Atmospheric Waves Turn Three South Atlantic Harbors Into Very Different Resonators

On the southeastern coast of South America, the sea can rise and fall dramatically without any earthquake at all. These events, known as meteotsunamis, are long ocean waves generated by fast-moving atmospheric disturbances such as squalls, cold fronts, and atmospheric gravity waves. Along the coasts of Argentina and Uruguay, they have long been recognized as a recurring hazard, capable of whipping up sudden currents and damaging moored vessels in ports that were built for calmer water. Yet while the generation and propagation of these waves across the wide Buenos Aires continental shelf has been studied for decades, what actually happens to them once they enter a harbor has remained surprisingly murky. A new comparative study suggests that the answer depends on frequency, geometry, and even the direction from which the disturbance arrives.

The research, published in the journal Natural Hazards, was carried out by Fernando Oreiro of Argentina’s Servicio de Hidrografía Naval and the University of Buenos Aires, Iael Perez of the Finnish Environment Institute, and Walter Dragani of CONICET and several Argentine research institutions. The team took advantage of a rare observational asset: simultaneous sea-level records collected between January and April 2018 at paired offshore and inner-harbor stations associated with three very different ports along the southwestern Atlantic coast. Those ports were Montevideo, the Uruguayan capital sitting on the Río de la Plata; Mar del Plata, a busy fishing and tourist harbor on the open Argentine coast; and Quequén, a deepwater grain port farther south, whose estuary entrance is famous among coastal scientists for its violent short-period oscillations.

The raw tide-gauge data, like all sea-level records, contains a mixture of signals: slow tides, storm surges that build over hours or days, and the rapid oscillations that interest meteotsunami researchers. To isolate the latter, the authors applied a high-pass filter to each record, stripping away the long-period background and leaving the oscillations with periods shorter than roughly a few hours. What emerged was a striking pattern in time. Episodes of energetic long-wave activity did not appear at one port in isolation; they arrived in sequence, first at Quequén, then at Mar del Plata, and finally at Montevideo. This northward progression matched the northeastward track of cold fronts sweeping across the region, pointing to atmospheric gravity waves trailing those fronts as the likely trigger for the ocean oscillations.

To go beyond visual inspection of the filtered records, the team turned to spectral analysis, a mathematical technique that decomposes a wobbly time series into the amplitudes of the individual frequencies that make it up. Comparing the spectrum measured offshore with the spectrum measured inside each harbor reveals how the local basin transforms incoming wave energy. If a harbor acts as a resonator, it amplifies particular frequencies, just as a wine glass rings at a specific pitch when struck. The classic theory of harbor oscillation, developed in the early 1960s by researchers such as John Miles and Walter Munk, predicts that each basin has a set of natural, or eigen, periods determined by its size, depth, and geometry. The new study put that theory to a natural test across three basins of very different shape.

The results were anything but uniform. Montevideo Bay displayed the strongest amplification of the three sites, with a persistent enhancement of sea-level energy concentrated at relatively low frequencies. In other words, when long waves associated with frontal passages swept into the Río de la Plata, the broad bay rang like a resonating chamber, steadily boosting energy at the low end of the spectrum. Mar del Plata Harbor behaved differently: its amplification was weaker and spread across a broader, more irregular band of frequencies, suggesting a more complicated resonant structure with multiple modes of varying strength rather than a single dominant one. Quequén Harbor, despite its reputation for dramatic oscillations, showed comparatively weak spectral enhancement inside the port relative to the offshore signal, maintaining a much closer correspondence with the long-wave field arriving from the shelf.

Because spectra averaged over the whole four-month record can hide how the relationship between offshore and harbor signals evolves through individual events, the researchers also applied wavelet coherence analysis, a technique that measures how tightly two time series are linked at each frequency and at each moment in time. The method, popularized for geophysical data in a widely cited 2004 paper by Grinsted and colleagues, allowed the team to see when harbor and offshore oscillations were locked in step and when they drifted apart. At Quequén, the coherence between the offshore long-wave field and the harbor response was persistent and strong, reinforcing the picture of a port that largely transmits and modestly reshapes the incoming wave energy. At Mar del Plata, coherent coupling was present but less continuous. Montevideo showed the weakest and most intermittent coherence, implying that the bay’s response is governed more by its own internal resonance than by a direct, moment-to-moment coupling with the offshore signal.

These findings carry a subtle but important message for how coastal scientists think about harbor hazards. It is tempting to assume that a port’s vulnerability to meteotsunamis can be predicted from its theoretical oscillation periods alone: compute the natural modes of the basin, compare them with the frequencies contained in the incoming atmospheric disturbance, and flag any overlap. The comparative data from the southwestern Atlantic complicates that picture. The authors conclude that harbor amplification depends not only on basin geometry and theoretical resonant periods, but also on the trajectory and incidence angle of the incoming disturbance. A wave train arriving along one bearing may couple efficiently into a harbor’s modes, while the same basin may barely respond to an energetically equivalent disturbance approaching from a different direction. Numerical work by other groups, including studies of harbor oscillation induced by pressure disturbances moving in different directions along the Yellow Sea coast, has pointed to the same conclusion, but few observational studies have documented it across multiple real ports at once.

The regional context amplifies the significance of the work. The Buenos Aires continental shelf is exceptionally wide and shallow, and previous research, including a 2022 case study by Dragani and colleagues and a 2024 review of global meteotsunami hazards published in Reviews of Geophysics, has established that atmospheric disturbances crossing this shelf frequently generate long ocean waves through a resonant mechanism known as Proudman resonance, in which a fast-moving pressure disturbance drags a growing ocean wave beneath it. When these waves encounter the coast, they can excite seiches, the standing oscillations of bays and harbors, with catastrophic local consequences. The 2022 event was particularly remarkable, occurring simultaneously along the Argentine and Uruguayan coasts and coinciding with the arrival of the Tonga volcanic tsunami, an overlap documented in a 2025 study by the same research group. Understanding which harbors transform such wave energy into dangerous currents is therefore a matter of practical port safety as well as fundamental science.

For port authorities, the comparative framework offers a concrete lesson: two harbors facing the same open ocean can be exposed to very different risks from the same storm system. Montevideo’s persistent low-frequency amplification means that slow, large-volume oscillations are its signature hazard, with implications for mooring design and berthing operations during frontal passages. Mar del Plata’s irregular, broad-band response suggests that many different atmospheric disturbance types can find some resonant frequency to excite there. Quequén’s relatively faithful reproduction of the offshore signal implies that its risk profile is tied directly to the strength of the shelf wave field itself. The work, which was supported by Argentina’s National Scientific and Technical Research Council, also demonstrates the value of simply measuring the same events at paired offshore and harbor stations, an approach the authors suggest can sharpen meteotsunami hazard assessments well beyond the classical eigenperiod calculation. As climate-driven changes in atmospheric circulation continue to alter the frequency and character of frontal systems worldwide, knowing not just where meteotsunamis form but how each harbor listens to them may prove essential for the ports of the southwestern Atlantic and beyond.

Subject of Research: Frequency-dependent harbor response to meteotsunamis along the Argentine and Uruguayan coasts

Article Title: Comparative frequency-dependent harbor response to meteotsunamis along the Argentine and Uruguayan coasts

Article References: Oreiro, F., Perez, I., & Dragani, W. (2026). Comparative frequency-dependent harbor response to meteotsunamis along the Argentine and Uruguayan coasts. Natural Hazards, 122(20), Article 648. https://doi.org/10.1007/s11069-026-08408-y

Image Credits: AI Generated

DOI: 10.1007/s11069-026-08408-y

Keywords: meteotsunami, harbor resonance, sea level oscillations, atmospheric gravity waves, spectral analysis, wavelet coherence, Argentina, Uruguay, Natural Hazards, coastal hazards, seiches, southwestern Atlantic