Southern annular mode (1887–2014)

The Southern Annular Mode (SAM) is an index that describes climate variation around the South Pole and Antarctica, as far north as New Zealand. It indicates short-term climate variations that can influence New Zealand’s climate. Such climate variations can impact on our environment, industries, and recreational activities.
The variation is caused by the movement of a low-pressure belt that generates westerly winds. During a negative phase, the low pressure belt moves north, towards the equator. In New Zealand, this can cause increased westerly winds, unsettled weather, and storm activity over most of the country. Over the southern oceans, there are relatively less westerly winds and less storm activity.
During a positive phase, the low pressure belt moves south towards Antarctica. In New Zealand, this can cause relatively light winds and more settled weather. Over the southern oceans, there is increased westerly winds and storm activity.
This dataset relates to the "Southern annular mode" measure on the Environmental Indicators, Te taiao Aotearoa website.