Sentia Goursaud

As part of the Comprehensive Nuclear-Test-Ban Treaty, six hydrophone stations of the International Monitoring System transmit continuous data in real time. These stations have recorded low-frequency underwater acoustic waves propagating in the SOund Fixing And Ranging channel for decades. Automated processing of this large data volume is desirable, particularly to discriminate records by source type. However, no catalog currently exists. We present a methodology based on a rule-based expert system to establish such a catalog, covering seven source types: earthquakes, volcanic activity, cryospheric activity, whales, vessels, airguns, and chemical explosions. The catalog consists of 49 452 events from moored hydrophone stations, with an assignment error of less than 1%. Because the process is interpretable and reproducible, the catalog can be readily expanded to incorporate additional inputs. This catalog can be used to identify and analyze specific source types in greater detail.

Vertical wind structure plays a central role in tropospheric dynamics, yet its variability is rarely characterized beyond surface-level fields. Summarizing this variability over multi-decadal timescales requires reducing the dimensionality of wind profiles while preserving their dynamical content. Here, we develop an objective classification of vertical wind regimes using the ERA reanalysis (1940–2024), to identify a compact set of representative tropospheric structures and quantify their temporal evolution.We first derive spatio-temporal averaged wind profiles from the reference regions defined within the IPCC framework. Although these regions are based on surface climate characteristics, the resulting regional wind profiles provide a baseline against which we compare new wind profile classifications from vertical climate variability.Dominant modes of variability are extracted using empirical orthogonal functions applied to multi-level wind profiles. Clustering (k-means and hierarchical approaches) is then performed in the reduced phase space to identify dynamical regimes, with robustness assessed through bootstrap resampling and multiple validation metrics. We show that a limited number of regimes capture most of the tropospheric wind variance over the 84-year period, each characterized by distinct vertical shear and directional signatures. The length of the record allows us to examine persistence, transition probabilities, and modulation across seasonal to multi-decadal variability.Overall, this framework provides a physically interpretable compression of vertical wind variability over a uniquely long ERA dataset, offering new diagnostic tools for atmospheric dynamics and a potentially valuable input for transport, dispersion, and predictability studies.

Stable water isotopes recorded in Antarctic ice cores have traditionally been used to infer past surface air temperatures (SATs). During the historical period (1850 onward), observational data and good-quality ice core records overlap, yielding an opportunity to investigate key relationships between ice core stable water isotope (δ¹⁸O) measurements and the Antarctic climate. We present a new ensemble of climate model simulations covering 1851–2004 using the UK Met Office HadCM3 general circulation model equipped with stable water isotopes. Our ensemble captures observed historical SAT and precipitation trends and weak δ¹⁸O trends. The weak δ¹⁸O trends mean there is no significant relationship between SAT and δ¹⁸O over one-third of Antarctica, and also half of our considered ice core sites, though relationships are stronger when using regional averages. The strongest regional relationships occur in the West Antarctic Ice Sheet (WAIS) region. This decoupling between SAT and δ¹⁸O occurs primarily because of the impact of autumnal sea ice loss during the simulated warming. The warming and sea ice loss are associated with (i) changes in near-coastal air mass intrusions (synoptic effects) induced by changes in the large-scale circulation and/or sea ice; (ii) direct sea-ice-driven changes in moisture pathways (especially lengths) to Antarctica; and (iii) precipitation seasonality changes, again mostly driven by sea ice changes. Consequently, when reconstructing temperatures over these timescales, changes in sea ice need to be considered, both to determine the most appropriate SAT and δ¹⁸O relationship and to understand how uncertainties affect the inference of past temperature from ice core δ¹⁸O measurements.

Antarctic ice core records covering the last glacial cycle generally reflect a common climate and environmental history overlain with local influences such as changes in altitude, atmospheric circulation, local dust sources, or regional sea ice extent. Here we investigate records from the 651 m Skytrain Ice Rise core, drilled within the WACSWAIN (WArm Climate Stability of the West Antarctic ice sheet in the last Interglacial) project. This ice rise is adjacent to the Ronne Ice Shelf and the WAIS, and extends into the last interglacial period, including a continuous record of the last glacial cycle. The water isotope record shows the clearly recognisable pattern of all the Antarctic Isotopic Maxima of the last 100 kyr, but with different amplitudes to those seen in the well-known WAIS Divide or EPICA ice cores. We will consider what these differences in amplitude tell us about ice elevation at Skytrain, using total air content data to aid our interpretation. The information from sea salt ions can tell us about ice shelf extent, and taking the water isotopes and ions together will allow us to diagnose the status of the Ronne Ice Shelf throughout the glacial. Terrestrial material (Ca, dust) reflects both a common continent-wide input of dust from other continents (especially South America) but also local inputs. We will use the differences for terrestrial dust between Skytrain Ice Rise and other sites to diagnose the input of local dust from the Ellsworth Mountains.Finally combining all three sources of information we expect to make statements about the wider advance and retreat of the West Antarctic Ice Sheet and Ronne Ice Shelf in the region surrounding Skytrain Ice Rise.

Polar lows are intense but short duration maritime cyclones occurring in both hemispheres. In the northern pole, they are mainly located in the Barents and Norwegian seas, with significant damages for coastal populations. So far, a fully understanding of the physical processes at play is still lacking. This is due to the suddenness of such events, as well as a scarcity of meteorological observations in these areas. Infrasounds are sound waves with frequency ranges below the audible domain. It was shown that polar lows can be a source of infrasound. Only one study looked at the infrasound signature for two particular polar lows using data obtained from two stations, in Northern Norway and on Svalbard. Here we show the potentiality of a systematic polar low-induced signature in infrasound data.Within the frame of the Comprehensive nuclear-test-ban treaty organization, infrasound stations were set up worldwide. One was settled in northern Norway (IS37NO) in 2003 and made fully operational since 2004. Its records consist in a timeseries of sub-daily pressure data, that are processed through a Progressive Multi Channel Cross Correlation method, resulting in variables such as the mean frequencies, azimuths and amplitudes of the detections, and covering 17 complete years (2004-2021). These variables were used to train statistical models to learn the occurrence of polar lows refered in a polar low database. Our models yield very good results, specially in term of precision and recall. They provide a basis for different research opportunities, such as the prediction of polar lows and a deeper comprehension of its climate controls.

The historical period  (from 1850 to present) yields a window when ice core  and good historical data are both available. It thus represents an important period over which to test the relationship between ice core measurements, here stable water isotopes, and Antarctic climate.  Water stable isotopes from ice cores from Antarctica have traditionally been used to infer past surface air temperatures. Here we run an ensemble over the period 1850-2004 using the UK Met Office HadCM3 general circulation model equipped with water stable isotopes.  Simulations of water stable istopes from general circulation model can help in the interpretation of Antarctic ice cores.  This ensemble captures observed temperature and precipitation trends. Interestingly however the water isotopes exhibit little trend. This appears to be explained by compensating effect of two modes of atmospheric dynamics throughout the period. Further we use these results to examine the relationships used in Last Millienium reconstructions based on Antarctic stable water isotopes data from ice cores.  

This collaborative article discusses the opportunities and challenges of adopting integrated, coordinated, open, and networked (ICON) principles in atmospheric sciences. From the global nature of the atmosphere, there has always been a need for atmospheric science to be an ICON science. With the help of evolving technology, it is possible to go further in implementing and spreading the ICON principles for productive global collaboration. In particular, technology transfer and applications could be approached with reproducibility in mind, and data‐sharing infrastructure could enable easier and better international collaboration. There are, however, various challenges in following the ICON principles in the acquisition, quality control, and maintenance of data, and the publication of results in a systematic way. Moreover, the extent of such issues varies geographically and hence poses different challenges to implementing ICON principles. In this commentary article, we briefly state our perspectives on the state of ICON, challenges we have met, and future opportunities. Furthermore, we describe how atmospheric science researchers have benefited from these collaborative multi‐dimensional approaches that fulfill the core goal of ICON.

This collaborative article discusses the opportunities and challenges of adopting Integrated, Coordinated, Open, and Networked (ICON) principles in atmospheric sciences. From the global nature of the atmosphere, there has always been a need for atmospheric science to be an ICON science. With the help of evolving technology, it is possible to go further in implementing and spreading the ICON principles for productive global collaboration. In particular, technology transfer and applications could be approached with reproducibility in mind, and data-sharing infrastructure could enable easier and better international collaboration. There are, however, various challenges in following the ICON principles in the collection, quality control, and maintenance of data, and the publication of results in a systematic way. Moreover, the extent of such issues varies geographically and hence poses different challenges to ICON principles. In this commentary article, we briefly state our perspectives on the state of ICON, challenges we have met, and future opportunities. Furthermore, we describe how atmospheric science researchers have benefited from these collaborative multi-dimensional approaches that fulfill the core goal of ICON.