real-timers@dartmouth.edu Hello All, As of Thursday night, we are enjoying light winds and calm seas. In general things are going well. Survey operations commenced at about 8pm, and drifter releases are scheduled for early tomorrow morning. A summary of the activities completed thus far follows. we can't send the figures along with the text. Cheers, Dennis Jim: Could you send along a header for the buoy observations? I don't have a record of the column identifiers. Charlie: All is well with the ADCP and connection with our computers. At the beginning we experienced a problem with the ship's gyro, but that has been fixed. EN323 Cruise Narrative as of 2115 May 6, 1999. May 4 ----- Operational forecasting began with a "best prior estimate" (BPE) simulation forced by climatological tides and mean elevation [run EN323_FC.01]. Mass fields are initialized with objectively analyzed hydrography from recent Oceanus broadscale cruise [provided by Jim Manning]. Wind forcing based on Leuttich winds. Time dependent boundary conditions (TDBCs) provided by Leuttich far-field model. Climatological heat fluxes. Calculation begins on May 1 (day 120) with a 1-day ramp-up of forcing (both elevation BCs and surface fluxes). A 5x5 array of fluid-following drifters is released at the surface in the operational area on May 4 (day 123). The forecast is run through May 7 (day 126). A schematic timeline is displayed below. ##################################################################### Forecast run: EN323_FC.01 * DR------------------------ * CS Date 05/01 05/02 05/03 05/04 05/05 05/06 05/07 YD 120 121 122 123 124 125 126 Legend ------ CS: cold start *: ramp-up of clim BCs DR: numerical drifter release ##################################################################### Generally speaking, the drifters move westward (Figure 1a). Drifters in the southern portion of the array are displaced slightly more than those in the northern. In order to assess the impact of the time-dependent boundary forcing provided by Leuttich's far field forecast, an identical twin experiment was conducted with that forcing removed [EN323_FC.02]. Without the TDBC forcing, the westward displacement is reduced by approximately half of that in the prior experiment (Figure 1b). Slight northward movement (toward the crest of the bank) is also evident. May 5 ----- Shipboard preparations prevented forecasting activities until after departure. Set sail at 1920. Conducted another BPE forecast based on the latest meteorological products [EN323_FC.03]. Did not receive any new information from Leuttich, so TDBCs were not used. Surface forcing record created from an amalgamation of NMFS (Manning) and UNC (Leuttich) forecast products. Wind stress: UNC(120.00-126.45) + NMFS(124.12-127.50). Heat flux: Climatology(120.00-122.12) + NMFS(122.12-125.50) + NMFS(124.12-127.50). The records are merged under the assumption that later products are more accurate because more observations have been assimilated into the system; thus, newer records replace older ones in cases of temporal overlap. See the forcing log for more details regarding the incoming atmospheric forcing. Run EN323_FC.03 essentially extends run EN323_FC.02 by one day. Due to the fact that there has been little change in the weather, results are similar to the prior run (Figure 2). The drifters are simply displaced further in the same direction. Curvature in the columns of the array is slightly different, perhaps due to the phasing of the tide one day later. May 6 ----- ADCP data acquisition began just after midnight. Examination of the first two pingdata files in the morning revealed a problem which was traced to the ship's gyro being significantly different from the ADCP compass. The Captain reported that the ship's gyro was set for the southern hemisphere. He switched it back to northern hemisphere at approximately 1030 and the problem appears to be solved. Watching the ADCP computer readout (which displays the difference between the two compass readings), it was clear that it was taking time for the adjustment to settle in. It was not until about noon local time before the two compasses were once again in synch. Thus good data start at about 1600GMT, about year day 125.7 (Figure 3). New meteorological information from both UNC and NMFS was received on board via email during mid-morning. UNC products included hindcast data, but no forecast. Therefore the EN323_FC.02-03 series (no TDBC forcing) was continued in run EN323_FC.04. Testing of the VPR began at approximately 1200. By 1500, those operations were completed. At that point, the ship began a four hour steam to the starting location of first survey grid. In advance of a drifter deployment scheduled for the early morning hours of May 7, a trial assimilation experiment [EN323_FC.05] was launched using the ADCP data collected between 1100 and 1800 (only about 40km worth of track line). Consistent with earlier experiments, the prior was fairly close and the inversion procedure brought the error right down into the noise level: Prior: 24.3 cm/sec 2nd Q4 run: 7.8 cm/sec 3rd Q4 run: 6.9 cm/sec