Lagrangian particle transport in the Indian Ocean: A model study

Lagrangian transport of “passive” particles in the Indian Ocean is diagnosed using the global Modular Ocean Model 2 of the Geophysical Fluid Dynamics Laboratory. First, the model is forced by time‐varying monthly mean climatological wind stresses, and a particle cloud released in the Indonesian throughflow (ITF) region is tracked for one year. In the next experiment, two separate clouds, one released in the ITF region and the other in the Arabian Sea region, are followed for three years by forcing the model with weekly varying NMC9195 wind stress data. In both the experiments, short‐term Liapounov exponents indicate that particle trajectories are chaotic, with typical e‐folding stretching time about 125 days. The zonal dispersion of the ITF cloud is faster than the shear‐flow‐dominated transport process in the first experiment, as well as for the first two years in the second experiment. However, at later times the zonal dispersion rate is subquadratic in the latter experiment. For the Arabian Sea cloud, zonal dispersion is diffusive when the whole time range of three years is considered. However, for the initial six months, it is shear‐flow‐dominated and thereafter becomes even subdiffusive. The meridional dispersion rate is roughly superdiffusive, in both experiments, when the whole time range is taken into account. Our estimates of correlation dimension, a lower bound on the fractal dimension, suggest that none of the particle clouds reach the area‐filling limit in the time range of the model integration. We also compare the present results with those from earlier studies of chaotic stirring in the oceans.