Variational assimilation of Geosat altimeter data into a two-layer quasi-geostrophic model over the Newfoundland ridge and basin

AbstractIn this study, we determined the alignment of the laser altimeter aboard Hayabusa2 with respect to the spacecraft using in-flight data. Since the laser altimeter data were used to estimate the trajectory of the Hayabusa2 spacecraft, the pointing direction of the altimeter needed to be accurately determined. The boresight direction of the receiving telescope was estimated by comparing elevations of the laser altimeter data and camera images, and was confirmed by identifying prominent terrains of other datasets. The estimated boresight direction obtained by the laser link experiment in the winter of 2015, during the Earth’s gravity assist operation period, differed from the direction estimated in this study, which fell on another part of the candidate direction; this was not selected in a previous study. Assuming that the uncertainty of alignment determination of the laser altimeter boresight was 4.6 pixels in the camera image, the trajectory error of the spacecraft in the cross- and/or along-track directions was determined to be 0.4, 2.1, or 8.6 m for altitudes of 1, 5, or 20 km, respectively.

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Satellite Investigation of Semidiurnal Internal Tides in the Sulu-Sulawesi Seas

Remote Sensing ◽

10.3390/rs13132530 ◽

2021 ◽

Vol 13 (13) ◽

pp. 2530

Author(s):

Xiaoyu Zhao ◽

Zhenhua Xu ◽

Ming Feng ◽

Qun Li ◽

Peiwen Zhang ◽

...

Keyword(s):

Interference Pattern ◽

Energy Flux ◽

Internal Tide ◽

Tidal Energy ◽

Internal Tides ◽

Altimeter Data ◽

Band Pass Filter ◽

Pass Filter ◽

Sulu Sea ◽

Tidal Energy Flux

The mode-1 semidiurnal internal tides that emanate from multiple sources in the Sulu-Sulawesi Seas are investigated using multi-satellite altimeter data from 1993–2020. A practical plane-wave analysis method is used to separately extract multiple coherent internal tides, with the nontidal noise in the internal tide field further removed by a two-dimensional (2-D) spatial band-pass filter. The complex radiation pathways and interference patterns of the internal tides are revealed, showing a spatial contrast between the Sulu Sea and the Sulawesi Sea. The mode-1 semidiurnal internal tides in the Sulawesi Sea are effectively generated from both the Sulu and Sangihe Island chains, forming a spatially inhomogeneous interference pattern in the deep basin. A cylindrical internal tidal wave pattern from the Sibutu passage is confirmed for the first time, which modulates the interference pattern. The interference field can be reproduced by a line source model. A weak reflected internal tidal beam off the Sulawesi slope is revealed. In contrast, the Sulu Island chain is the sole energetic internal tide source in the Sulu Sea, thus featuring a relatively consistent wave and energy flux field in the basin. These energetic semidiurnal internal tidal beams contribute to the frequent occurrence of internal solitary waves (ISWs) in the study area. On the basis of the 28-year consistent satellite measurements, the northward semidiurnal tidal energy flux from the Sulu Island chain is 0.46 GW, about 25% of the southward energy flux. For M2, the altimetric estimated energy fluxes from the Sulu Island chain are about 80% of those from numerical simulations. The total semidiurnal tidal energy flux from the Sulu and Sangihe Island chains into the Sulawesi Sea is about 2.7 GW.

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Seasonal variability of mesoscale eddies in the Banda Sea inferred from altimeter data

Acta Oceanologica Sinica ◽

10.1007/s13131-020-1665-2 ◽

2020 ◽

Vol 39 (12) ◽

pp. 11-20

Author(s):

Baiyang Chen ◽

Lingling Xie ◽

Quanan Zheng ◽

Lei Zhou ◽

Lei Wang ◽

...

Keyword(s):

Seasonal Variability ◽

Mesoscale Eddies ◽

Altimeter Data

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Multicore structures and the splitting and merging of eddies in global oceans from satellite altimeter data

10.5194/os-2018-96 ◽

2018 ◽

Author(s):

Wei Cui ◽

Wei Wang ◽

Jie Zhang ◽

Jungang Yang

Keyword(s):

Intermediate Stage ◽

Altimeter Data ◽

Western Boundary ◽

Mean Flow ◽

Sea Level Anomalies ◽

Strong Current ◽

A Cell ◽

Circumpolar Current ◽

Overlap Ratio ◽

Global Oceans

Abstract. This study investigated the statistics of eddy splitting and merging in the global oceans based on 23 years’ altimetry data. Multicore structures were identified using an improved threshold-free closed-contour algorithm of sea surface height. Splitting and merging events were discerned from continuous time series maps of sea level anomalies. Multicore structures represent an intermediate stage in the process of eddy evolution, similar to the generation of multiple nuclei in a cell as a preparatory phase for cell division. Generally, splitting or merging events can change substantially (by a factor of two or more) the eddy scale, amplitude, and eddy kinetic energy. Specifically, merging (splitting) generally causes an increase (decrease) of eddy properties. Multicore eddies were found to tend to split into two eddies with different intensities. Similarly, eddy merging is not an interaction of two equal-intensity eddies, and that it tends to manifest as a strong eddy merging with a weaker one. A hybrid tracking strategy based on the eddy overlap ratio, considering both multicore and single-core eddies, was used to confirm splitting and merging events globally. The census revealed that eddy splitting and merging do not always occur most frequently in eddy-rich regions, e.g., their frequencies of occurrence in the Antarctic Circumpolar Current and western boundary currents were found obviously higher than mid-latitude regions (20°–35°) north and south. Eddy splitting and merging are caused primarily by an unstable configuration of multicore structures due to obvious current– or eddy–topography interaction, strong current variation, and eddy–mean flow interaction.

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A New Method for Tracking Meddies by Satellite Altimetry

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-13-00080.1 ◽

2014 ◽

Vol 31 (6) ◽

pp. 1434-1445 ◽

Cited By ~ 8

Author(s):

Federico Ienna ◽

Young-Heon Jo ◽

Xiao-Hai Yan

Keyword(s):

Remote Sensing ◽

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Saline Water ◽

Ensemble Empirical Mode Decomposition ◽

Altimeter Data ◽

In Situ Techniques ◽

The North ◽

The North Atlantic

Abstract Subsurface coherent vortices in the North Atlantic, whose saline water originates from the Mediterranean Sea and which are known as Mediterranean eddies (meddies), have been of particular interest to physical oceanographers since their discovery, especially for their salt and heat transport properties into the North Atlantic Ocean. Many studies in the past have been successful in observing and studying the typical properties of meddies by probing them with in situ techniques. The use of remote sensing techniques would offer a much cheaper and easier alternative for studying these phenomena, but only a few past studies have been able to study meddies by remote sensing, and a reliable method for observing them remotely remains elusive. This research presents a new way of locating and tracking meddies in the North Atlantic Ocean using satellite altimeter data. The method presented in this research makes use of ensemble empirical mode decomposition (EEMD) as a means to isolate the surface expressions of meddies on the ocean surface and separates them from any other surface constituents, allowing robust meddies to be consistently tracked by satellite. One such meddy is successfully tracked over a 6-month time period (2 November 2005 to 17 May 2006). Results of the satellite tracking method are verified using expendable bathythermographs (XBT).

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