Internal Solitary Waves in the Andaman Sea: New Insights from SAR Imagery
The Andaman Sea in the Indian Ocean has been a classical study region for Internal Solitary Waves (ISWs) for several decades. Papers such as Osborne and Burch (1980) usually describe mode-1 packets of ISWs propagating eastwards, separated by distances of around 100 km. In this paper, we report on sh...
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| Format: | Article |
| Language: | English |
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MDPI AG
2018-06-01
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| Series: | Remote Sensing |
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| Online Access: | http://www.mdpi.com/2072-4292/10/6/861 |
| _version_ | 1828882118172737536 |
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| author | Jorge M. Magalhaes José C. B. da Silva |
| author_facet | Jorge M. Magalhaes José C. B. da Silva |
| author_sort | Jorge M. Magalhaes |
| collection | DOAJ |
| description | The Andaman Sea in the Indian Ocean has been a classical study region for Internal Solitary Waves (ISWs) for several decades. Papers such as Osborne and Burch (1980) usually describe mode-1 packets of ISWs propagating eastwards, separated by distances of around 100 km. In this paper, we report on shorter period solitary-like waves that are consistent with a mode-2 vertical structure, which are observed along the Ten Degree Channel, and propagate side-by-side the usual large mode-1 solitary wave packets. The mode-2 waves are identified in TerraSAR-X images because of their distinct surface signatures, which are reversed when compared to those that are typical of mode-1 ISWs in the ocean. These newly observed regularly-spaced packets of ISW-like waves are characterized by average separations of roughly 30 km, which are far from the nominal mode-1 or even the mode-2 internal tidal wavelengths. On some occasions, five consecutive and regularly spaced mode-2 ISW-like wave envelopes were observed simultaneously in the same TerraSAR-X image. This fact points to a tidal generation mechanism somewhere in the west shallow ridges, south of the Nicobar Islands. Furthermore, it implies that unusually long-lived mode-2 waves can be found throughout the majority of the fortnightly tidal cycle. Ray tracing techniques are used to identify internal tidal beams as a possible explanation for the generation of the mode-2 solitary-like waves when the internal tidal beam interacts with the ocean pycnocline. Linear theory suggests that resonant coupling with long internal waves of higher-mode could explain the longevity of the mode-2 waves, which propagate for more than 100 km. Owing to their small-scale dimensions, the mode-2 waves may have been overlooked in previous remote sensing images. The enhanced radiometric resolution of the TerraSAR-X, alongside its wide coverage and detailed spatial resolutions, make it an ideal observational tool for the present study. |
| first_indexed | 2024-12-13T10:22:43Z |
| format | Article |
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| institution | Directory Open Access Journal |
| issn | 2072-4292 |
| language | English |
| last_indexed | 2024-12-13T10:22:43Z |
| publishDate | 2018-06-01 |
| publisher | MDPI AG |
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| series | Remote Sensing |
| spelling | doaj.art-1f57f7bfeac24365a5f8ca51a9f42dcb2022-12-21T23:51:09ZengMDPI AGRemote Sensing2072-42922018-06-0110686110.3390/rs10060861rs10060861Internal Solitary Waves in the Andaman Sea: New Insights from SAR ImageryJorge M. Magalhaes0José C. B. da Silva1Department of Geosciences, Environment and Spatial Planning (DGAOT), Faculty of Sciences, University of Porto, 4169-007 Porto, PortugalDepartment of Geosciences, Environment and Spatial Planning (DGAOT), Faculty of Sciences, University of Porto, 4169-007 Porto, PortugalThe Andaman Sea in the Indian Ocean has been a classical study region for Internal Solitary Waves (ISWs) for several decades. Papers such as Osborne and Burch (1980) usually describe mode-1 packets of ISWs propagating eastwards, separated by distances of around 100 km. In this paper, we report on shorter period solitary-like waves that are consistent with a mode-2 vertical structure, which are observed along the Ten Degree Channel, and propagate side-by-side the usual large mode-1 solitary wave packets. The mode-2 waves are identified in TerraSAR-X images because of their distinct surface signatures, which are reversed when compared to those that are typical of mode-1 ISWs in the ocean. These newly observed regularly-spaced packets of ISW-like waves are characterized by average separations of roughly 30 km, which are far from the nominal mode-1 or even the mode-2 internal tidal wavelengths. On some occasions, five consecutive and regularly spaced mode-2 ISW-like wave envelopes were observed simultaneously in the same TerraSAR-X image. This fact points to a tidal generation mechanism somewhere in the west shallow ridges, south of the Nicobar Islands. Furthermore, it implies that unusually long-lived mode-2 waves can be found throughout the majority of the fortnightly tidal cycle. Ray tracing techniques are used to identify internal tidal beams as a possible explanation for the generation of the mode-2 solitary-like waves when the internal tidal beam interacts with the ocean pycnocline. Linear theory suggests that resonant coupling with long internal waves of higher-mode could explain the longevity of the mode-2 waves, which propagate for more than 100 km. Owing to their small-scale dimensions, the mode-2 waves may have been overlooked in previous remote sensing images. The enhanced radiometric resolution of the TerraSAR-X, alongside its wide coverage and detailed spatial resolutions, make it an ideal observational tool for the present study.http://www.mdpi.com/2072-4292/10/6/861SARinternal wavesAndaman Sea |
| spellingShingle | Jorge M. Magalhaes José C. B. da Silva Internal Solitary Waves in the Andaman Sea: New Insights from SAR Imagery Remote Sensing SAR internal waves Andaman Sea |
| title | Internal Solitary Waves in the Andaman Sea: New Insights from SAR Imagery |
| title_full | Internal Solitary Waves in the Andaman Sea: New Insights from SAR Imagery |
| title_fullStr | Internal Solitary Waves in the Andaman Sea: New Insights from SAR Imagery |
| title_full_unstemmed | Internal Solitary Waves in the Andaman Sea: New Insights from SAR Imagery |
| title_short | Internal Solitary Waves in the Andaman Sea: New Insights from SAR Imagery |
| title_sort | internal solitary waves in the andaman sea new insights from sar imagery |
| topic | SAR internal waves Andaman Sea |
| url | http://www.mdpi.com/2072-4292/10/6/861 |
| work_keys_str_mv | AT jorgemmagalhaes internalsolitarywavesintheandamanseanewinsightsfromsarimagery AT josecbdasilva internalsolitarywavesintheandamanseanewinsightsfromsarimagery |