LAGRANGIAN MEASUREMENTS IN LAKE ONTARIO

Satellite-tracked trajectories of 19 drifters involving six experiment s between 1983 and 1989 in Lake Ontario were analyzed. Three aspects o f the observed motions at 3.5 m depth are examined: (I) the spatial st ructure of the mean and variance velocity fields, (2) the Lagrangian s tatistics (dispersion and eddy diffusion characteristics) of the varia nce field based on single-particle analysis, and (3) the Eulerian stat istics of the fluctuating velocity field. The spatial structure of the mean velocity field is consistent with that obtained from dynamic hei ght and current meter measurements. The lake circulation is cyclonic. A coastal jet with mean speed in excess of II cm/s dominates the mean circulation. The jet is most intense along the southern shore. Two rec irculation zones are observed in the western part of the lake. The cur rent variability is strongly anisotropic in the coastal zone. Away fro m the coastline, the flow is quasi-isotropic. The theory of single-par ticle diffusion by homogeneous random motion (Taylor 1921) describes t he dispersive motions reasonably well. In the western part of the lake , zonal scales greatly exceed the meridional scales while in the easte rn part of the lake they are similar. In the western part of the lake, the zonal and meridional integral time and length scales and eddy dif fusivities are, respectively, (T-11,T-22) = (17.2, 5.5) hr, (L-11,L-22 ) = (10.1, 2.1) km and (K-11,K-22) = (16.5, 2.2) x 10(6) cm(2)/s. In t he eastern part of the lake, these values are (T-11,T-22) = (79, 14.7) hr, (L-11,L-22) = (1.7, 2.7) km, and (K-11,K-22) (1.1, 1.5)x 106 cm(2 )/s. The presence of inertial oscillations does not affect the diffusi vity estimates. The eddy kinetic energy of single-particle motion in t he western part of the lake is 189 cm(2)/s(2) which is about six times that of the eastern part. The Eulerian decorrelation scales tend to b e larger than those of the single-particle estimates. The space scales indicate that the eddy field is quasi-isotropic.