GP6-04-RB NOAA Ship RONALD H. BROWN Panama - Arica, Chile October 27 - November 30, 2004 Chief Scientist: Dave Zimmerman Survey Department: CST Jonathan Shannahoff CTD Personnel: CST Jonathan Shannahoff Final Processing: K. McTaggart ACQUISITION: Forty-nine CTD profiles were collected during this cruise. Twenty- seven profiles were collected from 8S to 12N along 95W. Twenty-two profiles were collected from 8N to 8S along 110W. The majority of casts were to 1000m, three were deep casts to 3000m. PMEL's Sea-Bird 9plus CTD s/n 209 measuring pressure (s/n 53586), temp sensors s/n 1455 and 1370, and cond sensors s/n 1177 and 1180 were used for all casts. The .CON file used was 4Oct04.CON. The CTD was mounted in a yellow 10-liter 24-bottle frame with PMEL SBE carousel pylon s/n 471. The CTD data stream was passed through 11plus deck unit s/n 367 with factory settings. Digitized data were sent to the ship's designated computer equipped with SBE's SEASAVE Win32 v5.32 acquisition software. Calibrated data were displayed in a fixed listing and graphical form in real-time, as well as stored in raw form on hard disk. A recycled VCR tape recorded the analog signal each cast. Raw data files were archived to Zip disk each cast, and CDs were returned to PMEL for processing. SALINITIES: No duplicate samples were taken this cruise. Salinity analysis was performed using Guildline Autosal 8400B salinometer s/n 61.668 for casts 1-39, and s/n 60.843 for casts 40-49. Samples were analyzed using Ocean Scientific ACI2000, and IAPSO standard seawater batch #P142 for casts 1-5, #P143 for casts 6-39, and #P144 for casts 40-49. The bath temper- ature was set to 24 degrees Celsius. This season, only 8 samples will be collected per cast instead of 12, and no samples will be collected from the half-degree stations between 3N-3S. Raw data were archived along with CTD data on CD. At PMEL, ACI2000 .dat files were ammended in Excel such that only 1 header line, 1 standard correction line, and 3 salinity lines per sample were included in the file. Corrected salinity values were fixed to 4 decimal places and saved as a space delimited file. POST-CRUISE CONDUCTIVITY CALIBRATIONS: Primary and secondary data were considered. Both sensor pairs behaved very similarly. Primary data were chosen for reduction owing to the slower historical drift of temp sensor 1455, and the slightly better calibration results of cond sensor 1177. GP604S.CAL was created at PMEL and included all stations, 1-49. Final pressure calibrations were pre-cruise. A historical drift correction of -0.0007 C, as well as a viscous heating correction of -0.0006 C was applied to temp sensor 1455 before calibrating conductivity. The best fit for conductivity was determined using CALCOS0 on casts 1-49. number of points used 263 total number of points 302 % of points used in fit 87.09 fit standard deviation 0.002407 fit bias -0.010671096 min fit slope 1.0002966 max fit slope 1.0002966 Slope and bias correction values were applied to CTD burst data and converted directly into netCDF format using CALMSTR and CLB_EPS. FINAL PROCESSING: The following are the standard SEASOFT processing modules used to reduce Sea-Bird CTD data: DATCNV converts raw data to engineering units and creates a bottle file if a Sea-Bird rosette sampler was used. Both down and up casts are processed. ROSSUM averages the bottle data specified in the DATCNV output and derives salinity, theta, and sigma-theta. Bottle data are used to calibrate the CTD sensors post-cruise. WILDEDIT makes two passes through the data in 100 scan bins. The first pass flags points greater than 2 standard deviations; the seond pass removes points greater than 20 standard deviations from the mean with the flagged points excluded. Data were kept within 0.01 of the mean. FILTER applies a low pass filter to pressure with a time constant of 0.15 seconds. In order to produce zero phase (no time shift) the filter is first run forward through the file and then run backwards through the file. CELLTM uses a recursive filter to remove conductivity cell thermal mass effects from the measured conductivity. In areas with steep temperature gradients the thermal mass correction is on the order of 0.005 psu. In other areas the correction is negligible. The value used for the thermal anomaly amplitude (alpha) is 0.03. The value used for the thermal anomaly time constant (1/beta) is 7.0. LOOPEDIT removes scans associated with pressure slowdowns and reversals. If the CTD velocity is less than 0.25 m/s or the pressure is not greater than the previous maximum scan, the scan is omitted. BINAVG averages the data into 1 db bins. Each bin is centered around a whole pressure value, e.g. the 1 db bin averages scans where pressure is between 0.5 db and 1.5 db. There is no surface bin. DERIVE uses 1 db averaged pressure, temperature, and conductivity to compute salinity, theta, sigma-theta, and dynamic height. TRANS converts the data file from binary to ASCII format. Program CNV_EPS1 applies post-cruise temperature corrections and conductivity calibration coefficients, as well as any offset to salinity, recomputes the derived variables in DERIVE, and converts the ASCII data files to netCDF format. CNV_EPS1 skips bad records near the surface (typically the top 3 m) as well as any records containing -9.990e-29, and copies back raw data to the surface (0 db) within 15 db. Because the SBE module LOOPEDIT does not handle package slowdowns and reversals well in the thermocline where gradients are large, CNV_EPS1 removes raw data records where a sigma-theta inversion is greater than -0.01 kg/m3. Data are linearly interpolated such that a record exists for every 1 db. When data are copied back to the surface, the WOCE quality word is '888'; when interpolated over greater than 2 db, the WOCE quality word is '666'. The WOCE quality word consists of a 1-digit flag for pressure, temperature (ITS-90), and salinity. Two bottles were flagged bad: station 0211 sample 106; and station 0241 sample 107. Final CTD and bottle files were moved to /home/plover/insitu2/DATA/hayes /gp604/ctd/ and /bot and included in the MySQL data management tables on March 15, 2005.