ESTIMATING OCEAN MIDDLE-DEPTH VELOCITIES FROM ARGO FLOATS: ERROR ESTIMATION AND APPLICATION TO PACIFIC

摘要

The Array for Real-time Geostrophic Oceanography (ARGO) project creates a unique opportunity to estimate the absolute velocity at mid-depths of the global oceans. However, the estimation can only be made based on float surface trajectories. The diving and resurfacing positions of the float are not available in its trajectory file. This surface drifting effect makes it difficult to estimate mid-depth current. Moreover, the vertical shear during decent or ascent between parking depth and the surface is another major error source. In this presentation, we first quantify the contributions of the two major error sources using the current estimates from Estimating the Climate and Circulation of the Ocean (ECCO) and find that the surface drifting is a primary error source. Then, a sequential surface trajectory prediction/estimation scheme based on Kalman Filter is introduced and implemented to reduce the surface drifting error in the Pacific during November 2001 to October 2004. On average, the error of the estimated velocities is greatly reduced from 2.7 to 0.2 cm s~(-1) if neglecting the vertical shear. These velocities with relative error less than 25% are analyzed and compared with previous studies on mid-depth currents. The current system derived from ARGO floats in Pacific at 1000 and 2000 Db is comparable to other measured by ADCP (Reid, 1997; Firing et al., 1998). This presentation is based on two submitted manuscripts of the same authors (Xie and Zhu, 2006; Zhu et al., 2006). More detailed results can be found in the two manuscripts.