The purpose of this research was to create the longest possible, homogeneous, historical daily temperature dataset for Southern New Zealand, analyse the changes in extreme temperatures and investigate atmospheric circulation patterns that contributed to these changes. Daily minimum and maximum temperature data for Southern New Zealand were captured from paper records and extended to include all available archival data from the region. This dataset was digitised and contains temperatures from 26 stations that began operation sometime in the period between 1852 and 1953. Stations include the Chatham and Campbell islands. Adjustments for inhomogeneities in the dataset were made using a frequency distribution matching method. Dunedin has a record dating from 1852, the longest in the Southern Hemisphere south of 40�S latitude. Reconstruction of a homogeneous record for Dunedin was made by taking into account site changes from contemporaneous modem data logger measurements and from an analysis of overlapping period data. Temperatures showed no clear pattern of change in Southern New Zealand from the mid 1800s through to the early 1900s with the exception of a brief cold period that occurred around 1900. However, from the 1940s through to the 1970s both minimum and maximum extreme temperatures showed strong warming. These trends were duplicated over the shorter length period of record for other regions, especially in Eastern Canterbury. The warming trend was maintained over the period 1979 - 2003, but only in the colder ends of minimum and maximum distributions. Temperatures have become less cold due to the recent compression of the temperature distribution. There was a marked decrease in cold days at stations in the south and offshore islands. Atmospheric circulation pattems, and in particular ENSO, were shown to affect extreme temperatures recorded in Southern New Zealand. Anomalous southwesterlies associated with El Nino events produce cooler temperatures and increase the numbers of cold extreme temperatures, while anomalous northeasterlies typical of La Nina increase the numbers of warm extreme temperatures. Monthly frequencies of extreme temperatures were primarily affected by anomalous south/north meridional airflows to increase cold/warm extreme temperature frequencies. Zonal airflows have a lesser, but topographically influenced effect. Record hot and cold temperatures in Southern New Zealand were a product of the interaction between advective northerly and southerly airflows respectively, and local climatic effects caused by topography.
| Identifer | oai:union.ndltd.org:ADTP/217719 |
| Date | January 2006 |
| Creators | Brown, Paula, n/a |
| Publisher | University of Otago. Department of Geography |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Paula Brown |
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