CRUISE PLAN

Synopticity and variability
The question of synopticity is a difficult one, since as for all ship work, the survey will necessarily take a finite period of time to complete. Variability in the Agulhas Current is small compared to the Gulf Stream, owing to the strong topographic control of the jet, but it is not insignificant. The dominant form of the variance seems predictable - as Natal Pulses which divert the course of the current from 30 to 200 km offshore (dependent on latitude) and propagate with speeds of 13 to 22 km/d, occurring four, five or six times per year (Lutjeharms and Roberts, 1988; van Leeuwen et al., 2000). This makes it about 50% likely that there will be a meander event in our survey area during the experiment. The combined use of real-time shipboard ADCP data of the surface currents and near-real-time satellite sea surface temperature images will enable an adjustment of the survey plan to incorporate any such meander events, so that the jet is still captured. Near-real-time (daily) satellite SST imagery of the Agulhas Current is available through an NSF funded server at RSMAS, http://www.rsmas.miami.edu/images.html. We will arrange for these images to be emailed aboard ship each day during the experiment. The variability of the Undercurrent itself is not well known; the single available time series does not allow for a statistically significant analysis (Harry Bryden, personal communication). The Undercurrent does appear more steady than the WBC, with only short fluctuations disturbing the continuous northeastward flow (Figure 2).