There are exceptions near bays and rivers where significant cross-shore tidal flow occurs, but for most coastlines, tidal water movement is primarily alongshore - which makes sense since strong onshore currents would flood coastal cities.
In my paper, we found alongshore currents were 10x stronger than cross-shore currents (Figure 3, bottom panel). But even if cross-shore currents were much stronger, they wouldn't significantly affect wave frequency. A wave in 20ft of water travels at roughly 7.5m/s, while tidal currents are about 1-2cm/s alongshore and 0.1-0.2cm/s cross-shore. That's only 0.1% of the wave's phase speed - any frequency shift would be totally indistinguishable between high and low tide.
The lull is more likely psychological (we pay attention when expecting something to happen and are really good at finding patterns that we want to be there) or from coincidental wind patterns. Besides, in San Diego and along the West Coast, most current variability occurs at frequencies lower than tidal (think Gulf Stream, California Current), so tides matter less to wave dynamics than these larger-scale flows.
Very interesting. What about how tides affect waves? Is there any sciece behind the popular notion of there being a lull during the turning of tides?
How tides affect waves was actually my first article here (https://www.scienceofsurfing.com/p/how-does-an-incoming-or-outgoing). Short answer: not really.
There are exceptions near bays and rivers where significant cross-shore tidal flow occurs, but for most coastlines, tidal water movement is primarily alongshore - which makes sense since strong onshore currents would flood coastal cities.
In my paper, we found alongshore currents were 10x stronger than cross-shore currents (Figure 3, bottom panel). But even if cross-shore currents were much stronger, they wouldn't significantly affect wave frequency. A wave in 20ft of water travels at roughly 7.5m/s, while tidal currents are about 1-2cm/s alongshore and 0.1-0.2cm/s cross-shore. That's only 0.1% of the wave's phase speed - any frequency shift would be totally indistinguishable between high and low tide.
The lull is more likely psychological (we pay attention when expecting something to happen and are really good at finding patterns that we want to be there) or from coincidental wind patterns. Besides, in San Diego and along the West Coast, most current variability occurs at frequencies lower than tidal (think Gulf Stream, California Current), so tides matter less to wave dynamics than these larger-scale flows.