18 Eddies in the Red Sea as seen by Satellite SAR Imagery
369
18.4 Mesoscale Eddies
In total we detected 39 mesoscale eddies, whose diameters were ranging from about
30 km to almost 100 km. Like the smaller, sub-mesoscale eddies they were visualized in the SAR imagery both through surfactant films (23 eddies) and through
wave/current interactions (16 eddies). 24 eddies were cyclonically rotating, while
the rest, 15, were anti-cyclonical. The locations of all anti-cyclonic and cyclonic
mesoscale eddies are shown in Fig. 18.8.
Both anticyclonic and cyclonic mesoscale eddies can be found in different parts
of the Red Sea, but most of them (especially the cyclonic eddies) are located along
the longer axis of the basin where probably there are more favorable conditions for
cyclonic eddy generation/evolution. For instance, mesoscale cyclonic eddies in the
central part of the sea can be a result of the (preceding) evolution of sub-mesoscale
eddies. Eddies in the near-coastal zone (both cyclonic and anti-cyclonic) can appear
as a result of a lateral friction of a general flow.
Spatial distributions of both meso- and basin-scale eddies at different seasons are
given in Fig. 18.9, separated by their vorticity sign (left column: anti-cyclonic and
right column: cyclonic) and by the season (Fig. 18.9a: winter and spring, i.e., Jan–
Mar and Apr–Jun, respectively, and Fig. 18.9b: summer and autumn, i.e., Jul–Sep
and Oct–Dec, respectively). The sizes of the circles correspond to the sizes of the
eddies, and according to our nomenclature, “black” eddies are marked by a solid
circle and “white” eddies by an open circle.
From Fig. 18.9a, b we draw the following conclusions:
• In general, the detected anti-cyclonic eddies are larger than the cyclonic eddies.
• Most of the eddies were found in the central Red Sea.
• During the warm period (spring and summer), the anti-cyclonic eddies are dominating, while the cyclonic eddies dominate during the cold period (autumn and
winter).
• Mostly “black” eddies were found during the warm period, i.e. during spring and
summer.
• During the warm period (spring and summer), the “black” eddies dominate, while
the “white” eddies dominate during the cold period (autumn and winter).
18.4.1 Basin-Scale Eddies
Eddies with a diameter greater than 100 km were regarded in the present paper as
basin-scale. The maximum diameter of such eddies reached almost 200 km. Totally,
there were 15 basin-scale eddies detected. Again, they were manifested due to both
surfactant films (8 eddies) and wave/current interactions (7 eddies). Only two of
them were cyclonically rotating.
369
18.4 Mesoscale Eddies
In total we detected 39 mesoscale eddies, whose diameters were ranging from about
30 km to almost 100 km. Like the smaller, sub-mesoscale eddies they were visualized in the SAR imagery both through surfactant films (23 eddies) and through
wave/current interactions (16 eddies). 24 eddies were cyclonically rotating, while
the rest, 15, were anti-cyclonical. The locations of all anti-cyclonic and cyclonic
mesoscale eddies are shown in Fig. 18.8.
Both anticyclonic and cyclonic mesoscale eddies can be found in different parts
of the Red Sea, but most of them (especially the cyclonic eddies) are located along
the longer axis of the basin where probably there are more favorable conditions for
cyclonic eddy generation/evolution. For instance, mesoscale cyclonic eddies in the
central part of the sea can be a result of the (preceding) evolution of sub-mesoscale
eddies. Eddies in the near-coastal zone (both cyclonic and anti-cyclonic) can appear
as a result of a lateral friction of a general flow.
Spatial distributions of both meso- and basin-scale eddies at different seasons are
given in Fig. 18.9, separated by their vorticity sign (left column: anti-cyclonic and
right column: cyclonic) and by the season (Fig. 18.9a: winter and spring, i.e., Jan–
Mar and Apr–Jun, respectively, and Fig. 18.9b: summer and autumn, i.e., Jul–Sep
and Oct–Dec, respectively). The sizes of the circles correspond to the sizes of the
eddies, and according to our nomenclature, “black” eddies are marked by a solid
circle and “white” eddies by an open circle.
From Fig. 18.9a, b we draw the following conclusions:
• In general, the detected anti-cyclonic eddies are larger than the cyclonic eddies.
• Most of the eddies were found in the central Red Sea.
• During the warm period (spring and summer), the anti-cyclonic eddies are dominating, while the cyclonic eddies dominate during the cold period (autumn and
winter).
• Mostly “black” eddies were found during the warm period, i.e. during spring and
summer.
• During the warm period (spring and summer), the “black” eddies dominate, while
the “white” eddies dominate during the cold period (autumn and winter).
18.4.1 Basin-Scale Eddies
Eddies with a diameter greater than 100 km were regarded in the present paper as
basin-scale. The maximum diameter of such eddies reached almost 200 km. Totally,
there were 15 basin-scale eddies detected. Again, they were manifested due to both
surfactant films (8 eddies) and wave/current interactions (7 eddies). Only two of
them were cyclonically rotating.