Abstract
The main objective of the present study is to detect manually individual anomaly trajectories
using filtered sea surface height (SSH) anomaly to the east of Okinawa Island and to understand
the influence of bathymetry on their life cycles. Initially seasonal monthly mean background is
computed using running mean in space (1000 km x 1000 km) and time (five months) using
composite sea level anomaly maps of TOPEX/POSEIDON (T/P) and ERS-1&2 altimeters. These
seasonal mean background is removed from each original Maps of Sea Level Anomaly (MSLA)
cycles to get the filtered SSH anomaly to detect individual mesoscale eddy trajectories based on
certain criteria. Spectral power in frequency domain along 25.875° N latitude using the filtered
SSH anomaly shows maximum peaks in 50, 136-150, and 365 day's periods. Trajectories of
ARGOS drifting buoys east of Okinawa Island show large meandering of a drifting buoy around
Daito Island. In this region high (＞0.8°C) variability is detected using root-mean-square (rms) of
sea surface temperature. The typical scale of the detected mesoscale eddy was 350 km and the
lifetime was 115 days. The total number of the detected warm and cold eddies is 94 in six
years period. More typical eddies are located in deeper region compared with shallow region.
Seasonal distribution of mesoscale eddies changes in space and time. The warm (cold) core ed
dies are coming from southeast (northeast) direction avoiding Daito Sea mount. Passage of tra
jectory of eddies are through deeper ocean. It has been found that along Ryukyu ridge region
eddies decay around shallow continental steep slope. It seems that the trajectory of eddies is
crucially affected by bathymetry. These bathymetric features may have an important role on the
generation and growth of mesoscale anomalies.
