459
The Q-vector can be calculated from the distributions of density and geostrophic
velocity, and convergence of this vector indicates the regions where upward forcing exists
(Hoskins and Pedder, 1980). In a recent paper, Strass (1994) compared three different
methods of estimating vertical motions respectively based on the density equation, the
vorticity equation and the omega equation. He showed that the omega equation gives the
best estimates of vertical velocity.
The first application of the omega equation was carried out by Leach (1987). A study
of vertical motion in the Alborn Sea was also carried Qut by Tinton~ et al. (1991) who
diagnosed vertical velocities up to 50 m/day. At a Sargasso Sea front, Pollard and Regier
(1992) applied a two dimensional version of the omega equation to SeaSoar undulating
CTD data and shipboard ADCP data to estimate vertical motions. Their calculations
showed that vertical velocities in excess of 40 m/day could be found in intense frontal
regions.
A major result of the vertical motion diagnostic studies is the dependence of the
vertical velocity magnitude on the scale of the considered horizontal motion. Tinton~
et al. (1991) and Vilidez et al. (1994a) experimentally found that vertical velocities
associated with frontal waves of the western Alboran gyre were one order of magnitude
higher than those diagnosed in the large scale gyre itself, Figure 5a and b. A similar result
was shown in Haidvogel et al. (1991) who found that vertical velocities were higher in the
frontal waves associated with the density front south of the filament than at the edge of
the filament itself. In the Sargasso Sea, Pollard and Regier (1992) observed that maximum
vertical velocities (40 m/day) were associated with small surface-trapped frontal eddies
(40 km). Allen and Smeed (1995) have recently diagnosed vertical velocities in excess of
90 m/day in an analysis of SeaSoar and ADCP data from an experimental observation
of (20-30 km scale) eddies and meanders at the Iceland Faeroes Front. Estimates made
from three data sources (RAFOS floats, current meters and IES) by Lindstrom and Watts
(1994) also assessed the occurrence of intense vertical motions at short scales.
The Q-vector can be calculated from the distributions of density and geostrophic
velocity, and convergence of this vector indicates the regions where upward forcing exists
(Hoskins and Pedder, 1980). In a recent paper, Strass (1994) compared three different
methods of estimating vertical motions respectively based on the density equation, the
vorticity equation and the omega equation. He showed that the omega equation gives the
best estimates of vertical velocity.
The first application of the omega equation was carried out by Leach (1987). A study
of vertical motion in the Alborn Sea was also carried Qut by Tinton~ et al. (1991) who
diagnosed vertical velocities up to 50 m/day. At a Sargasso Sea front, Pollard and Regier
(1992) applied a two dimensional version of the omega equation to SeaSoar undulating
CTD data and shipboard ADCP data to estimate vertical motions. Their calculations
showed that vertical velocities in excess of 40 m/day could be found in intense frontal
regions.
A major result of the vertical motion diagnostic studies is the dependence of the
vertical velocity magnitude on the scale of the considered horizontal motion. Tinton~
et al. (1991) and Vilidez et al. (1994a) experimentally found that vertical velocities
associated with frontal waves of the western Alboran gyre were one order of magnitude
higher than those diagnosed in the large scale gyre itself, Figure 5a and b. A similar result
was shown in Haidvogel et al. (1991) who found that vertical velocities were higher in the
frontal waves associated with the density front south of the filament than at the edge of
the filament itself. In the Sargasso Sea, Pollard and Regier (1992) observed that maximum
vertical velocities (40 m/day) were associated with small surface-trapped frontal eddies
(40 km). Allen and Smeed (1995) have recently diagnosed vertical velocities in excess of
90 m/day in an analysis of SeaSoar and ADCP data from an experimental observation
of (20-30 km scale) eddies and meanders at the Iceland Faeroes Front. Estimates made
from three data sources (RAFOS floats, current meters and IES) by Lindstrom and Watts
(1994) also assessed the occurrence of intense vertical motions at short scales.