Southern Annular Mode (SAM)
SAM refers to the belt of westerly winds (or low pressure systems) that circulate around Antarctica in the Southern Ocean.
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Read the transcript: Climatedogs - Sam
Click a Climatedog below to view animation:
Key things to know about SAM
- The changing position of the SAM influences the strength and position of frontal activity.
- Frontal activity is important for bringing moisture from the Southern Ocean for rainfall.
- Fronts also trigger rainfall events when combined with other climate processes (ENSO & IOD).
- Victorian farmers know that seasons with regular or stronger frontal activity tend to provide more rainfall.
- SAM has its greatest influence in southern Victoria and during winter.
- SAM is therefore important for farmers. It has two phases which can vary fortnightly.
- The phases describe the northward and southward position of the low pressure belt.
Positive SAM
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When the belt of westerly winds contracts around Antarctica less (or weaker) rain producing fronts move across southern Australia. This is called the positive SAM phase and decreases the chance of rainfall (from fronts) during winter.
Negative SAM
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When the westerly wind belt expands, more (or stronger) fronts can come closer to southern Australia. Negative SAM increases the likelihood of above average winter rainfall in southern Victoria.
Where to go for more information
For more information about the SAM visit some of the pages below.
- Go to the Bureau of Meteorology website to read more about Sam – including where and when Sam is most influential.
- You can also see an example of a SAM event on that site.
- Read a fact sheet from the South East Australian Climate Initiative about how the region's climate is changing, including research into how Sam influences our climate.
