• Golden Ogle posted an update 1 year, 5 months ago

    A displacement series was computed by stepping this integral through a velocity series. The relative importance of higher frequency motions in material transport was quantified as a ratio, R, of the root mean square of the displacements computed from Vlp to root mean square of the displacements computed from Vhp. Values of R computed from the near-surface velocity records from the mid-plateau moorings S1 and S2, and for T in the range of 24–40 h, are of order 15 for N–S (alongshore) displacements and 7 for E–W displacements. R values tend to increase with increasing T beyond 40 h, reaching 57 and 26 for, respectively, N–S and E–W displacements at T=5 days. Sub-inertial flows may thus be regarded as the principal agent responsible AZD6244 mouse for the transport of material over the mid-plateau. The relative importance of higher-frequency currents in material transport appears to be greater over the inner plateau. R values computed from the near-surface velocity record from S3, and with T in the 24–40 h range, are of order 9 for N–S displacements and 6 for E–W displacements. Our study area, a plateau adjacent to the Red Sea basin, is one of many different features of the bathymetrically complex Red Sea coastal zone (which includes fringing reefs and deep channels flanked by reef structures). Nevertheless, many of our findings may be deemed, with some caution, generally applicable to the coastal zone of the central Red Sea. Notably, tidal currents are particularly weak. The most energetic tidal constituent, the M2 tide, has a magnitude of order 4 cm s−1 (Table 3). Semidiurnal-band currents, which include the S2 tide and wind-forced flow, seldom exceed 8 cm s−1 (Fig. 10). Within the upper water column, currents in the diurnal and inertial bands are somewhat more energetic, with magnitudes occasionally in the 10–15 cm s−1 range (Fig. 10). These currents are surface intensified, particularly during times of strong vertical density stratification, and so appear to be principally wind-driven. The frequent appearance of a diurnal warm layer associated with surface heating, which is seen during all seasons, is likely a principal factor limiting the correlation of the diurnal-band wind stress and near-surface currents (Section 4.6). As demonstrated by modeling and observational studies, the development of a diurnal warm layer complicates the wind-current relationship, as the near-surface thermal stratification influences the downward transfer of momentum imparted by wind and is itself influenced by wind-induced vertical mixing (Kondo et al., 1979, Price et al., 1986, Woods and Strass, 1986, Kawai and Wada, 2007 and Noh et al., 2011). Our calculations suggest that the transport of material over the mid-plateau is principally due to the sub-inertial flow, with higher frequency currents (periods <1.5 days) making a small contribution.