June '97 Summary Cruise Narrative Science Party List Browse SeaSoar Sections

Local time is used throughout this narrative- GMT is five hours ahead.

26 JUNE, 1997
Sailed from Narragansett at 08:30 in foggy weather, bound for the southern flank of Georges Bank. AVHRR imagery revealed what we believed to be a warm core ring impinging on the southern flank of the bank. After analyzing the imagery, we set the first survey site to examine the leading edge of the ring-Bank interaction, just west of the central part of the feature and near Ron Schlitz's moored array. Smooth sailing throughout the day as we proceeded to the initial waypoint.

27 JUNE, 1997
We arrived at the first waypoint, south of the moored array, and deployed SeaSoar at 02:03, 40° 02.5' N, 68° 03.5' W. Approximately three hours after the initial deployment SeaSoar collided with some fishing gear, resulting in transmissometer failure and a degradation in flight characteristics. Upon recovery at 05:27, 40° 26.1' N, 68° 12.3' W, we found the transmissometer hanging loosely in its mounting brackets and a length of loose faring tangled in the impeller. After making repairs, we redeployed at 05:43 and continued towing northward along the first survey line. Later that afternoon, flight characteristics deteriorated. Attempts to correct the situation by varying tow speed and control parameters failed, and we brought the vehicle aboard at 16:38, 40° 27.7' N, 67° 52.4' W to add weight to the undercarriage. We redeployed SeaSoar at 17:01 and continued the survey.

28 JUNE, 1997
Completed the first survey at 02:23 and set sail for the start of the second pattern. ADCP velocities in the off-bank region of the first survey reveal significant westward flow, indicating that the feature is not a simple warm-core ring. Flow patterns observed during the second survey, in the region where the warm feature extended farthest on-bank, suggest a that it is a plume-like extension of Gulf Stream water.

29 JUNE, 1997
Completed the third survey in the region where flow associated with the plume separates from the Bank. Following this, we executed an east-west section across what the imagery suggested to be a streamer extending off to the south. Currents and hydrography from this section indicated that the streamer was actually oriented more eastward, and we thus planned and executed two cross-bank sections east of the plume.

30 JUNE, 1997
Based on twice-daily imagery, we set a repeat survey pattern to straddle the region where the plume extends farthest on-bank and the separation region to the east. After completing the 'streamer' sections, we joined the repeat survey at its southeastern corner and steamed anticlockwise through the first pattern. During the first repeat, satellite imagery revealed a tendril of warm water separating from the primary plume and penetrating far onto the southern flank of the Bank.

1 JULY, 1997
Completed the first iteration of the intensive survey at 11:00 and immediately turned around to begin the next repeat, steaming clockwise through the pattern. Waters associated with the warm feature intrude much farther onto the bank than observed in the previous survey. There was a striking difference in cross-bank structure between the westernmost track and the line just to the east of it, with Gulf Stream waters sitting much farther south along the western transect. The VPR strobe failed around 15:30, going from synchronized flashes to intermittent operation. We recovered SeaSoar at 16:05, 40° 53.6' N, 67° 27.8' W to check for leakage in the underwater connectors linking the strobe and the engineering unit. Cleaning, regreasing and reseating the connectors failed to revive the strobe. Lacking spares, we redeployed SeaSoar with the intermittent strobe, in hopes of collecting some VPR data despite the failure. SeaSoar flight characteristics deteriorated around 18:00, with the fish refusing to dive below 30 m. Impeller turns were down, wings and pitch would not turn over into a dive configuration, and roll was more stable than usual. After trying to remedy the situation by varying ship speed and cable length, we began to suspect hydraulic unit failure. We recovered SeaSoar at 23:27, 40° 34.5' N, 67° 04.7' W and replaced the hydraulic unit with a tested spare.

2 JULY, 1997
Deck tests showed little variation between the two hydraulic units, and we found no significant changes in flight characteristics after redeploying SeaSoar. At this point, the VPR strobe had failed completely. To reduce the number of drag elements on the fish and minimize flow disturbance around the impeller, we recovered SeaSoar at 03:02, 40° 39.9' N, 67° 08.4' W and removed the VPR cameras and strobe. We redeployed SeaSoar without the VPR and found its flight characteristic to be even worse than before. For reasons that we do not yet fully understand, both excessive roll and not enough roll prevent the SeaSoar from diving. In the absence of the VPR, the set of stabilizing weights centered on the undercarriage prevented SeaSoar from rolling during its dive cycle. We recovered SeaSoar at 05:27, 40° 46.4' N, 67° 02.8' W and reverted to the configuration flown in the Arabian Sea Experiment, which included the entire instrument suite, less the non-functioning VPR, with a slightly different scheme of stabilizing weights. SeaSoar flew well after reconfiguration, and we continued with the second iteration of the repeat survey.

3 JULY, 1997
Lost telemetry at 03:00, 40° 44.8' N, 67° 29.1' W in less than 100 m of water, part way through the third repeat. When SeaSoar was brought back on board, several signs suggested the fish had collided with fishing gear. The section of faring closest to SeaSoar had been torn away from the cable, though it was still hanging on when the instrument was brought aboard, and the PAR sensor had sustained minor damage. The ground line (which is a separate wire running from the armored shield of the sea cable to the electronics) had been severed, presumably by the same event which caused the rest of the damage, and was responsible for the failure. SeaSoar was redeployed after repairs to the ground line and faring. Imagery indicated that the repeat surveys were sampling a tendril of Gulf Steam water which extended northwestward away from the main plume, far onto the bank. Several of the sections were extended farther on-bank to capture the inshore extent of the feature. The off-bank ends of some sections passed back through shelf water and into the main body of the plume.

4 JULY, 1997
Continued towing SeaSoar though a fourth repeat of the intensive survey pattern. The warm tendril seemed to be moving farther on-bank, and all of the survey lines were extended to follow the feature's progress.

5 JULY, 1997
We recovered SeaSoar at 12:44, 41° 06.4' N, 67° 03.3' W, concluding SeaSoar operations for Phase II GLOBEC. Following recovery, we set course for the last known position of a drifting guard buoy which we'd sighted several times over the course of the cruise. Flat, calm conditions and a good reflector made the buoy an excellent radar target, and it proved The Endeavor's crew recovered the buoy at 17:00, 40° 46.1' N, 67° 43.1' W and we began steaming for Woods Hole.

6 JULY, 1997
Arrived in Woods Hole at 12:10.