180
M.B. Framiiian . M.P. Etala . E.M. Acha . R. A. Guerrero· C.A. Lasta . O.B. Brown
halo cline occurs when wind decreases. The three profiles of the innermost station
(Fig. 8.na) were acquired under similar tidal condition, during flood tide, according
to the predicted values at Montevideo. The first profile was obtained with west-northwestward wind of 6.2 m s-', the second with calm 3 m s-' north-northwestward wind,
and the last with westward wind of 6.7 m s-'. The maximum vertical gradients of
the three profiles were: 7.3, 8.9 and 4.4 m-" respectively. Another example, from a
station located southeast from the previous analysed (Fig. 8.nb) shows similar results. These two profiles were taken during ebb tide. The first profile was acquired
during calm condition and has a difference of salinity of 22.{ units from surface to
bottom. The next day at the same location and similar tidal condition, but with northnorthwest-ward winds of 8 m s-', the water column was almost homogeneous with a
small vertical gradient (1.02 m-') near the bottom. At the center of the estuary
(Fig. 8.nc) and at the Samboromb6n Bay (Fig. 8.nd) there is a typical two-layer stratification, with a salinity difference of 15 between surface and bottom layer. Over the
shallow banks, the water column can be homogeneous even with light wind conditions (Fig. 8.nf). At the eastward part of the Oriental Channel (Fig. 8.ne) an almost
homogeneous column occurs, with a very weak stratification (0.44 m-') at 16-17 m.
Two stations on the inner shelf in the southern part (Figs 8.ng,h) still have strong
stratification with maximum gradients of 2.{6 and 4.43 m- I • The upper layer at the
southernmost station (Fig. 8.nh) is fresher than in the station located to the north
(Fig. 8.ng), showing good agreement with the southern extension of the river plume
observed in the mean seasonal distribution (Fig. 8.lOb). The upper layer of fresher
water (salinity less than 25) at the southernmost station (Fig. 8.nh) is 7 m deep, occupying 30% of the water column. The thickness of the upper layer shows the importance of this buoyant plume.
The previous analysis gives a qualitative description of the vertical structure in
the estuary, and the effect of the wind on stratification. Analysis of vertical profiles
together with wind conditions, as well as field-work experience, suggest that atmospheric forcing plays a major role in the mixing process in the estuary. The authors
are aware that, to fully understand local, short-term variations in the vertical structure, detailed information of tidal currents should be included in the analysis. But,
the combined effects of tidal and storm-driven currents must be considered, as was
discussed in section II, so these two forces are not independent in terms of mixing
processes.
8.5
Temperature
A description of the temperature field in the upper estuary have been presented in
CARP (1989). In the present study, as was done for salinity, the focus is on the outer
estuary. Guerrero et al. (1997) presented a seasonal analysis of temperature distribution in the lower estuary based on field observations. Part of these results are reviewed
here, along with the analysis of the horizontal fields obtained using the expanded
database. A description of surface temperature fields obtained from remote sensing
data is also presented. Remote sensing information has been especially useful for detecting features that are difficult to observe using in situ techniques because of their
limited duration and spatial coverage and resolution.
M.B. Framiiian . M.P. Etala . E.M. Acha . R. A. Guerrero· C.A. Lasta . O.B. Brown
halo cline occurs when wind decreases. The three profiles of the innermost station
(Fig. 8.na) were acquired under similar tidal condition, during flood tide, according
to the predicted values at Montevideo. The first profile was obtained with west-northwestward wind of 6.2 m s-', the second with calm 3 m s-' north-northwestward wind,
and the last with westward wind of 6.7 m s-'. The maximum vertical gradients of
the three profiles were: 7.3, 8.9 and 4.4 m-" respectively. Another example, from a
station located southeast from the previous analysed (Fig. 8.nb) shows similar results. These two profiles were taken during ebb tide. The first profile was acquired
during calm condition and has a difference of salinity of 22.{ units from surface to
bottom. The next day at the same location and similar tidal condition, but with northnorthwest-ward winds of 8 m s-', the water column was almost homogeneous with a
small vertical gradient (1.02 m-') near the bottom. At the center of the estuary
(Fig. 8.nc) and at the Samboromb6n Bay (Fig. 8.nd) there is a typical two-layer stratification, with a salinity difference of 15 between surface and bottom layer. Over the
shallow banks, the water column can be homogeneous even with light wind conditions (Fig. 8.nf). At the eastward part of the Oriental Channel (Fig. 8.ne) an almost
homogeneous column occurs, with a very weak stratification (0.44 m-') at 16-17 m.
Two stations on the inner shelf in the southern part (Figs 8.ng,h) still have strong
stratification with maximum gradients of 2.{6 and 4.43 m- I • The upper layer at the
southernmost station (Fig. 8.nh) is fresher than in the station located to the north
(Fig. 8.ng), showing good agreement with the southern extension of the river plume
observed in the mean seasonal distribution (Fig. 8.lOb). The upper layer of fresher
water (salinity less than 25) at the southernmost station (Fig. 8.nh) is 7 m deep, occupying 30% of the water column. The thickness of the upper layer shows the importance of this buoyant plume.
The previous analysis gives a qualitative description of the vertical structure in
the estuary, and the effect of the wind on stratification. Analysis of vertical profiles
together with wind conditions, as well as field-work experience, suggest that atmospheric forcing plays a major role in the mixing process in the estuary. The authors
are aware that, to fully understand local, short-term variations in the vertical structure, detailed information of tidal currents should be included in the analysis. But,
the combined effects of tidal and storm-driven currents must be considered, as was
discussed in section II, so these two forces are not independent in terms of mixing
processes.
8.5
Temperature
A description of the temperature field in the upper estuary have been presented in
CARP (1989). In the present study, as was done for salinity, the focus is on the outer
estuary. Guerrero et al. (1997) presented a seasonal analysis of temperature distribution in the lower estuary based on field observations. Part of these results are reviewed
here, along with the analysis of the horizontal fields obtained using the expanded
database. A description of surface temperature fields obtained from remote sensing
data is also presented. Remote sensing information has been especially useful for detecting features that are difficult to observe using in situ techniques because of their
limited duration and spatial coverage and resolution.