Some Expectations for Submesoscale Sea Surface Height Variance Spectra

2019 ◽  
Vol 49 (9) ◽  
pp. 2271-2289 ◽  
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.

Global Assessment of Semidiurnal Internal Tide Aliasing in Argo Profiles

2019 ◽  
Vol 49 (10) ◽  
pp. 2523-2533 ◽  
Author(s):  
Tyler D. Hennon ◽  
Matthew H. Alford ◽  
Zhongxiang Zhao
Keyword(s):  
Internal Waves ◽  
Internal Tide ◽  
Internal Tides ◽  
Stationary Mode ◽  
Argo Floats ◽  
New Information ◽  
In Situ Observations ◽  
Argo Profiles

AbstractThough unresolved by Argo floats, internal waves still impart an aliased signal onto their profile measurements. Recent studies have yielded nearly global characterization of several constituents of the stationary internal tides. Using this new information in conjunction with thousands of floats, we quantify the influence of the stationary, mode-1 M2 and S2 internal tides on Argo-observed temperature. We calculate the in situ temperature anomaly observed by Argo floats (usually on the order of 0.1°C) and compare it to the anomaly expected from the stationary internal tides derived from altimetry. Globally, there is a small, positive correlation between the expected and in situ signals. There is a stronger relationship in regions with more intense internal waves, as well as at depths near the nominal mode-1 maximum. However, we are unable to use this relationship to remove significant variance from the in situ observations. This is somewhat surprising, given that the magnitude of the altimetry-derived signal is often on a similar scale to the in situ signal, and points toward a greater importance of the nonstationary internal tides than previously assumed.

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

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

<p>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° latitude every 21 days over a swath of 120 km (20 km nadir gap). Today’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.</p><p>SWOT’s unprecedented 2D ocean SSH observations include “balanced” 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’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’s new technology will be a forerunner for the future altimetric observing system.</p><p>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. </p>

scholarly journals Impacts of mean dynamic topography on a regional ocean assimilation system

2015 ◽  
Vol 12 (3) ◽  
pp. 1083-1105
Author(s):  
C. Yan ◽  
J. Zhu ◽  
C. A. S. Tanajura
Keyword(s):  
Sea Surface Height ◽  
Sea Surface ◽  
Dynamic Topography ◽  
Altimetry Data ◽  
Mean Dynamic Topography ◽  
Mean Sea Surface ◽  
In Situ Observations ◽  
The Mean

Abstract. An ocean assimilation system was developed for the Pacific-Indian oceans with the aim of assimilating altimetry data, sea surface temperature, and in-situ measurements from ARGO, XBT, CTD, and TAO. The altimetry data assimilation requires the addition of the mean dynamic topography to the altimetric sea level anomaly to match the model sea surface height. The mean dynamic topography is usually computed from the model long-term mean sea surface height, and is also available from gravimeteric satellite data. In this study, different mean dynamic topographies are used to examine their impacts on the sea level anomaly assimilation. Results show that impacts of the mean dynamic topography cannot be neglected. The mean dynamic topography from the model long-term mean sea surface height without assimilating in-situ observations results in worsened subsurface temperature and salinity estimates. The gravimeter-based mean dynamic topography results in an even worse estimate. Even if all available observations including in-situ measurements, sea surface temperature measurements, and altimetry data are assimilated, the estimates are still not improved. This further indicates that the other types of observations do not compensate for the shortcoming due to the altimetry data assimilation. The mean dynamic topography computed from the model's long-term mean sea surface height after assimilating in-situ observations presents better results.

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 Blending Sea Surface Temperatures from Multiple Satellites and In Situ Observations for Coastal Oceans

2009 ◽  
Vol 26 (7) ◽  
pp. 1415-1426 ◽  
Author(s):  
Yi Chao ◽  
Zhijin Li ◽  
John D. Farrara ◽  
Peter Hung
Keyword(s):  
Coastal Upwelling ◽  
Sea Surface ◽  
High Temporal Resolution ◽  
Potential Applications ◽  
Independent Observations ◽  
Ocean Flows ◽  
In Situ Observations ◽  
Continuous Fields ◽  
Mean Square Errors

Abstract A two-dimensional variational data assimilation (2DVAR) method for blending sea surface temperature (SST) data from multiple observing platforms is presented. This method produces continuous fields and has the capability of blending multiple satellite and in situ observations. In addition, it allows specification of inhomogeneous and anisotropic background correlations, which are common features of coastal ocean flows. High-resolution (6 km in space and 6 h in time) blended SST fields for August 2003 are produced for a region off the California coast to demonstrate and evaluate the methodology. A comparison of these fields with independent observations showed root-mean-square errors of less than 1°C, comparable to the errors in conventional SST observations. The blended SST fields also clearly reveal the finescale spatial and temporal structures associated with coastal upwelling, demonstrating their utility in the analysis of finescale flows. With the high temporal resolution, the blended SST fields are also used to describe the diurnal cycle. Potential applications of this SST blending methodology in other coastal regions are discussed.

scholarly journals Modeling and Analysis of Internal-Tide Generation and Beamlike Onshore Propagation in the Vicinity of Shelfbreak Canyons

2014 ◽  
Vol 44 (3) ◽  
pp. 834-849 ◽  
Author(s):  
Weifeng G. Zhang ◽  
Timothy F. Duda ◽  
Ilya A. Udovydchenkov
Keyword(s):  
Internal Wave ◽  
Internal Waves ◽  
Internal Tide ◽  
Propagation Model ◽  
Internal Tides ◽  
Wave Radiation ◽  
Beam Radiation ◽  
Control Simulation ◽  
Conversion Rates ◽  
The Cross

Abstract A hydrostatic numerical model with alongshore-uniform barotropic M2 tidal boundary forcing and idealized shelfbreak canyon bathymetries is used to study internal-tide generation and onshore propagation. A control simulation with Mid-Atlantic Bight representative bathymetry is supported by other simulations that serve to identify specific processes. The canyons and adjacent slopes are transcritical in steepness with respect to M2 internal wave characteristics. Although the various canyons are symmetrical in structure, barotropic-to-baroclinic energy conversion rates Cυ are typically asymmetrical within them. The resulting onshore-propagating internal waves are the strongest along beams in the horizontal plane, with the stronger beam in the control simulation lying on the side with higher Cυ. Analysis of the simulation results suggests that the cross-canyon asymmetrical Cυ distributions are caused by multiple-scattering effects on one canyon side slope, because the phase variation in the spatially distributed internal-tide sources, governed by variations in the orientation of the bathymetry gradient vector, allows resonant internal-tide generation. A less complex, semianalytical, modal internal wave propagation model with sources placed along the critical-slope locus (where the M2 internal wave characteristic is tangent to the seabed) and variable source phasing is used to diagnose the physics of the horizontal beams of onshore internal wave radiation. Model analysis explains how the cross-canyon phase and amplitude variations in the locally generated internal tides affect parameters of the internal-tide beams. Under the assumption that strong internal tides on continental shelves evolve to include nonlinear wave trains, the asymmetrical internal-tide generation and beam radiation effects may lead to nonlinear internal waves and enhanced mixing occurring preferentially on one side of shelfbreak canyons, in the absence of other influencing factors.

Oceanwide Precise Determination of Sea Surface Height from In-Situ Measurements on Cargo Ships

2014 ◽  
Vol 37 (1) ◽  
pp. 77-96 ◽  
Author(s):  
Ole Roggenbuck ◽  
Jörg Reinking ◽  
Alexander Härting
Keyword(s):  
Sea Surface Height ◽  
Precise Determination ◽  
In Situ Measurements ◽  
Sea Surface

scholarly journals Seawater Salinity Estimating Module Based on the Sound Velocity Measurements

2021 ◽  
Vol 28 (1) ◽  
Author(s):  
А. P. Tolstosheev ◽  
E. G. Lunev ◽  
S. V. Motyzhev ◽  
V. Z. Dykman ◽  
◽  
...  
Keyword(s):  
Sound Velocity ◽  
Ocean Dynamics ◽  
Sea Surface ◽  
Temperature Measurements ◽  
Velocity Measurements ◽  
In Situ Tests ◽  
Salinity Field ◽  
In Situ Observations

Purpose. Reliability of knowledge about the ocean dynamics and climate variability is largely limited for lack of systematic in situ observations of the sea surface layer salinity, which is one of the basic hydrological parameters determining circulation and stratification of the water masses. The study is aimed at developing an autonomous device for long-term monitoring of salinity in the seawater upper layer. Methods and Results. One of the most effective tools for in situ observations of the ocean upper layer is the global network of surface drifting buoys – drifters. At present, the network consists of more than 1500 buoys, but only a few of them provide sea surface salinity observations within the framework of a limited number of pilot experiments. In the drifters, salinity is calculated by the traditional method using the results of the electrical conductivity and temperature measurements. There are a few problems related both to the principle of determining salinity by this method and to providing long-term stable running of conductivity sensors under the conditions of pollution and biological fouling. A drifter equipped with the module for the sound velocity and temperature measurements used for calculating salinity by an alternative method just aboard the drifter, was developed in Marine Hydrophysical Institute, Russian Academy of Sciences. The sound velocity and temperature module includes a specially designed time-of-flight sound velocity sensor with the fixed base and a quartz temperature sensor. In course of two years, numerous laboratory and in situ tests of several prototypes of the sound velocity and temperature module were performed. The laboratory tests showed that the repeatability limits for the results of the sound velocity measurements in the distilled water were 0.02 m/s. According to the data of the long-term in situ tests performed at intensive biological fouling, the error of salinity estimation resulted from of the sound velocity and temperature measurements were within 0.05 ‰. This result permits to expect that the sound velocity and temperature module parameters will remain stable in real conditions of long-term autonomous operation. Conclusions. The obtained results make it possible to recommend application of the drifters equipped with the modules for the sound velocity and temperature measurements as an effective tool for regular operational monitoring of the salinity field of the upper sea layer.

scholarly journals Impacts of mean dynamic topography on a regional ocean assimilation system

Ocean Science ◽  
2015 ◽  
Vol 11 (5) ◽  
pp. 829-837 ◽  
Author(s):  
C. Yan ◽  
J. Zhu ◽  
C. A. S. Tanajura
Keyword(s):  
Data Assimilation ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Dynamic Topography ◽  
Altimetry Data ◽  
Mean Dynamic Topography ◽  
Mean Sea Surface ◽  
The Mean

Abstract. An ocean data assimilation system was developed for the Pacific–Indian oceans with the aim of assimilating altimetry data, sea surface temperature, and in situ measurements from Argo (Array for Real-time Geostrophic Oceanography), XBT (expendable bathythermographs), CTD (conductivity temperature depth), and TAO (Tropical Atmosphere Ocean). The altimetry data assimilation requires the addition of the mean dynamic topography to the altimetric sea level anomaly to match the model sea surface height. The mean dynamic topography is usually computed from the model long-term mean sea surface height, and is also available from gravimetric satellite data. In this study, the impact of different mean dynamic topographies on the sea level anomaly assimilation is examined. Results show that impacts of the mean dynamic topography cannot be neglected. The mean dynamic topography from the model long-term mean sea surface height without assimilating in situ observations results in worsened subsurface temperature and salinity estimates. Even if all available observations including in situ measurements, sea surface temperature measurements, and altimetry data are assimilated, the estimates are still not improved. This proves the significant impact of the MDT (mean dynamic topography) on the analysis system, as the other types of observations do not compensate for the shortcoming due to the altimetry data assimilation. The gravimeter-based mean dynamic topography results in a good estimate compared with that of the experiment without assimilation. The mean dynamic topography computed from the model long-term mean sea surface height after assimilating in situ observations presents better results.

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