Sezonnaya izmenchivost' kineticheskoy energii vikhrey v tsentral'noy chasti Indiyskogo okeana: analiz eksperimenta «Poligon-67» s sovremennykh pozitsiy

Abstract

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