Circulation in Tasman-Golden bays and Greater Cook Strait, New Zealand

Abstract

ABSTRACT Analyses are presented of model simulations and Lagrangian drifter experiments designed to quantify circulation and dispersal in Tasman and Golden Bays, and their connection to Cook Strait, New Zealand. Observations made in autumn 2017 and summer 2018 are compared with numerical model results. The drifter experiments were focussed on three repeat experiments in each bay designed to measure the local horizontal eddy diffusivity. An additional experiment investigated the connection with, and flow through, Greater Cook Strait. Point by point velocities extracted from the model show low correlation with, but on average are in the same direction as observed velocities. Eddy diffusivities computed from the drifter experiments are highly variable, but the observations support the modelling. We find that the mean velocity in Tasman and Golden Bays is weak and the circulation is dominated by wind and tidal flows. The mean depth-averaged velocity shows anticyclonic flows in the south of both Tasman and Golden Bays, with cyclonic flow in the north of Golden Bay. The mean near-surface velocity is generally out of each bay and is compensated for by inward circulation at depth.