Some Expectations for Submesoscale Sea Surface Height Variance Spectra

Abstract

In 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.

Surface Kinetic Energy Distributions in the Global Oceans From a High‐Resolution Numerical Model and Surface Drifter Observations

“…Satellite remote sensing has been extensively used to advance our understanding of ocean dynamics over the last several decades (Fu et al, ; Morrow & Le Traon, ). With the advent of wide‐swath radar interferometry, the upcoming Surface Water and Ocean Topography (SWOT) mission is expected to measure, for the first time, the sea surface height globally and at spatial scales down to 15–50 km depending on the local sea state (Callies & Wu, ; Morrow et al, ; Wang et al, ). It is anticipated that these unprecedented sea surface height measurements will capture ocean variability in the submesoscale range (Durand et al, ; Fu & Ubelmann, ).…”

Predictability of non-phase-locked baroclinic tides in the Caribbean Sea

“…Efforts to map the baroclinic tide with satellite altimeter data are generally only capable of identifying the phaselocked part of the tidal signals (Ray and Mitchum, 1996;Carrère et al, 2004). Attempts to quantify the energy transport, and dissipation, of the baroclinic tide from altimetry data must make assumptions about the partitioning of en-ergy between the phase-locked and non-phase-locked tides; however, present estimates for non-phase-locked tidal steric height suffer from sampling limitations (Zilberman et al, 2011;Kelly et al, 2015;Zaron, 2015Zaron, , 2017.…”

“…This study has examined the predictability of non-phaselocked baroclinic tides using 4 d ocean forecast products from the AMSEAS system. It was motivated by the desire to understand our present capability for predicting baroclinic tidal SLA, which is expected to be a key limitation for measuring mesoscale and submesoscale processes with the forthcoming SWOT wide-swath satellite altimeter (Callies and Wu, 2019). The AMSEAS system is well suited to this task since it represents the state of the art among data-assimilating ocean forecast systems; it has resolution sufficient to realistically represent baroclinic tide generation and propagation, and the 4 d forecast cycle is adequate to separate the SLA signals of low-frequency balanced motions from highfrequency processes, the latter being dominated by baroclinic tides.…”

Predictability of Non-Phase-Locked Baroclinic Tides in the Caribbean Sea

“…This study has examined the predictability of non-phase-locked baroclinic tides using four-day ocean forecast products from the AMSEAS system. It was motivated by the desire to understand our present capability for predicting baroclinic tidal SLA, which is expected to be a key limitation for measuring mesoscale and submesoscale processes with the forthcoming SWOT wide-swath satellite altimeter (Callies and Wu, 2019). The AMSEAS system is well-suited to this task since it represents the state-of-the-art among data-assimilating ocean forecast systems; it has resolution sufficient to realistically represent baroclinic tide generation and propagation, and the four-day forecast cycle is adequate to separate the SLA signals of low-frequency balanced motions from high-frequency processes, the latter being dominated by baroclinic tides.…”