Masters Thesis Abstract: Jeremy Chirnside
The distribution of precipitation types across the South Island.
Precipitation variation across New Zealand has been widely documented in the form of statistical summaries for individual locations and maps showing the distribution across the country interpolated from these points. More recently, with increased understanding of the El- Niño Southern Oscillation phenomenon, there have been a number of studies into the relationship between precipitation variation and synoptic scale atmospheric circulation, which have found a significant positive relationship between onshore airflow and precipitation. The most recent studies have looked into the variation in this circulation and how it affects precipitation over periods of a decade or greater. There have been, however, few studies into the underlying precipitation processes that can significantly influence the intensity and duration of a precipitation event at a specific location, and how widely it is distributed. Sumner (1988) defined three main types of precipitation in terms of the initial processes that result in the potential for precipitation, these are orographic, cyclonic and convective.
Precipitation data from around the South Island covering a variety of time scales are used to determine whether Sumner’s three types of precipitation can be easily identified within the South Island’s spatial and temporal precipitation distribution. Each precipitation type has its own unique spatial and temporal pattern and a combination of spatial and temporal statistics are used at a range of scales. The South Island has two characteristic features affecting precipitation patterns. These are, spillover and the impact of a southerly change. This research will attempt to identify how these features relate to the three main types of precipitation.