Noise-induced flow in quasigeostrophic turbulence with bottom friction

Randomly-forced fluid flow in the presence of scale-unselective dissipation develops mean currents following topographic contours. Known mechanisms based on the scale-selective action of damping processes are not at work in this situation. Coarse-graining reveals that the phenomenon is a kind of noise-rectification mechanism, in which lack of detailed balance and the symmetry-breaking provided by topography play an important role.Comment: 8 pages Revtex, no figures. Related material at http://www.imedea.uib.es

Variational interpolation of high-frequency radar surface currents using DIVAnd

DIVAnd (Data-Interpolating Variational Analysis, in n-dimensions) is a tool to interpolate observations on a regular grid using the variational inverse method. We have extended DIVAnd to include additional dynamic constraints relevant to surface currents, including imposing a zero normal velocity at the coastline, imposing a low horizontal divergence of the surface currents, temporal coherence and simplified dynamics based on the Coriolis force and the possibility of including a surface pressure gradient. The impact of these constraints is evaluated by cross-validation using the HF (High-Frequency) radar surface current observations in the Ibiza Channel from the Balearic Islands Coastal Ocean Observing and Forecasting System (SOCIB). A small fraction of the radial current observations are set aside to validate the velocity reconstruction. The remaining radial currents from the two radar sites are combined to derive total surface currents using DIVAnd and then compared to the cross-validation data set and to drifter observations. The benefit of the dynamic constraints is shown relative to a variational interpolation without these dynamical constraints. The best results were obtained using the Coriolis force and the surface pressure gradient as a constraint which are able to improve the reconstruction from the Open-boundary Modal Analysis, a quite commonly used method to interpolate HF radar observations, once multiple time instances are considered together.SeaDataCloud project; JERICO-S3 projec

Air-sea fluxes based on observed annual cycle surface climatology and ocean model internal dynamics: a precise, non-damping zero-phase-lag approach applied to the Mediterranean Sea

A new model-based method of determining the surface fluxes of heat and freshwater that are needed to force ocean models is presented. In contrast to deriving the fluxes from a simulation with a restoring surface boundary condition, the new method determines the fluxes as a residual within the framework of physically realistic and natural boundary conditions on the sea surface temperature (SST) and sea surface salinity (SSS). The fluxes are computed (diagnosed) in such a way that an ensemble average of the model-simulated annual cycles of SST and SSS match the observed climatological annual cycles of SST and SSS, respectively. The surface boundary condition on the SST implicitly includes a net radiative flux (diagnosed) and a physically realistic heat exchange with the atmosphere (restoring flux), while the boundary condition on the SSS is the real freshwater flux (diagnosed) as proposed by Huang (J. Phys. Oceanogr., 33 (1993) 2428). Apart from being based on physically realistic surface boundary conditions, the advantage of the method is that it results in a realistic model simulation of the observed annual cycle of SST and SSS with no artificial damping of surface watermass fronts. The resulting heat fluxes and freshwater sources are realistic if the observed climatological data and model internal physics are accurate. The performance of the method is demonstrated using the DieCAST ocean model adapted to the Mediterranean Sea where the obtained model fluxes are compared with observations