116
L. G.-Weil et al.
5.4 Concluding Remarks
The combination of different RS data types, with different spatial and temporal resolutions, and obtained in different regions of the electromagnetic spectrum, allows for
the effective monitoring of a region with complex mesoscale variability patterns such
as the Canary Islands area. It has been shown that this area has a higher mesoscale
activity than other parts of the Northwest African coastal transition zone. Its distinctive mesoscale activity has a clear seasonality, with a maximum in October and a
minimum in April, and is strongly related to the eddy generation processes typical
of the Canarian Archipelago.
The detailed analysis of the 1998–1999 historical data record, combining the complementary characteristics of various RS data sources, shows that most of the the
long-lived mesoscale eddies develops during the second half of the year. A similar
number of cyclonic and anticyclonic eddies was generated, in the period of observation, but over extended periods the mesoscale dynamics seemed to be dominated by
anticyclones. These displayed a bigger size (∼ 150 km) and were observed during a
longer time than cyclones.
Eddy trajectories and velocities revealed that the actual motion observed depended
on advection by ocean currents; on the influence of other eddies; on the arresting
effect exerted by the coast, when eddies were close to the upwelling area; and
also on the own drift of eddies, produced by the planetary beta effect. Related to
this, a common characteristic of the path of eddies was the westward movement of
the vortices, certainly conditioned by the combined influence of the southwestward
Canary Current and the westward drift of the beta effect. Consequently, it is possible
to find long-lived anticyclonic eddies more than 1000 km west of the island where
they were generated, at approximately 26
◦ N.
Finally, the available data set has revealed significant interactions between eddies
generated in the Canary Islands area. Drastic structural changes could be observed
when anticyclonic eddies became quite close, giving place to a new eddy resultant
by their coalescence. The observations suggest that this kind of interaction can occur
commonly south of the Canarian Archipelago. Island-shed eddies interact also with
waters of the upwelling region, and can operate jointly with upwelling filaments to
export effectively coastal waters far offshore. At the same time, if the eddies get
closer to the continental shelf, they can induce the formation of upwelling filaments,
as observed for the cyclonic and anticyclonic eddy pair, observed south of Cape Juby
and Cape Bojador.
Acknowledgments The authors would like to thank AVISO Altimetry for providing the altimeter
data, and also CREPAD (INTA) for supplying the Level-1b ESA-Sharp AVHRR data. SeaWiFS
Level-2 data were provided by the NASA Ocean Biology Processing Group (Feldman and McClain
2007). This work was supported by Spanish Ministerio de Ciencia e Innovación through the INTEGCAN (MCINN, CGL2004 02235) project and the MOMAC (MCINN, CTM2008-05914/MAR)
project.
L. G.-Weil et al.
5.4 Concluding Remarks
The combination of different RS data types, with different spatial and temporal resolutions, and obtained in different regions of the electromagnetic spectrum, allows for
the effective monitoring of a region with complex mesoscale variability patterns such
as the Canary Islands area. It has been shown that this area has a higher mesoscale
activity than other parts of the Northwest African coastal transition zone. Its distinctive mesoscale activity has a clear seasonality, with a maximum in October and a
minimum in April, and is strongly related to the eddy generation processes typical
of the Canarian Archipelago.
The detailed analysis of the 1998–1999 historical data record, combining the complementary characteristics of various RS data sources, shows that most of the the
long-lived mesoscale eddies develops during the second half of the year. A similar
number of cyclonic and anticyclonic eddies was generated, in the period of observation, but over extended periods the mesoscale dynamics seemed to be dominated by
anticyclones. These displayed a bigger size (∼ 150 km) and were observed during a
longer time than cyclones.
Eddy trajectories and velocities revealed that the actual motion observed depended
on advection by ocean currents; on the influence of other eddies; on the arresting
effect exerted by the coast, when eddies were close to the upwelling area; and
also on the own drift of eddies, produced by the planetary beta effect. Related to
this, a common characteristic of the path of eddies was the westward movement of
the vortices, certainly conditioned by the combined influence of the southwestward
Canary Current and the westward drift of the beta effect. Consequently, it is possible
to find long-lived anticyclonic eddies more than 1000 km west of the island where
they were generated, at approximately 26
◦ N.
Finally, the available data set has revealed significant interactions between eddies
generated in the Canary Islands area. Drastic structural changes could be observed
when anticyclonic eddies became quite close, giving place to a new eddy resultant
by their coalescence. The observations suggest that this kind of interaction can occur
commonly south of the Canarian Archipelago. Island-shed eddies interact also with
waters of the upwelling region, and can operate jointly with upwelling filaments to
export effectively coastal waters far offshore. At the same time, if the eddies get
closer to the continental shelf, they can induce the formation of upwelling filaments,
as observed for the cyclonic and anticyclonic eddy pair, observed south of Cape Juby
and Cape Bojador.
Acknowledgments The authors would like to thank AVISO Altimetry for providing the altimeter
data, and also CREPAD (INTA) for supplying the Level-1b ESA-Sharp AVHRR data. SeaWiFS
Level-2 data were provided by the NASA Ocean Biology Processing Group (Feldman and McClain
2007). This work was supported by Spanish Ministerio de Ciencia e Innovación through the INTEGCAN (MCINN, CGL2004 02235) project and the MOMAC (MCINN, CTM2008-05914/MAR)
project.