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Severe storms produce ocean waves with periods of 18–26 s, corresponding to wavelengths 500–1,055 m. These waves radiate globally as swell, generating microseisms and affecting coastal areas. Despite their significance, long waves often elude detection by existing remote sensing systems when their height is below 0.2 m. The new Surface Water Ocean Topography (SWOT) satellite offers a breakthrough by resolving these waves in global sea level measurements. Here we show that SWOT can detect 25‐s waves with heights as low as 3 cm, and resolves period and direction better than in situ buoys. SWOT provides detailed maps of wave height, wavelength, and direction across ocean basins. These measurements unveil intricate spatial patterns, shedding light on wave generation in storms, currents that influence propagation, and refraction, diffraction and reflection in shallow regions. Notably, the magnitude of reflections exceeds previous expectations, illustrating SWOT's transformative impact. Plain Language Summary: Wind storms at sea make waves that increase in size with wind speed, and with the distance over which the high winds have been able to amplify the waves. Once generated these waves propagate as swell around the world ocean: in that stage the wave period remains constant while the wave height decay away from the source. Waves with periods longer than 18 s are relatively infrequent, but they are an important source of seismic waves and coastal impacts. However, current remote sensing techniques miss long waves under 0.2 m high. The Surface Water Ocean Topography (SWOT) satellite mission changes this, spotting 25‐s waves with heights as low as 3 cm. SWOT maps wave height, wavelength, and direction worldwide, revealing the influence of winds, currents and water depth. For example, We found stronger than expected coastal reflection, which will help revise wave forecasting models and their application in seismology. Key Points: Surface Water Ocean Topography (SWOT) data provide the first open ocean spatial measurements of phase‐resolved swells with wavelength 500–1,050 mSwells with heights as low as 3 cm are well detected by SWOT, allowing tracking across oceansSwell reflection off the coast can be separated from incident waves [ABSTRACT FROM AUTHOR]

We study optimal policy in an economy where interest rates are low because public debt serves as collateral or buffer stock. Issuing more public debt raises welfare by easing the underlying friction but also reduces the private valuation of this service, raising interest rates. This trade-off shapes the optimal quantity of public debt in the long run, justifies a departure from tax smoothing in the short run, and calls for larger deficits during financial crises. Our analysis illustrates the possible robustness of these insights to different microfoundations and helps clarify when exactly low interest rates represent an opportunity for cheap government borrowing. [ABSTRACT FROM AUTHOR]

Polar-orbiting satellite observations are of fundamental importance to explore the main scientific challenges in the Arctic Ocean, as they provide information on bio-geo-physical variables with a denser spatial and temporal coverage than in-situ instruments in such a harsh and inaccessible environment. However, they are limited by the lack of coverage near the North Pole (Polar gap), the polar night, and frequent cloud cover or haze over the ocean and sea ice, which prevent the use of optical satellite instruments, as well as by the limited availability of external validation data. The satellite sensors' coverage and repeat cycles may also have limitations in properly identifying and resolving the dominant spatial and temporal scales of atmospheric, ocean, cryosphere and land variability and their interactive processes and feedback mechanisms. In this paper, we provide a state of the art of contribution of satellite observations to the understanding of the polar environment and climate scientific challenges tackled within the Arktalas Hoavva project funded by the European Space Agency. We identify the current limitations to the wider use of polar orbiting remote sensing data, as well as the observational gaps of the existing satellite missions. A comprehensive overview of all satellite missions and applications is given provided with a primary focus on the European satellites. Finally, we assess the expected capability of the approved future satellite missions to answer today's scientific challenges in the Arctic Ocean. [ABSTRACT FROM AUTHOR]

In the previous companion study, satellite data were used to describe peculiar characteristics of ocean surface wave fields, generated by two extra-tropical cyclones (ETCs) rapidly propagating in the North Atlantic. Based on a 2D parametric wave model, further details are now provided to analyse and interpret the spatio-temporal evolution of very intense ETC-generated waves. Significant wave height and wavelength values are shown to reach extreme values, 18 m and 500 m, respectively. Resulting energetic swell systems waves then radiate in the whole eastern part of the North Atlantic, and more particularly in the Norwegian sea region. Moving to higher latitudes, wind forcing characteristics of ETCs evolve, with the shape of the wind field changing from quasi-cyclonic to "air jets/Icelandic lows". In this paper, the resulting swell generation and propagation, after the deformation of an individual ETC, were studied, as well. Confirmed with comparisons with multi-satellite observations, the application of the parametric-2D wave-ray model was demonstrated to provide robust and highly detailed information on wave generation under very complex wind regime changes. [ABSTRACT FROM AUTHOR]

Surface waves generated by Extra-Tropical Cyclones (ETCs) can significantly affect shipping, fishing, offshore oil and gas production, and other marine activities. This paper presents the results of a satellite data-based investigation of wind waves generated by two North Atlantic ETCs. These ETCs were fast-moving systems, inhibiting resonance (synchronism) between the group velocity of the generated waves and the ETC translation velocity. In these cases, wave generation begins when the front boundary of the storm appears at a given ocean location point. Since developing waves are slow, they move backward relative to the storm, grow in time, and then leave the ETC stormy area through the rear sector. Multi-satellite observations confirm such a paradigm, revealing that the storm regions are filled with young developing wind waves, the most developed in the rear-right sector. As observed, the energy of these waves grew in time during the ETC life span. It is demonstrated that the extended-fetch concept (inherent for Tropical Cyclones) does not apply to ETC. Instead, by analogy, the concept of extended-duration wave growth is more relevant. Satellite observations confirmed the validity of duration-laws for waves generated by ETCs, and demonstrated that extended-fetch solutioncan be valid at time scales exceeding the lifespan of considered ETCs. [ABSTRACT FROM AUTHOR]

Wind‐generated waves strongly interact with sea ice and impact air‐sea exchanges, operations at sea, and marine life. Unfortunately, the dissipation of wave energy is not well quantified and its possible effect on upper ocean mixing and ice drift is still mysterious. As the Arctic is opening up and wave energy increases, the limited amount of in situ observations is a clear limitation to our scientific understanding. Both radar and optical remote sensing has revealed the frequent presence of waves in ice, and could be used more systematically to investigate wave‐ice interactions. Here we show that, in cloud‐free conditions, Sentinel‐2 images exhibit brightness modulations in ice‐covered water, consistent with the presence of waves measured a few hours later by the ICESat‐2 laser altimeter. We show that a full‐focus SAR processing of Sentinel‐3 radar altimeter data also reveals the presence and wavelengths of waves in sea ice, within minutes of Sentinel‐2 imagery. The SWIM instrument on CFOSAT is another source of quantitative evidence for the direction and wavelengths of waves in ice, when ice conditions are spatially homogeneous. In the presence of sea ice, a quantitative wave height measurement method is not yet available for all‐weather near‐nadir radar instruments such as altimeters and SWIM. However, their systematic colocation with optical instruments on Sentinel‐2 and ICESat‐2, which are less frequently able to observe waves in sea ice, may provide the empirical transfer functions needed to interpret and calibrate the radar data, greatly expanding the available data on wave‐ice interactions. Plain Language Summary: Waves generated by winds over the ocean propagate in ice‐covered regions where they can be strongly attenuated and can contribute to breaking up the ice and pushing the ice around. Wavy patterns are clearly visible in remote sensing data collected by different instruments including the ICESat‐2 laser altimeter, Sentinel‐1 imaging radar, the Sentinel‐2 optical imager, Sentinel‐3 radar altimeter, and CFOSAT wave‐measuring instrument SWIM. Here, we show examples of such patterns and propose a quantitative interpretation of ICESat‐2 and Sentinel‐2 that is consistent with waves generated by storms in the Barents Sea that are observed to travel under the ice over hundreds of kilometers. For Sentinel‐3 and SWIM, a quantification of wave heights will have to be validated, possibly based on data from the other two instruments. This may strongly expand the quantity of available information for scientific investigations and operational applications. Key Points: Wave patterns in sea ice can be found in radar and optical remote sensing dataWe provide a quantitative estimation of wave height, wavelength and direction from ICESat‐2 and Sentinel‐2 dataWavelengths and directions in full‐focus SAR altimetry and CFOSAT SWIM are consistent with other sensors [ABSTRACT FROM AUTHOR]