Diurnal variability on the continental shelf of Southern Brazil
Section snippets
Introduction: motivations and objectives of the study
Many physical variables in the upper oceanic layer, such as temperature, mixed layer depth, turbulent heat flux, turbulent kinetic energy dissipation rate, stratification and shear, exhibit periodic diurnal variations in response to day-to-night changes in surface forcing. Altogether, these phenomena are referred to as the diurnal cycling. The importance of the diurnal cycling in the upper ocean is now widely recognized. Although often relatively small in magnitude, these variations repeat
Experimental details
Field data used in this study were obtained at 10 individual sites, distributed between 24°S and 33°S as shown in Fig. 1. Some stations, such as 1, 2, 5, 7, and 10, were on the shelf in the depth range of 45–200 m, some others (3, 4, 6 and 9) were located slightly offshore of the shelf break. Measurements at stations 1 through 5 and 10 were carried out in the austral summer, and 6 through 9 in the austral winter. Data were collected by three Brazilian research vessels: Professor W. Besnard of
Diurnal cycle of SST
Overall, diurnal range of SST (hereafter RSST) varied between 0.1 and 1.2°C (Table 3). In average for all summer observations, it was about 0.5°C. As expected, because of weaker insolation, in three out of the four winter observations, the diurnal cycle of temperature was smaller than that in summer, with RSST of 0.3°C or less. However at station 7, in a winter series corresponding to an exceptionally calm and cloudless day, the estimated SST range was as large as 1.2°C.
Based on observational
Conclusions
In this section, we shall briefly summarize the results of our observations. On 12 individual days examined, the diurnal range of SST varied from 0.1°C to over 1.2°C. The mean SST range was about 0.5°C for 8 summer observations and about 0.4°C for 4 winter observations. The SST range appears to be controlled mostly by cloudiness and wind stress. Linear regression of observed SST ranges against (1−N)/W2 and J3/2hτ−1 (where N is cloudiness, W is wind speed, Jh is net surface heat flux, and τ is
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