On improving storm surge forecasting using an adjoint optimal technique

A three-dimensional ocean model and its adjoint model are used to simultaneously optimize the initial conditions (IC) and the wind stress drag coefficient (C-d) for improving storm surge forecasting. To demonstrate the effect of this proposed method, a number of identical twin experiments (ITEs) with a prescription of different error sources and two real data assimilation experiments are performed. Results from both the idealized and real data assimilation experiments show that adjusting IC and C-d simultaneously can achieve much more improvements in storm surge forecasting than adjusting IC or C-d only. A diagnosis on the dynamical balance indicates that adjusting IC only may introduce unrealistic oscillations out of the assimilation window, which can be suppressed by the adjustment of the wind stress when simultaneously adjusting IC and C-d. Therefore, it is recommended to simultaneously adjust IC and C-d to improve storm surge forecasting using an adjoint technique. (C) 2013 Elsevier Ltd. All rights reserved.