SEMINAR: OI Seminar Series - David Griffin

Title: Extreme oceanic events

Abstract: Extreme oceanic events have received much less attention than they deserve. There are two good reasons why we have tended not to focus on ocean extremes: one is that by definition, they are rare, so direct observations probably don’t exist unless the record is very long, which is only true for a small number of quantities, at a few places. This rareness effect is exaggerated, too, if the extreme condition impacts on the measurement platform or sensor somehow. Think of what happens to a string of current meters if the flow is too fast for the mooring design. The second reason is that observations are usually subjected to some form of ‘quality control’. A correct observation of an extreme event is more likely to be thrown away than a correct observation of a normal condition. But times are changing. Several oceanographic data sets are now suitable for characterising ocean extremes. One data set that has broad spatial coverage, is not blind to extreme values, and is now, 20 yrs after the launch of the Topex-Poseidon, long enough to include ‘very rare’ events, is satellite altimetry. Maps of the extreme values of sea level, and the geostrophic currents we estimate from sea level gradients, reveal many interesting features. In this presentation we’ll look at a number of oceanic extreme events, witnessed by a variety of observing systems.