![]() In agreement with the CFB effect found for lower frequency dynamics, tidal currents are anti-correlated with the surface stress response: a negative zonal current causes a positive surface stress anomaly and vice versa (a similar result is found for the meridional current, See Supplementary Fig. The spatial pattern of the stress anomaly is very similar to that of surface currents. On this broad, shallow continental shelf with little mesoscale ocean activity, the essential difference between the two simulations can be attributed to tides. Note that focus is done on the zonal component of the tidal current as it dominates the signal over this region (See Supplementary Fig. 2b, a snapshot at the same time of surface stress anomaly estimated as the surface stress difference between CTRL and NOCFB, expressing the drag of the ocean on the atmosphere. 2a).įull size image Ocean drag on the atmosphereįigure 2a shows a snapshot of the zonal surface currents from CTRL, and Fig. Tidal currents can reach more than 3 m s −1 near the coast and 2 m s −1 in the middle of the Channel (Fig. For tidal currents, the M2 component of the model largely dominates the surface current spectrum as expected 23. The amplitudes of the main diurnal (K1), semi-diurnal (M2) and even nonlinear quarter- and sixth-diurnal tides are well reproduced by the model (while higher-frequency components of lesser importance appear overestimated). CROCO shows good overall agreement with the data. Consistent with the literature, the English Channel, both in the observation and in the model, is affected by a wide range of tides, with M2 (12.42 h) being the most energetic tidal constituent. 1a) compared to a regional simulation using the ocean model CROCO fully coupled with the atmospheric model WRF. Figure 1b shows a spectral description of the sea surface height at the Bournemouth gauge (black star in Fig. 1a) separates Southern England from Northern France and is home to some of the strongest and most complex tides in the world. The comparison between the simulations will highlight the top drag effect on tides and will demonstrate the existence of a regime of tidal winds induced by tidal currents. The simulation set consists of two twin experiments that involve a control simulation with tides and CFB (CTRL) and an identical simulation without CFB (NOCFB). ![]() To examine these issues, coupled eddy-rich ocean-atmosphere simulations are performed over the English Channel for the period 2010. However, as we will see here, it may explain a diurnal frequency observed in surface observations such as over the English Channel (Fig. Tidal winds are generally considered only as an S2 component in the upper atmosphere due to thermal heating rather than gravitational forces 22, but never as a friction effect of oceanic tides. But surprisingly, the amount of energy that would be dissipated in this way and the effectiveness of this process in generating tidal winds are questions that have never been asked. ![]() Tidal currents can interact with the overlying atmosphere, directly modifying surface stress and low-level winds. In particular, tides should also be affected and some of their energy should be transferred to the atmosphere instead of being dissipated in the ocean. In essence, CFB acts as a top drag 21, which affects all spatial and temporal scales. The wind can no longer be considered only as a large-scale energy source that triggers a turbulent cascade, as it can interact on a fine scale, directly affecting the whole oceanic spectrum. 20 demonstrate that CFB changes the usual conception of wind-driven currents. As a result, CFB can reduce eddy-mean flow interactions, and thus partly control very energetic current systems such as western boundary currents 19, 20. Second, the transfer of momentum from currents to winds also causes CFB to act as an eddy killer, reducing (sub)mesoscale activity by about 30% 13, 14, 15, 16, 17, 18. At large scales, by reducing the mean energy input from the atmosphere to the ocean, it causes a slowdown in the mean ocean circulation 10, 11, 12. CFB has two main direct effects on ocean circulation. In particular, the CFB (Current FeedBack) effect expresses the influence of surface ocean currents on the overlying atmosphere. Recently, air-sea interactions at the oceanic mesoscale (i.e., scales of 10–100 km and 10–100 days 7, 8, 9) have received a growing interest from the scientific community.
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