New Zealand is affected by weather systems which originate over the seas around the country, whether in the warm tropical region or the cold Antarctic region. A set of 12 daily weather types for the New Zealand region was determined by Kidson (2000) which fall into three regimes – troughs (low pressure systems) crossing the country, high pressure systems to the north and west-east flow in the south, and blocking patterns with high pressure systems in the south.
Blocking patterns, when high pressure systems sit over the south of the country and result in sunny, dry weather, are more frequent in summer and autumn. They are associated with above normal temperatures, less precipitation in the southwest of the country and more precipitation in the northeast. Zonal patterns, where more west-east wind flows over the country, brings below normal precipitation to the northeast and milder conditions in the south, and are less common in summer. Lastly, the trough regime, which is associated with lower than normal air pressure and potentially stormy conditions, is less frequent in autumn and is linked to cooler temperatures in the west and above normal precipitation over New Zealand.
Analysing how the frequency of occurrence of these synoptic types have changed over time, or other climatic drivers that influence the synoptic types, is of interest to researchers at NIWA.
Under the Climate Present and Past project, NIWA undertakes research about synoptic types in the following areas:
- Little Ice Age climate reconstructed from Southern Alps glaciers using a synoptic type approach
- The effect of the Madden-Julian Oscillation on New Zealand's weather regimes
- Drivers of extreme daily rainfall in New Zealand
- Past Interpretation of Climate Tool (PICT)
- The influence of large-scale climate modes on daily synoptic weather types over New Zealand
- Regional climate regime classification as a qualitative tool for interpreting multi-proxy palaeoclimate data spatial patterns in New Zealand
- Regional climate regime classification and synoptic circulation reconstructions for NZ covering the last 2000 years, the mid-Holocene, and the Last Glacial Coldest Period at ~21ka