the Little Ice Age and the boom in global industrialisation. This suggests that ENSO may operate differently under natural (pre-industrial) and anthropogenically influenced background states. This study asserts that recent ENSO variability appears anomalous in the context of the past five centuries. Given the considerable socio-economic impacts of ENSO events, future investigation into the implications an increasingly anthropogenically-warmed world may have on ENSO is vital.

M.Phil. (Energy Studies) / Southern Africa is a major source of regional aerosols and trace gases from biomass burning, and this creates a need for experimental validation and systematics of the magnitude and frequency of aerosol transport episodes affecting the atmosphere of the region. This study links surface measurements of biomass burning atmospheric aerosols and trace gases with air mass trajectory analysis to determine transport pathways for periods of high and low concentrations. The hypothesis of this study is that from chemical signatures of trace gases and aerosols, as well as trajectory analyses, it is possible to identify sources of these emissions from industrial, traffic, marine and biomass burning activities. Consequently, frequencies, durations, intensities and seasonal variations of trace gases can be established. The study aims to interpret the long-term atmospheric monitoring record from a remote monitoring station at Botsalano (North West Province, South Africa) to determine the origin, frequencies, durations, intensities and seasonal occurrences of aerosol/haze episodes influencing the atmosphere of southern Africa. A suite of trace gas analysers and a Differential Mobility Particle Sizer (DMPS®) were used to measure ground level trace gas and aerosol quantities. MATLAB® scripts were used in performing quality assurance and processing to provide a working set of data from which different fire periods could be selected. Fire signatures, based on excess CO above average tropospheric levels and episodes of enhanced particulate matter concentrations in the 10 to 200 nm range, were identified using MATLAB® scripts and Excel®. Altogether 36 plumes were accepted as biomass burning plumes. Twenty-nine fire plumes had weak signals with excess CO ratios ranging between 0.07 and 0.32; seven plumes had strong signals ranging between 0.41 and 0.64. The occurrence of identified biomass burning plumes was high in the dry season from May to October (83%) and low (17%) during the wet season from November to April. Four pathways were identified for the long-range transportation of biomass burning aerosols to the site: easterly, south-westerly, re-circulation and northerly modes, with occurrence frequencies of 39%, 31%, 22% and 8%, respectively. Anti-cyclonic circulation was observed over southern Africa and was evident in the re-circulation and Indian Ocean slow modes. CO and Aitken-mode aerosol number intensities were generally larger for fire emissions arriving in the easterly and south-westerly air masses when compared with those arriving in re-circulation and northerly air masses. Easterly and south-westerly flows were dominated by Aitken-mode aerosol, whereas accumulation mode particles dominated in the re-circulation and northerly modes. Consequently, easterly and south-westerly flows transported emissions from young/fresh fire plumes, with source regions probably close to Botsalano. Re-circulation and northerly flows were responsible for transport of rather aged plumes from more distant regional fires. Based on forward trajectories, this study revealed that the 2006/2007 measurement period exhibited transport features of a La Niña ENSO during which transport of biomass v burning aerosols towards the south in the Indian Ocean slow and Indian Ocean fast modes was most frequent. This study is significant in that it complements earlier studies of regional aerosol transport over the sub-continent and adds to the understanding of the regional scale generation and transport of trace substances through the atmosphere. Furthermore, the study combines a technique for identifying enhanced CO concentrations as a unique identifier of large scale biomass combustion events with the use of the Aitken-mode particle number densities and size distributions. This technique reveals aspects of aerosol growth dynamics through the changing size distributions, thereby adding fresh insights normally not available through conventional particle volume/mass concentrations measurements.