Jorge Manuel Magalhães

University of Porto | UP · DGAOT

The Amazon shelf is a key region for intense internal tides (ITs) and nonlinear internal solitary wave (ISWs) generation associated with them. The region shows well-marked seasonal variability (from March to July, MAMJJ, and from August to December, ASOND) of the circulation and stratification, which can both induce changes in the ISW physical char...

Location of the leading wave of mode-1 and mode-2 internal solitary wave (ISW) packet off the Amazon shelf from 2005 to 2021 visible in MODIS-Terra images. Each mapped ISW signature is associated with one ID number and has 12 points of latitude and longitude to describe the location of its crest.

This study focuses on the Amazon ISWs occurrence, their velocity/wavelength, and variability at seasonal cycles. The analysis is based on a data set composed of 71 MODIS/TERRA images, where more than 250 internal solitary wave (ISW) signatures were identified in the sun glint area. ISWs packets separated by typical mode-1 and mode-2 internal tides...

Satellite altimetry has been providing a continuous record of ocean measurements with numerous applications across the entire range of ocean sciences. A reference orbit has been used since 1992 with TOPEX/Poseidon, which was repeated in the Jason missions, and in the newly launched Sentinel-6 Michael Freilich (in November 2020) to continually monit...

Timescales in the ocean can range from the transient turbulence to the long-term climate scales. Quantifying its changes involves establishing meaningful background states, but that can be challenging if an extensive array of wave phenomena is masking the ocean's variability. Internal Waves (IWs) are a fundamental part of these wave phenomena, whic...

We address surface wave breaking caused by oceanic Internal Solitary Waves (ISWs) and how ISWs are manifested in the SAR altimeter onboard Sentinel-3A and -3B satellites by means of their effects in Significant Wave Height (SWH). Two different regions of the ocean are selected, namely the tropical Atlantic Ocean off the Amazon shelf and the Banda S...

Breaking surface waves play a key role in the exchange of momentum, heat, and gases between the atmosphere and the ocean. Waves break at the ocean’s surface at high or medium wind speeds or in the absence of wind due to shoaling of the seafloor. However, surface waves also break due to interactions with internal solitary waves (ISWs). In this paper...

Physical oceanography is increasingly relying on satellite remote sensing to survey the perpetually undersampled ocean, whereas the latest Synthetic Aperture Radars (SARs) are moving forward to provide a more continuous monitoring of the ocean. In this study we use a collection of SAR images to document the two-dimensional horizontal structure of I...

Internal waves (IWs) in the ocean span across a wide range of time and spatial scales and are now acknowledged as important sources of turbulence and mixing, with the largest observations having 200 m in amplitude and vertical velocities close to 0.5 m s−1. Their origin is mostly tidal, but an increasing number of non-tidal generation mechanisms ha...

Internal waves are density oscillations propagating along the ocean’s inner stratification, which are now acknowledged as a key constituent of the ocean’s dynamics. They usually result from barotropic tides, which flow over bottom topography, causing density oscillations to propagate along the pycnocline with a tidal frequency (i.e. internal tides)...

Semi-diurnal internal waves generated by tides in a high resolution numerical model that includes the Andaman Sea archipelago are found to propagate into the central Bay of Bengal and reach the coasts of India and Sri Lanka. The waves are also present in subsurface temperature records from RAMA moorings, and their propagation speed across the Bay o...

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 consiste...

It is well known that internal waves (IWs) of tidal frequency (i.e., internal tides) are successfully detected in sea surface height (SSH) by satellite altimetry. Shorter period internal solitary waves (ISWs), whose periods (and spatial scales) are an order of magnitude smaller than tidal internal waves, have been generally assumed too small to be...

An extended satellite image data set is used to investigate the two dimensional structure of internal waves (IWs) that propagate along the Patagonian shelf break and continental slope in the opposite direction of the Malvinas Current (MC). Intense surface manifestations of IWs are found throughout the semidiurnal and fortnightly tidal cycles, propa...

The large-amplitude internal solitary waves commonly observed in the coastal ocean can propagate for long distances for long times, so that it may be necessary to take account of the effects of the Earth’s background rotation. In this case an appropriate model wave evolution equation is the Ostrovsky equation, whose typical solutions indicate that...

Internal waves (IWs) are typically the most energetic high-frequency events in the coastal ocean. These large-wavelength waves are difficult to measure with in-situ or shipboard instruments. Therefore, remote sensing has been the main tool for IW observations. Although IWs have been observed in the Portuguese offshore region using from satellite-ba...

High sampling rate altimetry and near-simultaneous synthetic aperture radar image data reveal short-period oscillations, which are identified for the first time as internal solitary waves. Their rough and slick patterns introduce mixed contributions in the altimeter's footprint, contradicting the assumption of a uniform Brown surface. The resulting...

Despite evidence of internal waves in the NW Iberian upwelling region, their action and role on nutrient supply dynamics and phytoplankton community structure remain unexplored. A multidisciplinary approach, combining analysis of Synthetic Aperture Radar (SAR) images acquired during the summer months of 2008–2011, together with high-frequency sampl...

A satellite synthetic aperture radar (SAR) data set facilitates investigation of the two-dimensional structure of internal solitary waves (ISWs) that propagate near the Amazon River mouth. Three distinct groups of waves are identified according to their propagation direction. While cross-shelf ISW propagation has been previously documented, it is f...

Synthetic Aperture Radar (SAR) imagery from the Amazon shelf-break region in the tropical West Atlantic reveals for the first time the two-dimensional horizontal structure of an intense Internal Solitary Wave (ISW) field, whose first surface manifestations are detected several hundred kilometers away from the nearest forcing bathymetry. Composite m...

Synthetic aperture radar (SAR) imagery from the Amazon shelf break region in the tropical west Atlantic reveals for the first time the two-dimensional horizontal structure of an intense Internal Solitary Wave (ISW) field, whose first surface manifestations are detected several hundred kilometres away from the nearest forcing bathymetry. Composite m...

In this paper we will show coincident multi-sensor airborne and satellite SAR observations that reveal the 3D structure of air bubble entrainment in the internal wave field and frontal zones. It is suggested that these bubble clouds are probably related with strong convergence and vertical downwelling in the front portion of the internal waves and...

Poster presented at workshop NewWave in Lyon, France (14-16 October 2015). The poster shows some results of research conducted in Brazil in the frame of a Research Project funded by CNPq (Programa Ciência Sem fronteiras), titled: "Internal wave systems in the tropical and western south Atlantic: from satellite views to local predictability", hosted...

Here we present a first account of the coherence crest-lengths, propagation characteristics and seasonal variability of ISWs on and off the shelf, based on Synthetic Aperture Radar (SAR) images.

The Brazilian continental shelf break in the tropical Atlantic Ocean off the Amazon River mouth is amongst the most energetic regions in the world for generation of internal tides (Baines, 1982). Since the early 1980s there have been in situ observations of Internal Solitary Waves (ISWs) near the North Equatorial Counter Current (NECC) off the Braz...

In this paper we aim to clarify the generation of Internal Solitary Waves (ISWs) at work to the east of the Mascarene Plateau (Indian Ocean) using Synthetic Aperture Radar (SAR) imagery and MITgcm fully nonlinear and nonhydrostatic simulations. Realistic representations of stratification and bathymetry are used with asymmetric tidal forcing (includ...

A multi-sensor satellite approach based on ocean colour, sunglint and Synthetic Aperture Radar imagery is used to study the impact of interacting internal tidal (IT) waves on near-surface chlorophyll-a distribution, in the central Bay of Biscay. Satellite imagery was initially used to characterize the internal solitary wave (ISW) field in the study...

Satellite images of the Mozambique Channel (MC), collected by Synthetic Aperture Radars (SARs) from the Envisat and European Remote Sensing (ERS) satellites, reveal sea surface signatures of oceanic Internal Solitary Waves (ISWs). The MC has been expected to be a major hotspot for the generation of Internal Tides (ITs) in the ocean. New results now...

Strong tidal flow over a sill generates Internal Solitary Waves (ISWs) close to the area of topographic interaction. This may occur either upstream or downstream of the sill, being respectively explained by two different mechanisms: “internal tide release” or “lee wave generation”. We aim to clarify the generation process at work to the east of the...

Energetic Internal Solitary Waves (ISWs) were recently discovered radiating from the central region of the Mascarene Plateau in the south-western Indian Ocean (da Silva et al., 2011). SAR imagery revealed the two-dimensional structure of the waves which propagated for several hundred kilometres in deep water both to the east and west of a sill, loc...

[1] The first results of a multisensor airborne survey conducted off the western Iberian Coast are presented (including visible, lidar, and infrared imagery) and reveal the presence of internal solitary waves (ISWs) propagating into the nearshore region. For the first time, two-dimensional lidar imagery is shown to detect the presence of ISWs, and...

A comprehensive dataset of Synthetic Aperture Radar (SAR) images from the west Iberian coast is used to identify the Estremadura Promontory as an oceanic hotspot for internal solitary waves. The full two-dimensional structure and the main physical properties of these waves are revealed for the first time. Composite maps and a statistical analysis s...

Internal Solitary Waves (ISWs) are ubiquitous features in the coastal oceans. The propagation and breaking of ISWs contribute significantly to turbulent mixing in the near-surface layers, through the continual triggering of instabilities as they propagate into shallow water over the continental shelf. We report on the first results of an EU funded...

The off-shelf region between 16.0° and 16.5°N in the southern Red Sea is identified as a new hotspot for the occurrence of oceanic internal solitary waves. Satellite observations reveal trains of solitons that, surprisingly, appear to propagate from the center of the Red Sea, where it is deepest, toward the continental shelf, but they do not surviv...

In this paper, we present the first laboratory experiments that show the generation of internal solitary waves by the impingement of a quasi-two-dimensional internal wave beam on a pycnocline. These experiments were inspired by observations of internal solitary waves in the deep ocean from synthetic aperture radar (SAR) imagery, where this so-calle...

Analysis of a comprehensive dataset of Synthetic Aperture Radar (SAR) images acquired over the sea area around the Mascarene Plateau in the western Indian Ocean reveals, for the first time, the full two-dimensional spatial structure of internal solitary waves in this region of the ocean. The satellite SAR images show that powerful internal waves ra...

The region of the Middle East around the Red Sea (between 32° E and 44° E longitude and 12° N and 28° N latitude) is a currently undocumented hotspot for atmospheric gravity waves (AGWs). Satellite imagery shows evidence that this region is prone to relatively high occurrence of AGWs compared to other areas in the world, and reveals the spatial cha...

A recent study revealed that Race Point Channel (in Cape Cod, Massachusetts) is a hotspot of internal solitary wave generation. SAR images suggest that the waves are generated within the channel (which has a flat bottom) during the ebb phase of the tide (flowing offshore) and propagate upstream during the initial stages of their formation. Some of...

Possibilities of oil films detection on the sea surface and distinction them from natural marine slicks and look-alikes phenomena are discussed.

This paper presents new results showing that the Sofala shelf in the Mozambique Channel (20°S, 36°E) is a previously unknown “hot spot” for the generation of internal tides and internal waves. We investigate available Envisat advanced synthetic aperture radar imagery of the region, which is capable of showing the surface signatures of the internal...

Satellite imagery (MODIS‐Terra and Aqua, ASAR and MERIS‐Envisat) has revealed signatures consistent with horizontally propagating large‐scale atmospheric gravity waves which are frequently observed during the winter season in the Mozambique Channel. We examine and characterize statistically the full horizontal structure of these atmospheric gravity...

Large-scale Atmospheric Gravity Waves (AGWs) are frequently observed during the winter season in the Mozambique Channel. Satellite imagery revealed the full horizontal structure of these "giant" AGWs, which have dispersive average wavelengths ranging from 8.5 to 3.5 km, and a mean along-crest "coherence" length of 443 km. The Scorer parameter, calc...

Internal waves in fluids owe their existence to the restoring forces of gravity (in a stably stratified fluid) and the Coriolis force (in rotating fluids). Examples are the inertio-gravity waves in the ocean, a special class of which are those at tidal frequency (internal tides), which are generated by barotropic tidal flow over large-scale topogra...