Seasonal Variability of Eddy Kinetic Energy in the Central Indian Ocean: POLYGON-67 Revised

Abstract

Purpose. The main goal of this study is to analyse the seasonal variability of meso-scale eddy activity in the north tropical Indian Ocean. The selected area coincides with the location of POLYGON-67 experiment where the mesoscale eddies of the open ocean were first discovered. Methods and results. The variability of mesoscale eddy kinetic energy in surface ocean layer, enstrophy of larger scale circulation, spatial and temporal patterns of surface currents and surface winds are jointly analysed using a 20-year long daily time series of eddy-resolving ocean reanalysis data obtained from EU Copernicus Marine Environment Monitoring Service and climatic wind data from US National Oceanographic and Atmospheric Administration. The fast mesoscale and slow large-scale processes are separated using a Savitsky – Golay filter with the cut-off time of 103 days which corresponds to a local minimum in the full kinetic energy power spectrum. In contrast to other parts of the tropical ocean, the seasonal variability of EKE exhibits 2 maxima – the largest being in April, and the secondary being in October which are related to the maxima in enstrophy of larger scale currents. Conclusions. The double peak variability in EKE corresponds to the seasonal variability of large scale enstrophy and monsoon wind circulation and supports a hypothesis that the main mechanism of EKE generation is barotropic instability of larger scale currents. The EKE variability within P67 is mostly controlled by advection of energy from neighbouring areas, and to a lesser extent by local generation.