Observation of a turbid plume using MODIS imagery: The case of Douro estuary (Portugal)

Mendes, Renato; Vaz, Nuno; Fernández-Nóvoa, Diego; Silva, J.C.B. da; deCastro, M.; Gómez‐Gesteira, M.; Dias, João Miguel

doi:10.1016/j.rse.2014.08.003

Cited by 34 publications

(36 citation statements)

References 61 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…New et al, 2013 andHelfrich, 2008), two particularities may introduce misleading errors in the deduced origin (in time and space) for the waves: (1) sampling restrictions due to the sun-synchronous satellite orbit (within the flood-ebb cycle) results in aliasing, so that near spring tides (when the IWs are observed) the images always correspond to a similar flood-ebb phase of the semi-diurnal tide (see e.g. Valente and da Silva, 2009;Mendes et al, 2014); (2) da Silva et al (2011) neglected IW phase speed variations across shallow bathymetry, which may introduce non-negligible bias from true ISW trajectories in the travel-time graphs.…”

Section: Study Regionmentioning

confidence: 99%

Internal waves on the upstream side of a large sill of the Mascarene Ridge: a comprehensive view of their generation mechanisms and evolution

Silva

Buijsman

Magalhaes

2015

Deep Sea Research Part I: Oceanographic Research Papers

Self Cite

View full text Add to dashboard Cite

a b s t r a c tIn 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 (including the steady South Equatorial Current which is assumed barotropic in the model) along a 2D transect aligned with the propagation direction of the wave signatures identified in the SAR. The combined flow (i.e. steady and tidal currents) is subcritical with respect to first-mode Internal Waves (IWs), but supercritical with respect to higher wave modes. Different types of nonlinear wave trains with distinct origins (i.e. tidal phase and location) have been identified with the combined aid of model and SAR: (1) large-scale primary mode-1 ISWs evolve from the disintegration of a multimodal baroclinic structure that appears on the upstream side of the sill; (2) mode-2 ISW-like waves that evolve from this same baroclinic structure and are arrested over the sill before being released upstream at the change of flow condition; (3) a large mode-2 lee wave is generated downstream of the sill (i.e. on the west side), which is trapped there during maximum westward tidal flow and released upstream when the tide relaxes; and (4) mode-2 ISW-like waves whose length-scales are O (20 km) appear some 50 km upstream of the sill, after an Internal Tide (IT) beam scatters into the pycnocline, itself originating from critical topography on the leeward (i.e. westward) side of the sill. The underwater sill being investigated is in the mixed-tidal-lee wave regime, where the internal tide release mechanism, lee wave generation and IT beams can coexist. The large-scale mode-2 ISW-like waves that form far upstream from the sill are long-lived features and can be identified in the SAR due to associated short-scale mode-1 ISWs which propagate with the same phase speed, i.e. in resonance. This coupling is also seen in the model, and here it is argued that the formation of those mode-2 ISW-like waves appears to originate from the IT beam after it reflects from the sea surface and interacts with the pycnocline, a generation mechanism referred in the literature as "local generation of ISWs". This IW generation process may be easily overlooked and could be at work in many more regions of the world than previously thought.

show abstract

Section: Study Regionmentioning

confidence: 99%

Internal waves on the upstream side of a large sill of the Mascarene Ridge: a comprehensive view of their generation mechanisms and evolution

Silva

Buijsman

Magalhaes

2015

Deep Sea Research Part I: Oceanographic Research Papers

Self Cite

View full text Add to dashboard Cite

show abstract

“…It allows discerning between turbid water related to river discharge and ocean water due to their different optical properties [ Dzwonkowski and Yan , ; Shi and Wang , ; Valente and da Silva , ; Saldías et al ., ]. Thus, several studies related to turbid plumes have been conducted using this technology all over the world [ Walker et al ., ; Palacios et al ., ; Molleri et al ., ; Petus et al ., ; Mendes et al ., ; Fernández‐Nóvoa et al ., ]. In addition, satellite technology has also been used to analyze sea surface temperature (SST) in areas influenced by river plumes because of the high spatial and temporal resolution provided [ Walker et al ., ; de Boer et al ., ; Hopkings et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Modulation of sea surface temperature warming in the Bay of Biscay by Loire and Gironde Rivers

et al. 2016

Self Cite

View full text Add to dashboard Cite

The influence of Loire and Gironde River discharges over the sea surface temperature (SST) in the eastern Bay of Biscay (0.6º–36.6ºW, 44.2º–47.8ºW) was analyzed by means of two complementary databases (MODIS and OISST1/4). The area influenced by river plume showed a different SST when compared with the adjacent oceanic area for the months when the plume attains its highest extension (December, January, and February). Ocean was observed to warm at a rate of approximately 0.3ºC dec−1 while temperature at the area influenced by the rivers cooled at a rate of −0.15ºC dec−1 over the period 1982–2014. The mere presence of a freshwater layer is able to modulate the warming observed at adjacent ocean locations since the coastal area is isolated from the rest of the Bay. This nearshore strip is the only part of the Bay where changes in SST depend on North Atlantic Oscillation (NAO) but not on North Atlantic SST represented by the Atlantic Multidecadal Oscillation (AMO). These different cooling‐warming trends are even more patent over the last years (2002–2014) under atmospheric favorable conditions for plume enhancement. River runoff increased at a rate on the order of 120 m3s−1dec−1 over that period and southwesterly winds, which favor the confinement of the plume, showed a positive and significant trend both in duration and intensity. Thus, the coastal strip has been observed to cool at a rate of −0.5°C dec−1.

show abstract

“…Observational studies confirm that the bulge is a naturally occurring phenomenon with many rivers (Chant et al, 2008;Horner-Devine et al, 2008;Horner-Devine, 2009;Valente and da Silva, 2009;Saldías et al, 2012;Hopkins et al, 2013;Mendes et al, 2014;Pan et al, 2014;Fernández-Nóvoa et al, 2015), but an anti-cyclonic rotation inside a bulge is observed seldom (Kudela et al, 2010;Horner-Devine, 2009;Chant et al, 2008). Observations of the evolution of the bulge over a certain time period are almost non-existent, with the ex-418 E. Soosaar et al: River bulge evolution and dynamics in a non-tidal sea ception of the Niagara River plume (Horner-Devine et al, 2008) and the Tagus estuary plume (Valente and da Silva, 2009).…”

Section: Introductionmentioning

confidence: 90%

River bulge evolution and dynamics in a non-tidal sea – Daugava River plume in the Gulf of Riga, Baltic Sea

et al. 2016

View full text Add to dashboard Cite

Abstract. Satellite remote sensing imagery and numerical modelling were used for the study of river bulge evolution and dynamics in a non-tidal sea, the Gulf of Riga (GoR) in the Baltic Sea. Total suspended matter (TSM) images showed a clearly formed anti-cyclonically rotating river bulge from Daugava River discharge during the studied low wind period. In about 7-8 days the bulge grew up to 20 km in diameter, before being diluted. A high-resolution (horizontal grid step of 125 m) General Estuarine Transport Model (GETM) was used for detailed description of the development of the river plume in the southern GoR over the period when satellite images were acquired. In the model simulation, the bulge growth rate was estimated as r b ∼ t 0.5±0.04 (R 2 = 0.90). Both the model simulation and the satellite images showed that river water was mainly contained in the bulge and there were numerous intrusions at the outer perimeter of the bulge. We performed numerical sensitivity tests with actual bathymetry and measured river runoff without wind forcing (1) having an initial three-dimensional density distribution, and (2) using initially a homogeneous ambient density field. In the first case, the anti-cyclonic bulge did not develop within the course of the model simulation and the coastal current was kept offshore due to ambient densitydriven circulation. In the second case, the river plume developed steadily into an anti-cyclonically recirculating bulge, with r b ∼ t 0.28±0.01 (R 2 = 0.98), and a coastal current. Additional simulations with constant cross-shore and alongshore winds showed a significant effect of the wind in the evolution of the river bulge, even if the wind speed was moderate (3-4 m s −1 ). While previous studies conclude that the midfield bulge region is governed by a balance between centrifugal, Coriolis and pressure gradient terms, our study showed that geostrophic balance is valid for the entire mid-field of the bulge, except during the 1-1.5 rotation period at the beginning of the bulge formation. In addition, while there is discharge into the homogenous GoR in the case of a high inflow Rossby number, the river inflow might split into two jets, with strong mixing zone in-between, in the plume nearfield region.

show abstract

Observation of a turbid plume using MODIS imagery: The case of Douro estuary (Portugal)

Cited by 34 publications

References 61 publications

Internal waves on the upstream side of a large sill of the Mascarene Ridge: a comprehensive view of their generation mechanisms and evolution

Internal waves on the upstream side of a large sill of the Mascarene Ridge: a comprehensive view of their generation mechanisms and evolution

Modulation of sea surface temperature warming in the Bay of Biscay by Loire and Gironde Rivers

River bulge evolution and dynamics in a non-tidal sea – Daugava River plume in the Gulf of Riga, Baltic Sea

Contact Info

Product

Resources

About