The project, named STRAT-NAV, forms part of ARIA’s Enduring Atmospheric Platforms Programme, a £70 million, three-and-a-half-year initiative led by Programme Director Rico Chandra. The programme has funded 18 research and development teams, all working on the same fundamental challenge: how to keep aircraft operating reliably and cost-effectively in the stratosphere for extended periods. The ambition behind the programme is considerable. Platforms capable of lingering aloft for weeks or months could provide the high-performance communications infrastructure needed for truly global connectivity, support the next generation of AI and digital services, and reduce dependence on conventional satellites, which are expensive to launch and impossible to repair once in orbit.

The aircraft at the centre of this vision are known as High-Altitude Pseudo-Satellites, or HAPS. These long-endurance vehicles fly in the stratosphere, a layer of the atmosphere that is relatively calm, above most weather, and far below orbital space. From this vantage point, a HAPS platform can deliver remote-sensing observations or communications services over a wide area, behaving in many respects like a satellite but with the crucial advantage of being recoverable, upgradable and re-deployable. Most HAPS designs are solar-powered ultralight gliders, exquisitely engineered to be as light as possible. That lightness, however, comes at a cost: the onboard battery capacity is limited, and the aircraft face acute power challenges, particularly during the long winter nights experienced at UK latitudes, when solar energy falls to its lowest levels.

This is where the Bath team sees an opportunity hiding in plain sight. Atmospheric gravity waves are created when air is forced upwards — by mountain ranges or by deep convection — and then falls back down under gravity in a wave-like motion, transferring energy through the atmosphere much as ripples transfer energy across the surface of a pond. The vertical air motions associated with these waves can be strong enough for a suitably equipped aircraft to exploit. Just as eagles ride thermals to gain altitude without flapping their wings, STRAT-NAV aims to guide HAPS platforms to soar on atmospheric gravity waves. According to the project team, the energy savings from this ‘gravity wave assist’ would be equivalent to carrying at least a 20 to 40 per cent bigger battery — at no additional cost, weight or complexity to the aircraft itself.

Dr Neil Hindley, a research fellow in the Centre for Climate Adaptation and Environment Research and the project’s lead, described the award as an exciting opportunity to translate decades of atmospheric science into a practical tool. In his words, the project could transform high-altitude aviation and unlock the stratosphere as an operating environment. He noted that atmospheric gravity waves have been studied by scientists for decades, but that until recently the community lacked the sub-kilometre-scale forecasting capability needed to predict them accurately enough to use operationally. If HAPS aircraft can be helped to navigate and exploit these naturally occurring energy sources, he argued, it could fundamentally change what is possible for long-endurance flights over the UK and beyond.

The choice of the United Kingdom as a proving ground is not accidental. The country sits beneath the undulating path of the jet stream, a fast-moving ribbon of air whose meanders are a prolific generator of gravity waves. Add the rugged mountain terrain of Wales and the Pennines, which forces air upward as weather systems pass over, and the stratospheric polar vortex that forms over the pole each winter, and the UK becomes a global hotspot for gravity wave activity. Hindley described exploiting stratospheric gravity waves as a uniquely advantageous strategy for the UK because of this geography. Crucially, the timing works in the aircraft’s favour: while available solar energy falls to a minimum during winter, gravity wave activity over the UK reaches its maximum at exactly the moment it is most needed. This seasonal complementarity between sunlight and wave energy is what could allow HAPS to operate year-round, realising the vision of an operational fleet providing services that until now have only been possible from orbit.

The technical challenge lies in the fact that gravity waves, despite containing abundant energy, are notoriously difficult to forecast and exploit. They are small in horizontal scale compared with the synoptic weather systems that drive them, often just a few kilometres across, which places them below the resolution of standard numerical weather prediction models. A HAPS aircraft therefore needs reliable, high-accuracy forecasts and intelligent routing systems to find and use these rising currents safely and efficiently. STRAT-NAV will tackle this with AI-enhanced, ultra-high-resolution, real-time atmospheric modelling, validated against observations, to forecast the gravity wave field around a HAPS platform up to 72 hours in advance. On top of the forecast layer, the project will develop platform-specific intelligent routing algorithms that maximise the energy harvested from gravity waves through soaring while maintaining the communications coverage that these aircraft exist to provide.

The programme is structured to move from simulation to the real sky. Work begins in September 2026 with model development, followed by observational campaigns in late 2026 and 2027 designed to validate the gravity-wave forecasts against direct measurements of the atmosphere. Only once the forecasts have been proven will the project progress to flight trials with HAPS industry partners later in the programme. This staged approach reflects a broader lesson from aviation history: exploiting natural atmospheric energy is not a new idea — glider pilots have ridden mountain waves and thermals for a century — but doing so autonomously, at 20 kilometres altitude, guided by machine-learned forecasts, is something genuinely novel.

One of the most commercially significant aspects of the design is its platform-agnostic nature. The gravity wave assist capability is intended to work with any HAPS platform, whether a lightweight fixed-wing aircraft or even a rotary-wing vehicle, and requires no modifications to the aircraft and no expensive ground infrastructure. That could lower the barrier to adoption across an industry in which every gram of payload and every watt-hour of battery counts. For operators, the prospect of effectively free energy harvested from the sky — savings equivalent to a battery a fifth to two-fifths larger — could be the difference between a seasonal demonstrator and a viable year-round service.

If STRAT-NAV succeeds, the implications extend well beyond the UK. A demonstrated ability to forecast and exploit stratospheric gravity waves would give long-endurance aircraft a renewable energy source that no battery chemistry or solar array can match in cost, and it would arrive precisely when solar power is weakest at high latitudes. The wider Enduring Atmospheric Platforms Programme, with its 18 funded teams and £70 million budget, is betting that the stratosphere can become a routine operating environment — a physical backbone for next-generation communications and a path to connectivity for underserved regions. The energy to make that happen, the Bath team argues, is already there, rippling invisibly through the sky, waiting to be navigated.

Subject of Research: Exploiting atmospheric gravity waves to extend the endurance of stratospheric high-altitude pseudo-satellite aircraft

Article Title: Bath receives £1.9 million funding to unlock energy hidden in the sky

Article References: Bath receives £1.9 million funding to unlock energy hidden in the sky. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: atmospheric gravity waves, stratosphere, HAPS, high-altitude pseudo-satellites, University of Bath, ARIA, STRAT-NAV, long-endurance flight, atmospheric modelling, soaring, renewable energy, connectivity

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