Atmospheric Surface Forcing Corrections Derived from assimilating Ocean Observations using the NCOM-4DVAR

In this study, a weak constraint assimilation is carried out using the Navy Coastal Ocean Model 4DVAR (NCOM-4DVAR) to fit the ocean observations collected in the Gulf of Mexico, including satellite sea surface temperature, sea surface height, and in-situ profiles of temperature and salinity, as well as surface velocity measurements derived from surface drifters. The tangent linear and adjoint of NCOM are written with the surface atmospheric forcing terms as part of the control. The representer algorithm is used in NCOM-4DVAR, which allows for the control of both initial conditions and model errors while minimizing the cost function in the observations space. Retrieved corrections to the atmospheric forcing are validated by adding them to the prior estimates and integrating the nonlinear model, and comparing the resulting solution to independent and non-assimilated observations. Examples of numerical experiments will be shown.