Sea Surface Signature of Internal Tides

Abstract. Meddies, intra-thermocline eddies of Mediterranean water, can often be detected at the sea surface as positive sea-level anomalies. Here we study the surface signature of several meddies tracked with RAFOS floats and AVISO altimetry. While pushing its way through the water column, a meddy raises isopycnals above. As a consequence of potential vorticity conservation, negative relative vorticity is generated in the upper layer. During the initial period of meddy acceleration after meddy formation or after a stagnation stage, a cyclonic signal is also generated at the sea-surface, but mostly the anticyclonic surface signal follows the meddy. Based on geostrophy and potential vorticity balance, we present theoretical estimates of the intensity of the surface signature. It appears to be proportional to the meddy core radius and to the Coriolis parameter, and inversely proportional to the core depth and buoyancy frequency. This indicates that surface signature of a meddy may be strongly reduced by the upper ocean stratification. Using climatic distribution of the stratification intensity, we claim that the southernmost limit for detection in altimetry of small meddies (with radii on the order of 10–15 km) should lie in the subtropics (35–45° N), while large meddies (with radii of 25–30 km) could be detected as far south as the northern tropics (25–35° N). Those results agree with observations.

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

Jurnal Ilmu dan Teknologi Kelautan Tropis ◽

10.29244/jitkt.v6i2.9003 ◽

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

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Diurnal internal tides detected in the Adriatic

Annales Geophysicae ◽

10.5194/angeo-24-2773-2006 ◽

2006 ◽

Vol 24 (11) ◽

pp. 2773-2780 ◽

Cited By ~ 11

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.

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Quantifying Tidal Fluctuations in Remote Sensing Infrared SST Observations

Remote Sensing ◽

10.3390/rs11192313 ◽

2019 ◽

Vol 11 (19) ◽

pp. 2313 ◽

Cited By ~ 1

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.

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Internal-Tide Spectroscopy and Prediction in the Timor Sea

Journal of Physical Oceanography ◽

10.1175/jpo-d-14-0007.1 ◽

2015 ◽

Vol 45 (1) ◽

pp. 64-83 ◽

Cited By ~ 12

Author(s):

Samuel M. Kelly ◽

Nicole L. Jones ◽

Gregory N. Ivey ◽

Ryan J. Lowe

Keyword(s):

Time Scales ◽

Prediction Models ◽

Internal Tide ◽

Surface Displacement ◽

Internal Tides ◽

Sea Surface ◽

Mean Flow ◽

Long Time ◽

Timor Sea ◽

Response Method

AbstractSpectral analyses of two 3.5-yr mooring records from the Timor Sea quantified the coherence of mode-0 (surface) and mode-1 (internal) tides with the astronomical tidal potential. The noncoherent tides had well-defined variance and were most accurately quantified for tidal species (as opposed to constituents) in long records (>6 months). On the continental slope (465 m), the semidiurnal mode-0 and mode-1 velocity and mode-1 pressure variance were 95%, 68%, and 56% coherent, respectively. On the continental shelf (145 m), the semidiurnal mode-0 and mode-1 velocity and mode-1 pressure variance were 98%, 34%, and 42% coherent, respectively. The response method produced time series of the semidiurnal coherent and noncoherent tides. The spectra and decorrelation time scales of the semidiurnal tidal amplitudes were similar to those of the barotropic mean flow and mode-1 eigenspeed (~4 days), suggesting local mesoscale variability shapes noncoherent tidal variability. Over long time scales (>30 days), mode-1 sea surface displacement amplitudes were positively correlated with mode-1 eigenspeed on the shelf. At both moorings, internal tides were likely modulated during both generation and propagation. Self-prediction using the response method enabled about 75% of semidiurnal mode-1 sea surface displacement to be predicted 2.5 days in advance. Improved prediction models will require realistic tide–topography coupling and background variability with both short and long time scales.

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The Droguing of Meddy Pinball and Seeding with Alace Floats

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315400015332 ◽

1995 ◽

Vol 75 (1) ◽

pp. 235-252 ◽

Cited By ~ 35

Author(s):

R.D. Pingree

Keyword(s):

Continental Slope ◽

Abyssal Plain ◽

Sea Surface ◽

Time Data ◽

Hydrographic Survey ◽

Period 2 ◽

Real Time Data ◽

Infra Red ◽

Kinematic Properties ◽

Surface Signature

This paper reports the results of a hydrographic survey and the successful deliberate deep droguing of a meddy (Pinball) and the seeding of its core with two ALACE floats. The drogued buoy results give important kinematic properties of the eddy core in real timesemicolon the ALACE have allowed the position of the meddy to be tracked for seven months. Pinball was found against the continental slope near Lisbon canyon. The maximum core salinity was 36·564 psu, at a depth of 1260 m, but the maximum rotation rate with period ~2·5 d was in the upper core near 700 m, where temperatures reached 13·2°C. The azimuthal transport to a radius of 50 km was ~13 Sv. Pinball moved from the continental slope near Lisbon to the central Tagus Abyssal Plain, returned towards the continental slope and then moved westwards crossing the central Tagus Abyssal Plain a second time. At times it had a marked remote sensing infra-red sea-surface signature. It moved ~550 km over 204 d and the near real-time data meant that, in principle, this eddy could have been re-surveyed, redrogued or reseeded with floats during this period.

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Preparing for fine-scale ocean surface topography observations with the Surface Water and Ocean Topography (SWOT) Mission

10.5194/egusphere-egu2020-7535 ◽

2020 ◽

Author(s):

Rosemary Morrow ◽

Lee-Lueng Fu

Keyword(s):

Surface Water ◽

High Frequency ◽

Sea Surface Height ◽

Internal Tides ◽

Ocean Dynamics ◽

Sea Surface ◽

Fine Scale ◽

In Situ Data ◽

Ocean Topography

The future international Surface Water and Ocean Topography (SWOT) Mission, planned for launch in late 2021, will make high-resolution 2D observations of sea-surface height using SAR radar interferometric techniques. SWOT will map the global and coastal oceans up to 77.6&#176; latitude every 21 days over a swath of 120 km (20 km nadir gap). Today&#8217;s 2D mapped altimeter data can resolve ocean scales of 150 km wavelength whereas the SWOT measurement will extend our 2D observations down to 15-30 km, depending on sea state. SWOT will offer new opportunities to observe the oceanic dynamic processes at these smaller scales, that are important in the generation and dissipation of ocean kinetic energy, and are one of the main gateways connecting the surface to the ocean interior. Active vertical exchanges linked to these scales have impacts on the local and global budgets of heat and carbon, and on nutrients for biogeochemical cycles.SWOT&#8217;s unprecedented 2D ocean SSH observations include &#8220;balanced&#8221; geostrophic eddy motions and high-frequency internal tides and internal waves. SWOT will provide global observations of the 2D structure of these phenomena, enabling us to learn more about their interactions, and helping us to interpret what is currently observed in 1D with conventional altimetry. Yet this mix of balanced and unbalanced motions is a challenge for calculating geostrophic currents directly from SSH or for reconstructing the 4D upper ocean circulation. At these small scales, the ocean dynamics evolve rapidly, and even with SWOT&#8217;s 2D SSH images, one satellite cannot observe the temporal evolution of these processes. SWOT data will need to be combined with other satellite and in-situ data and models to better understand the upper ocean 4D circulation (x,y,z,t) over the next decade. SWOT&#8217;s new technology will be a forerunner for the future altimetric observing system.We will present recent progress in understanding the ocean dynamics contributing to fine-scale sea-surface height, including high-frequency processes such as internal tides, from 1D alongtrack altimetry, SAR data, in-situ data and models. We will also discuss the specific problems of validating the SWOT 2D small, rapid dynamics with in-situ data and other satellite data.&#160;

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Nonstationary Internal Tides Observed Using Dual-Satellite Altimetry

Journal of Physical Oceanography ◽

10.1175/jpo-d-15-0020.1 ◽

2015 ◽

Vol 45 (9) ◽

pp. 2239-2246 ◽

Cited By ~ 18

Author(s):

E. D. Zaron

Keyword(s):

Sampling Error ◽

Temporal Correlation ◽

Internal Tides ◽

Sea Surface ◽

Novel Approach ◽

Nonstationary Variance ◽

Time Lagged ◽

Nonstationary Tides ◽

Ocean Topography ◽

Wide Swath

AbstractDual-satellite crossover data from the Jason-2 and Cryosat-2 altimeter missions are used in a novel approach to quantify stationary and nonstationary tides from time-lagged mean square sea surface height (SSH) differences, computed for lags from 1 to 1440 h (60 days). The approach is made feasible by removing independent estimates of the stationary tide and mesoscale SSH variance, which greatly reduces the sampling error of the SSH statistics. For the semidiurnal tidal band, the stationary tidal variance is approximately 0.73 cm2, and the nonstationary variance is about 0.33 cm2, or 30% of the total. The temporal correlation of the nonstationary tide is examined by complex demodulation and found to be oscillatory with first 0 crossing at 400 h (17 days). Because a significant fraction of the time-variable mesoscale signal is resolved at time scales of roughly 150 h by the present constellation of satellite altimeters, the results suggest that it may be feasible to predict the nonstationary tide from modulations of the resolved mesoscale, thus enhancing the efficacy of tidal corrections for planned wide-swath altimeters such as the Surface Water and Ocean Topography (SWOT) mission.

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

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/944/1/012056 ◽

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.

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Some Expectations for Submesoscale Sea Surface Height Variance Spectra

Journal of Physical Oceanography ◽

10.1175/jpo-d-18-0272.1 ◽

2019 ◽

Vol 49 (9) ◽

pp. 2271-2289 ◽

Cited By ~ 3

Author(s):

Jörn Callies ◽

Weiguang Wu

Keyword(s):

Internal Wave ◽

Internal Waves ◽

Sea Surface Height ◽

Internal Tides ◽

Sea Surface ◽

Fourth Power ◽

Modest Improvement ◽

In Situ Observations ◽

Balanced Flow

AbstractIn anticipation of the Surface Water and Ocean Topography (SWOT) wide-swath altimetry mission, this study reviews expectations for sea surface height (SSH) variance spectra at wavelengths of 10–100 km. Kinetic energy spectra from in situ observations and numerical simulations indicate that SSH variance spectra associated with balanced flow drop off steeply with wavenumber, with at least the negative fourth power of the wavenumber. Such a steep drop-off implies that even drastic reductions in altimetry noise yield only a modest improvement in the resolution of balanced flow. This general expectation is made concrete by extrapolating SSH variance spectra from existing altimetry to submesoscales, the results of which suggest that in the extratropics (poleward of 20° latitude) SWOT will improve the resolution from currently about 100 km to a median of 51 or 74 km, depending on whether or not submesoscale balanced flows are energetic. Internal waves, in contrast to balanced flow, give rise to SSH variance spectra that drop off relatively gently with wavenumber, so SSH variance should become strongly dominated by internal waves in the submesoscale range. In situ observations of the internal-wave field suggest that the internal-wave signal accessible by SWOT will be largely dominated by internal tides. The internal-wave continuum is estimated to have a spectral level close to but somewhat lower than SWOT’s expected noise level.

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