# Seminar: Variational interpolation of high-frequency radar surface currents using DIVA

**Speaker: Alexander Barth, from Department of Astrophysics, Geophysics and Oceanography of Liège University.**

Figure: Reconstructed surface currents of the 2014-10-03 (right panel) and the corresponding radial currents and HF radar observations (colored dots) for the site FORM (middle panel) and GALF (right panel).

**Esporles, October 24, 2017. **DIVA (data-interpolating variational analysis) is a tool that allows to interpolate observations on a regular grid. It is commonly applied to in situ observations such as temperature, salinity or nutrients to obtain gridded climatologies. It takes the bathymetry, ocean currents and the spatial connectivity of water bodies into account to interpolate these tracers. For vector quantities, like ocean surface currents, a new set of constraints must be taken into consideration.

We extended DIVA to include additional dynamic constraints relevant to surface currents:

• imposing a zero normal velocity at the coastline

• imposing a low divergence of the surface currents

• temporal coherence

• simplified dynamics based on inertial oscillations

• simplified dynamics based on inertial oscillations and a surface pressure gradient

The impact of these constraints is evaluated by cross-validation using the HF radar observations from SOCIB. A small fraction of the radial current observations are set aside to validate the velocity reconstruction. The remaining radial currents from two radar sites are combined to derive total current and then compared to the cross-validation data set. The benefit of the dynamics constraints is assessed relative to a naive variational interpolation ignoring these dynamical constraints.

**Date and Time: **Monday, October 30, 10:00-11:00h

**Place: **IMEDEA Seminar Room

**Organized by: **SOCIB + TMOOS (UIB-CSIC)

**Fuente: **IMEDEA (CSIC-UIB)