Adjustment of Near-Equatorial Wind Stress with Four-Dimensional Variational Data Assimilation in a Model of the Pacific Ocean

Abstract

Abstract A four-dimensional variational scheme is described in which ocean observations are assimilated into an ocean general circulation model using wind stress forcing fields as control variables. Idealized (“twin”) experiments are performed to evaluate the possibility of reconstructing wind stress variability and its oceanic response from synthetic observations of the ocean state. Two types of wind stress errors are considered: time-varying errors associated with a wind burst and constant errors associated with a wind stress bias. Both sets of experiments demonstrate that the spatial structure of the wind stress variations is well reconstructed, while the estimation of their amplitude and time evolution is less accurate. Sparser equatorial sampling, similar to that of the Tropical Atmosphere–Ocean array, only slightly degrades the analysis. Omitting velocity and salinity observations leads to a less accurate amplitude and time evolution of the wind stress increment. Still, general features are captured...