Estimation And Validation Of Surface Currents In The Global Ocean From Argo Floats

As an important part in the world climate system, the ocean surface currents play an essential role in the circulation of heat, water and nutrients. People have studied the oceans for a long time; however, for some technical reasons, not many observations had been obtained until quite recent, especially in the open oceans. Later, people started to study floats, which soon make ocean studies in large scale possible. Since the price is low and the deployment is easy, floats began to be deployed in the world ocean quickly. And it was in this moment that Argo appeared. It was mainly used for temperature-salinity profile records from a certain depth (as 2000m) to the surface. Through the collaboration of many countries, Argo grows fast and will complete the array of 3,000 floats in the near future to monitor the global ocean in near real time with 3×3 coverage.In this paper, the ocean surface currents were evaluated from the trajectories of Argo floats in ocean surface. Argo floats are fixed by satellites when they are drifting on the surface, but these fixes have errors of 150m to 1,500m. In order to reduce the errors, a Kalman filter based trajectory prediction model was introduced in this paper to optimize the use of information from prediction and observation to improve the evaluation of float trajectory. In this way, Argo data from 7/1997-12/2006 were studied and the surface currents in the global ocean as well as the relative errors were evaluated. Based on these results, the main features of yearly and seasonal averaged currents were discussed and compared with the work of other people. Results show that Argo floats can effectively describe the state of surface currents.In the end two other float arrays were introduced: TAO array of moored floats in the tropical ocean and global array of drifter floats. Using the current observations from these two arrays and simple temporal-spatial control, speed and direction of Argo currents were calibrated respectively. Results show that in most of the times there are not much difference between currents evaluated from Argo floats and those from the other two observing systems, both current speed and direction. It can be observed that current speed from Argo is larger than that of TAO at 10m, which is easy to understand since the surface currents are driven by winds. In conclusion, surface currents evaluated from Argo floats in this paper are reliable.