Numerical Model Study of the Mesoscale Dipolar Eddy
Date Issued
2015
Date
2015
Author(s)
Jheng, You-Teng
Abstract
Mesoscale eddies are common features of the open ocean and they can provide an efficient mechanism for the water masses and transport of energy. Recent studies found mesoscale dipolar eddy that consists of two counter-rotating eddies in the ocean. This study aims to investigate characteristics and dynamics of mesoscale dipolar eddy in f-plane. A reduced-gravity primitive equation eddy-resolving model was used to study them. Five sets of experiments (A-F) are simulated. The results are described as follow. We add a pair of anticyclonic eddy and cyclonic eddies with same radius and intensity to the model. The anticyclonic eddy sits on the north, whereas the cyclonic eddy locates 720 km apart on the south (experiment A, control case). These two eddies are both still on experiment A. When the distance between these two eddies is 640 km (experiment B), the eddies begin to slowly propagate westward and the trajectory is translation. If the distance between eddies decreases to 560 km (experiment C), they not only propagate westward but also become closer meridionally. The eddies have tendency to move because the northern anticyclonic eddy is advected by velocity of the southern cyclonic eddy, and vice versa. In other words, the dipole has mechanism of self-propelling in itself. The vortex force makes the anticyclonic eddy generate southward acceleration and makes the cyclonic eddy generate northward acceleration, so the eddies meridionally approach to each other while propagating zonally. This acceleration results in a convergence of the westward momentum flux and a strengthening of the westward velocity between the two eddies. Experiments E and F are tested using same radius but different intensity. The results show that the weaker eddy would move faster than the stronger. The dipole would move around their common center of mass instead of along a straight trajectory zonally. The energy increases between the two eddies (the interaction zone), but decreases elsewhere. The conversion between them is due to the effect of the vortex force, which generates the northward and southward acceleration. The energy then increases (decreases) and results in convergence (divergence) in (outside) the interaction zone.
Subjects
Reduced-gravity
Eddy-resolving model
Dipolar eddy
Type
thesis
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