Miller, A. J., D. S. Luther and M. C. Hendershott, 1993:
The fortnightly and monthly tides:
Resonant Rossby waves or nearly
equilibrium gravity waves?
Journal of Physical Oceanography,
The fortnightly and monthly tides are discussed in the light of recent sea level observations and numerical modeling
results. Within the tide gauge network of the low-latitude Pacific, the fortnightly tide is shown to possess a
large-scale phase lag of roughly 10-40 degrees. Although the nonequilibrium part of the fortnightly tide is
traditionally thought to be dominated by Rossby wave dynamics, it is shown, via global shallow-water modeling
studies, that this large-scale phase lag is explicable in terms of remotely forced gravity waves whose origin is mainly
in the Arctic Ocean. Although future observations outside the low-latitude region of the Pacific may eventually reveal
Rossby wave excitation, the fortnightly tidal signal in the tide gauge network at hand appears to reveal at most only
weak excitation of Rossby waves compared to the phase lag due to remotely forced gravity waves. The observed
monthly tide appears to be only slightly closer to equilibrium than the fortnightly tide. The reason for this remains
unclear since the monthly tide is less affected by the remotely forced gravity waves than the fortnightly tide.