Southern swell

Image of the Month - August 2011

Significant wave height measured by the current altimetry satellites (Jason-1, Envisat, Jason-2) over the Indian Ocean and south of it on August 3, 2011, left, from the along-track measurements of that day. Right wind speed (gridded merged altimetry data, using two days of data, and smoothing), that show the rather low winds at La Réunion latitude (21°S) (view also the wave height animation over a few days). (Credits Aviso)

On August 1st, 2011, Meteo France emitted an alert for La Réunion Island about high Southern swell for August 3. Such a swell, coming from some of the storms swiping the "roaring forties" (i.e. the Southern Ocean at about 40° latitude), is not abated nor lessen by the low winds in this area of the Indian Ocean. Southern swell occur from time to time, and can cause serious damages.

If altimetry in itself is not the mean to forecast them, the assimilation of altimetry significant wave height data in marine weather forecast models improve wave heights forecasts, if only by the fact that the satellites provide worldwide measurements.

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