Semidiurnal internal tides in Massachusetts Bay

Semidiurnal tidal internal gravity waves consisting of the first five modes account for over 50% of the fluctuations that occurred in temperature measurements made at fixed depths in Massachusetts Bay. The amplitude of the lowest mode is the largest, while that of the second mode is negligible. The minimum value of the Richardson number of the internal wave of five modes is unity, and there is an indication that during each tidal cycle a dynamic instability may occur. The total internal wave energy occurring in a bandwidth of 7.32×10−3 cph, centered on the semidiurnal frequency, is approximately 4.3×105 ergs/cm2, which is about 8.6% of the total energy of the barotropic tide. These results, which were deduced from linear theory, may not be entirely accurate because the asymmetry of the temperature trace suggests nonlinear wave profiles, and because of the possible presence of microstructure.