HR: 0800h
AN: A31B-05    [Abstracts]
TI: High resolution ensemble forecasting for the Gulf of Mexico eddies and fronts
AU: * Counillon, F
EM: francois@nersc.no
AF: Mohn-Sverdrup Center / NERSC, Thormoehlensgate 47, Bergen, N-5006 Ber, Norway
AU: Bertino, L
EM: laurent.bertino@nersc.no
AF: Mohn-Sverdrup Center / NERSC, Thormoehlensgate 47, Bergen, N-5006 Ber, Norway
AB: As oil production moves further into deeper waters, the costs related to strong current hazards are increasing accordingly, and accurate three-dimensional forecasts of currents are urgently needed. To be useful, models have to locate eddies and fronts to an accuracy of 30 km at a nowcast stage, which is almost impossible to accomplish with the use of satellite data of the same accuracy. The use of stochastic forecast allows us to give confidence of our prediction. We are using a nested configuration of the Hybrid coordinate ocean model (HYCOM), where the TOPAZ system, which covers the Atlantic and the Artic, gives lateral boundary condition to a high-resolution (5km) model of the Gulf of Mexico (GOM). TOPAZ is a real-time forecasting coupled ocean-ice model, which assimilates sea level anomaly (SLA), sea surface temperature, and sea ice concentration, with the ensemble Kalman filter. The high- resolution model assimilates SLA using the ensemble optimal interpolation, which updates accordingly the currents, salinity, temperature, and layer interface at all depths. Here, we evaluate the ensemble forecast capabilities of our high-resolution model, for eddy Extreme that has been observed from altimeters around the 15th of July. We run 6 successive ensemble runs composed of 10 members of equal likelihood. Members differ by perturbations of the initial state, of the lateral boundary conditions, and of the atmospheric boundary conditions. We have started the experiment 1 month prior to the shedding event, because it was the time necessary for perturbation of boundary conditions to spread uniformly and reach a significant level across the GOM. The ensemble reproduces well the dynamics of the eddy shedding and produces a significant spread at the boundary of the eddy, but underestimates the RMS error of the SLA. Prior to the shedding time, the error growth increase, induced by the highly non-linear growth of cyclonic eddies at the boundary of the Loop Current. Additionally, this ensemble has allowed for optimization of data assimilation parameters depending on the range of the forecast.
DE: 3260 Inverse theory
DE: 3300 ATMOSPHERIC PROCESSES
DE: 4260 Ocean data assimilation and reanalysis (3225)
DE: 4520 Eddies and mesoscale processes
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly