In run 1 we have removed only the float data, in run 2 we have removed only the tomography data and in run 3 we have removed both datasets. In this last case only two types of datasets are used, first the CTD profiles performed just before and during the first days of the period of analysis and second the fixed temperature sensors and current meters, which provide time series for the duration of the period.
To study the impact of the different datasets in the resolution of horizontal scales, we will now examine the temperature and velocity fields at particular instants. The 4D analysis provides the temperature and velocity profiles at all grid points within the modelled area. We will restrict the discussion to the part of the array located east of T5, where the error maps indicate that the estimation is reliable. Fig. 3 shows the maps of temperature and current for March 27 as given by the reference and test runs 1 to 3 at the 300 m level. The estimate produced by run 3 (no floats or tomography) shows a strong current at T1 and T2 (east of the convection area), and we observe around T1 a temperature dipole, although no temperature data are provided in the vicinity of this point. The trace of the convection mixed patch appears in the western part of the map as a cold temperature anomaly centered on mooring T5 and as a slight cold around T6.
When tomography data are used (run 1), the temperature structure is strongly modified, a warm water patch appears in the eastern part. The cold anomaly intensifies north of T6 and the dipole on T1 is reduced. The current structure is no longer confined to the moorings vicinity, a link is now established between all moorings, except may be along T5-T3 section. A strong north-eastward current relates T6 to T1, and a return current exists between T1 and T5. The float data (run 2), which provide current and temperature along the trajectories, have sampled a cold eddy in the middle of the triangle defined by T1-T5-T6. The current associated with this mesoscale structure is compatible with the large scale current detected by tomography. The best estimate is obtained by combining all datasets (the reference run): float data bring their estimate of the local structure, with exact amplitude and position, tomography adds a number of large scale features in the temperature and velocity field which escaped the local measurements.
