An accurate procedure for estimating the phase speed of ocean waves from observations by satellite borne altimeters

De-Leon, Yair; Paldor, Nathan

doi:10.1016/j.actaastro.2016.11.016

Cited by 4 publications

(4 citation statements)

References 14 publications

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“…The trapped wave theory is valid when the meridional range is larger than (2 + ζ n ) ag H 4 2 sin 2φ w 1 3 (see Eq. 7 of Gildor et al, 2016). For n = 0, for typical values of (g H ) 1 2 of 2 to 3 m s −1 and φ w = 30 • this condition is satisfied when the domain is wider than about 500 km.…”

mentioning

confidence: 90%

“…The meridional structure of the height field of trapped waves is (see Eq. 5 in Gildor et al, 2016 with the modifications outlined in Sect. 4.1)…”

Section: Explicit Expressions For the Meridional Structure Of The Twomentioning

confidence: 99%

“…(3) vanishes (in contrast to Gildor et al, 2016, where the wall was placed at y w = −L/2, where L is the channel width). In addition, the boundary condition at φ w in Gildor et al (2016) is the vanishing of the meridional velocity, whereas in the present application Fig. 2b implies that the meridional derivative of the height field vanishes at φ w .…”

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confidence: 99%

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Trapped planetary (Rossby) waves observed in the Indian Ocean by satellite borne altimeters

De-Leon¹,

Paldor²

2017

Ocean Sci.

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Using 20 years of accurately calibrated, highresolution observations of sea surface height anomalies (SSHAs) by satellite borne altimeters, we show that in the Indian Ocean south of the Australian coast the low-frequency variations of SSHAs are dominated by westward propagating, trapped, i.e., non-harmonic, Rossby (Planetary) waves. Our results demonstrate that the meridional-dependent amplitudes of the SSHAs are large only within a few degrees of latitude next to the southern Australian coast while farther in the ocean they are uniformly small. This meridional variation of the SSHA signal is typical of the amplitude structure in the trapped wave theory. The westward propagation speed of the SSHA signal is analyzed by employing three different methods of estimation. Each one of these methods yields speed estimates that can vary widely between adjacent latitudes but the combination of at least two of the three methods yields much smoother variation. The estimates obtained in this manner show that the observed phase speeds at different latitudes exceed the phase speeds of harmonic Rossby (planetary) waves by 140 to 200 % (which was also reported in previous studies). In contrast, the theory of trapped Rossby (planetary) waves in a domain bounded by a wall on its equatorward side yields phase speeds that approximate more closely the observed phase speeds in the study area.

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confidence: 90%

“…The meridional structure of the height field of trapped waves is (see Eq. 5 in Gildor et al, 2016 with the modifications outlined in Sect. 4.1)…”

Section: Explicit Expressions For the Meridional Structure Of The Twomentioning

confidence: 99%

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Trapped planetary (Rossby) waves observed in the Indian Ocean by satellite borne altimeters

De-Leon¹,

Paldor²

2017

Ocean Sci.

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“…A possible reason for this lack of success in bridging the gap between observations and theory is that the observed estimates are not reliable. De-Leon and Paldor (2017a) examined the accuracy of various methods in estimating the phase speed of waves by applying these methods to an artificially generated signal made of 3 sine functions (modes) with known phase speeds and amplitudes, compounded by large-amplitude random white noise. All methods have successfully filtered out the high amplitude white-noise from the 3-harmonic signal and accurately detected the main mode (some of them also detected the secondary modes).…”

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confidence: 99%

Commonly used methods fail to detect known phase speeds of simulated signals of Sea Surface Height Anomalies

De-Leon

Paldor

2019

Preprint

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Abstract. This work examines the accuracy and validity of two variants of Radon transform and two variants of the Two-Dimensional Fast Fourier Transform (2D FFT) that have been previously used for estimating the propagation speed of Sea Surface Height Anomalies (SSHA) derived from satellite borne altimeters. The examination employs numerically simulated SSHA signals made up of 20 or 50 modes where one, randomly selected, mode has a larger amplitude than the uniform amplitude of the other modes. Since the dominant input mode is ab-initio known, we can clearly define "success" in detecting its phase/propagation speed. We show that all previously employed variants fail to detect the phase speed of the dominant input mode even when its amplitude is 5 times larger than all other modes and that they successfully detect the phase speed of the dominant input mode only when its amplitude is 10 times (or more) larger than the other modes. This requirement is an unrealistic limitation on oceanic SSHA observations. In addition, three of the variant methods “detect” a dominant mode even when all modes have the exact same amplitude. The accuracy with which the four algorithms identify a dominant input mode decreases with the increase in the number of modes in the signal. Our findings cast a doubt on the reliability of phase speed estimates of SSHA observations and the reported “too fast” phase speed of baroclinic Rossby waves in the ocean.

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Computer simulation of surface hydrophysical anomalies detected by spacecraft radars

Galyaev

Guryev²,

Silnikov

et al. 2023

Acta Astronautica

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An accurate procedure for estimating the phase speed of ocean waves from observations by satellite borne altimeters

Cited by 4 publications

References 14 publications

Trapped planetary (Rossby) waves observed in the Indian Ocean by satellite borne altimeters

Trapped planetary (Rossby) waves observed in the Indian Ocean by satellite borne altimeters

Commonly used methods fail to detect known phase speeds of simulated signals of Sea Surface Height Anomalies

Computer simulation of surface hydrophysical anomalies detected by spacecraft radars

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