Met Office, Exeter, UK

We present a coflowing integral plume model for the transition from an eruption column to an umbrella cloud. This transition occurs above the level of neutral buoyancy where the rising plume is surrounded by a descending annulus. We model this transition by extending the coflowing integral plume model of Bloomfield and Kerr (2000, https://doi.org/10.1029/2018JB015841), which was originally developed for Boussinesq fountains, to volcanic plumes. In addition to the transition region, the new model includes the part of the eruption column below the level of neutral buoyancy. The eruption column and the transition to an umbrella cloud are treated as a continuous process from the vent upward. Equations for the variation with height of the mass, momentum, enthalpy, and moisture fluxes are presented for both the upward and downward plumes. The interaction between the upward and downward plumes is accounted for by two entrainment relations: from the upward to the downward plume and vice versa; entrainment from the environment into the downward plume (or the upward plume in the absence of a downward plume) is also accounted for. The model is applied to the two eruptions considered by Costa et al. (2016, https://doi.org/10.1016/j.jvolgeores.2016.01.017) for the volcanic-plume intercomparison study. Profiles of the mass and momentum fluxes are compared with those from an equivalent large-eddy simulation. The new model captures the order of magnitude of the fluxes, the relative magnitudes of the upward and downward fluxes and aspects of the profiles’ shape. In particular, the upward plume reaches a maximum before decreasing toward the top of the plume consistent with the large-eddy simulation plume.

The value of global (e.g., altimetry, satellite sea-surface temperature, Argo) and regional (e.g., radars, gliders, instrumented mammals, airborne profiles, 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, information content 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.

During the last 15 years, operational oceanography systems have emerged in several countries around the world. This emergence has been largely fostered by the GODAE experiment, during which each nation engaged in this activity have organised partnership and constructive competition. This trans-national coordination was very beneficial for the development of operational oceanography, leading to economies of scales and more targeted actions. Today, several systems provide routine real-time ocean analysis and forecast and/or reanalysis products. They are all based on (i) state-of-the-art primitive equation baroclinic Ocean General Circulation Model (OGCM) configurations, either global or regional (basin-scale), with resolutions that range from coarse to eddy resolving and (ii) data assimilation techniques whose complexity ranges from simple analysis correction to advanced 4D variational schemes. They assimilate altimeter sea level anomalies, remotely sensed SST such as GHRSST products and in situ profiles of T and S, including ARGO. Some systems have implemented downscaling capacities in specific regions of interest including shelf/coastal seas. Some also have implemented coupling with the atmosphere and/or the prognostic sea ice in polar regions. They are the GODAE system in operation. They are reviewed in this paper. The GODAE system discussed here include: (1) BLUElink OceanMAPS, (2) C-NOOFS, , (3) ECCO, (4) FOAM, (5) HYCOM/NCODA, (6) MERCATOR, (7) MFS, (8) MOVE/MRI.COM, (9) NLOM/NCOM, (10) NMEFC, (11) RTOFS and (12) TOPAZ.