Abstract
Abstract. Ocean currents play a key role in Earth's climate – they impact almost any process taking place in the ocean and are of major importance for navigation and human activities at sea. Nevertheless, their observation and forecasting are still difficult. First, no observing system is able to provide direct measurements of global ocean currents on synoptic scales. Consequently, it has been necessary to use sea surface height and sea surface temperature measurements and refer to dynamical frameworks to derive the velocity field. Second, the assimilation of the velocity field into numerical models of ocean circulation is difficult mainly due to lack of data. Recent experiments that assimilate coastal-based radar data have shown that ocean currents will contribute to increasing the forecast skill of surface currents, but require application in multidata assimilation approaches to better identify the thermohaline structure of the ocean. In this paper we review the current knowledge in these fields and provide a global and systematic view of the technologies to retrieve ocean velocities in the upper ocean and the available approaches to assimilate this information into ocean models.
Highlights
Surface ocean currents contribute to the characterization of the Earth’s climate (WMO, 2015)
The routine retrieval of ocean velocities on global scales is based on measurements of the sea surface height (SSH) done by altimeters, which are used to derive surface currents invoking the geostrophic approximation
This is a robust approach: it is an all-weather, global and well-understood methodology that has become the standard for oceanographic research and has had a deep impact in our vision and understanding of ocean dynamics
Summary
Surface ocean currents contribute to the characterization of the Earth’s climate (WMO, 2015). Knowledge of ocean surface velocities is a key and cross-cutting issue that impacts on many societal challenges far beyond the research context in geophysical fluid dynamics. Ocean surface currents have been included in the list of essential climate variables (Bojinski et al, 2014). Strong ocean currents define corridors used by marine mammals, birds and fish and sustain their migration in search for food, breeding sites and spawning areas. Knowledge of the detailed structure and variability of ocean currents is required for fisheries and environmental management. Surface currents directly affect many important socioeconomic activities such as global maritime trade and shipping or issues such as marine pollution and safety, to mention a few
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