Showing papers by "Rob Allan published in 2009"

Fluctuations in autumn-winter severe storms over the British Isles: 1920 to present.

Abstract: An examination of extreme storms across the British Isles over the last 85 years during the boreal autumn [October, November, December (OND)] and winter [January, February, March (JFM)] shows that large-scale natural climate variability plays an important role in modulating the intensity and frequency of these events. Severe storms across the British Isles were most prominent in the 1920s and 1990s in OND, and in the 1920s, 1980s and 1990s in JFM. There is a significant correlation between JFM severe storminess across the British Isles and both the Gibraltar–South-West (SW) Iceland and Azores–Iceland indices of the North Atlantic Oscillation (NAO), but this relationship fluctuates over the 85 years of data. Strongest NAO relationships occur during 1970–1990 and 1940–1960, with a weaker correlation in the 1920s–1940s, and effectively no correlation in 1950–1970. There is no significant relationship between the Gibraltar–SW Iceland NAO and severe storms in OND, but a significant correlation exists with the Azores–Iceland NAO and there is a clear link to a pattern in mean sea level pressure (MSLP) extending from the tropical Atlantic to higher latitudes of the North Atlantic. El Nino Southern Oscillation (ENSO) influences from the Pacific Ocean also appear to play a role in modulating OND severe storms over the British Isles. Importantly, severe storms in OND and JFM seasons respond to different physical mechanisms. Future work is needed to extend this study back into the late 19th century in order to evaluate fully any changes in severe storms across the British Isles using a longer instrumental record. This may be best achieved through long historical surface-observations-only global reanalyses, which can reconstruct tropospheric weather variables using longer instrumental records of daily to sub-daily MSLP. Copyright © 2008 Royal Meteorological Society

A climate reconstruction of Sydney Cove, New South Wales, using weather journal and documentary data, 1788-1791

Abstract: This study presents the first analysis of the weather conditions experienced at Sydney Cove, New South Wales, during the earliest period of the European settlement of Australia. A climate analysis is presented for January 1788 to December 1791 using daily temperature and barometric pressure observations recorded by William Dawes in Sydney Cove and a temperature record kept by William Bradley on board the HMS Sirius anchored in Port Jackson (Sydney Harbour) in the early months of the First Fleet’s arrival in Australia. Remarkably, the records appear comparable with modern day measurements taken from Sydney Observatory Hill, displaying similar daily variability, a distinct seasonal cycle and considerable inter-annual variability. To assess the reliability of these early weather data, they were cross-verified with other data sources, including anecdotal observations recorded in First Fleet documentary records and independent palaeoclimate reconstructions. Some biases in the temperature record, likely associated with the location of the thermometer, have been identified. Although the 1788–1791 period experienced a marked La Nina to El Nino fluctuation according to palaeoclimatic data, the cool and warm intervals in Sydney over this period cannot be conclusively linked to El Nino– Southern Oscillation (ENSO) conditions. This study demonstrates that there are excellent opportunities to expand our description of pre-20th century climate variability in Australia while contributing culturally significant material to the emerging field of Australian environmental history.