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Date: Mon, 24 Oct 1994 12:13:47 +0000 (GMT)

R/V THOMPSON is on its way back to Muscat after successfully setting a five-mooring dynamics array centered at 15 30'N, 61 30'E. Before setting the moorings, we carried out an XBT survey which confirmed that the scale of the array was appropriate to detecting mesoscale current and density gradients. The array consists of five moorings set at four corners of a 50 km square and one at the center. The center element of the array is a WHOI discus buoy carrying a meteorological package. Hung below it are various temperature, salinity, current, bio-optics, and bio-acoustics sensors to 250 m depth. The two western elements are SIO toroidal buoys each carrying a meteorological package, a downward-looking acoustic Doppler current profiler, and temperature sensors at various depths to 150 m. The two eastern elements are subsurface moorings carrying a current and density profiler operating between 25 and 200 m depth. One of these carries 5 current meters at depths to 3000 m while the other carries a bioacoustics package. We list below the acoustically-surveyed anchor positions of each mooring. These locations are being given for the use of our fellow investigators. We wish to limit their distribution and avoid their publication in order to deter commercial fishing activity and vandalism. We request research vessels to avoid dumping garbage within 60 km, to refrain from launching XBTs, performing net tows, making deep casts, or fishing within 15 km, and to avoid making shallow casts or SeaSoar tows within 2 km of any mooring. The coordinates given below are based on GPS fixes of the ship while measuring ranges to acoustic releases. WHOI Buoy: 15 30.04'N 61 29.99'E SIO-North: 15 43.53'N 61 15.94'E SIO-South: 15 16.53'N 61 16.11'E UW-North: 15 43.90'N 61 44.53'E UW-South: 15 16.37'N 61 44.07'E We invite investigators to visit the moorings to make complementary measurements subject to the above exclusion rules. We plan to make data available to other JGOFS and Arabian Sea Dynamics investigators. It will be particularly helpful to have SeaSoar and shallow CTD measurements made near the moorings to calibrate moored salinity, bio-optical, and bio-acoustic measurements. We were somewhat surprised (pleasantly) as we set the array to find substantial current and density contrasts across it. These persisted through the 11 days we were in the area and consisted of an eastward jet that grew in strength equatorward, confined to the upper 200 m or less. We found peak surface current speeds of 1 m/s which were supported by a meridional density gradient confined largely to between 50 and 200 m. Sea surface temperature gave no indication of this structure's existence. Satellite SST images we received were accordingly bland in the vicinity of the array. Temperature inversions found in the XBT survey were confirmed by CTD casts to be compensated in density by salinity. Several salinity extrema persisted in the upper 200 m or so and could not be mapped by casts only 18 km apart. Our final survey act was a 50-km tow-yo across the array and the current feature. This revealed the interleaved structure of salinity and temperature inversion filaments. The portion of the feature we were able to survey (we never did determine its meridional extent) maintained order one Rossby and Richardson numbers. We anticipate the moored measurements will follow the evolution of this feature. We have had smooth sailing for all but one of our days at sea. Unfortunately, high winds and rough seas beset us on our last day in the area when we had to recover and reset the UW-North mooring because it was mistakenly set too shallow (the ship's digital bathymetric sounding system reported depths biased deep by up to 20 m). The extra mooring operation is causing us to arrive in port one day late (arrival tomorrow, Tuesday 25 October at 0800L). We apologize to all who are inconvenienced by the delay. The officers and crew of the THOMPSON have been extremely helpful as always. We thank them for their efforts. The cruise has been highly successful and quite pleasant. We take as a sign of endearment that the PIs aboard were thrown in the fantail swimming pool by a crew member this afternoon. Charles Eriksen is