Last SIO drifter releases: May 17

Sorry for the late post, but… Thursday May 17 was the last day of SIO drifter releases. Again weather (rain and potential T-storms) cut the releases short and we only did two releases. Both releases were during ebb tide and were generally similar (thus only the first is examined in detail here) but novel compared to previous releases during ebb tide. We’ll get to the novelty shortly… For both releases all 35 drifters were released upstream of the inlets “S” turn, however, downstream of previous ebb releases which were released near the ICW. We hoped that by spreading them out at this location (where the inlet is wider) we might avoid the mass convergence that we had seen in the past. The mass convergence still occurred!

Fig.1 Tracks of drifters during ebb tide. Notice the convergence through the “S”. During this release, the exit of the drifters was different than previous ebb releases in which drifters were released upstream of the “S”. Notice that some drifters (blue) are exiting the old channel while others (red) are exiting the new channel. Previously, converged drifters exited either the “old” or “new” channel.

Fig 2. Blue drifters quickly exiting the “old” channel and red drifters sampling the inlet width: the last two (21,26) are completely in the “new” channel and the others are spread over the shoal between new and old channels.

Fig. 3. The exit location of the drifter is spread out entirely over the inlet mouth. Many drifters exit through the “old” channel heading north, many over the shoal between “new” and “old”, and 2 exit the “new” channel and head south. This spreading of the exit had not been seen in previous releases. What dictates (tide phase, tide magnitude, wind, waves?) the final drifter location is not known.


SWIFT runs complete

Yesterday we completed the final set of SWIFT runs, measuring surface turbulence, waves, winds, and currents through the inlet. Below is the composite of all tracks from 26 Apr to 21 May, color scaled by turbulent dissipation rate. Across all conditions, there is consistent enhanced dissipation at the channel outlets (old and new), as well as over the shoals. Other, more localized features, such as enhanced turbulence crossing fronts (and dye plumes!) are evident in the daily runs. Preliminary data products and summaries are at

Surface turbulent dissipation rate from SWIFT drifters.