Classic explanation challenged: Satellite data reveal tidal bulges do not physically exist
Science China Press
image:
(A1) Global pattern derived from satellite altimetry. (A2) Pacific Ocean pattern. (A3) Atlantic Ocean pattern. (B) Pattern derived from 166 tide-gauge stations. In the polar plot, the radial axis denotes the number of observed high- or low-tide events, and the radial sectors indicate the lunar angle in degrees.
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This study is led by Yongfeng YANG from the Water Resources Comprehensive Development Center of Shandong Province, Jiajia Yuan from the School of Geomatics at Anhui University of Science and Technology, and Mingyuan Fan from Water Resources Research Institute of Shandong Province.
The researchers set out to address a fundamental question that has remained unanswered since the 18th century: Do the two water bulges—the cornerstone of the double water bulge model used to explain tides in many physics, oceanography, and geography textbooks—actually exist on the Earth's surface?
For centuries, the double water bulge model has been the classical paradigm explaining why most of the world's oceans experience alternations of high and low tide each day. The model holds that the Moon's gravitational pull creates two symmetric bulges of water on opposite sides of the Earth. As the Earth spins, an earthly site would pass these bulges of water, experiencing high tide, and through the depressed region of water, experiencing low tide. This explanation is also featured on the websites of authoritative institutions including NOAA, National Geographic, and NASA.
Using tidal data at 362,370 oceanic locations spotted by the Jason-3 satellite of AVISO throughout 2021, the researchers correlated the number of high and low tides with the lunar angle—the angle between a location and the Moon relative to Earth’s center.
The results show that, among the 175,402 oceanic locations in the 0°–60° and 120°–180° lunar angle phases—which spatially correspond to the bulging regions of water predicted by the model—56.84% experienced low tides, while only 43.16% experienced high tides. Conversely, among the 186,968 locations in the 60°–120° phase—which corresponds to the depressed region of water—56.38% experienced high tides.
"The findings directly contradict the physical existence of two water bulges on the Earth's surface," the authors state. The researchers investigated tidal data from 166 tide-gauge stations in August of 2014, the same thing remains true that low tides occur predominantly in the 0°–60° and 120°–180° lunar angle phases, and high tides occur predominantly in the 60°–120° lunar angle phase.
While many tide researchers have long doubted that water bulges truly form—given the influences of landmasses, basin topography, the Coriolis force, and bottom friction—this skepticism had remained largely theoretical (oral), with no observational evidence presented until now.
The study mentions a recently proposed perspective: rather than water being pulled into bulges, tides may instead be a manifestation of the oscillating ocean basin. As the solid Earth deforms under the Moon’s gravitational force, the elongated Earth’s spinning causes ocean basins to be uplifted and depressed continuously, inducing water movements that produce alternation of high and low tides per day. This "solid Earth deformation drives sea water to move" provides a physical explanation consistent with the observed data above: low tides predominantly occur where the solid Earth bulges upward (creating shallower water), and high tides predominantly occur where it is compressed (creating deeper water).
See the article:
Yang Y, Yuan J, Fan M. 2026. Testing the physical reality of tidal bulges in the world’s oceans. Science China Earth Sciences, 69(6): 2015–2021, https://doi. org/10.1007/s11430-025-1878-3
Journal
Science China Earth Sciences
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