in an initial inertial dynamics damped by upwelling-associated pressure
gradients. Finally, a mass field formed by warm offshore nuclei surrounded by frontal regions consequence of coastal upwelling (on the
southern side) and cold exterior waters (on the northem side) becomes
quasi-geostrophically adjusted as antiq'clonic sub-mesoscale eddies (Sânchez
& Gil 2000).
Figure 2 - Water masses pattem after the Poleward Current vanished and appeared.
However, this ideal seasonal pattern may be affected by a number of disturbances that also modify the year-to-year strength, extension and duration
of the summer upwelling. A typical summer picture is presented in
figure 3 for both July 1998 and 1999, where at 40 metres the presence of a
density ffont between the cold upwelled waters occupting the continental
shelf and warm off-shelf structures was observed. Nevertheless, both
events are scaled with different relative magnitude. In July 1999, a wide,
strong and continuous upwelling region developed whereas in 1998 appeared as a broken stripe of altemating mesoscale nuclei of different sign.
Figure 3 - Summer upwelling and mesoscale activity from temperature at 40 metres.
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