Internal Solitary Waves

MODIS/Terra/Aqua satellite sensors allowed us to obtain 250-m resolution true-color images of internal solitary waves during sun glint conditions. These internal solitons packets were generated at 8° 50.9’ N and 92° 49.3’ E, about 4 km Northwest off Batti Malv Island of the Nicobar Archipelago in the Andaman Sea during a 3-day period of strong semidiurnal surface tides.  About 20 km from the origin, the packet consists of 6 to 7 internal solitary waves, but 100 km farther from the origin position the number of waves in each packet doubled. The waves were ranked in amplitude order and their intra wave distance decreased from 7 km to 2.5 km.  These packets moved West (270°) and crossed 1270 km in about 5.4 days to reach the entrance of Trincomalee Bay, Sri Lanka. The average inter packet distance is 122 km, suggesting that the packets were phase locked with the internal tide.  Offshore of Trincomalee Bay entrance a nonlinear internal wave field was observed.  The intra wave distance was 2.5 to 5 km.  A nonlinear internal wave can excite a 42-minute coastal seiche in the Bay with an amplitude of 7 cm. Using a novel approach called seichelogía we estimated that the amplitude of the nonlinear internal wave was 8 m.

El Mar Caribe no es tan sereno y apacible como lo imaginan muchas personas. En su interior ocurren fenómenos físicos que transportan y disipan la energía de las mareas, como lo es, la ola solitaria interna o un grupo de ellas, a las que llamamos solitones internos.  Estas olas de gran amplitud se mueven por debajo de la superficie del mar, en la interface entre aguas de diferente densidad entre 500 a 600 m de profundidad. La ola puede alcanzar en algunos casos una amplitud de 90 m. En la mitad sur del Caribe Oriental, cuando se encuentra a unos 100 km de su punto de origen, el frente de la ola pueda abarcar una longitud de 250 km.  Se originan en la Cresta Submarina de Aves, un umbral submarino que se levanta bruscamente desde su base a 3000 m de profundidad hasta alcanzar los 500 m de profundidad.  Esta presentación esta dirigida a estudiantes de escuela superior y público general.

An in-house fully nonlinear, nonhydrostatic numerical code is utilized for simulations of internal solitary waves (ISWs) generated by tidal flow over a Gaussian sill topography. A complete, rigorous theoretical framework is then adopted for the energetics analysis of these ISWs. It is found that ISWs contain most of the baroclinic energy in the internal wave field. The nonhydrostatic energy flux is in opposite direction to the hydrostatic and nonlinear fluxes. For fixed tidal excursion parameter ( ), the nonlinear portion of the total baroclinic flux decreases as the slope parameter ( ) increases. In addition, the ISW energy, energy flux and barotropic-to-baroclinic energy conversion rate all peak when the bottom topography is critical (  1). For typical ISWs generated in the Luzon Strait, 87.9% of the total barotropic input energy is converted into baroclinic energy, and the other part of the energy is used for barotropic dissipation. 63.7% of the converted baroclinic energy is radiated far away and the remaining part of the baroclinic energy is dissipated through local mixing. When compared to the energy budget of linear internal tides, the percentages of the energy that are converted and radiated decrease, or equivalently, the percentages of the energy that are used for barotropic and baroclinic dissipations increase. Thus, the emergence of ISWs can effectively enhance both barotropic and baroclinic dissipations.

Keywords: internal solitary waves, baroclinic energy, energy flux, energy conversion, dissipation

Recently, satellite images of MODIS/Terra/Aqua sensor and photos taken by NASA astronauts from the ISS (International Space Station) during fortuitous sunglint conditions in the waters of the Mona Passage, reveal the surface signal associated with a packet of nonlinear internal waves, called solitons or solibore, generated 10 NM due SW of Banco Engaño, in the western margin of the Mona Passage, east of the Dominican Republic. Specifically, the generation area is located near the 18.439 N 68.166 W position, about 12.48 NM of Cap Cana Marina, True Heading 107.30 °. Three different MODIS images show the packets moving south and southwest. Two of the images, corresponding to 2011 and 2013, indicate the same point of origin. The three MODIS images correspond to the following dates: 18-MAY-2011 15:15 UTC, 23-MAY-2013 15:20 UTC, 25-MAY-2013 15:05 UTC. The photo taken from the ISS (International Space Station) on day JUN-14-2010 14:23 UTC and the image of MODIS/Aqua on AGO-01-2013 17:45 UTC shows a generation point of the packet inside a circle of about 6 NM around Banco Engaño (POS 18.55 N 68.03 W). These packets move north unlike previous events.

Un evento extraordinario de seiches costeros grandes y extremos fue registrado por el mareógrafo de Isla Magueyes - en el suroeste de Puerto Rico - durante 10 días consecutivos, además se registraron cuatro seiches extremos en un periodo de cuatro días, algo nunca antes visto en el registro de eventos que abarca del 1995-2019. Condiciones astronómicas favorables (sizigia, perigeo y declinación lunar cero) generaron corrientes semidiurnas fuertes en el Canal de St. Lucia y Pasaje de St. Vincent, que a su vez generaron una marea interna semidiurna que se propagó hacia el oeste a lo largo de un corredor (14° N a 14.8° N, -62° O a -63.5° O), donde enfrentó un componente zonal U hacia el Este con una magnitud de hasta 0.4 m/s. Esta corriente de trasfondo dentro del corredor fue opuesta a la propagación de la marea interna semidiurna durante una semana completa, facilitando así su evolución no-lineal, y ésta al pasar sobre la Cresta Submarina de Aves generó olas solitarias internas de tamaño mayor y con separación de alrededor de 10 km. Revisando unos 15 eventos de seiches costeros extremos registrados en Isla Magueyes desde el 1995 hasta el 2019, hemos encontrado que en 14 de éstos (93%), el componente zonal U es positivo dentro del corredor de la marea interna semidiurna. Por el contrario, cuando el componente zonal U es negativo, la mayoría de las veces no suelen ocurrir seiches costeros extremos. Por lo anterior, podemos concluir que la dirección-magnitud y duración del componente zonal U de la corriente de trasfondo dentro del corredor es un factor necesario, en adición a los astronómicos, para determinar la amplitud y extensión del campo de olas solitarias internas de amplitud mayor, que se propagan hacia el Mar Caribe Nororiental y que terminarán excitando seiches costeros extremos en Isla Magueyes, en el suroeste de Puerto Rico.

250-m resolution MODIS images acquired by the Earth Observing System Terra and Aqua Satellites during sunglint conditions allowed us to survey high-frequency nonlinear internal solitary wave occurrences in the Indian Ocean. These images clearly show packets of internal solitary waves (ISWs) generated in the Nicobar Islands passages during the extraordinary coincidence of the following astronomical factors: perigee, syzygy, zero lunar declination, spring equinox, longitude of the lunar node equal to 180°. The relatively fast ISWs packets (2.7 m/s) propagated southwest (245°) and crossed 2420 km of Indian Ocean in about 10.5 days to excite coastal seiches in the waters of the Addu Atoll-the southernmost atoll of the Maldives Islands-located near the Equator. Satellite images and sea level data evidence the concurrence of these two physical phenomena. Our finding sustains that ISWs can travel very long distances and impinge on distant archipelagos far from their generation region.

La seichelogía nos permite medir propiedades del interior del océano mediante un cuidadoso análisis de la señal del seiche costero. Resultados exitosos en el Mar Caribe sugieren que este método puede aplicarse en el Océano Índico Tropical. En este documento exploramos esa posibilidad

Este estudio demuestra que los eventos de seiches costeros extremos en Isla Magueyes, en el suroeste de Puerto Rico son excitados por una actividad intensa de olas solitarias internas de tamaño mayor que se generan en la Cresta Submarina de Aves luego de la evolución no-lineal de una marea interna semidiurna M2 que se enfrenta a una corriente zonal positiva. Condiciones astronómicas favorables (coincidencia de sizigia, perigeo y cruce del Ecuador Celeste) no son suficientes para generar una actividad mayor. Es necesaria la presencia de una corriente contraria a la propagación de la marea interna semidiurna. Esta corriente se manifiesta cuando hay vorticidad ciclónica entre la isla de Martinique y la Cresta Submarina de Aves. El lado sur del vórtice ciclónico genera la corriente zonal positiva dentro del corredor de la marea interna semidiurna. Presentamos tres eventos concretos que cumplen esa misma condición oceanográfica.

Large amplitude (~100 m) and fast (3 m/s) mode-1 internal solitary wave packets generated by the interaction of strong tidal currents with a central sill (12.61°S, 60.84°E) in the Mascarene Plateau during perigean-spring tides (28-SEP-2015; 14-NOV-2016), propagated northwestward and southeastward hundred of kilometers before impinged on Agalega (2 days later) and Rodrigues islands (3 days later), respectively. The arrival of the ISWs packets coincided with a simultaneous increase in coastal seiche activity at both islands.

G1SST images clearly show the enhancement of a colder (23.5 °C) water patch during strong tidal forcing, between 29-SEP and 3-OCT 2015. The patch is located just west of a warmer water plume that exits the Sape Strait producing a local surface temperature gradient in the Sumba Strait. Concurrent ISWs are seen departing from the same location and crossing the Sumba Strait. Both ISWs generation and cold patch enhancement by tidal mixing occurred in the same location and on the same day. Strong internal tide activity could be linked to both phenomena.

MODIS true-color images during fortuitous sunglint conditions allows easy detection of internal solitary waves (ISWs) packets. This document catalogs about fifteen 250m-resolution true color MODIS images of ISWs in the Sumba Strait mostly during strong semidiurnal tidal forcing. Two periods of strong semidiurnal forcing occurred between March 19-24, 2015 and September 27-October 02, 2015. The 18.61 year lunar nodal precession has a large effect on the Moon’s declination (its celestial latitude), minimizing the declination when N = 180° (23° 27′ − 5°9′ = 18°18′). The low lunar declination increases the semidiurnal form of the tides. In addition, these two time periods are near the equinoxial tides then increasing the semidiurnal form of the tides. More important, on March 20 and September 27 the perigean and spring tides coincide. The sum of all the above factors explains why during these two time periods in 2015 we expected to see a strong semidiurnal forcing. Strong semidiurnal tidal currents are necessary to generate large amplitude ISW’s.

Based on 12 years (2000–2011) of Moderate Resolution Imaging Spectroradiometer (MODIS) true-colour images, statistical characteristics of internal solitary waves (ISWs) in the southern Taiwan Strait were studied. Two types of ISWs with a distinct scale of wave crest length and geographic distributions were identified: Type-I waves have larger wave crest lengths and span a large area from the southern Taiwan Strait to the northern South China Sea, while Type-II waves have smaller wave crest lengths and appear only at the southeastern corner of the Taiwan Strait. Further analyses based on an empirical model of ISW propagation and on the calculations of the depth-integrated internal tide-generating body force suggested that Type-I waves mainly originate from the Luzon Strait, while Type-II waves are locally generated at the shelf break in the southeastern corner of the Taiwan Strait.