Oceanographic Institution. Taunton, Massachusetts: William S.
Sullwold Publishing, Inc., by A. C. Redfield.
Yes, the double tops (plateaus) on the high tides are real, and described in this book with reference to Falmouth Harbor which is near by.
Redfield's book can be found on line here:
https://darchive.mblwhoilibrary.org/handle/1912/1136
A great read.
Here's an engineer's (not oceanographer) summary. The tidal range at Falmouth in Vineyard sound is very small (around 1.5 feet). As the tidal rise (wave) moves toward the coast, it gets into the sound through 2 major openings, one around Monomoy, the other near Cuttyhunk. These waves destructively interfere (a node) around Falmouth. Thus the small tidal range in Falmouth becomes progressively larger as you proceed east or west.
The tide consists of multiple harmonics. Some are semidiurnal, and some are diurnal. Semi are roughly 12 hr, diurnal are roughly 24 hr. The harmonics are causing the double tops.
The primary harmonics are:
M2: the moon which is semidiurnal - 12.42 hr period
S2: the sun which is semidiurnal - 12.00 hr period
K1: a lunar diurnal component - 23.94 hr period
O1: a lunar diurnal component - 25.83 hr period
P1: a solar diurnal component - 24.06 hr period
K1, O1, and P1 are related to declination.
M2 and S2 are the big components, but Vineyard Sound is tuned to reduce these components. These tide components propagate from Cuttyhunk and Monomoy and nearly cancel near Falmouth. The K1, O1, and P1 harmonics are smaller but are different period, so the Sound is not tuned to cancel them at Falmouth. Their small amplitude appears relatively larger as M2 and S2 are reduced, resulting in the strangely shaped waves.
The primary harmonics are:
M2: the moon which is semidiurnal - 12.42 hr period
S2: the sun which is semidiurnal - 12.00 hr period
K1: a lunar diurnal component - 23.94 hr period
O1: a lunar diurnal component - 25.83 hr period
P1: a solar diurnal component - 24.06 hr period
K1, O1, and P1 are related to declination.
M2 and S2 are the big components, but Vineyard Sound is tuned to reduce these components. These tide components propagate from Cuttyhunk and Monomoy and nearly cancel near Falmouth. The K1, O1, and P1 harmonics are smaller but are different period, so the Sound is not tuned to cancel them at Falmouth. Their small amplitude appears relatively larger as M2 and S2 are reduced, resulting in the strangely shaped waves.
Any readers of this blog that are tide experts, please comment so I get this right!!
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