Vertical motion in the upper ocean from glider and altimetry data

Abstract

This study represents a first attempt to combine new glider technology data with altimetry measurements to understand the upper ocean dynamics and vertical exchanges in areas with intense horizontal density gradients. In July 2008, just two weeks after Jason‐2 altimeter was launched, a glider mission took place along a satellite track in the Alboran Sea (Western Mediterranean). The mission was designed to be almost simultaneous with the satellite passage. Dynamic height from glider reveals a sharp gradient (∼15 cm) and corresponds very well with the absolute dynamic topography from Jason‐1 & Jason‐2 tandem mission (r > 0.97, rms differences < 1.6 cm). We blend both data sets (glider and altimetry) to obtain a consistent and reliable 3D dynamic height field. Using quasi‐geostrophic dynamics, we diagnose large‐scale vertical motions (∼1 m day−1) which may provide a local mechanism for the subduction of the chlorophyll tongue observed by the glider.

Towards high resolution mapping of 3-D mesoscale dynamics from observations

“…Though more complicated techniques such as the semi-geostrophic omega equation (Viúdez and Dritchel, 2004) have been proposed, the most used technique is based on the solution of the quasi-geostrophic (QG) omega equation (e.g. Tintoré et al, 1991;Buongiorno Nardelli et al, 2001;Pascual et al, 2004;Ruiz et al, 2009), which has already been shown to give reasonable estimates of the vertical velocities compared to primitive equation models (Pinot et al, 1996).…”

“…On the other hand, simplified diagnostic models can be applied to retrieve the vertical velocity field from both 2-D and/or 3-D estimates of geostrophic currents and density fields (e.g. Tintoré et al, 1991;Allen and Smeed, 1996;Buongiorno Nardelli et al, 2001;Pascual et al, 2004;Isern-Fontanet et al, 2008;Ruiz et al, 2009).…”

“…In this work, the algorithm for the solution of the Q vector formulation of the omega equation ( et Ruiz et al, 2009) was adapted to the specific products considered. Actually, the omega equation requires as input both the geostrophic field and the density stratification.…”

“…As a second step, a quasi-geostrophic (QG) diagnostic numerical model (the Q vector formulation of the omega equation) has been used to estimate the vertical velocities (Pascual et al, 2004;Ruiz et al, 2009). The omega equation was applied to different MyOcean products (both model and observation-based) in order to quantify the differences/limitations in the diagnostic tools used and the impact of the spatial resolution on the retrieved velocity.…”

“…Stammer et al, 2010, and references therein). Data assimilation is based on statistical or variational approaches that combine the observational data with the underlying (approximated) dynamical principles that govern the evolution of the system, taking into account some estimates of the errors and uncertainties associated with both components.…”