Cyclone Signatures in the South-West Indian Ocean from Two Decades of Microseismic Noise

Tropical Cyclones (TC) represent the most destructive natural disaster affecting the islands in the South-West Indian Ocean (SWIO) each year. Monitoring ocean activity is therefore of primary importance to secure lands, infrastructures and peoples, but the little number of oceanographic instruments makes it challenging, particularly in real time. Long-term seismological records provide a way to decipher and quantify the past cyclonic activity by analyzing microseisms, seismic waves generated by the ocean activity and propagating through the solid Earth. In the present study, we analyze this microseismic noise generated by cyclones that develop in the SWIO basin between 1999 and 2020, using broadband seismic stations in La Réunion. The power spectral density (PSD), together with the root mean square (RMS) analyses of continuous seismic data recorded by the permanent Geoscope RER seismic station, indicate the intensification of the microseismic noise amplitude in proportion to the cyclone intensity. Thus, we establish a relationship between the cyclone intensity and the PSD of the Secondary Microseisms (SM) in frequency band ∼0.14 to 0.25 Hz (4 to 7 s period). The Pearson coefficient between the observed and estimated TC intensity are >0.8 in the presence of a cyclone with mean wind speeds >75 km/h and with a seismic station distance-to-storm center D < 3000 km. A polarization analysis in the time and frequency domains allows the retrieval of the backazimuth of the SM sources during isolated cyclone events and well-polarized signal, i.e., CpH > 0.6. We also analyzed the RMS of the Primary Microseisms (PM frequency between ∼0.05 and 0.1 Hz, i.e., for 10 to 20 s period) for cyclones passing nearby La Réunion (D < 500 km), using the available temporary and permanent broadband seismic stations. We also found high correlation coefficients (>0.8) between the PM amplitude and the local wave height issued from the global hindcast model demonstrating that the PM amplitude can be used as a robust proxy to perform a real-time wave-height monitoring in the neighboring ocean. Transfer functions are calculated for several cyclones to infer wave height from the seismic noise amplitude recorded on land. From the analysis of two decades of data, our results suggest that it is possible to quantify the past ocean activity for as long as continuous seismic archives are available, emphasizing microseismic noise as a key observable for quantifying and understanding the climate change.

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Latitudinal and seasonal variability of gravity-wave energy in the South-West Indian Ocean

Annales Geophysicae ◽

10.5194/angeo-25-2479-2007 ◽

2007 ◽

Vol 25 (12) ◽

pp. 2479-2485 ◽

Cited By ~ 5

Author(s):

F. Chane-Ming ◽

D. Faduilhe ◽

J. Leveau

Keyword(s):

Energy Density ◽

Indian Ocean ◽

Total Energy ◽

Seasonal Variability ◽

La Réunion ◽

Raman Lidar ◽

Total Energy Density ◽

South West Indian Ocean ◽

South West ◽

West Indian Ocean

Abstract. Vertical temperature profiles obtained by radiosonde and Raman lidar measurements are used to investigate a climatology of total energy density of gravity waves (GW) in the Upper Troposphere (UT) and the Lower Stratosphere (LS) from 1992 to 2004 above Mahé (4° S, 55° E), Tromelin (15° S, 54° E) and La Réunion (21° S, 55° E) located in the tropical South-West Indian Ocean. The commonly used spectral index value (p≈5/3) of the intrinsic frequency spectrum is used for calculating estimated total energy density in the UT and LS. Estimated total energy density provides good estimation of total energy density in the LS but underestimates total energy density by one half in the UT above Mahé and Tromelin probably due to the activity of near-inertial frequency waves. Estimated total energy density reveals a strong seasonal variability as a function of latitude and convection as an evident active source of GW activity in the LS in austral summer. Above La Réunion, a semi-annual GW activity is observed in the LS with the signature of the subtropical barrier in the UT. Moreover, radiosondes and Raman lidar provide consistent GW surveys in the UT/LS at heights<23 km above La Réunion.

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HTLV-I infection in the South West Indian Ocean islands, particularly in La Réunion and the Seychelles

Bulletin de la Société de pathologie exotique ◽

10.1007/s13149-013-0314-9 ◽

2013 ◽

Vol 106 (4) ◽

pp. 248-253 ◽

Cited By ~ 1

Author(s):

P. Aubry ◽

P. Bovet ◽

D. Vitrac ◽

F. Schooneman ◽

J. Hollanda ◽

...

Keyword(s):

Indian Ocean ◽

West Indian ◽

La Réunion ◽

The South ◽

South West Indian Ocean ◽

South West ◽

West Indian Ocean ◽

Ocean Islands

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Population Structure of the South West Indian Ocean Islands: Implications for Precision Medicine

Frontiers in Genetics ◽

10.3389/fgene.2021.758563 ◽

2021 ◽

Vol 12 ◽

Author(s):

Anisah W. Ghoorah ◽

Toto Chaplain ◽

Rakotoarivony Rindra ◽

Smita Goorah ◽

Ganessen Chinien ◽

...

Keyword(s):

Health Care ◽

Indian Ocean ◽

Precision Medicine ◽

Genomic Medicine ◽

La Réunion ◽

The South ◽

South West Indian Ocean ◽

South West ◽

The World ◽

West Indian Ocean

Precision medicine has brought new hopes for patients around the world with the applications of novel technologies for understanding genetics of complex diseases and their translation into clinical services. Such applications however require a foundation of skills, knowledge and infrastructure to translate genetics for health care. The crucial element is no doubt the availability of genomics data for the target populations, which is seriously lacking for most parts of Africa. We discuss here why it is vital to prioritize genomics data for the South West Indian Ocean region where a mosaic of ethnicities co-exist. The islands of the SWIO, which comprise Madagascar, La Reunion, Mauritius, Seychelles and Comoros, have been the scene for major explorations and trade since the 17th century being on the route to Asia. This part of the world has lived through active passage of slaves from East Africa to Arabia and further. Today’s demography of the islands is a diverse mix of ancestries including European, African and Asian. The extent of admixtures has yet to be resolved. Except for a few studies in Madagascar, there is very little published data on human genetics for these countries. Isolation and small population sizes have likely resulted in reduced genetic variation and possible founder effects. There is a significant prevalence of diabetes, particularly in individuals of Indian descent, while breast and prostate cancers are on the rise. The island of La Reunion is a French overseas territory with a high standard of health care and close ties to Mauritius. Its demography is comparable to that of Mauritius but with a predominantly mixed population and a smaller proportion of people of Indian descent. On the other hand, Madagascar’s African descendants inhabit mostly the lower coastal zones of the West and South regions, while the upper highlands are occupied by peoples of mixed African-Indonesian ancestries. Historical records confirm the Austronesian contribution to the Madagascar genomes. With the rapid progress in genomic medicine, there is a growing demand for sequencing services in the clinical settings to explore the incidence of variants in candidate disease genes and other markers. Genome sequence data has become a priority in order to understand the population sub-structures and to identify specific pathogenic variants among the different groups of inhabitants on the islands. Genomic data is increasingly being used to advise families at risk and propose diagnostic screening measures to enhance the success of therapies. This paper discusses the complexity of the islands’ populations and argues for the needs for genotyping and understanding the genetic factors associated with disease risks. The benefits to patients and improvement in health services through a concerted regional effort are depicted. Some private patients are having recourse to external facilities for molecular profiling with no return of data for research. Evidence of disease variants through sequencing represents a valuable source of medical data that can guide policy decisions at the national level. There are presently no such records for future implementation of strategies for genomic medicine.

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ReNovRisk: a multidisciplinary programme to study the cyclonic risks in the South-West Indian Ocean

Natural Hazards ◽

10.1007/s11069-021-04624-w ◽

2021 ◽

Author(s):

Pierre Tulet ◽

Bertrand Aunay ◽

Guilhem Barruol ◽

Christelle Barthe ◽

Remi Belon ◽

...

Keyword(s):

Indian Ocean ◽

West Indian ◽

Ocean Basin ◽

Transport Processes ◽

The South ◽

South West Indian Ocean ◽

South West ◽

The Face ◽

West Indian Ocean ◽

Solid Transport

AbstractToday, resilience in the face of cyclone risks has become a crucial issue for our societies. With climate change, the risk of strong cyclones occurring is expected to intensify significantly and to impact the way of life in many countries. To meet some of the associated challenges, the interdisciplinary ReNovRisk programme aims to study tropical cyclones and their impacts on the South-West Indian Ocean basin. This article is a presentation of the ReNovRisk programme, which is divided into four areas: study of cyclonic hazards, study of erosion and solid transport processes, study of water transfer and swell impacts on the coast, and studies of socio-economic impacts. The first transdisciplinary results of the programme are presented together with the database, which will be open access from mid-2021.

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Diversity and Geographical Structure of Xanthomonas citri pv. citri on Citrus in the South West Indian Ocean Region

Microorganisms ◽

10.3390/microorganisms9050945 ◽

2021 ◽

Vol 9 (5) ◽

pp. 945

Author(s):

Olivier Pruvost ◽

Damien Richard ◽

Karine Boyer ◽

Stéphanie Javegny ◽

Claudine Boyer ◽

...

Keyword(s):

Indian Ocean ◽

Host Range ◽

Disease Surveillance ◽

West Indian ◽

Copper Resistance ◽

The South ◽

South West Indian Ocean ◽

South West ◽

Strain Collection ◽

West Indian Ocean

A thorough knowledge of genotypic and phenotypic variations (e.g., virulence, resistance to antimicrobial compounds) in bacteria causing plant disease outbreaks is key for optimizing disease surveillance and management. Using a comprehensive strain collection, tandem repeat-based genotyping techniques and pathogenicity assays, we characterized the diversity of X. citri pv. citri from the South West Indian Ocean (SWIO) region. Most strains belonged to the prevalent lineage 1 pathotype A that has a wide host range among rutaceous species. We report the first occurrence of genetically unrelated, nonepidemic lineage 4 pathotype A* (strains with a host range restricted to Mexican lime and related species) in Mauritius, Moheli and Réunion. Microsatellite data revealed that strains from the Seychelles were diverse, grouped in three different clusters not detected in the Comoros and the Mascarenes. Pathogenicity data suggested a higher aggressiveness of strains of one of these clusters on citron (Citrus medica). With the noticeable exception of the Comoros, there was no sign of recent interisland movement of the pathogen. Consistent with this finding, the copL gene, a marker for the plasmid-borne copLAB copper resistance that was recently identified in Réunion, was not detected in 568 strains from any islands in the SWIO region apart from Réunion.

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