INTRODUCTION

TEMPERATURE CHAIN CALIBRATIONS

DATA PROCESSING

ACKNOWLEDGMENTS

REFERENCES

I. INTRODUCTION.

As part of the CONVEX field program, UNH's Ocean Process Analysis Laboratory (OPAL) deployed a cluster of moored buoys in Wilkinson Basin in the western Gulf of Maine between late fall of 1997 and early winter of 1997-1998 (Figure 1, Table 1). The main instrument buoy (A) was equipped with meteorological sensors, an array of eight water temperature and conductivity sensor pairs, and an upward-looking/downward-looking pair of ADCPs. (See Figure 2 and Tables 2a-d). Two 10-sensor temperature chains (B and C) with a pressure sensor on their subsurface buoys were deployed nearby mooring A. Two of the "guard" buoys (D, E) were equipped with fixed-depth water temperature/conductivity sensor pairs. The third guard buoy was not instrumented.

II. TEMPERATURE CHAIN CALIBRATIONS.

The calibrations of the Buoy B temperature chain (T-chain B) were conducted in a 2m diameter x 2m deep cylindrical concrete tank, beginning on 25 September 1700 UTC and ending at 2000 UTC the same day. The tank temperature was increased in steps of about 2 degrees from about 8 dC to 16 dC. The "steady" segments of the original one-minute T-chain B thermistor series at each step were fit to the corresponding one-minute MicroCat 209 reference temperature time series. We assumed a linear relation between the MicroCat 209 reference temperature T_true and the n^th thermistor temperature T(n) according to:

The offset (a) and slope (b) of the linear correction relationship, as well as the misfit standard deviation (sigma) for each T-Chain B thermistor (Table 3a) was determined using the REGRESS routine in the Ocean Analysis Software Package (OASP, Irish and Brown, 1986). The typical misfit standard deviation (i.e. precision uncertainty) of a calibrated T-Chain B temperature was +/- 0.015 dC.

The calibrations of the 10 thermistors on the Buoy C temperature chain (T-Chain C) were also conducted in the 2m diameter x 2m deep cylindrical concrete tank, beginning on 7 January 1998 at 2200 UTC and ending on 8 January 1998 1239 UTC. Linearly increasing segements (beginning on 08 January 98 0315 UTC and continuing for 541 minutes) from each of the original five-minute T-chain C thermistor time series were linearly interpolated to the one-minute sample interval of the MicroCat 251 reference temperature time series. For this calibration run, temperatures ranged from approximately 2 dC to approximately 6.5 dC. In determining the corrections, we assumed a linear relation between the MicroCat reference temperature T_true and the n^th thermistor temperature according to Equation (1) (see Table 3b). The typical precision uncertainty of a calibrated T-Chain C temperature record was +/- 0.008 dC.

III. DATA PROCESSING.

The measured temperatures (based on the factory calibrations) on both T-chain B and T-chain C were corrected according to the Tables 3a and 3b calibration relationships. The 15-minute T-chain B time series are presented in Figure 3. A comparison of the 5-minute T-chain C time series and the corresponding segment of the T-chain B time series is shown in Figures 4a and 4b.

The instantaneous depths of the T-chain water temperature measurements (see Figure 4) varied from their nominal depths, due to the effects of current drag and tidal sea level change. The pressure measurement at the top of the thermistor chain (nominal depth of 20m) was used to estimate the instantaneous depth z_i(t) of the i^th sensor of each T-chain using the following procedure.

1. Determine the instantaneous depth of the pressure sensor at the top of the array, z_p(t) according to the hydrostatic relation ­ correcting for atmospheric pressure patmos.

where p_m(t) is measured pressure, p_atmos is atmospheric pressure, roe is water density, and g is gravitational acceleration.

2. Determine the depth of the i^th T-chain temperature sensor according to

where delta-z_i is the depth of the i^th temperature sensor relative to the pressure sensor.

The depth-time contour plot of these depth-correlated T-chain temperature measurements is presented in Figure 4. These depth-corrected 10-temperature time series T_i(z_i(t),t) have also been used (via linear interpolation) to create constant-depth temperature time series from 20m to 155m in 15m increments.

The Buoy A SeaBird temperature/conductivity sensors and MicroCats were mounted on a taut mooring wire and thus were constrained to be at constant depths (except for tide-induced water depth changes of around 2m). Thus no depth-correction was necessary. Unfortunately, the Buoy A temperature and salinity time series at 6m, 70m and 129m ended before the others (see Figure 6 and Table 4). To permit a more comprehensive analysis, we augmented these short series with "patches" generated by temperature and salinity correlations.

# To estimate the missing part of the Buoy A 6m temperature and salinity series, we linearly regressed the overlapping parts of the 6m and 25m records and used the fits to predict the missing end sections.

# The missing portion of the Buoy A 70m salinity time series was estimated by taking vertical distance-weighted averages of the measured salinity records at 39m and 99m respectively.

# The missing portion of the Buoy A 129m salinity time series was estimated by taking vertical distance-weighted averages of the measured MicroCat salinities at the 99m and the 172m salinities (see Figure 6) respectively.

# The missing portions of the 70m and 90m temperature series from Buoy A were replaced by the appropriate sections of the linearly interpolated, depth-corrected, temperatures from the T-chain C.

Figure 6 illustrates the results before and after the augmentation procedure. The temperature and salinity time series were used with the International Equation of State of Seawater (Pond and Pickard, 1983) to compute the Brunt-Vaisala frequency (BVF, i.e. water column stability).

Temperature and salinity records from the guard buoys D and E are presented in Figure 7. The 97m MicroCat temperature record, which was corrupted by instrument failure, was repaired by a depth-weighted interpolation of the T-chain 92m and 107m records. This replacement temperature was used with the measured conductivity to produce what appears to be an unusually noisy salinity record. Time-depth contour plots of the Buoy A Brunt-Vaisala frequency, temperature, and salinity series are presented in Figure 8.

A pair of RD Instrument 4-Beam Sentinel Broadband Workhorse Acoustic Doppler Current Profilers (ADCP) were deployed in an upward-downward looking configuration on mooring A, at depths of 133m and 136m respectively, in 270 meters of water. Ensembles of 180-pings-per-10-minutes were obtained in 15 eight-meter bins centered at depths between 15 and 127 meters (inclusive) (ADCP-up) and 15 eight-meter bins centered at depths between 142 and 254 meters (inclusive) (ADCP-down). These were obtained for the period beginning 11 January and ending on 25 April 1998 or ADCP-up and ending on 6 May 1998 for ADCP-down. A selected set of the horizontal currents are presented in Figure 9. (See Table 5 for statistics of the 11 January 1998 0000 UTC through 25 April 1998 0000 UTC currents.)

IV. ACKNOWLEDGMENTS.

These data were collected with the help of a great many people, including Ken Morey, Karen Garrison, Prashant Mupparapu, and the crews of the R/V Endeavor and the R/V Oceanus.

The research was funded by the National Science Foundation under grant OCE-9530249.

V. REFERENCES.

Irish, J.D., and W.S. Brown, 1986. An Archiving and Analysis System for Geophysical Data. Marine Data Systems International Symposium (MDS86): 64-69.

Pond, Stephen, and George L. Pickard, 1983. Introductory Dynamical Oceanography. Oxford, England: Butterworth-Heinemann.