The value of global (e.g. altimetry, satellite sea-surface temperature, Argo) and regional (e.g. radars, gliders, instrumented mammals, airborne profiles and biogeochemical) observation-types for monitoring the mesoscale ocean circulation and biogeochemistry is demonstrated using a suite of global and regional prediction systems and remotely-sensed data. A range of techniques is used to demonstrate the value of different observation-types to regional systems and the benefit of high-resolution and adaptive sampling for monitoring the mesoscale circulation. The techniques include Observing System Experiments, Observing System Simulation Experiments, adjoint sensitivities, representer matrix spectrum, observation footprints and spectral analysis. It is shown that local errors in global and basin-scale systems can be significantly reduced when assimilating observations from regional observing systems.

No abstract

Progress in Oceanography j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / p o c e a n changes in sea ice extent, will have a significant impact on the arctic atmosphere. We present up-to-date freshwater transport numbers for the East Greenland Current in the Fram Strait, as well as the first map of the annual cycle of freshwater layer thickness in the East Greenland Current along the east coast of Greenland, from data obtained by CTDs mounted on seals that traveled back and forth across the Nordic Seas. We have taken advantage of the real-time transmission of some of these platforms and demonstrate the use of ice-tethered profilers in validating satellite products of sea ice motion, as well as the use of Seagliders in validating ocean forecasts, and we present a sea ice drift product-significantly improved both in space and time-for use in operational ice-forecasting applications. We consider real-time acquisition of data from the ocean interior to be a vital component of a sustained Arctic Ocean Observing System, and we conclude by presenting an outline for an observing system for the European sector of the Arctic Ocean.

The circulation along the Norwegian coast is characterized by many transient smallscale features such as eddies and meanders that are challenging to reproduce by means of numerical modeling. In this thesis I investigate the use of advanced data assimilation (DA) techniques in high-resolution coastal models to improve the circulation estimates. One particularly interesting observational platform for the coastal ocean is highfrequency (HF) radars, which measure surface currents in the coastal zone up to 200 km offshore. The suitability of such observations for use in high-resolution coastal DA systems is assessed by quantifying which components of the near-surface current field are observed by the HF radars. Our results show that there are no contributions from wave drift in the measurements, thus they are suitable for use in coastal DA. Assimilation of HF radar currents in a high-resolution model shows clear improvement in the circulation estimates. Further improvement is obtained when CTD profiles of temperature and salinity are included in the assimilated data set. A reanalysis of a period, during which in-situ observations were abundant in the study area, is used to assess how an observational network dense enough to constrain the water mass distribution affects the upper ocean circulation estimates. Our investigations of the results show a weakening of the topographically steered currents and, as the stratification increases the effective resolution of the model, more small-scale circulation features are developed. Such changes may have a significant effect on upper ocean transport. Finally, the potential of using high-resolution coastal reanalyses to study specific physical processes is demonstrated for the case of the mechanisms causing variability in the Norwegian Coastal Current.

Abstract. Assimilation of high-frequency (HF) radar current observations and CTD hydrography is performed with the 4D-Var analysis scheme implemented in the Regional Ocean Modeling System (ROMS). We consider both an idealized case, with a baroclinic slope current in a periodic channel, and a realistic case for the coast of Vesterålen in northern Norway. In the realistic case, the results of the data assimilation are compared with independent data from acoustic profilers and surface drifters. Best results are obtained when background error correlation scales are small (10 km or less) and when the data assimilation window is short, i.e. about 1 day. Furthermore, we find that the impact of assimilating HF radar currents is generally larger than the impact of CTD hydrography. However, combining the HF radar currents with a few hydrographic profiles gives significantly better results, which demonstrates the importance of complementing surface observations with observations of the vertical structure of the ocean.