Global Kinetic Energy Content of Oceanic Scales from Satellites and Models

How much energy resides in the oceanic mesoscales? What is their temporal variation? Traditionally, the mesoscales have been treated as deviations from a long-time mean. Here, we apply a coarse-grained decomposition of the ocean's surface geostrophic flow derived from satellite and numerical model products. In the extra-tropics we find that roughly 60% of the global surface geostrophic kinetic energy is at scales between 100 km and 500 km, peaking at 300 km. Our analysis also reveals a clear seasonality in the kinetic energy with a spring peak. We show that traditional mean-fluctuation (or Reynolds) decomposition is unable to robustly disentangle length-scales since the time-mean flow consists of a significant contribution (greater than 50%) from scales < 500 km. By coarse-graining in both space and time, we find that every length-scale evolves over a wide range of time-scales. Consequently, a running time-average of any duration reduces the energy content of all length-scales, including those larger than 1000 km, and is not effective at removing length-scales smaller than 300 km. By contrasting our spatio-temporal analysis of numerical model and satellite products, we show that the AVISO gridded satellite product suppresses temporal variations of less than 10 days for all length-scales, especially between 100 km and 500 km.