Analysis of velocity field in the eastern Black Sea from satellite data during the Black Sea '99 experiment

Afanasyev, Y. D.; Kostianoy, Andrey G.; Зацепин, А. Г.; Poulain, Pierre-Marie

doi:10.1029/2000jc000578

Cited by 31 publications

(28 citation statements)

References 17 publications

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“…(26) withĊ = 0. In general, the resulting velocity field is sparse and is postprocessed to retrieve a smoother field (e.g., Afanasyev et al, 2002) or it is combined with altimetric measurements (e.g., Abraham, 1998;Wilkin et al, 2002). Notice that the MCC approach requires high-resolution data such as the observations provided by infrared and visible radiometers (resolutions ∼ 1 km) but the resulting velocity field has spatial resolutions on the order of the window used to track features (∼ 20 km, e.g., Bowen et al, 2002).…”

Section: Currents From a Sequence Of Tracer Imagesmentioning

confidence: 99%

“…As stated before, direct measurements of surface currents by satellites remain quite limited. This situation has prompted the development of various indirect methods, either by assuming dynamical constraints to sea surface temperature (SST) images (Kelly, 1989;Vigan et al, 2000b;Chen et al, 2008) by applying pattern recognition techniques as neural networks (Côté and Tatnall, 1997) or the maximum cross-correlation (MCC) technique Afanasyev et al, 2002;Dransfeld et al, 2006). A better understanding of the dynamics in the upper layers of the ocean has allowed the proposal of a new framework based on the surface quasi-geostrophic (SQG) equations (Held et al, 1995;Lapeyre and Klein, 2006), which is able to retrieve sea surface currents from a single SST image (LaCasce and Mahadevan, 2006;Isern-Fontanet et al, 2006a;.…”

Section: Introductionmentioning

confidence: 99%

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Remote sensing of ocean surface currents: a review of what is being observed and what is being assimilated

Isern‐Fontanet

Ballabrera-Poy

Turiel

et al. 2017

Nonlin. Processes Geophys.

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Abstract. Ocean currents play a key role in Earth's climate -they impact almost any process taking place in the ocean and are of major importance for navigation and human activities at sea. Nevertheless, their observation and forecasting are still difficult. First, no observing system is able to provide direct measurements of global ocean currents on synoptic scales. Consequently, it has been necessary to use sea surface height and sea surface temperature measurements and refer to dynamical frameworks to derive the velocity field. Second, the assimilation of the velocity field into numerical models of ocean circulation is difficult mainly due to lack of data. Recent experiments that assimilate coastal-based radar data have shown that ocean currents will contribute to increasing the forecast skill of surface currents, but require application in multidata assimilation approaches to better identify the thermohaline structure of the ocean. In this paper we review the current knowledge in these fields and provide a global and systematic view of the technologies to retrieve ocean velocities in the upper ocean and the available approaches to assimilate this information into ocean models.

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Section: Currents From a Sequence Of Tracer Imagesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Remote sensing of ocean surface currents: a review of what is being observed and what is being assimilated

Isern‐Fontanet

Ballabrera-Poy

Turiel

et al. 2017

Nonlin. Processes Geophys.

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“…According to Fedorov (1986), the dipole is one of the most widespread forms of non-stationary and non-linear motion in the ocean. Many studies reported observations of surface layer dipolar structures using remote sensing methods (e.g., Ginzburg et al, 2002;Afansyev et al, 2002) and the important contribution of these dipoles to the coastal/deep-basin water exchange was recognized. Due to their high drift speed, the dipoles are able to advect properties very efficiently.…”

Section: N Serra Et Al: Surface Expression Of Mw Dipolesmentioning

confidence: 99%

Surface expression of Mediterranean Water dipoles and their contribution to the shelf/slope – open ocean exchange

2010

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Abstract. The generation of dipolar eddies within the Mediterranean Water (MW) layers, at the Portuguese continental slope, was observed using subsurface RAFOS floats. The surface expression of these mid-depth dipoles is here characterized with remote sensing data, namely with sea surface temperature, chlorophyll concentration and sea surface height measurements. Two cases are presented demonstrating the remote detection of these underwater structures in the Gulf of Cadiz during 1998 and 2001. The presence of subsurface MW dipoles in the Iberian coastal zone is shown to influence the development of coastal upwelling filaments. The surface circulation induced by the dipoles causes the upwelling filaments to extend offshorewards and thus to enhance the transport of physical, chemical and biological properties into the open ocean. A numerical model simulation of the ocean circulation around the Iberian Peninsula forced by heat and freshwater fluxes (computed using the NCEP reanalysis atmospheric state) and by the overflow of MW at the Strait of Gibraltar, corroborates the connection between the surface and the mid-depth flows. The highresolution numerical experiment is used to help clarifying the occurrence of the MW dipoles surface expression and the impact of these dipoles on the eddy kinetic energy of the upper ocean and on the exchange of volume and salt between the shelf/slope and the open ocean.

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“…Modern algorithms are complex, sometimes combining several approaches or in situ measurements, e.g., [52,56]. In the Black Sea region, MCC and optical flow methods were used in [46,48,57,58].…”

Section: Introductionmentioning

confidence: 99%

“…Sequences of time-ordered images allow for the estimation of two-dimensional image motion as either instantaneous image velocities or discrete image displacements. Primary approaches to estimating velocity fields from image sequences can be divided into two groups [38]: differential methods, which are mostly based on heat or optical flow equations inversion [39][40][41][42][43][44], and the Maximum Cross Correlation (MCC) technique [45][46][47][48][49][50][51][52][53][54][55]. Modern algorithms are complex, sometimes combining several approaches or in situ measurements, e.g., [52,56].…”

Section: Introductionmentioning

confidence: 99%

Reconstructing Large- and Mesoscale Dynamics in the Black Sea Region from Satellite Imagery and Altimetry Data—A Comparison of Two Methods

2018

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Two remote sensing methods, satellite altimetry and 4D-Var assimilation of satellite imagery, are used to compute surface velocity fields in the Black Sea region. Surface currents derived from the two methods are compared for several cases with intense mesoscale and large-scale dynamics during low wind conditions. Comparison shows that the obtained results coincide well quantitatively and qualitatively. However, satellite imagery provides more reasonable results on the spatial variability of coastal dynamics than altimetry data. In particular, this is related to the reconstruction of eddy coastal dynamics, such as Black Sea near-shore anticyclones. Current streamlines in these eddies are not closed near the coast in altimetry data, which we relate to the extrapolation during mapping procedure in the absence of coastal along-track measurements. On the other hand, in offshore areas, imagery-derived currents can be underestimated due to the absence of thermal contrasts and smoothing during the procedure of the 4D-Var assimilation. Wind drift currents are another source of inconsistency, as their impact is directly observed in satellite imagery but absent in altimetry data. The advantage of the 4D-Var method for reconstructing coastal dynamics is used to compute surface currents in the Marmara Sea on the base of 250 m resolution Modis optical data. The results reveal the very complex dynamics of the basin, with a large number of mesoscale and sub-mesoscale eddies. 4D-Var assimilation of Modis imagery is used to obtain information about dynamic characteristics of these small eddies with radiuses of 4-10 km.

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Analysis of velocity field in the eastern Black Sea from satellite data during the Black Sea '99 experiment

Cited by 31 publications

References 17 publications

Remote sensing of ocean surface currents: a review of what is being observed and what is being assimilated

Remote sensing of ocean surface currents: a review of what is being observed and what is being assimilated

Surface expression of Mediterranean Water dipoles and their contribution to the shelf/slope – open ocean exchange

Reconstructing Large- and Mesoscale Dynamics in the Black Sea Region from Satellite Imagery and Altimetry Data—A Comparison of Two Methods

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