Sign in to use this feature.

Years

Between: -

Subjects

remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline

Journals

Article Types

Countries / Regions

remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline

Search Results (104)

Search Parameters:
Keywords = Tonga

Order results
Result details
Results per page
Select all
Export citation of selected articles as:
13 pages, 8146 KiB  
Communication
A Morphometric Analysis of Starch Granules from Two Dioscorea Species
by Sara Rickett, Lisbeth A. Louderback and Adrian V. Bell
Plants 2025, 14(12), 1869; https://doi.org/10.3390/plants14121869 - 18 Jun 2025
Viewed by 462
Abstract
Dioscorea is a genus comprising over 600 species, many of which possess edible tubers that are commonly referred to as yams. While Dioscorea is a significant crop across the globe, it holds a unique cultural significance to the people of Tonga in western [...] Read more.
Dioscorea is a genus comprising over 600 species, many of which possess edible tubers that are commonly referred to as yams. While Dioscorea is a significant crop across the globe, it holds a unique cultural significance to the people of Tonga in western Polynesia. Presently, Dioscorea is known for its essential role in festivals and ceremonies, as well as for its nutritional contributions to Tongan diets. To understand and to assess the significance of Dioscorea in the distant past, however, archeologists rely on plant residues (e.g., starch granules) preserved on ancient tools. This study provides the necessary first step in archeological starch analysis by examining the granule morphometrics of two culturally significant Dioscorea species, D. alata and D. bulbifera from Tonga. Tubers from three individuals of each species were collected on the island of Vava’u and processed for starch granule extraction and analysis. Morphometric characteristics, including two novel that describe shape (eccentricity ratio and hilum angle), were measured on approximately 300 granules per species. When statistically compared, these novel characteristics allow D. alata and D. bulbifera to be readily distinguished from one another, and therefore increase confidence in assigning archeological granules to a specific taxon. Full article
(This article belongs to the Special Issue Advances in Vegetation History and Archaeobotany)
Show Figures

Figure 1

31 pages, 5746 KiB  
Article
Twilight Near-Infrared Radiometry for Stratospheric Aerosol Layer Height
by Lipi Mukherjee, Dong L. Wu, Nader Abuhassan, Thomas F. Hanisco, Ukkyo Jeong, Yoshitaka Jin, Thierry Leblanc, Bernhard Mayer, Forrest M. Mims, Isamu Morino, Tomohiro Nagai, Stephen Nicholls, Richard Querel, Tetsu Sakai, Ellsworth J. Welton, Stephen Windle, Peter Pantina and Osamu Uchino
Remote Sens. 2025, 17(12), 2071; https://doi.org/10.3390/rs17122071 - 16 Jun 2025
Viewed by 549
Abstract
The impact of stratospheric aerosols on Earth’s climate, particularly through atmospheric heating and ozone depletion, remains a critical area of atmospheric research. While satellite data provide valuable insights, independent validation methods are necessary for ensuring accuracy. Twilight near-infrared (NIR) radiometry offers a promising [...] Read more.
The impact of stratospheric aerosols on Earth’s climate, particularly through atmospheric heating and ozone depletion, remains a critical area of atmospheric research. While satellite data provide valuable insights, independent validation methods are necessary for ensuring accuracy. Twilight near-infrared (NIR) radiometry offers a promising approach for investigating aerosol properties, such as optical depth and layer height, at high altitudes. This study aims to evaluate the effectiveness of twilight radiometry in corroborating satellite data and assessing aerosol characteristics. Two methods based on twilight radiometry—the color ratio and the derivative method—are employed to derive the aerosol layer height and optical depth. Radiances at 450, 550, 762, 775, and 1050 nm wavelengths are analyzed at varying solar zenith angles, using zenith viewing geometry for consistency. Comparisons of aerosol optical depths (AODs) between Research Pandora (ResPan) and AErosol RObotic NETwork (AERONET) data (R = 0.99) and between ResPan and Modern-Era Retrospective analysis for Research and Applications (MERRA-2) data (R = 0.86) demonstrate a strong correlation. Twilight ResPan data are also used to estimate the aerosol layer height, with results in good agreement with SAGE and lidar measurements, particularly following the Hunga Tonga eruption in Lauder, New Zealand. The simulation database, created using the libRadtran DISORT and Monte Carlo packages for daylight and twilight calculations, is capable of detecting AODs as low as 10−3 using the derivative method. This work highlights the potential of twilight radiometry as a simple, cost-effective tool for atmospheric research and satellite data validation, offering valuable insights into aerosol dynamics at stratospheric altitudes. Full article
Show Figures

Figure 1

23 pages, 616 KiB  
Review
Indigenous Knowledge, Gender and Agriculture: A Scoping Review of Gendered Roles for Food Sustainability in Tonga, Samoa, Solomon Islands and Fiji
by Jasmina Thomas, Nidhi Wali, Nichole Georgeou and Seeseei Molimau-Samasoni
Land 2025, 14(6), 1210; https://doi.org/10.3390/land14061210 - 5 Jun 2025
Viewed by 741
Abstract
This scoping review examines the state of academic knowledge around gender and its role in Indigenous/traditional knowledge for food sustainability in Tonga, Samoa, Solomon Islands and Fiji. The different roles played by all genders—men, women and non-binary—in the Pacific Islands can contribute to [...] Read more.
This scoping review examines the state of academic knowledge around gender and its role in Indigenous/traditional knowledge for food sustainability in Tonga, Samoa, Solomon Islands and Fiji. The different roles played by all genders—men, women and non-binary—in the Pacific Islands can contribute to climate adaptation and knowledge preservation for sustainable food production. The gender lens is especially relevant given the fact that women’s knowledge has, in recent years, been disregarded and marginalised as a consequence of colonial influences and increasing reliance on imported foods. We analysed 14 studies published in English between 2015 and 2024—six from refereed journal articles and eight from grey literature. Three themes emerged linking agriculture, gender and traditional knowledge, as follows: (1) there is a gendered division of labour and culturally defined roles between women and men, although the roles played by non-binary groups remain unclear; (2) intergenerational traditional knowledge transmission has declined; (3) climate change adaptation could be reinforced through passing on traditional knowledge. The findings demonstrate that gendered knowledge is distinct and complementary, and this knowledge should be integrated into Pacific agricultural production to achieve resilient and sustainable farming in the face of climate change. Full article
Show Figures

Figure 1

16 pages, 1005 KiB  
Article
Motivators and Facilitators of Fruit and Vegetable Intake in Tongan Adults
by Emily Mitchell, Crystal Áke, Steven Underhill and Sarah Burkhart
Nutrients 2025, 17(9), 1510; https://doi.org/10.3390/nu17091510 - 29 Apr 2025
Viewed by 457
Abstract
Background/Objectives: Changes to food systems and food environments across the Pacific Islands region have influenced dietary behaviors. While dietary intake is limited, it is believed that fruit and vegetable consumption is low within these populations. Given the benefits of fruit and vegetable consumption, [...] Read more.
Background/Objectives: Changes to food systems and food environments across the Pacific Islands region have influenced dietary behaviors. While dietary intake is limited, it is believed that fruit and vegetable consumption is low within these populations. Given the benefits of fruit and vegetable consumption, this exploratory study aimed to identify the motivators and facilitators of fruit and vegetable intake in a subset of Tongan adults. Methods: Semi-structured, 30 min interviews were conducted in Tongan with 12 participants (5 fieldworkers and 3 female community members who were interviewed separately and 4 women who took part in a small group interview). The responses were translated into English and were analyzed using thematic analysis. Results: Most participants thought that low fruit and vegetable consumption was of concern in Tongan communities. All participants agreed that diverse fruit and vegetable consumption is a priority for Tongan people and that communities are motivated to consume more fruits and vegetables. A total of 12 themes were derived from the results: 6 motivational and 6 facilitating, including determinants such as dietary patterns (taste and culture), community engagement/working in groups, and financial factors. Conclusions: While using a small sample size from Tongatapu, this provides a valuable insight from the Tongan communities’ perspectives on motivators and facilitators of fruit and vegetable consumption. The results offer policymakers, government, and NGOs contextually relevant and up-to-date data that can be used when developing health and nutrition programs. Full article
Show Figures

Figure 1

12 pages, 1539 KiB  
Article
Purpuramine R, a New Bromotyrosine Isolated from Pseudoceratina cf. verrucosa Collected in the Kingdom of Tonga
by Jennie L. Ramirez-Garcia, Hannah Lee-Harwood, David Ackerley, Michelle Kelly, S. Vailala Matoto, Patricia Hunt, A. Jonathan Singh and Robert A. Keyzers
Mar. Drugs 2025, 23(5), 186; https://doi.org/10.3390/md23050186 - 27 Apr 2025
Viewed by 567
Abstract
Sponges in the verongiid genus Pseudoceratina Carter are well-known producers of bioactive secondary metabolites. Chemical screening of a Tongan P. cf. verrucosa Bergquist using NMR highlighted the presence of aromatic natural products. Subsequent extraction and purification of P. cf. verrucosa yielded a new [...] Read more.
Sponges in the verongiid genus Pseudoceratina Carter are well-known producers of bioactive secondary metabolites. Chemical screening of a Tongan P. cf. verrucosa Bergquist using NMR highlighted the presence of aromatic natural products. Subsequent extraction and purification of P. cf. verrucosa yielded a new bromotyrosine, purpuramine R (1), that exhibits moderate (MIC 16 µg/mL) antibacterial activity against Gram-positive Staphylococcus aureus. The E-geometry of the oxime was confirmed using a combination of NMR and computational approaches. Additionally, computational conformational analysis indicates that purpuramine R adopts a hairpin orientation, stabilized by intramolecular hydrogen and halogen bonds. Knowledge of this stabilized conformation can inform synthetic approaches to make analogues of the purpuramines for future SAR studies. Full article
(This article belongs to the Special Issue Structural Diversity in Marine Natural Products)
Show Figures

Figure 1

19 pages, 1743 KiB  
Review
Some Recent Key Aspects of the DC Global Electric Circuit
by Michael J. Rycroft
Atmosphere 2025, 16(3), 348; https://doi.org/10.3390/atmos16030348 - 20 Mar 2025
Viewed by 1255
Abstract
The DC global electric circuit, GEC, was conceived by C.T.R. Wilson more than a century ago. Powered by thunderstorms and electrified shower clouds, an electric current I ~1 kA flows up into the ionosphere, maintaining the ionospheric potential V ~250 kV with respect [...] Read more.
The DC global electric circuit, GEC, was conceived by C.T.R. Wilson more than a century ago. Powered by thunderstorms and electrified shower clouds, an electric current I ~1 kA flows up into the ionosphere, maintaining the ionospheric potential V ~250 kV with respect to the Earth’s surface. The circuit is formed by the current I, flowing through the ionosphere all around the world, down through the atmosphere remote from the current sources (J ~2 pA/m2 through a resistance R ~250 Ω), through the land and sea surface, and up to the thunderstorms as point discharge currents. This maintains a downward electric field E of magnitude ~130 V/m at the Earth’s surface away from thunderstorms and a charge Q ~−6.105 C on the Earth’s surface. The theoretical modelling of ionospheric currents and the miniscule geomagnetic field perturbations (ΔB ~0.1 nT) which they cause, as derived by Denisenko and colleagues in recent years, are reviewed. The time constant of the GEC, τ = RC, where C is the capacitance of the global circuit capacitor, is estimated via three different methods to be ~7 to 12 min. The influence of stratus clouds in determining the value of τ is shown to be significant. Sudden excitations of the GEC by volcanic lightning in Iceland in 2011 and near the Tonga eruption in 2022 enable τ to be determined, from experimental observations, as ~10 min and 8 min, respectively. It has been suggested that seismic activity, or earthquake precursors, could produce large enough electric fields in the ionosphere to cause detectable effects, either by enhanced radon emission or by enhanced thermal emission from the earthquake region; a review of the quantitative estimates of these mechanisms shows that they are unlikely to produce sufficiently large effects to be detectable. Finally, some possible links between the topics discussed and human health are considered briefly. Full article
(This article belongs to the Special Issue Atmospheric Electricity (2nd Edition))
Show Figures

Figure 1

18 pages, 4853 KiB  
Article
Exploring the Potential of a Normalized Hotspot Index in Supporting the Monitoring of Active Volcanoes Through Sea and Land Surface Temperature Radiometer Shortwave Infrared (SLSTR SWIR) Data
by Alfredo Falconieri, Francesco Marchese, Emanuele Ciancia, Nicola Genzano, Giuseppe Mazzeo, Carla Pietrapertosa, Nicola Pergola, Simon Plank and Carolina Filizzola
Sensors 2025, 25(6), 1658; https://doi.org/10.3390/s25061658 - 7 Mar 2025
Cited by 2 | Viewed by 750
Abstract
Every year about fifty volcanoes erupt on average, posing a serious threat for populations living in the neighboring areas. To mitigate the volcanic risk, many satellite monitoring systems have been developed. Information from the medium infrared (MIR) and thermal infrared (TIR) bands of [...] Read more.
Every year about fifty volcanoes erupt on average, posing a serious threat for populations living in the neighboring areas. To mitigate the volcanic risk, many satellite monitoring systems have been developed. Information from the medium infrared (MIR) and thermal infrared (TIR) bands of sensors such as the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Visible Infrared Imaging Radiometer Suite (VIIRS) is commonly exploited for this purpose. However, the potential of daytime shortwave infrared (SWIR) observations from the Sea and Land Surface Temperature Radiometer (SLSTR) aboard Sentinel-3 satellites in supporting the near-real-time monitoring of thermal volcanic activity has not been fully evaluated so far. In this work, we assess this potential by exploring the contribution of a normalized hotspot index (NHI) in the monitoring of the recent Home Reef (Tonga Islands) eruption. By analyzing the time series of the maximum NHISWIR value, computed over the Home Reef area, we inferred information about the waxing/waning phases of lava effusion during four distinct subaerial eruptions. The results indicate that the first eruption phase (September–October 2022) was more intense than the second one (September–November 2023) and comparable with the fourth eruptive phase (June–August 2024) in terms of intensity level; the third eruption phase (January 2024) was more difficult to investigate because of cloudy conditions. Moreover, by adapting the NHI algorithm to daytime SLSTR SWIR data, we found that the detected thermal anomalies complemented those in night-time conditions identified and quantified by the operational Level 2 SLSTR fire radiative power (FRP) product. This study demonstrates that NHI-based algorithms may contribute to investigating active volcanoes located even in remote areas through SWIR data at 500 m spatial resolution, encouraging the development of an automated processing chain for the near-real-time monitoring of thermal volcanic activity by means of night-time/daytime Sentinel-3 SLSTR data. Full article
(This article belongs to the Special Issue Feature Papers in Remote Sensors 2024–2025)
Show Figures

Figure 1

38 pages, 19057 KiB  
Article
Review of the Mackerel Genus Rastrelliger (Teleostei: Scombridae) with Redescription of R. chrysozonus (Rüppell, 1836) and R. kanagurta (Cuvier, 1816)
by Sergey V. Bogorodsky, Nozomu Muto, Harutaka Hata, Hiroyuki Motomura and Tilman J. Alpermann
Diversity 2025, 17(1), 72; https://doi.org/10.3390/d17010072 - 20 Jan 2025
Viewed by 2172
Abstract
The Indo-West Pacific scombrid genus Rastrelliger Jordan & Starks is reviewed. Formerly, the genus was considered to contain three valid species, viz., R. brachysoma (Bleeker, 1851) known from the south-east coast of India to Samoa Islands; R. faughni Matsui, 1967 reported from the [...] Read more.
The Indo-West Pacific scombrid genus Rastrelliger Jordan & Starks is reviewed. Formerly, the genus was considered to contain three valid species, viz., R. brachysoma (Bleeker, 1851) known from the south-east coast of India to Samoa Islands; R. faughni Matsui, 1967 reported from the south-east coast of India to Fiji; and R. kanagurta (Cuvier, 1816), the most widespread species known from the east coast of Africa and the Persian/Arabian Gulf east to Tonga. Herein, R. chrysozonus (Rüppell, 1836), restricted to the Red Sea, is resurrected from the synonymy with R. kanagurta and both species are redescribed in detail, based on an integrative morphological and molecular assessment. Consequently, Scomber microlepidotus Rüppell, 1836 is moved from the synonymy with R. kanagurta to synonymy with R. chrysozonus. Rastrelliger chrysozonus differs from R. kanagurta primarily by a longer upper jaw. Rastrelliger brachysoma differs from the other three species by a deeper body, a deeper caudal peduncle, and a very long intestine. Rastrelliger faughni differs from the other three species in having a more slender body, usually X spines in the first dorsal fin (versus IX spines), shorter and fewer gill rakers, a shorter maxilla, and a shorter intestine. The phylogenetic analysis of mitochondrial genes of all Rastrelliger species also demonstrated that R. chrysozonus forms a well divergent evolutionary lineage, with R. kanagurta being its closest relative. In addition to the redescriptions of R. chrysozonus and R. kanagurta, brief species accounts for R. brachysoma and R. faughni and the key to the four species are provided. Full article
(This article belongs to the Section Marine Diversity)
Show Figures

Figure 1

56 pages, 48151 KiB  
Article
Excitation of ULF, ELF, and VLF Resonator and Waveguide Oscillations in the Earth–Atmosphere–Ionosphere System by Lightning Current Sources Connected with Hunga Tonga Volcano Eruption
by Yuriy G. Rapoport, Volodymyr V. Grimalsky, Andrzej Krankowski, Asen Grytsai, Sergei S. Petrishchevskii, Leszek Błaszkiewicz and Chieh-Hung Chen
Atmosphere 2025, 16(1), 97; https://doi.org/10.3390/atmos16010097 - 16 Jan 2025
Viewed by 1083
Abstract
The simulations presented here are based on the observational data of lightning electric currents associated with the eruption of the Hunga Tonga volcano in January 2022. The response of the lithosphere (Earth)–atmosphere–ionosphere–magnetosphere system to unprecedented lightning currents is theoretically investigated at low frequencies, [...] Read more.
The simulations presented here are based on the observational data of lightning electric currents associated with the eruption of the Hunga Tonga volcano in January 2022. The response of the lithosphere (Earth)–atmosphere–ionosphere–magnetosphere system to unprecedented lightning currents is theoretically investigated at low frequencies, including ultra low frequency (ULF), extremely low frequency (ELF), and very low frequency (VLF) ranges. The electric current source due to lightning near the location of the Hunga Tonga volcano eruption has a wide-band frequency spectrum determined in this paper based on a data-driven approach. The spectrum is monotonous in the VLF range but has many significant details at the lower frequencies (ULF, ELF). The decreasing amplitude tendency is maintained at frequencies exceeding 0.1 Hz. The density of effective lightning current in the ULF range reaches the value of the order of 10−7 A/m2. A combined dynamic/quasi-stationary method has been developed to simulate ULF penetration through the lithosphere (Earth)–atmosphere–ionosphere–magnetosphere system. This method is suitable for the ULF range down to 10−4 Hz. The electromagnetic field is determined from the dynamics in the ionosphere and from a quasi-stationary approach in the atmosphere, considering not only the electric component but also the magnetic one. An analytical/numerical method has been developed to investigate the excitation of the global Schumann resonator and the eigenmodes of the coupled Schumann and ionospheric Alfvén resonators in the ELF range and the eigenmodes of the Earth–ionosphere waveguide in the VLF range. A complex dispersion equation for the corresponding disturbances is derived. It is shown that oscillations at the first resonance frequency in the Schumann resonator can simultaneously cause noticeable excitation of the local ionospheric Alfvén resonator, whose parameters depend on the angle between the geomagnetic field and the vertical direction. VLF propagation is possible over distances of 3000–10,000 km in the waveguide Earth–ionosphere. The results of simulations are compared with the published experimental data. Full article
(This article belongs to the Special Issue Feature Papers in Upper Atmosphere (2nd Edition))
Show Figures

Figure 1

12 pages, 7913 KiB  
Article
SO2 Diffusion Features of the 2022 Hunga Tonga–Hunga Ha’apai Volcanic Eruptions from DSCOVR/EPIC Observations
by Yi Huang and Wentao Duan
Atmosphere 2024, 15(10), 1164; https://doi.org/10.3390/atmos15101164 - 29 Sep 2024
Viewed by 1036
Abstract
Understanding the volcanic SO2 diffusive characteristics can enhance our knowledge of the impact of volcanic eruptions on climate change. In this study, the SO2 diffusion features of the Hunga Tonga–Hunga Ha’apai underwater volcano (HTHH) 2022 eruptions are investigated based on the [...] Read more.
Understanding the volcanic SO2 diffusive characteristics can enhance our knowledge of the impact of volcanic eruptions on climate change. In this study, the SO2 diffusion features of the Hunga Tonga–Hunga Ha’apai underwater volcano (HTHH) 2022 eruptions are investigated based on the Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Imaging Camera (EPIC) dataset, which could provide longer term, more consistent, and higher temporal sampling rate observations to complement current low-orbit satellite-based research. SO2 plume major-direction profile analysis indicates that the SO2 diffusion extent of subaerial eruption initiating at 15:20/13 January 2022 was approximately 1500 km in the Southeast–Northwest major diffusive direction by 20:15/14 January 2022 (about 29 h after the HTHH subaerial eruption). All-direction SO2 plume analysis shows that the HTHH subaerial eruption-emitted SO2 plume could diffuse as far as 6242 km by 02:20/15 January 2022. Furthermore, these two analyses in terms of the HTHH major eruption initiating at 04:00/15 January 2022 imply that HTHH major eruption-emitted SO2 plume could diffuse as far as 8600 km in the Southeast–Northwest major diffusive direction by 02:24/18 January 2022 (about 70 h after the HTHH major eruption). It is also implied that HTHH major eruption-emitted SO2 plume could extend to approximately 14,729 km away from the crater by 13:12/18 January 2022. We believe that these findings could provide certain guidance for volcanic gas estimations, thus helping to deepen our understanding of volcanic impacts on climate change. Full article
(This article belongs to the Special Issue Satellite Remote Sensing Applied in Atmosphere (2nd Edition))
Show Figures

Figure 1

11 pages, 1055 KiB  
Article
Manniosides G-J, New Ursane- and Lupane-Type Saponins from Schefflera mannii (Hook.f.) Harms
by Simionne Lapoupée Kuitcha Tonga, Billy Toussie Tchegnitegni, Xavier Siwe-Noundou, Ulrich Joël Tsopmene, Beaudelaire Kemvoufo Ponou, Jean Paul Dzoyem, Madan Poka, Patrick H. Demana, Léon Azefack Tapondjou, Denzil R. Beukes, Edith M. Antunes and Rémy Bertrand Teponno
Molecules 2024, 29(15), 3447; https://doi.org/10.3390/molecules29153447 - 23 Jul 2024
Cited by 3 | Viewed by 1407
Abstract
Four previously unreported triterpenoid saponins named 3β-hydroxy-23-oxours-12-en-28-oic acid 28-O-β-D-glucopyranosyl ester (mannioside G) (1), 23-O-acetyl-3β-hydroxyurs-12-en-28-oic acid 28-O-β-D-glucopyranosyl ester (mannioside H) (2), ursolic acid 28-O-[α-L-rhamnopyranosyl-(1→4)-β-D-glucopyranosyl-(1→6)-β- [...] Read more.
Four previously unreported triterpenoid saponins named 3β-hydroxy-23-oxours-12-en-28-oic acid 28-O-β-D-glucopyranosyl ester (mannioside G) (1), 23-O-acetyl-3β-hydroxyurs-12-en-28-oic acid 28-O-β-D-glucopyranosyl ester (mannioside H) (2), ursolic acid 28-O-[α-L-rhamnopyranosyl-(1→4)-β-D-glucopyranosyl-(1→6)-β-D-glucopyranosyl] ester (mannioside I) (3), and 3β-hydroxy-23-oxolup-20(29)-en-28-oic acid 28-O-β-D-glucopyranosyl ester (mannioside J) (4) were isolated as minor constituents from the EtOAc soluble fraction of the MeOH extract of the leaves of Schefflera mannii along with the known compounds 23-hydroxyursolic acid 28-O-β-D-glucopyranosyl ester (5), ursolic acid 28-O-β-D-glucopyranosyl ester (6), pulsatimmoside B (7) betulinic acid 28-O-[α-L-rhamnopyranosyl-(1→4)-β-D-glucopyranosyl-(1→6)-β-D-glucopyranosyl] ester (8), 23-hydroxy-3-oxo-urs-12-en-28-oic acid (9), hederagenin (10), ursolic acid (11), betulinic acid (12), and lupeol (13). Their structures were elucidated by a combination of 1D and 2D NMR analysis and mass spectrometry. The MeOH extract, the EtOAc and n-BuOH fractions, and some of the isolated compounds were evaluated for their antibacterial activity against four bacteria: Staphylococcus aureus ATCC1026, Staphylococcus epidermidis ATCC 35984, Escherichia coli ATCC10536, and Klepsiella pnemoniae ATCC13882. They were also screened for their antioxidant properties, but no significant results were obtained. Full article
Show Figures

Figure 1

16 pages, 18068 KiB  
Article
Multi-Wave Structures of Traveling Ionospheric Disturbances Associated with the 2022 Tonga Volcanic Eruptions in the New Zealand and Australia Regions
by Xiaolin Li, Feng Ding, Bo Xiong, Ge Chen, Tian Mao, Qian Song and Changhao Yu
Remote Sens. 2024, 16(14), 2668; https://doi.org/10.3390/rs16142668 - 21 Jul 2024
Cited by 1 | Viewed by 1343
Abstract
Using dense global navigation satellite system data and brightness temperature data across the New Zealand and Australia regions, we tracked the propagation of traveling ionospheric disturbances (TIDs) associated with the 15 January 2022 Tonga volcanic eruptions. We identified two shock wave-related TIDs and [...] Read more.
Using dense global navigation satellite system data and brightness temperature data across the New Zealand and Australia regions, we tracked the propagation of traveling ionospheric disturbances (TIDs) associated with the 15 January 2022 Tonga volcanic eruptions. We identified two shock wave-related TIDs and two Lamb wave-related TIDs following the eruptions. The two shock wave-related TIDs, propagating with velocities of 724–750 and 445–471 m/s, respectively, were observed around New Zealand and Australia within a distance of 3500–6500 km from the eruptive center. These shock wave-related TIDs suffered severe attenuation during the propagation and disappeared more than 6500 km from the eruptive center. Based on the TEC data from the nearest ground-based receivers, we estimated the onset times of two main volcanic explosions at 04:20:54 UT ± 116 s and 04:24:37 UT ± 141 s, respectively. The two shock wave-related TIDs were most likely generated by these two main volcanic eruptions. The two Lamb wave-related TIDs propagated with velocities of 300–370 and 250 m/s in the near-field region. The Lamb wave-related TIDs experienced minimal attenuation during their long-distance propagation, with only a 0.17% decrease observed in the relative amplitudes of the Lamb wave-related TIDs from the near-field to far-field regions. Full article
(This article belongs to the Special Issue Application of GNSS Remote Sensing in Ionosphere Monitoring)
Show Figures

Figure 1

15 pages, 50410 KiB  
Article
Hydroacoustic Monitoring of Mayotte Submarine Volcano during Its Eruptive Phase
by Aude Lavayssière, Sara Bazin and Jean-Yves Royer
Geosciences 2024, 14(6), 170; https://doi.org/10.3390/geosciences14060170 - 17 Jun 2024
Cited by 4 | Viewed by 2627
Abstract
Submarine volcanoes are more challenging to monitor than subaerial volcanoes. Yet, the large eruption of the Hunga Tonga-Hunga Ha’apai volcano in the Tonga archipelago in 2022 was a reminder of their hazardous nature and hence demonstrated the need to study them. In October [...] Read more.
Submarine volcanoes are more challenging to monitor than subaerial volcanoes. Yet, the large eruption of the Hunga Tonga-Hunga Ha’apai volcano in the Tonga archipelago in 2022 was a reminder of their hazardous nature and hence demonstrated the need to study them. In October 2020, four autonomous hydrophones were moored in the sound fixing and ranging channel 50 km offshore Mayotte Island, in the North Mozambique Channel, to monitor the Fani Maoré 2018–2020 submarine eruption. Between their deployment and July 2022, this network of hydrophones, named MAHY, recorded sounds generated by the recent volcanic activity, along with earthquakes, submarine landslides, marine mammals calls, and marine traffic. Among the sounds generated by the volcanic activity, impulsive signals have been evidenced and interpreted as proxy for lava flow emplacements. The characteristics and the spatio-temporal evolution of these hydroacoustic signals allowed the estimation of effusion and flow rates, key parameters for volcano monitoring. These sounds are related to the non-explosive quenching of pillow lavas due to the rapid heat transfer between hot lava and cold seawater, with this process releasing an energy equivalent to an airgun source as used for active seismic exploration. Volcano observatories could hence use autonomous hydrophones in the water column to detect and monitor active submarine eruptions in the absence of regular on-site seafloor survey. Full article
(This article belongs to the Section Geophysics)
Show Figures

Figure 1

10 pages, 2002 KiB  
Review
The Impact of the Hunga Tonga–Hunga Ha’apai Volcanic Eruption on the Stratospheric Environment
by Qian Sun, Taojun Lu, Dan Li and Jingyuan Xu
Atmosphere 2024, 15(4), 483; https://doi.org/10.3390/atmos15040483 - 13 Apr 2024
Cited by 3 | Viewed by 2849
Abstract
In this study, an overview of two years of research findings concerning the 2022 Hunga Tonga–Hunga Ha’apai (HTHH) volcanic eruption in the stratospheric environment is provided, focusing on water vapor, aerosols, and ozone. Additionally, the potential impacts of these changes on aviation equipment [...] Read more.
In this study, an overview of two years of research findings concerning the 2022 Hunga Tonga–Hunga Ha’apai (HTHH) volcanic eruption in the stratospheric environment is provided, focusing on water vapor, aerosols, and ozone. Additionally, the potential impacts of these changes on aviation equipment materials are discussed. The HTHH volcanic eruption released a large amount of particles (e.g., ash and ice) and gases (e.g., H2O, SO2, and HCl), significantly affecting the redistribution of stratospheric water vapor and aerosols. Stratospheric water vapor increased by approximately 140–150 Tg (8–10%), with a concentration peak observed in the height range of 22.2–27 km (38–17 hPa). Satellite measurements indicate that the HTHH volcano injected approximately 0.2–0.5 Tg of sulfur dioxide into the stratosphere, which was partially converted into sulfate aerosols. In-situ observations revealed that the volcanic aerosols exhibit hygroscopic characteristics, with particle sizes ranging from 0.22–0.42 μm under background conditions to 0.42–1.27 μm. The moist stratospheric conditions increased the aerosol surface area, inducing heterogeneous chlorine chemical reactions on the aerosol surface, resulting in stratospheric ozone depletion in the HTHH plume within one week. In addition, atmospheric disturbances and ionospheric disruptions triggered by volcanic eruptions may adversely affect aircraft and communication systems. Further research is required to understand the evolution of volcanic aerosols and the impact of volcanic activity on aviation equipment materials. Full article
(This article belongs to the Section Meteorology)
Show Figures

Figure 1

13 pages, 4055 KiB  
Article
A Review of Historical Volcanic Tsunamis: A New Scheme for a Volcanic Tsunami Monitoring System
by Tingting Fan, Yuchen Wang, Zhiguo Xu, Lining Sun, Peitao Wang and Jingming Hou
J. Mar. Sci. Eng. 2024, 12(2), 278; https://doi.org/10.3390/jmse12020278 - 3 Feb 2024
Cited by 2 | Viewed by 3680
Abstract
Tsunami monitoring and early warning systems are mainly established to deal with seismogenic tsunamis generated by sudden seafloor fault displacement. However, a global tsunami triggered by the 2022 Tonga volcanic eruption promoted the need for tsunami early warning and hazard mitigation of non-seismogenic [...] Read more.
Tsunami monitoring and early warning systems are mainly established to deal with seismogenic tsunamis generated by sudden seafloor fault displacement. However, a global tsunami triggered by the 2022 Tonga volcanic eruption promoted the need for tsunami early warning and hazard mitigation of non-seismogenic tsunamis in coastal countries. This paper studied the spatiotemporal distribution characteristics of historical volcanic tsunamis and summarized high-risk areas of volcanic tsunamis. The circum southwestern Pacific volcanic zone, including the Sunda volcanic belt and the Indo-Australian plate, is a concentrated area of active volcanoes and major volcanic tsunamis. In addition, the challenges associated with adapting seismogenic tsunami techniques for use in the context of volcanic tsunamis were elucidated. At the same time, based on historical records and post-disaster surveys, typical historical volcanic tsunami events and involved mechanisms were summarized. The results show that a majority of volcanic tsunamis may involve multiple generation mechanisms, and some mechanisms show geographical distribution characteristics. The complexity of volcanic tsunami mechanisms poses challenges to tsunami early warning by measuring tsunami sources to evaluate the possible extent of impact, or using numerical modeling to simulate the process of a tsunami. Therefore, a concise overview of the lessons learned and the current status of early warning systems for volcanic tsunamis was provided. Finally, a conceptual scheme of monitoring systems for volcanic tsunamis based on historical volcanoes, real-time volcanic eruption information and sea level data, as well as remote sensing images, was presented. Full article
Show Figures

Figure 1

Back to TopTop