Baroclinic Tidal Sea Level from Exact-Repeat Mission Altimetry

Abstract

A near-global model for the sea surface expression of the baroclinic tide has been developed using exact-repeat mission altimetry. The methodology used differs in detail from other altimetry-based estimates of the open ocean baroclinic tide, but it leads to estimates that are broadly similar to previous results. It may be used for prediction of the baroclinic sea level anomaly at the frequencies of the main diurnal and semidiurnal tides , , , and , as well as the annual modulates of , denoted and . The tidal predictions are validated by computing variance reduction statistics using independent sea surface height data from the CryoSat-2 altimeter mission. Typical midocean baroclinic tidal signals range from a few millimeters to centimeters of elevation, corresponding to subsurface isopycnal displacements of tens of meters; however, in a few regions, larger signals are present, and it is found that the present model can explain more than 13-cm2 variance at some sites. The predicted tides are also validated by comparison with a database of hourly currents inferred from drogued surface drifters. The database is large enough to permit assessment of a simple model for scattering of the low-mode tide. Results indicate a scattering time scale of approximately 1 day, consistent with a priori estimates of time-variable refraction by the mesoscale circulation.

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

“…Elipot et al () produced a unique global data set of surface drifter positions and velocities with hourly temporal resolution, which enables studies of near‐surface high‐frequency motion (e.g., inertial and tidal). The surface drifter measurements have been previously used to investigate a wide range of oceanic processes and dynamics, from global velocity climatology (Lumpkin & Johnson, ) and mesoscale coherent vortices (Lumpkin, ) to submesoscale motions (Lumpkin & Elipot, ; Zhang & Qiu, ), near‐inertial waves (Elipot et al, ; Liu et al, ), internal tides (Zaron, ), and relative dispersion (Corrado et al, ). In situ observations by oceanographic moorings or profiling instruments may be suited to obtaining depth‐dependent tidal and higher‐frequency variability for model assessment (e.g., Ansong et al, ; Savage et al, ) and thus complement surface drifter observations.…”

Mapping the nonstationary internal tide with satellite altimetry

“…First, for the forthcoming SWOT altimeter mission it will be necessary to remove baroclinic tidal signals in order to study small‐scale geostrophically‐balanced flows and achieve the science goals of the mission [ Fu and Ferrari , ]. Satellite altimetry is essentially the only means available to map, nearly globally, the baroclinic tides for developing these models, and it is crucial to quantify the tidal signals not present in these maps [ Dushaw , ; Egbert et al ., ; Ray and Zaron , ; Zaron , ; Zhao et al ., ]. Second, the low‐mode baroclinic tide is the principal pathway through which energy lost from the barotropic tide is transferred to smaller scales in the deep ocean [ Egbert and Ray , ], so closing the tidal energy budget requires knowledge of both the coherent and incoherent baroclinic tide.…”

Quantifying Tidal Fluctuations in Remote Sensing Infrared SST Observations

“…Maps of tidal sea level are provided on a 0.05-degree near-global grid for the 6 most important constituents (M2, S2, K1, O1, N2, and P1 tides). Tidal currents are derived from sea level maps assuming the following momentum equations [9]:…”

“…(Figure 1). These currents are masked over the continental shelf because HRET is not reliable there [9]. Barotropic currents are amplified over the shelf with M2 tidal currents up to 0.6-0.8 m s −1 .…”

“…We more precisely focus on the quantification of SST fluctuations induced by stationary baroclinic tides because atlases of their distributions are now available [9]. We will also quantify SST fluctuations induced by barotropic tides because the same methodology may be employed for that purpose.…”