scholarly journals Quantifying Tidal Fluctuations in Remote Sensing Infrared SST Observations

2019 ◽  
Vol 11 (19) ◽  
pp. 2313 ◽  
Author(s):  
Cristina González-Haro ◽  
Aurélien Ponte ◽  
Emmanuelle Autret
Keyword(s):  
Scalar Product ◽  
Tidal Currents ◽  
Internal Tides ◽  
Sea Surface ◽  
Spatial Structures ◽  
Tidal Flows ◽  
Geophysical Processes ◽  
Infrared Sst ◽  
Sst Fronts ◽  
Observing Systems

The expected amplitude of fixed-point sea surface temperature (SST) fluctuations induced by barotropic and baroclinic tidal flows is estimated from tidal current atlases and SST observations. The fluctuations considered are the result of the advection of pre-existing SST fronts by tidal currents. They are thus confined to front locations and exhibit fine-scale spatial structures. The amplitude of these tidally induced SST fluctuations is proportional to the scalar product of SST frontal gradients and tidal currents. Regional and global estimations of these expected amplitudes are presented. We predict barotropic tidal motions produce SST fluctuations that may reach amplitudes of 0.3 K. Baroclinic (internal) tides produce SST fluctuations that may reach values that are weaker than 0.1 K. The amplitudes and the detectability of tidally induced fluctuations of SST are discussed in the light of expected SST fluctuations due to other geophysical processes and instrumental (pixel) noise. We conclude that actual observations of tidally induced SST fluctuations are a challenge with present-day observing systems.

scholarly journals Internal solitary waves in the Northwest Sumatra Sea-Indonesia: from observation and modeling

2021 ◽  
Vol 944 (1) ◽  
pp. 012056
Author(s):  
I A Prasetya ◽  
A S Atmadipoera ◽  
S Budhiman ◽  
U C Nugroho
Keyword(s):  
Solitary Waves ◽  
High Tide ◽  
Tidal Currents ◽  
Internal Tides ◽  
Sea Surface ◽  
Radar Signal ◽  
Internal Solitary Waves ◽  
Tidal Waves ◽  
Submarine Ridge ◽  
Lee Waves

Abstract >The southern Andaman waters has been well known as one of the strongest generating and propagating area of internal solitary waves (ISWs), generated by semidiurnal barotropic tidal currents that impinge submarine ridge offshore western Weh. This study aims to investigate sea surface features of internal tides and tidal current around the submarine ridge and adjacent Weh-Aceh waters, derived from satellite imagery datasets (January-May 2018) and CROCO model-output datasets. The results show that sea surface signatures of ISWs are characterized by a strong radar signal backscattering of a dense ripple package in the generating area and two groups of ISWs arch in the propagating area, where the distance of the package groups and wavelengths vary 60-80 km and 9-163 km, respectively. Observed ISWs in March 2018 was 31. The satellite and model datasets suggest that generating area of internal waves is confined over the Breuh ridge. Here, the very strong semidiurnal (M2) barotropic tidal currents of 0.5-5.0 m/s are observed. During high-tide, amplified barotropic tidal currents acrossing the ridge flow partly southeastward into the Weh-Breuh passage. The model suggests that generating internal tidal waves over the ridge are manifested by strong vertical perturbation of isopycnal and current stratifications in the Lee-waves area.

scholarly journals INTRA-SEASONAL VARIABILITY OF NEAR-BOTTOM CURRENT IN THE HALMAHERA SEA

2015 ◽  
Vol 6 (2) ◽  
Author(s):  
Marlin C Wattimena ◽  
Agus S Atmadipoera ◽  
Mulia Purba ◽  
Ariane Koch-Larrouy
Keyword(s):  
Pacific Ocean ◽  
Seasonal Variability ◽  
Sea Surface Height ◽  
Equatorial Pacific ◽  
Internal Tides ◽  
Sea Surface ◽  
Bottom Current ◽  
Equatorial Pacific Ocean ◽  
Mean Flow ◽  
Zonal Winds

The secondary entry portal of the Indonesian Throughflow (ITF) from the Pacific to Indian Oceans is considered to be via the Halmahera Sea (HS). However, few ITF studies have been done within the passage. This motivated the Internal Tides and Mixing in the Indonesian Througflow (INDOMIX) program to conduct direct measurements of currents and its variability across the eastern path of the ITF. This study focused on the intra-seasonal variability of near-bottom current in HS (129°E, 0°S), its origin and correlation with surface zonal winds and sea surface height over the equatorial Pacific Ocean. The result showed a strong northwestward mean flow with velocity exceeding 40 cm/s, which represented the current-following topography with the northwest orientation. Meridional current component was much stronger than the zonal component. The energy of power spectral density (PSD) of the current peaked on 14-days and 27-days periods. The first period was presumably related to the tidal oscillation, but the latter may be associated with surface winds perturbation. Furthermore, cross-PSD revealed a significant coherency between the observed currents and the surface zonal winds in the central equatorial Pacific zonal winds (180°E-160°W), which corroborates westward propagation of intra-seasonal sea surface height signals along the 5°S with its mean phase speeds of 50 cm/s, depicting the low-latitude westward Rossby waves on intra-seasonal band. Keywords: current, equatorial Pacific Ocean,  zonal winds, sea surface height, Halmahera Sea

scholarly journals Toward Automated Identification of Sea Surface Temperature Front Signatures in Radarsat-2 Images

2012 ◽  
Vol 29 (1) ◽  
pp. 89-102 ◽  
Author(s):  
Chris T. Jones ◽  
Todd D. Sikora ◽  
Paris W. Vachon ◽  
John Wolfe
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Sea Surface ◽  
Canadian Forces ◽  
Automated Identification ◽  
Sar Images ◽  
Accurate Identification ◽  
Sst Front ◽  
Atmospheric Phenomena ◽  
Sst Fronts

Abstract The Canadian Forces Meteorology and Oceanography Center produces a near-daily ocean feature analysis, based on sea surface temperature (SST) images collected by spaceborne radiometers, to keep the fleet informed of the location of tactically important ocean features. Ubiquitous cloud cover hampers these data. In this paper, a methodology for the identification of SST front signatures in cloud-independent synthetic aperture radar (SAR) images is described. Accurate identification of ocean features in SAR images, although attainable to an experienced analyst, is a difficult process to automate. As a first attempt, the authors aimed to discriminate between signatures of SST fronts and those caused by all other processes. Candidate SST front signatures were identified in Radarsat-2 images using a Canny edge detector. A feature vector of textural and contextual measures was constructed for each candidate edge, and edges were validated by comparison with coincident SST images. Each candidate was classified as being an SST front signature or the signature of another process using logistic regression. The resulting probability that a candidate was correctly classified as an SST front signature was between 0.50 and 0.70. The authors concluded that improvement in classification accuracy requires a set of measures that can differentiate between signatures of SST fronts and those of certain atmospheric phenomena and that a search for such measures should include a wider range of computational methods than was considered. As such, this work represents a step toward the goal of a general ocean feature classification algorithm.

scholarly journals Sea Surface Signature of Internal Tides

2019 ◽  
Vol 46 (7) ◽  
pp. 3880-3890 ◽  
Author(s):  
Noé Lahaye ◽  
Jonathan Gula ◽  
Guillaume Roullet
Keyword(s):  
Internal Tides ◽  
Sea Surface ◽  
Surface Signature

scholarly journals Diurnal internal tides detected in the Adriatic

2006 ◽  
Vol 24 (11) ◽  
pp. 2773-2780 ◽  
Author(s):  
H. Mihanović ◽  
M. Orlić ◽  
Z. Pasarić
Keyword(s):  
Sea Level ◽  
Temperature Data ◽  
Internal Tides ◽  
Sea Surface ◽  
Sea Level Changes ◽  
Temperature Oscillations ◽  
Sea Level Oscillations ◽  
Wind Measurements ◽  
Diurnal Wind ◽  
Surface Variability

Abstract. Strong diurnal oscillations, documented by temperature data that were collected along a submarine cliff on the Lastovo Island (southern Adriatic), are studied and compared with sea level and wind measurements at Dubrovnik and Komiža (island of Vis). Three thermistors were deployed at the depths of 15, 22 and 36 m between March 2001 and March 2002. Pronounced diurnal temperature oscillations were detected at 15 and 22 m during the stratified season. The correlation between the sea surface and thermocline displacements was highest in June 2001, when diurnal wind changes were not significant, while diurnal sea level oscillations achieved annual maxima. Thermocline oscillations were in phase with sea level changes. The range of diurnal sea surface variability was close to 19 cm, while the range of corresponding thermocline variability was about 5.4 m. The findings summarize the outcome of the first dedicated study of internal tides in the Adriatic.

scholarly journals A comparison of atmospheric CO<sub>2</sub> flux signals obtained from GEOS-Chem flux inversions constrained by in situ or GOSAT observations

2018 ◽  
Author(s):  
Saroja M. Polavarapu ◽  
Feng Deng ◽  
Brendan Byrne ◽  
Dylan B. A. Jones ◽  
Micheal Neish
Keyword(s):  
Transport Model ◽  
Atmospheric Transport ◽  
Co2 Flux ◽  
Boreal Summer ◽  
Spatial Structures ◽  
Independent Observations ◽  
In Situ Observations ◽  
The Difference ◽  
Observing Systems

Abstract. The CO2 flux signal is defined as the difference of the four-dimensional CO2 field obtained by integrating an atmospheric transport model with posterior fluxes and that obtained with prior fluxes. It is a function of both the model and the prior fluxes and it can provide insight into how posterior fluxes inform CO2 distributions. Here, we use the GEOS-Chem transport model constrained by either GOSAT or in situ observations to obtain two sets of posterior flux estimates in order to compare the flux signals obtained from the two different observing systems. Flux signals are also computed using two different models. The global flux signal in the troposphere primarily reflects the northern extratropics whereas the global flux signal in the stratosphere mainly reflects tropical contributions. While both observing systems constrain the global budget for 2010 equally well, stronger seasonal variations of the flux signal are obtained with GOSAT. Posterior CO2 distributions obtained with in situ observations better agree with TCCON measurements over an 18-month time period, but GOSAT-informed posterior fluxes better constrain the seasonal cycle at northern extratropical sites. Zonal standard deviations of the flux signal exceed the minimal value (defined by uncertainty in meteorological analyses) through most of the year when GOSAT observations are used, but when in situ observations are used, the minimum value is exceeded only in boreal summer. This indicates a potential for flux estimates constrained by GOSAT data to retrieve spatial structures within a zonal band throughout the year in the tropics and through most of the year in the northern extratropics. Verification of such spatial structures will require a dense network of independent observations.

scholarly journals Multiple equilibria and oscillatory modes in a mid-latitude ocean-forced atmospheric model

2012 ◽  
Vol 19 (5) ◽  
pp. 479-499 ◽  
Author(s):  
B. Deremble ◽  
E. Simonnet ◽  
M. Ghil
Keyword(s):  
Multiple Equilibria ◽  
Low Frequency ◽  
Atmospheric Model ◽  
Sea Surface ◽  
Hopf Bifurcations ◽  
Barotropic Instability ◽  
Atmospheric Variability ◽  
Oceanic Forcing ◽  
Sst Fronts ◽  
Oceanic Model

Abstract. Atmospheric response to a mid-latitude sea surface temperature (SST) front is studied, while emphasizing low-frequency modes induced by the presence of such a front. An idealized atmospheric quasi-geostrophic (QG) model is forced by the SST field of an idealized oceanic QG model. First, the equilibria of the oceanic model and the associated SST fronts are computed. Next, these equilibria are used to force the atmospheric model and compute its equilibria when varying the strength of the oceanic forcing. Low-frequency modes of atmospheric variability are identified and associated with successive Hopf bifurcations. The origin of these Hopf bifurcations is studied in detail, and connected to barotropic instability. Finally, a link is established between the model's time integrations and the previously obtained equilibria.

New insights into sedimentary processes and related morphologies in tidal straits: the case of the Rio-Antirio Sill (Greece)

2021 ◽  
Author(s):  
Romain Rubi ◽  
Aurélia Hubert-Ferrari ◽  
Elias Fakiris ◽  
Dimitris Christodoulou ◽  
Xenophon Dimas ◽  
...  
Keyword(s):  
High Resolution ◽  
Tidal Currents ◽  
Internal Tides ◽  
Tectonic Activity ◽  
Depositional Model ◽  
Carbonate Production ◽  
Sea Floor ◽  
Bottom Currents ◽  
Gulf Of Corinth ◽  
Underwater Camera

&lt;p&gt;Straits are crossed by marine currents that are amplified due to the water constriction. These nearshore high-velocity flows are problematic for offshore infrastructures (bridge pillars, cables, pipelines etc), but constitute an under-estimated carbon-free kinematic energy source. Most of the straits are dominated by tidal currents which flow axially to the seaway, with reversal directions and phase difference between the two interlinked basins. These tidal currents interplay with: (i) sediment sources that also includes in situ carbonate production and deltas, (ii) tectonic activity, and (iii) inherited lowstand features, all shaping the sea floor into complex geomorphologies. Previous studies have highlighted a common tidal-strait depositional model with a strait-center zone in erosion and on each side a dune-bedded strait zone with 3D and 2D tidal dunes and tidal ripples.&lt;/p&gt;&lt;p&gt;Here, we present an alternative tidal-strait model based on an interdisciplinary approach using high-resolution geophysical and oceanographical data to better constrain the processes acting at the sea floor. We focus on the Rion-Antirion strait in Greece which controls the connection between the Gulf of Corinth and the Mediterranean Sea. Based on high-resolution multibeam bathymetry (MBES) over an area of 211km&lt;sup&gt;2&lt;/sup&gt;, we identify and quantify the morphologies by extracting bathymetric swath profiles. These results are integrated with currents data (ADCP) and CTD profiles. In addition, &amp;#160;we use high-resolution Chirp subbottom profiles and high-resolution sparker seismic reflection profiles to document the stratigraphy and morphology of the sedimentary beds and erosional features. To complete this dataset, we use a towed underwater camera to image the sea-floor.&lt;/p&gt;&lt;p&gt;We define three zones, each characterized by common hydrodynamics, bedforms and morpho-bathymetric features which reveal an asymmetric strait. (1) The western zone is dominated by tectonics with salt diapirism and faults which interact with bottom currents to form erosional pools and ridge systems. (2) The strait center zone displays abrasion surfaces which consists on a rough rock-paved plateau surface encrusted by living red corals and sponges. Moreover, a moat cuts this plateau that localizes the sill at its eastern tip. This strait center area is dominated by inherited hard-ground fluviatile deposits which are abraded by bidirectional tidal-currents. (3) The eastern zone shows a deeper bathymetry with smoother features. The sediments are veneered on slopes forming plastered drifts and spits while the basin axis presents large chutes and pools. The bottom-currents in this zone, are related to internal tides from the Gulf of Corinth that are delayed with respect to the tidal currents. These internal-tide currents (3m/s) are three times faster than the oceanic tidal-currents in the strait (1m/s).&lt;/p&gt;&lt;p&gt;In conclusion, we document a tidal-strait system, which is interacting with active tectonics, and internal-tides along its axis. In results, Rion strait displays complex bathymetric features without any 3D or 2D tidal dunes. Thus, it provides a new end member to the tidal-strait depositional model. This end member is characterized by a re-localization of the erosion, bypass and deposition. It illustrates the key role of internal tides for straits located at the boundary between a confined deep-basin and the open-sea.&lt;/p&gt;

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