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316 R. Sorgente et al.: Seasonal variability in the Central Mediterranean Sea circulation

(a)A) (b)B)

36.5 15 36.5
15.5 36
36 16
16 16 15 15.5 35.5
North Latitude 35
35.5

35

34.5 34.5
17 34
North Latitude 14.5
34 10 3116.5 33.5
30.517

33.5 24.5
24
33 33
25
32.5 16 25.5 17.5 16.5 32.5

26 0.5 m/s
30
32 32

31.5 18 31.5

10 11 12 13 14 15 16 17 10 11 12 13 14 15 16 17
East Longitude East Longitude

(c)C) (d)D)

36.5 36.5

36 24 19.5 36

35.5 35.5
24.5

35 24.5 25 35

34.5 34.5

North Latitude 34 26.5 25.5 31 28 34
North Latitude
33.5 33.5

33 29 29 33
25.5 30

32.5 32.5 0.5 m/s

32 32
26

31.5 31.5

10 11 12 13 14 15 16 17 10 11 12 13 14 15 16 17
East Longitude East Longitude

Fig. 17. Ten-day averaged temperature (a) and (c) and total velocity (b) and (d) horizontal fields at 5 m depth in February (a) and (b) and
August (c) and (d). The temperature contour intervall is 0.5 ◦C. One vector every two grid points is plotted for velocity. Units are m/s.

ries with it an appreciable mesoscale component with eddy shelf break to the east of Malta, and tending to deflect north-
formations of opposite sign alongside to the flow. Unfortu- ward with an intense looping meander, forming the charac-
nately, no comparisons are possible with the bibliography or teristic Ionian Shelf Break Vortex (Fig. 18b). The upshooting
the climatology due to a lack of data in this area, as under- of the AIS follows closely the Ionian shelf break and sub-
lined by Barnkart and Brasseur (1998). sequently extends as a relatively strong velocity front into
the northwestern Ionian, where the circulation is predom-
4.3.4 The AIS circulation inantly anticyclonic at this time of the year, in agreement
with Malanotte-Rizzoli et al. (1997). The contrast in tem-
The northern branch of the MAW flow constitutes the en- perature of the MAW exiting the Sicilian Channel with the
ergetic and meandering AIS moving eastward adjacent to warmer Ionian water produces a sharp temperature gradient
the southern coast of Sicily where there is also a strong up- (Fig. 11b) which is often evidenced over the Malta escarp-
welling activity. Its simulated progression follows that pro- ment by conspicuous thermal features on the sea surface tem-
posed by Robinson et al. (1999), starting its path as a mean- perature AVHRR maps (Champagne-Philippe and Harang,
der to the south of the Adventure Bank, proceeding south- 1982; Champagne-Philippe and Guevel, 1982). The model
eastwards and looping back to the north around Malta, form- results also show the presence of mesoscale extensions and
ing the Malta Channel Crest. In particular, during summer dynamic patterns associated with the instability of the AIS.
and autumn, the flow takes the consistency of a jet stream, The flow has a quasi-barotropic nature in the top layer, but is
gaining abruptly positive vorticity as it reaches the sharp