The Adriatic Sea surface circulation for the period 1990-1999 is studied using 
the data of more than 200 satellite-tracked drifters. The spatial structure and 
the temporal variability of the surface currents, at meso- to seasonal scales, 
are described in terms of Eulerian and Lagrangian statistics estimated from the 
low-pass filtered drifter velocities.

Maps of mean currents, subtidal velocity variance and mean kinetic energies 
were produced using 40-km-diameter circular bins. This averaging scale was 
chosen as a trade-off between horizontal resolution and statistical accuracy. 
Bins with a small number of independent observations or a strongly non-uniform 
seasonal data distribution were rejected to eliminate erroneous statistics. 
Sampling random and bias errors affecting the mean flow estimates were 
estimated.

Similar maps were produced for the four seasons of the year to assess the 
seasonal variability of the surface currents. James' test for the null 
hypothesis that means are equal was used to compare the mean velocity fields. 
The mean flow map confirms that the global cyclonic circulation in most of the 
Adriatic basin is broken into three re-circulation cells in the northern, 
central and southern sub-basins. Mean velocities in the cyclonic gyres can 
exceed 25 cm/s in the coastal areas where the velocity variance is also maximum 
(reaching 500 cm^2 s^-2).

Values near 2 x 10^7 cm^2 s^-1, 2 days and 18 km were obtained for the 
diffusivity and the Lagrangian integral time and spatial scales in the 
along-basin direction, respectively. In the across-basin direction, the 
statistics are typically 50% of the above values.