Characterizing the capability of mesoscale eddies to carry drifters in the northwest Pacific

Mesoscale eddies are common oceanic phenomena. Although many related studies have been conducted, the ability for mesoscale eddies to carry real particles remains poorly addressed. We considered the drifters as real particles to characterize the capability of mesoscale eddies to carry particles. Firstly, mesoscale eddies in the northwest Pacific (99°E–180°E, 0°–66°N) were identified using sea level anomaly (SLA) data from 1993 to 2015. Secondly, three important parameters (the carrying days, the number of circles the drifter revolving around the eddy center, and the carrying distances) were calculated by colocalizing eddy data with drifters. Finally, statistical analysis and composite analysis were conducted, reflecting the capability of mesoscale eddies to carry particles. The mechanisms on the carrying capability of eddies were also discussed. Results show that (1) the motion of carried drifters reflects the upper limit of rotational speed of eddies that the drifters revolve around the eddy center by ≤ 90° for one day in most cases; (2) the drifters tend to be carried for a longer time when their minimal distances to the eddy center measured with normalized distance are small; (3) there are two types of eddies (cyclonic and anticyclonic eddies) in different subregions of northwest Pacific, and each has a different carrying capability (on average, similar in the tropical ocean and Subtropical Countercurrent, cyclonic eddies tend to have stronger carrying capability in Southern Kuroshio Extension, and anticyclonic eddies tend to have stronger carrying capability in Northern Kuroshio Extension and Subarctic Gyre); (4) on average, the carried drifters tend to travel for a longer time around the normalized eddy radii ranging from 0.41 to 0.76; (5) the carrying days are related to the Rossby number of the eddy (in general when the Rossby number is smaller, the carrying days are longer).