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CalCOFI HYDROGRAPHIC CLIMATOLOGY
INTRODUCTION
Routine oceanographic sampling within the
California Current System has occurred under the auspices of the California Cooperative Oceanic Fisheries Investigations (CalCOFI) since 1949, providing one of the longest existing time series of the physics, chemistry and
biology of a dynamic oceanic regime. Our principle objective in preparing this CD is to make these data easily accessible to the general oceanographic community, as well as to provide a baseline data set from which water
property anomalies can be computed and compared between regions along the U.S. West Coast. Thus, in addition to providing the 50-year data set, we also include a climatology of the CalCOFI hydrographic data, as well as programs
for computing the mean values of various physical variables at any location within the CalCOFI domain and for any day of the year.
DATA
The
historical CalCOFI sampling grid extends from the southern reaches of Baja California
northward to the California-Oregon border and out to several hundred kilometers offshore, with 36 nominal lines oriented approximately perpendicular to the coastline. Stations are
designated by a line and station number (e.g., 77.60 is station 60 on line 77). Nominal station spacing is approximately 70 km offshore (e.g., the distance between 77.60 and 77.70), but
is considerably less inshore of station 60. The greatest spatial and temporal coverage occurred during the early years of the program (1950-1960), when multi-vessel cruises
occupied significant portions of the grid at monthly intervals (Moser et al., 1993). Quarterly surveys were conducted annually from 1961 to 1965, with target months of January, April, July and October. Monthly
coverage was resumed, but only triennially, between 1966 and 1984. Measurements were made on over 23,000 stations on this grid over the 35-year period from 1949 to 1984.
Through 1964, standard station sampling consisted of 12- to 18-bottle Nansen casts mostly to 500-m depth (and occasionally to 1200 m or 2000 m). STD or CTD casts were taken subsequently, often in conjunction with
a Nansen cast or with several water-bottle samples for calibration (Lynn et al., 1982). Values of oceanographic parameters were interpolated to standard depths. All data from observed and standard depths
are published in Scripps Institution of Oceanography data reports.
The present CalCOFI grid, a subset of the historical grid that has been occupied quarterly since 1984, comprises nearly 7,000 stations (through April 1999) from six
nominal lines between San Diego and Point Conception. Routine station activities on the present grid include CTD/Rosette casts to 500-m depth, bottom depth permitting,
with continuous measurements of pressure, temperature, conductivity, dissolved oxygen and chlorophyll fluorescence. Water samples are collected at 20 depths,
with variable spacing depending on depth of the chlorophyll, oxygen and salinity extrema and the thermocline depth (Hayward and Venrick, 1998). Salinity, oxygen and nutrients are
determined for all depths sampled, while chlorophyll-a and phaeopigments are determined within the top 200 m, bottom depth permitting. Details of the standard sampling and analysis procedures can be found in any of
the recent CalCOFI data reports, e.g. SIO (1999).
METHODS
We describe the mean seasonal variability of 7 hydrographic variables (temperature, salinity, density, oxygen
concentration, oxygen saturation, dynamic height anomaly and spiciness) at 14 standard levels (0, 10, 20, 30, 50, 75, 100, 125, 150, 200, 250, 300, 400 and 500 m) for all stations within the CalCOFI data set for which
sufficient data exist. Spiciness, as defined by Flament (1986), is a state variable (units of st) which is most
sensitive to isopycnal thermohaline variations and least correlated with the density field. It is conserved in isentropic motions, and is defined to be largest for warm and salty water.
Our approach follows that of Lynn (1967) and Lynn et al. (1982), in which the mean seasonal variation is
obtained by a least squares regression of the data to annually periodic sinusoids. Since the time intervals between measurements are irregular, and typically consist of 3-4 month gaps, we restrict our harmonic
analysis to include only the annual and semiannual harmonics.
The general form of the regression curve is:
y = A1cosq + B1sinq + A2cos2q + B2sin2q + C,
where q is the angular equivalent of the day of the year in radians and C is the annual mean value. In the least
squares regression, the sum of the squares of the data anomalies from the regression curve is minimized with respect to each of the five coefficients, with the resulting set of equations solved simultaneously for the
coefficients (Lynn, 1967). In order to maintain sufficient data for performing the regression, the criterion of at
least 5 occupations (for a given variable, at a particular station and standard depth) were required within each 60-day period of the time series.
The files containing the derived harmonic coefficients for each station, standard depth and variable for which sufficient data exist can be found on the coefficients page. These files are used in the Anomalies and Mean
Values (Anomean) program to compute the mean values for a selected variable, station, standard depth and day of year, or to compute anomalies for a particular set of measurements.
CLIMATOLOGICAL BASE PERIODS
Not all stations within the CalCOFI region have been regularly occupied since 1949. As mentioned above, there
have been several fundamental changes in the areal extent of the nominal sampling grid, with the latest change occurring in 1984. It was therefore necessary to construct several climatologies which represent
different portions of the region over different baseline periods. For the period 1950-1984, harmonic coefficients were computed for all stations on the entire historical grid, from Baja California to northern
California, which had sufficient data. The harmonic analysis was performed on only those data from the present grid for two additional baseline periods: 1950-1999 and 1984-1999. The latter period was chosen
because it represents the period in which various changes in sampling strategies and methods were employed.
We also include coefficient files for the baseline periods 1950-1976 and 1977-1999 for all stations on the
present grid, as these represent both sides of an observed "regime shift" in Pacific climate (e.g., Trenberth and Hurrell, 1994; Francis and Hare, 1994) and may be of use in diagnosing decadal variability in the region.
We encourage caution when using these climatologies to determine anomalies from independent observations made along the West Coast
 . Figures 1 and
2
 provide examples of the 10-m temperature and salinity
climatologies for both an inshore (90.30) and an offshore (90.90) station. The choice of baseline period has a significant effect on the derived mean values, due primarily to an upper-level warming
and freshening trend in the Southern California Bight over the past 15 years.
TABLES OF MEAN VALUES
The Anomean program can compute mean values of the physical variables for any location within the CalCOFI domain and for any day of the year. For convenience, we also include tables of monthly mean values of each of the physical variables for the periods 1950-1984 (historical grid) and 1950-1999 (present grid) for all
stations and standard depths for which sufficient data exist. These tables represent two separate CalCOFI hydrographic climatologies to which regional observations can be compared.
REFERENCES
Flament, P., 1986. Subduction and finestructure associated with upwelling filaments, Ph.D. dissertation,
University of California, San Diego, 123 pp.
Francis, R.C., and S.R. Hare, 1994. Decadal-scale regime shifts in the large marine ecosystems of the northeast Pacific: A case for historical science, Fisheries Oceanography, 3, 279-291.
Hayward, T.L., and E.L. Venrick, 1998. Nearsurface pattern in the California Current: Coupling between physical and biological structure, Deep-Sea Research II, 45, 1617-1638.
Lynn, R.J., 1967. Seasonal variations of temperature and salinity at 10 meters in the California Current, CalCOFI Reports, 11, 157-174.
Lynn, R.J., K.A. Bliss, and L.E. Eber, 1982. Vertical and horizontal distributions of seasonal mean temperature, salinity, sigma-t, stability, dynamic height, oxygen, and oxygen saturation in the California Current, 1950-1978, CalCOFI Atlas No. 30, 513 pp.
Moser, H.G., R.L. Charter, P.E. Smith, D.A. Ambrose, S.R. Charter, C.A. Meyer, E.M. Sandknop, and W. Watson,
1988. Distributional atlas of fish larvae and eggs in the California Current region: Taxa with 1000 or more total larvae, 1951 through 1984, CalCOFI Atlas No. 31, 233 pp.
Scripps Institution of Oceanography, University of California, 1999. Physical, chemical and biological data, CalCOFI cruises 9802, 9803, 9804, 9805 and 9806. SIO Ref. 99-9, 160 pp.
Trenberth, K.E., and J.W. Hurrell, 1994. Decadal atmosphere-ocean variations in the Pacific, Climate Dynamics, 9, 303-319.
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