The Southern Ocean

Southern Ocean weather

The Southern Ocean is the only ocean where wind, waves and currents can travel right around the world almost unhindered by land. As a result the weather systems behave almost as you would expect from a total "water planet" with polar lows tracking around the Antarctic continent in a never-ending succession.

Typical high and low pressure systems in the Southern hemisphere. This chart is from January 2001 (Southern summer) but the picture is similar to this all the year around. Source: Plotted from data provided by the South African Weather Service.

The Roaring Forties

The prevailing westerly winds that blow from the subtropical highs towards the polar lows are know as "the Roaring Forties". They are stronger and more consistent than the corresponding westerlies in the northern hemisphere and reach their peak in July-August (southern winter).

With average monthly wind speeds of more than 12 m s-1 in the windiest areas These strong and persistent winds can whip up enormous waves. Average monthly wave height in July is over 5 m in the stormiest region south of the Indian Ocean. For 5% of the time waves will be over twice as high as the monthly average.

Winds

Average monthly wind speed for July. The colour shows the wind speed, the arrows give the average direction.

Source: NOC from satellite scatterometer data.

Waves

Average significant wave height (HS) derived from satellite altimetry for the month of July. Significant wave height is the average height of the highest 1/3 of the waves. This is similar to the wave height estimates given by experienced observers. Source: NOC from Topex-Poseidon altimetry data.