Eastern Boundary Current (EBC)

EBC took place between June 1992 and June 1994 off the Northern California coast. These pages describe data from the EBC current meter array. The array contained both Aanderaa current meters and ADCPs. Only the Aanderaa data are described here. Please note also that we are concerned here with the portion of EBC that was conducted by Oregon State University and the Naval Postgraduate School. This data report does not deal with an additional portion conducted by Scripps Institute of Oceanography, the Rosenstiel School of Marine and Atmospheric Science, and Woods Hole Oceanographic Institute. The latter segment of EBC has been designated WOCE component PCM2. A description of PCM2, and the current meter records obtained during PCM2, can be found in the WOCE CD set issued by NODC.


The chart below shows the current meter array. Each mooring is represented as two columns of boxes. The left column represents the first deployment, June 92 - May 93, and the right column represents the second deployment, May 93 - June 94. The depth of each current meter is shown inside the box that represents it. To reach a particular current meter, click on its representation in the figure. This will take you to a page of metadata relevant to that instrument, plus descriptive data plots from it.

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Description of the Experiment

This segment of EBC was a cooperative venture between the Naval Postgraduate School and Oregon State University, and involved both current meters and hydrographic sampling off the coast of Northern California. For a more complete description of the project and some of the results, read the abstracts of the papers and presentations listed below under Publications.

EBC Publications

Discussion and analysis of the Eastern Boundary Current slope array data has been given in the following presentations:

Click here to return to the beginning of the EBC data report.

Current Meter Sampling and Processing Details

The moorings were instrumented with Aanderaa RCM-8 current meters and ADCP's manufactured by RD Instruments. This data report includes only Aanderaa data, and we will discuss only the Aanderaa processing.

All of the Aanderaa meters recorded speed, direction, and temperature. Some meters were equipped to record pressure. Although these instruments incorporated the RCM-7/8 solid state electronics, all of them employed the older RCM-5 savonius rotors and vanes.

The current meter recording interval was set to 60 minutes. During the 60-minute interval the number of rotor revolutions and compass directions were sampled 50 times. Each such sample represents a current vector, its magnitude given by the rotor revolutions and its direction by the compass reading. In the RCM-8 on-board circuitry resolves the vector into two components, eastward and northward. Successive components are added and immedidately stored. When the selected recording interval has elapsed, the resulting average vector magnitude and average angle are calculated and recorded as speed and direction.

Temperature and pressure are instantaneous measurements at the end of the sampling interval.

The current meter stores analogs in the range [0, 1023], rather than the actual speeds, temperatures, etc. In the case of the EBC data the analogs were converted to usable form (speeds in cm/sec, temperatures in degrees, etc.) by means of calibration equations supplied by the OSU Buoy Group's calibration facility. Speeds were calculated by means of a nonlinear equation obtained with the Group's tow tank. The threshold of the Savonius rotor is 1.86 cm/sec. Speeds below the threshold (i.e., analog values of 0) were set to half the threshold - 0.93 cm/sec.

Each current record is archived in three forms: the raw data, exactly as recorded by the instrument, processed data in which the analog values have been cleaned up and converted to metric units, and llp filtered data. The llp (low low passed) file is made from the processed file; it has a time increment of 6 hours and is produced with a 60+1+60 point Cosine-Lanczos filter with half-amplitude at 40 hours and half-power at 46.6 hours. This filter removes the diurnal tides and all higher frequencies.

Occasional problems appear in the data as isolated spikes, gaps, or short runs of unexplainably erratic values. Problem areas only a few data cycles in length are corrected by linear interpolation. Those longer than a few hours but shorter than a week are bridged by predictive interpolation. The latter technique employs Anderson's (1974) algorithm for a predictive filter that utilizes the data on both sides of the gap (Smylie et al, 1973; Ulrych et al, 1973). All corrections to the data are noted elsewhere on this disk.

References for predictive interpolation

Anderson, N. 1974. On the calculation of filter coefficients for maximum entropy spectral analysis. Geophysics 39,69-72.

Smylie, D.E., G.K.C. Clarke and T.J. Ulrych. 1973. Analysis of irregularities in the earth's rotation. Methods in Computational Phys. 13, 391-430.

Ulrych, T.J., D.E. Smylie, O.G. Jensen and G.K.C. Clarke. 1973. Predictive filtering and smoothing of short records by using maximum entropy. J. Geophys. Res. 78, 4959-4964.

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Time series plots, by mooring

To see all of the time series recorded at a particular mooring, click on the name of the mooring below. Note that there were two deployments - the first in June of 1992 and the second in May of 1993.

Click here to return to the beginning of the EBC data report.