Mesoscale eddies observed by moored current-meters at abyssal depths in the western North Pacific during 1978-1985

摘要

Observations by moored current-meters were carried out repeatedly in mid-ocean of the western North Pacific, providing 50 velocity records. A continuous velocity record for almost seven years was obtained at 5000 m depth. The overall mean velocity is directed to the north with a speed of less than 1 cm s~(-1). The kinetic energy of low-frequency velocity-fluctuations, or mesoscale eddies is more than 30 times larger than that of mean flow. Frequency spectra of eddy kinetic energy show that most of the energy is contained in mesoscale bands (periods of 31-235 days), with zonal (meridional) dominance of energy in the longer (shorter) period band. An array observation at 4000 m depth shows that the local change of relative vor-ticity of mesoscale eddies is balanced mainly with the advection of planetary vorticity, although the horizontal advection of relative vorticity and higher-order horizontal divergence may play some role. Those results suggest that the mesoscale eddies are understood as primarily plane barotropic Rossby waves with possible modification.