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.