15 DECEMBER 2002 GOWER 3709

Temperature, and Wave Climatologies, and Trends from Marine Meteorological Buoys in the Northeast Paci®c

J. F. R. GOWER Institute of Sciences, Sidney, British Columbia, Canada

(Manuscript received 16 May 2000, in ®nal form 28 February 2002)

ABSTRACT Time series of , wind speed, and signi®cant from meteorological buoys off the west coast of Canada and the adjacent United States are long enough and of suf®cient quality to be useful for studying interannual variability and trends. Long-term averages of data provide a precise climatology of surface temperature, wind speed, and wave height for locations along- and offshore. Data from many of the buoys suggest a warming trend, but only three buoys show statistical signi®cance, and sheltered buoys show no increases. Both the wind speed and the wave height data show an increasing trend with more statistical signi®cance. Future data from these buoys should bene®t from better calibration and a wider variety of sensors, as well as from longer time series.

1. Introduction indicator of long-term trends, and to show the signature of short-term ``climatic'' effects such as El NinÄo. Any An array of 26 meteorological buoys off the west apparent trends in temperature, wind speed, and wave coast of the United States and Canada provides height need to be evaluated as a check on the quality and surface ocean data for coastal and offshore waters of the buoy data. Wind and wave data from the Canadian in the Gulf of Alaska north of 45ЊN and east of 160ЊW buoys have been used in validation of satellite sensors (Fig. 1). The ®rst buoys were 12- and 10-m discus buoys such as the TOPEX/Poseidon altimeter (Gower 1996) installed in the 1970s by the U.S. National Data Buoy and of the Comprehensive Ocean±Atmosphere Data Set Center. These are now replaced by an expanded network (COADS; Cherniawsky and Crawford 1996). of 6-m Navy Oceanographic Meteorological Automatic This paper is based on monthly average values of sea Device (NOMAD) buoys offshore, and 3-m discus buoys surface temperature, wind speed, and signi®cant wave near shore and in sheltered waters, deployed by the Unit- height (SWH, the height exceeded by one-third of the ed States and by the environment and ®sheries depart- waves, H1/3, computed as 4 times the standard deviation ments of the Canadian federal government. The ®rst U.S. buoys were deployed in 1972±77 at six offshore locations of the measured height values) in the time period 1972± numbered 46001 to 46006. Four U.S. nearshore buoys 99. Recent Canadian data for the period May 1990 to were added in 1984±91. The ®rst Canadian buoys were May 1999 were derived from a new compilation pro- installed in 1987, at which time location 46004 was trans- vided by Environment Canada for this study. Data from ferred to Canadian responsibility. The Canadian network the U.S. buoys are available on the Web at http:// was brought up to its full strength of 16 operational buoys www.ndbc.noaa.gov. in 1993. An additional experimental buoy was added in 1998 for testing sensors for biological and optical vari- 2. Buoy data ables. The buoys measure wind speed and direction, wave height and spectrum, surface water and air temperature, The positions of the 26 buoys in the west coast U.S. and . All data are transmitted in real and Canadian networks are shown in Fig. 1. Offshore time at hourly intervals. buoys were originally 10- and 12-m discus buoys, but Although the operational purpose of the buoys is these were replaced in 1982±92 by NOMAD shiplike short-term , the time series of data hulls measuring 6 m ϫ 4 m. All other buoys have 3-m from the buoys are long enough (6±27 yr) to be a useful discus hulls. The offshore buoys are located about 400 km away from the coast, with the exception of 46006, Corresponding author address: Dr. J. F. R. Gower, Institute of which is positioned about 1000 km offshore to give Ocean Sciences, P.O. Box 6000, Sidney, BC V8L 4B2, Canada. greater warning of weather systems coming from the E-mail: [email protected] west. The weather at Ocean Papa

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FIG. 1. Map showing the locations of the buoys whose data are discussed here, and of weather station P, indicated by P at 50ЊN, 145ЊW.

(position indicated by the letter P in Fig. 1) provided of 10 m, and water temperature at a depth of 1.5 m. this same warning for Canada from 1949 to 1981. Signi®cant wave height accuracy is that maintained by The offshore buoys are listed in tables in this paper calibration on shore prior to deployment. Sensors are in an anticlockwise order starting at 46003. Data from rejected if errors measured in predeployment tests are the line of nearshore buoys, moored in exposed positions outside the 10% range. within 100 km of the coast, are listed in a north-to-south Buoys are rotated among locations on the annual ser- order from 46205 off the north end of the Queen Char- vice cruises, so that a reasonable error model is to as- lotte Islands south to 46027 off northern California. A sume independent random errors of the above-speci®ed further eight buoys are located in more sheltered Ca- magnitudes that remain ®xed for each year. On this ba- nadian coastal waters, behind the Queen Charlotte Is- sis, calibration errors will limit the accuracy with which lands and Vancouver Island. Two of these buoys (46131 average values and trends in the data can be determined and 46146) are located in the Strait of Georgia. A further to the values listed in Table 1 for time series covering two (46181 and 46134) are located in narrow coastal 5, 10, and 20 years. inlets. Buoy 46134 was installed only recently and its Both and temperatures are averages over 10- data are not considered here. min periods computed once each hour. Winds are vector Nominal measurement accuracy for the Canadian averages. The wave heights are deduced from vertical buoy data is Ϯ0.5ЊC for sea surface temperature, Ϯ0.3 ``heave'' accelerometers mounted inside the buoys. In msϪ1 for wind speed, and 10% for signi®cant wave the NOMAD hulls, the sensors are gimballed to remain height (Axys Environmental Consulting Ltd., 2001, per- vertical when the buoy tilts. In the 3-m hulls, the ac- sonal communication). Water temperatures are mea- celerometers are strapped down, and buoy tilt is a pos- sured by thermistor at a depth of 80 cm. The wind speed sible source of error. Buoy wave measurements are av- accuracy is that speci®ed for the Young Wind Monitor erages of 37 min of data collection. Model 05103, and is assumed to apply to all deployed This study is based on monthly mean values of sea instruments. An additional source of error at low wind surface temperatures (SST), wind speeds, and signi®- speeds is the threshold wind speed required to turn the cant wave heights computed from the hourly buoy mea- rotor, which is speci®ed as 1 m sϪ1. Wind speed ac- surements up to and including May 1999. Means are curacy for U.S. buoys is quoted as Ϯ1msϪ1 or 10%, computed for all months for which at least 300 hourly whichever is greater (Hamilton 1980). Wind speeds are values (approximately 40% of the maximum possible) measured by two propeller mounted at 3.7 are collected. For computing anomalies from the month- and 4.7 m above the water. The higher is ly values, a mean seasonal cycle is computed from all used unless its data are suspect. On the older 10- and available data for each buoy. The cycle is assumed to 12-m discus buoys, wind speed was measured at a height consist of an annual sinusoid and a second harmonic (2

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TABLE 1. Errors in long-term trends introduced by calibration uncertainties discussed in the text, for an avg of 1 yr of data, and for time series of 5, 10, and 20 yr. SST Wind speed SWH Length Mean Trend Mean Trend Mean Trend (yr) (ЊC) (ЊCyrϪ1) (m sϪ1) (m sϪ1 yrϪ1) (m at 3 m) (m yrϪ1 at 3 m) 1 0.50 0.30 0.30 5 0.22 0.12 0.13 0.08 0.13 0.08 10 0.16 0.06 0.10 0.03 0.10 0.03 20 0.11 0.03 0.07 0.015 0.07 0.015 cycles per year) whose amplitudes and phases minimize 4ЊC offshore, but is less near the coast where upwelling the standard deviation of the residual monthly values, tends to reduce summer temperatures. Coastal upwelling obtained by subtracting these cycles from the data. reduces the amplitude of the annual cycles at lower Sections 3 and 4 of the paper discuss ®rst the cli- latitudes from 3.8ЊC off the northern Queen Charlotte matologies and then the trends in sea surface temper- Islands to 2ЊC at buoy 46050 off central Oregon and ature, wind speed, and wave height. Response of the 0.6ЊC (less than the residual variation in monthly mean buoys to the major El NinÄo events in 1982/83 and 1997/ values) at buoy 46027 off northern California. It is high- 98 are discussed in section 5. Temperature trends mea- est (5ЊC) in the more strati®ed waters of the Georgia sured by the buoys are also compared to trends derived Strait and coastal inlets where a shallow surface layer from the global Reynolds dataset (Reynolds and Marisca is strongly warmed in summer. 1993) in section 6. The mean wind speed is highest at 7.9 m sϪ1 for buoy 46003. The three Canadian offshore buoys give very similar averages (7.47 Ϯ 0.03 m sϪ1), while the U.S. 3. Climatologies of sea surface temperature, wind buoy to the north and the three to the south all show speed, and wave height mean speeds 7.0 Ϯ 0.10 m sϪ1. This difference is an The mean value of SST, wind speed, and wave height order of magnitude larger than the 0.03 m sϪ1 error and the amplitude of the seasonal cycles deduced for expected from random calibration errors (Table 1) but each buoy are summarized in Table 2. The order of the observed wave heights are in the same ratio (see later), buoys (northwest to southeast in three series) re¯ects suggesting a real difference with position. Consistency their locations as shown in Fig. 1. Consistent patterns between several groups of buoys in Table 2 is about in the values in the table suggest that relative calibration Ϯ0.1 m sϪ1, comparable to the values in Table 1. is accurate to the levels suggested in Table 1. The amplitude of the annual cycle of wind speed for The mean temperatures are about 0.5ЊC lower for each most buoys is about 1.5 m sϪ1, or 0.22 Ϯ 0.05 of the degree of latitude northward (Fig. 2). The values at most mean wind speed. Buoy 46204 shows the highest an- NOMAD buoys (black diamonds) fall within 0.1ЊCof nual-cycle amplitude (2.4 m sϪ1). The exposed buoys the linear relation (solid line) SST (ЊC) ϭ 10.25ЊϪ 46208, 46132, and 46029 show low values near 1.1 m 0.475Њ (latitude Ϫ 50Њ), which applies for the latitude sϪ1. The southernmost buoys (46050 and 46027) form range 40Њ±55Њ. Buoy 46003 is about 2.5ЊC colder than a triangle of lower values (0.6 to 1.0 m sϪ1) with buoy this relation, and buoy 46184 is 0.7ЊC warmer. These 46002. The three buoys in sheltered waters also have two differences can be explained by greater than average low annual-cycle amplitudes in this range. horizontal heat ¯ux at these locations, the Alaska Stream The mean signi®cant wave heights are highest (2.7± bringing colder water from the northeast at 46003, and 3.0 m) for the offshore NOMAD buoys, with four the Alaska gyre bringing warmer water from the south- (46003 and the Canadian NOMADs) in the range 2.9± west at 46184. 3.0, and the remaining U.S. NOMADs (46001 and those All Canadian coastal 3-m buoys except 46206 follow to the south) giving values near 2.7 m. These are the an offset relation (dashed), which is about 1.3ЊC warmer same two groups noted earlier as showing different than the NOMAD relation. Such an increase would be mean wind speeds, suggesting that the differences in expected due to a combination of more hours of sun- mean wind speeds and in mean wave heights are both shine at locations in the rain shadows of the Vancouver real. Northern exposed 3-m buoys give values in this and Queen Charlotte Islands, and northward water ¯ow same range (2.6±2.8 m), while buoys to the south on near shore due to the buoyancy-driven Haida current. the continental shelf show lower SWH (2.1±2.4 m). The Southern coastal buoys will be cooled by the effects of three buoys in sheltered waters show a relatively low coastal upwelling. Buoys 46041 to 46050 lie close to annual-cycle amplitude, even allowing for the lower the NOMAD relation, while 46027 is about 3ЊC cooler. mean wind speed, as would be expected from the re- This buoy is closer to the shore (11 km) than the other duced fetches at these sites. U.S. buoys, in an area of intense upwelling. It is interesting to note that the measured long-term- The annual cycle of SST has an amplitude of about mean SWH values for all 18 exposed buoys are within

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TABLE 2. Buoy climatologies for SST, wind speed, and wave height, showing mean values and annual-cycle amplitudes. Numbers of months with suf®cient data are shown for SST and are roughly the same for all three types of data from each buoy. Wind speed SST annual Mean wind annual ampl. SWH mean SWH annual No. of months Buoy ID Mean SST (ЊC) ampl. (ЊC) speed (m sϪ1) (m sϪ1) (m) ampl. (m) of data Offshore buoys 46003 6.8 3.8 7.87 1.43 3.03 1.16 235 46001 7.4 4.3 7.14 1.42 2.69 1.03 255 46184 9.1 4.2 7.48 1.64 2.90 1.16 119 46004 9.9 3.9 7.49 1.60 2.98 1.22 219 46036 11.2 3.9 7.43 1.54 2.98 1.24 127 46005 12.3 3.8 6.96 1.36 2.69 1.09 219 46002 13.8 3.7 6.81 0.94 2.67 0.96 248 46006 14.5 3.7 7.12 1.76 2.73 1.25 179 Nearshore buoys, moored in exposed locations 46205 10.2 3.8 7.18 1.59 2.67 1.10 111 46208 10.8 3.7 6.97 1.16 2.77 1.14 97 46147 10.6 2.8 6.81 1.69 2.8 1.25 72 46207 11.1 3.5 6.98 1.48 2.76 1.22 109 46132 11.7 3.3 7.15 0.96 2.61 1.13 64 46206 11.4 2.9 5.83 1.53 2.28 0.91 119 46041 11.3 2.7 5.04 1.36 2.12 0.82 103 46029 11.9 3.0 5.72 1.17 2.23 0.84 83 46050 12.4 2.0 5.85 0.76 2.42 0.87 52 46027 10.9 0.6 5.41 0.59 2.21 0.57 135 Sheltered buoys 46145 9.4 2.9 6.57 1.38 1.64 0.68 97 46183 10.0 3.1 7.08 1.61 1.34 0.58 94 46185 10.7 3.4 6.98 1.59 1.88 0.84 103 46204 10.8 3.3 7.07 2.37 2.23 0.95 108 46131 11.5 5.0 4.71 0.79 0.45 0.18 79 46146 11.6 5.7 4.89 0.59 0.42 0.08 84 46181 9.6 5.8 4.62 0.85 0.23 0.14 96

5% of values computed using the measured long-term- about 5%. The ratio of the annual-cycle amplitude to mean wind speeds in the Joint North Sea Wave Project the mean wave height is about double the equivalent (JONSWAP) fully developed relation (Carter 1982), ratio found for the wind speeds, as would be expected with buoy wind speeds increased by 10% to convert from the square-law relation between wind speed and from 5- to 10-m measurement height (see later), and an fully developed wave height (Carter 1982). arbitrary 1.25 m added as contribution from swell. This suggests an absence of calibration errors larger than 4. Trends in sea surface temperature, wind speed, and wave height The trends of SST, wind speed, and wave height with time are shown in Table 3. Most trends in SST suggest warming, but only three of these have statistical sig- ni®cance. An apparent warm trend would be increased by the effect of the recent 1997/98 El NinÄo, which caused a signi®cant rise in sea surface temperatures near the end of the time period (see next section). For buoys deployed in 1982 or earlier, a compensating effect would be expected from the 1982/83 El NinÄo. Data for the periods affected by these two events (October 1982± May 1983 and August 1997±March 1998, see next sec- tion) are omitted from the trend analyses. The statistical signi®cance is calculated assuming that SST anomalies are correlated over 3 months, since autocorrelations for FIG. 2. Variation of mean SST with lat for all buoys, showing (solid line) the avg decrease of SST with lat, and (dashed line) the warmer, SST give values of about 0.7, 0.5, 0.3 for the ®rst 3 offset relation for coastal buoys not in¯uenced by upwelling. Solid months of lag. Wind speed and wave height anomalies diamonds indicate NOMAD buoys. were found to give autocorrelations below 0.2 for all

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TABLE 3. Measured trends in SST, wind speed, and wave height showing in each case the probability that the observed r2 value would occur by chance in normally distributed data with 3-month autocorrelation time. The length of the data record (months between and including ®rst and last values), is shown in the last column. SST trend SST chance Wind speed Wind speed SWH trend SWH chance Length Buoy ID (ЊCyrϪ1) prob. trend (m sϪ1 yrϪ1) chance prob. (m yrϪ1) prob. (months) Offshore buoys 46003 0.006 .54 Ϫ0.018 0.06 0.011 0.01 269 46001 0.029 .01 0.035 6 ϫ 10Ϫ5 0.009 0.005 315 46184 0.099 .02 0.020 0.28 0.020 0.14 141 46004 0.064 2 ϫ 10Ϫ5 Ϫ0.015 0.09 0.018 0.02 264 46036 0.028 .41 0.091 Ͻ10Ϫ5 Ϫ0.005 0.76 140 46005 0.014 .21 0.013 0.11 0.021 Ͻ10Ϫ5 268 46002 0.010 .35 0.020 0.007 0.019 10Ϫ5 279 46006 0.025 .12 Ϫ0.002 1 0.024 2 ϫ 10Ϫ5 260 Nearshore buoys, moored in exposed locations 46205 0.035 .35 0.002 1 Ϫ0.024 0.08 127 46208 Ϫ0.036 .49 0.058 0.08 0.004 0.75 107 46147 Ϫ0.003 1 0.142 0.008 0.028 0.38 73 46207 0.017 .65 0.060 0.09 0.028 0.11 115 46132 Ϫ0.048 .64 0.256 4 ϫ 10Ϫ4 0.080 0.03 68 46206 0.058 .15 0.087 0.01 0.028 0.05 127 46041 0.039 .41 0.069 0.004 Ϫ0.009 0.37 138 46029 0.048 .23 0.051 0.007 0.014 0.13 141 46050 0.062 .49 0.139 0.08 0.042 0.07 86 46027 0.026 .47 Ϫ0.043 0.07 Ϫ0.002 1 184 Sheltered buoys 46145 Ϫ0.014 .76 0.020 0.54 Ϫ0.004 0.7 98 46183 0.019 .63 0.022 0.47 0.001 1 98 46185 0.030 .32 0.077 0.01 Ϫ0.000 1 105 46204 Ϫ0.009 .85 0.092 0.01 Ϫ0.001 1 117 46131 0.004 1 0.093 0.07 0.013 0.14 80 46146 Ϫ0.104 .19 0.019 0.57 0.006 0.16 87 46181 Ϫ0.067 .22 Ϫ0.011 0.75 Ϫ0.007 0.25 109 lags, so statistical signi®cance is computed assuming statistical signi®cance. Those deployed by the United months are independent. States (sequentially numbered 46001 to 46006) have the The eight offshore buoys (®rst block of data in Table longest data records (22±26 yr) and therefore give the 3) all suggest positive trends, though ®ve show low best indication of real, long-term trends. Three neigh- boring buoys (46001, 46184, 46004) show trends that are relatively large (0.03Њ, 0.1Њ, 0.06ЊCyrϪ1) and sta- tistically signi®cant (0.02 chance of random occurrence, or less). Figure 3 shows the time series for buoy 46004, which gives the most signi®cant trend in Table 3. This and buoy 46184 are the only buoys that show a trend above the rates listed in Table 1. One possible contribution to a long-term temperature increase for some offshore buoys will be the reduction in sensor depth from 1.5 to 1 m, when the buoys were converted from large discus to NOMAD. This might contribute to a positive trend since the shallower sensor would sense slightly warmer temperatures in summer when the water is strati®ed, and about the same tem- perature in winter when the water would be better mixed by storms. The average effect is expected to be small, but could contribute at all offshore locations except 46184 and 46036, at which NOMAD buoys were de- FIG. 3. Sea surface temperature data from buoy 46004 (combining ployed from the start in 1987 and 1988. U.S. and Canadian data) showing (top plot) the original time series and (lower plot) the values with the annual cycle (®rst and second For buoy 46004 (Fig. 3), the conversion from large harmonics) removed. A linear regression indicates a strong warming discus to NOMAD was made in June 1983. If the data trend (0.064ЊCyrϪ1). before June 1983 are omitted, then the warming rate

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TABLE 4. Comparison of mean SST anomaly (ЊC) for buoy 46004 before and after Jun 1983 (hull type change 10/12-m discus to 6-m NOMAD) by 3-month season. JFM refers to Jan, Feb, Mar, etc. Num- bers of monthly averages and std dev (SD) of the individual monthly averages about the means are also shown. JFM AMJ JAS OND No. before 14 15 16 16 No. after 35 41 43 39 Mean before Ϫ0.59 Ϫ0.54 Ϫ0.76 Ϫ0.69 Mean after 0.23 0.26 0.33 0.24 Increase 0.82 0.80 1.09 0.93 SD before 0.56 0.53 0.84 0.39 SD after 0.50 0.70 0.90 0.82 drops to 0.041ЊCyrϪ1. No step in the data is evident, though the early data are on average about 1ЊC cooler than the average after June 1983. If this change is due to the change in hull type, then it should show a seasonal signal, but Table 4 shows that there is no sign of this. The increase is comparable in the spring and summer FIG. 4. Wind speed time series for buoy 46004 (legend as in Fig. when strati®cation is expected (0.80Њ, 1.09ЊC) and in 3) showing the effect of the change of anemometer height in Jun the fall and winter when it is not (0.93Њ, 0.82ЊC). 1983. This causes an apparent negative trend with time (Ϫ0.06 m Ϫ1 Ϫ1 Trend analysis in wind speed is complicated for some s yr ) as shown by the heavy line. buoys by the changeover from large discus to NOMAD hulls, with a reduction of anemometer height from 10 to with the longer time series are smaller and are com- 5 m. Figure 4 shows the time series for buoy 46004, parable to error values shown in Table 1, suggesting that which was changed over in June 1983. The best-®t es- the larger observed trends will not continue over long timate of the apparent reductions in measured wind speed periods. at the change of anemometer height for the six buoys Trends in signi®cant wave height are once again most- 46001 to 46006 are 0.915, 0.95, 0.862, 0.87, 0.925, 0.895. ly positive, and by roughly the same percentages as for The factor 0.87 applies to buoy 46004 as plotted in Fig. wind speed, but the computed rates of change are again 4. Since the same change in height occurred on all buoys, comparable to expected errors due to calibration shown an average factor of 0.9 was applied to all 10-m data (see in Table 1. The highest and most signi®cant trend listed Fig. 5 for buoy 46004). This is the average of the em- pirically determined factors and represents a slightly larg- er change than the factor 0.94 proposed by Smith (1988) for the ranges of wind speeds and air±sea temperature differences measured by the buoys. The computed trends are then as listed in Table 3. Table 3 shows that there is an apparent trend of in- creasing wind speed for most buoys, though among the long time series NOMAD buoys (those covering more than a 260-month time interval), three show positive and three show negative trends. However, positive trends are larger and more statistically signi®cant. The probabilities of random occurrence for wind speed and wave height are calculated assuming that monthly anomaly values are independent, as noted earlier. The data plot for 46004 (Fig. 5) suggests that the negative trend for this buoy is largely due to an apparent step (calibration error?) in early data before 1981. Buoy 46132 shows the fastest apparent increase of 0.25 m sϪ1 yrϪ1 (Fig. 6), though data from this buoy cover the relatively short period of 66 months (5.5 yr). All of the 10 buoys showing statistically signi®cant trends (prob- FIG. 5. Wind speed time series for buoy 46004 (legend as in Fig. 3) multiplying wind speeds measured before Jun 1983 by a factor of ability of random occurrence equal to or less than 1%) 0.9 to compensate for the change of anemometer height. This reduces Ϫ1 show increases, with an average value of 0.09 m s the apparent negative trend with time to Ϫ0.015 m sϪ1 yrϪ1 (as listed yrϪ1, or about 1 m sϪ1 over 10 yr. Trends for the buoys in Table 3), but does not remove the apparent step near 1982.

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FIG. 7. Monthly average signi®cant wave height time series from buoy 46005, showing apparent increase by 0.46 m (17%) in 22 yr. FIG. 6. Monthly mean wind speeds measured at buoy 46132 (legend Legend as in Fig. 3. as in Fig. 3). This is an example of a short time series, showing a large (0.26 m sϪ1 yrϪ1) and statistically signi®cant trend over the 5 yr 1994±99. See Table 3. before and after the 8-month periods, were used as a baseline to remove effects of long-term trends. The table shows a positive response to the 1997/98 is for buoy 46005 (Fig. 7). This plot suggests that most El NinÄo in temperature among coastal buoys, and a of the apparent trend is due to the low early (before much weaker response in wind speed and wave height. 1981) and high recent values, with a long static period The offshore NOMAD buoys show a response to both in between. Winds for this buoy show no corresponding events that appears positive in the north and negative relative low before 1981, though there is evidence of a in the south. All 3-m buoys were deployed after the recent increase after 1994. The anemometer height at 1982/83 event. During the 1997/98 event, the exposed this location was changed from 10 to5min1986. coastal buoys from 46205 in the north to 46050 in the Among the 3-m buoys, the computed rate of increase south warmed by an average of 1.4ЊϮ0.5ЊC. The more is again highest for buoy 46132 (15% in a 5-yr period). southerly buoys show the strongest warming, and it is Real long-term changes in SWH should correlate with a pity that data from buoys 46041 and 46027 are miss- the trends in wind speed, though there is a major con- ing. Data from the four sheltered buoys round the Queen tribution to SWH at exposed buoys from swell due to Charlotte Islands show similar warming (1.3ЊϮ remote winds as noted earlier. Figure 8 shows a com- 0.14ЊC). The two buoys in Georgia Strait (46131 and parison of trends expressed as fractions (trend divided 46146) show a very small response. by mean value). Buoys with long data records (solid diamonds) show small trends. Buoys 46050, 46131, 46132, 46147, and 46206 show positive trends in both wind speed and wave height, suggesting these trends may be real, if only short term. Buoy 46132 shows the most rapid increase in both wind speed and wave height. The two buoys in Georgia Strait (46146 and 46131) show an increase in SWH, though only buoy 46131 shows a signi®cant increase in wind speed.

5. Response to El NinÄo events in 1982/83 and 1997/98 Two major El NinÄo events occurred in the time period covered by these buoy observations, resulting in sig- ni®cant warming along the equatorial east Paci®c in the periods October 1982±May 1983 and July 1997±Feb- ruary 1998. Table 5 shows the mean anomalies in sea FIG. 8. Comparison of computed trends (fractional changes per year, trends divided by mean values) of wind speed and wave height surface temperature, wind speed, and wave height, cal- for all buoys. Buoys giving more than 20 yr of data are shown as culated over these two 8-month periods. Two 4-month solid diamonds. Seven buoys showing relatively large trends are iden- ``non±El NinÄo'' periods ending and starting two months ti®ed for comparison with Table 3.

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TABLE 5. Response to 1982/83 and 1997/98 El NinÄo events in SST, wind speed, and SWH. For the 1982/83 event, measurements are averaged over the 8 months of Oct 1982 to May 1983, and the average over the two 4-month periods Apr to Jul 1982 and Aug to Nov 1983 was subtracted. For the 1997/98 event the equivalent periods were Aug 1997 to Mar 1998, Feb to May 1997, and Jun to Sep 1998. Wind data for Sep 1996 to May 1997 are missing for buoy 46006, so only a single ``non±El NinÄo'' period is used. The lower, separate section of the table shows average values for buoys 46003 to 46006 (eight NOMAD buoys), 46205 to 46027 (eleven 3-m buoys on the exposed coast), 46145 to 46204 (four 3-m buoys north, east, and southeast of the Queen Charlotte Islands), and 46131, 46146, and 46181 [three 3-m buoys, two in the Georgia Strait, one in a northern inlet (Fig. 1)]. Ranges of values for these groups of buoys are indicated.

SST (ЊC) Wind speed (m sϪ1) SWH (m) Buoy ID 1982/83 1997/88 1982/83 1997/98 1982/83 1997/98 Offshore buoys 46003 0.41 0.58 0.53 0.02 Ϫ0.24 Ϫ0.14 46001 1.09 0.34 Ϫ0.78 0.37 Ϫ0.13 0.11 46184 Ð 1.11 Ð Ϫ0.15 Ð 0.06 46004 0.26 Ϫ0.20 0.39 Ϫ0.07 0.20 0.39 46036 Ð Ϫ0.42 Ð Ϫ0.01 Ð 0.14 46005 Ϫ0.08 Ϫ0.20 Ϫ0.30 0.41 0.07 0.49 46002 Ϫ0.40 Ϫ0.02 0.20 0.89 0.21 0.63 46006 Ϫ0.22 Ϫ1.71 0.55 0.73* 0.66 1.18 Nearshore buoys, moored in exposed locations 46205 Ð 1.36 Ð Ϫ0.24 Ð 0.02 46208 Ð 1.03 Ð 0.17 Ð 0.25 46147 Ð 0.64 Ð Ϫ0.03 Ð 0.15 46207 Ð 1.11 Ð 0.57 Ð 0.28 46132 Ð 1.22 Ð 0.03 Ð 0.27 46206 Ð 1.80 Ð 0.66 Ð 0.29 46041 Ð Ð Ð Ð Ð Ð 46029 Ð 2.05 Ð 0.51 Ð 0.12 46050 Ð 2.13 Ð 0.01 Ð 0.01 46027 Ð Ð Ð Ð Ð Ð Sheltered buoys 46145 Ð 1.44 Ð Ϫ0.24 Ð Ϫ0.04 46183 Ð 1.22 Ð Ϫ0.07 Ð 0.11 46185 Ð 1.19 Ð Ϫ0.28 Ð 0.17 46204 Ð 1.46 Ð 0.45 Ð 0.06 46131 Ð 0.12 Ð 0.16 Ð 0.04 46146 Ð 0.27 Ð Ϫ0.04 Ð 0.04 46181 Ð Ð Ð 0.01 Ð 0.00 NOMADs 0.18 Ϯ 0.54 Ϫ0.06 Ϯ 0.83 0.10 Ϯ 0.53 0.27 Ϯ 0.39 0.13 Ϯ 0.32 0.36 Ϯ 0.42 Coast Ð 1.42 Ϯ 0.53 Ð 0.21 Ϯ 0.33 Ð 0.17 Ϯ 0.12 Q.C. Islands Ð 1.33 Ϯ 0.14 Ð Ϫ0.04 Ϯ 0.34 Ð 0.08 Ϯ 0.09 Inside Ð 0.20 Ϯ 0.11 Ð 0.04 Ϯ 0.10 Ð 0.03 Ϯ 0.02

The apparent delay in response of local sea surface to the responses observed for the buoys for these two temperature to warming on the equator was calculated groups. Responses for the 1982/83 event were similar as 1 Ϯ 1 month, using the average response of buoys (0.26ЊϮ0.21ЊC and 1.00ЊϮ0.40ЊC), and showed the 46205 to 46204 in Table 5. This delay was used in same difference between the two groups. selecting the time periods for computing the results in Table 5 and for omitting periods of data from the trend 6. The observed trend in SST analysis (Table 3). Data from west coast Canadian coastal stations (Free- Taken together, the offshore buoys suggest a warming land 1990) also show the positive temperature response trend of about 0.04ЊCyrϪ1 for the period 1977±1999, to the El NinÄos. These stations started recording much with individual buoys showing trends between 0.01 and earlier (one before 1920, one in the 1920s, eight in the 0.1ЊCyrϪ1. Data from the ®ve southern-exposed coastal 1930s, one in the 1950s, ®ve in the 1960s, and three in buoys (46206 to 46027) suggest comparable trends, the 1970s for a total of 19) but are affected by greater though with low statistical signi®cance. The observed variability due to their coastal locations, and the fact trends suggest the possibility of dividing the buoys into that data are collected only once each day on the day- two groups. The eight offshore buoys and the ®ve south- light high tide. Five of these stations are in the Strait ern-exposed coastal buoys together show an average of Georgia. For the 1997/98 event these stations showed warming trend of 0.04ЊCyrϪ1 with rms scatter of a small negative response (Ϫ0.13ЊϮ0.32ЊC) compared 0.025ЊCyrϪ1 in individual buoy trends about this mean. to stations on the open coast (0.97ЊϮ0.41ЊC), similar All remaining buoys taken together show an average

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FIG. 9. Global trends in SST over the period 1982±99 derived from the Reynolds and satellite blend 1Њ dataset (Reynolds and Marsico 1993). Warming rates from (dark blue) negative, or cooling, to (red), the most rapid warming, up to 0.1ЊCyrϪ1, are indicated by the color sequence blue, green, yellow, red. Average global warming shown by these data for the period is about 0.01ЊCyrϪ1. The west coast of Canada is identi®ed as an area of relatively rapid warming at up to 0.07ЊCyrϪ1. Apparent rapid warming off Greenland and Labrador is in regions where data accuracy is reduced by ice cover. cooling trend of 0.015ЊCyrϪ1 with rms scatter of about for the global ocean is about 0.01ЊCyrϪ1. The image 0.04ЊCyrϪ1. The scatter in the observed trends is com- shows many ``hot spots'' of more rapid warming, among parable to the errors suggested by Table 1, indicating a them the area of the buoy array plotted in Fig. 1. Here, need for improved calibration. the Reynolds dataset shows average warming close to Data from west coast Canadian coastal stations (Free- the coast of about 0.07ЊCyrϪ1, with less warming land 1990) also show a warming trend. Freeland (1990) (0.02Њ±0.03ЊCyrϪ1) at the locations of the offshore computed an average trend from the full time series of buoys. Average warming trend of the NOMAD buoys 0.004ЊCyrϪ1 for exposed stations and 0.003ЊCyrϪ1 for is about 0.04ЊCyrϪ1 in rough agreement with the Reyn- sheltered ones including those in the Strait of Georgia, olds data. The low spatial resolution of the Reynolds using data to 1989. More recent warm temperatures in- data makes comparison with coastal buoys more prob- crease these warming trends to 0.010Њ and 0.007ЊCyrϪ1, lematic. Table 3 shows average warming of 0.05ЊCyrϪ1 respectively. The data show a more rapid warming (av- at the southern coastal stations (46206 and southward) erage for all stations) of 0.044ЊϮ0.016ЊCyrϪ1 since and no signi®cant warming farther north (buoys 46205± 1970, with a tendency for cooling since 1990. Stations 46132 and 46145±46204). in the Strait of Georgia show the strongest cooling since 1990 (Ϫ0.055ЊϮ0.045ЊCyrϪ1), compared to the av- 7. Conclusions erage for exposed buoys (0.00ЊϮ0.04ЊCyrϪ1), a similar result to the buoys. Southern-exposed stations suggest Time series from the buoys are now long enough to cooling (Ϫ0.03ЊϮ0.05ЊCyrϪ1) compared to northern start to show apparent long-term trends in temperature, stations (0.01ЊϮ0.02ЊCyrϪ1), the reverse of the pattern wind speed, and wave height, as well as signatures from suggested by the buoys. These errors are rms scatter in short-term climatic effects such as El NinÄo. These trends the individual values for four stations in the Strait of need to be evaluated both as a check on calibration of Georgia, and six northern- and four southern-exposed the buoy data and to investigate whether they represent stations. effects of long-term climatic change. Data quality from Reynolds and Marsico (1993) present a compilation the buoys, as indicated by the consistency of the long- of global monthly mean SST values derived from ships term buoy climatologies, appears to be good. Further and satellite measurements on a 1Њ degree grid. This improvements are planned in sensor calibration accu- started at the beginning of 1982 and continues to be racy initially for SST, and in the variety of sensors de- updated monthly. Figure 9 shows the global distribution ployed and variables measured. of temperature trends for January 1982±June 1999, com- The buoy data suggest trends of increasing values in puted from these data. The trends are shown as an image all three variables investigated. These trends apply only in which more rapidly warming areas are shown as yel- to the period 1977±99 for the NOMAD buoys, and low and red. The mean trend computed from these data roughly 1990±99 for the nearshore buoys. In the case

Unauthenticated | Downloaded 09/25/21 07:04 PM UTC 3718 JOURNAL OF CLIMATE VOLUME 15 of SST, the data affected by the 1997/98 El NinÄo event optical instruments will be made more permanent and were omitted from the trend analysis. The trends may will be extended to other buoys in the west coast net- not continue, and may represent part of a more local work, making a start to extending the variety of time cyclic variation, such as the Paci®c interdecadal oscil- series beyond those shown here. lation (Mantua et al. 1997). The average trend of about 0.04ЊCyrϪ1 is larger than the 0.01ЊCyrϪ1 which rep- Acknowledgments. This work was undertaken with resents the present global-mean rate of warming. It is funding from the Ocean Climate Program of Fisheries also larger than the long-term rate derived from shore and Canada, using data provided by the Mete- stations for this area by Freeland (1990), but is com- orological Service of Canada, and by the National Data parable to the rate shown by these shore stations since Buoy Center of the United States. 1970. Apparent trends in both wind speed and SWH have REFERENCES also been discussed for other areas of the world (Gulev Cardone, V. J., J. G. Greenwood, and M. A. Cane, 1990: On trends and Hasse 1998; Cardone et al. 1990; Carter and Draper in historical marine wind data. J. Climate, 3, 113±127. 1988; Neu 1984). Highest reported trends, of the order Carter, D. J. T., 1982: Prediction of wave height and period for a of 0.1±0.5 m sϪ1 decadeϪ1 in wind speed, and 0.1±0.4 constant wind velocity using the JONSWAP results. Ocean Eng., Ϫ1 9, 17±33. m decade in SWH, are found in the North Atlantic. ÐÐ, and L. Draper, 1988: Has the north-east Atlantic become rough- Many are at levels comparable to the accuracy of the er? Nature, 332, 494. data, and require longer data records for con®rmation, Cherniawsky, J. Y., and W. R. Crawford, 1996: Comparison between as is the case for the buoy data presented here. weather buoy and Comprehensive Ocean-Atmosphere Data Set wind data for the west coast of Canada. J. Geophys. Res., 101, Many buoys showed increased SST during the 1997/ 18 377±18 389. 98 El NinÄo event, with about 1-month delay between Freeland, H. J., 1990: Sea surface temperatures along the coast of the warming at the equator and that shown by the buoys. British Columbia: Regional evidence for a warming trend. Can. Warming was strongest along the coast, but was not J. Fish. Aquat. Sci., 47, 346±350. Gower, J. F. R., 1996: Intercalibration of wave and wind data from detected in the Georgia Strait. Offshore buoys showed TOPEX/Poseidon and moored buoys off the west coast of Can- a warming in the north, and a cooling in the south, both ada. J. Geophys. Res., 101, 3817±3829. for the 1997/98 event and for the earlier 1982/83 event. Gulev, S. K., and L. Hasse, 1998: North Atlantic wind waves and Buoy 46134 (Fig. 1) was deployed in November 1998 wind stress ®elds from voluntary observing ship data. J. Phys. Oceanogr., 28, 1107±1130. as part of a program to provide additional ocean data Hamilton, G. D., 1980: NOAA Data Buoy Of®ce programs. Bull. important for understanding marine ecosystems. In ad- Amer. Meteor. Soc., 61, 1012±1017. dition to the meteorological sensors, this buoy is Mantua, N. J., S. R. Hare, Y. Zhang, J. M. Wallace, and R. C. Francis, equipped with an insolation sensor measuring the pho- 1997: A Paci®c interdecadal climate oscillation with impacts on salmon production. Bull. Amer. Meteor. Soc., 78, 1069±1079. tosynthetically active radiation (PAR), and with in-water Neu, N. H. A., 1984: Interannual variations and longer term changes sensors measuring chlorophyll ¯uorescence, water color, in the of the North Atlantic from 1970 to 1982. J. underwater PAR and salinity. An acoustic pro®ler Geophys. Res., 89, 6397±6402. provides data on the distribution of zooplankton with Reynolds, R. W., and D. C. Marsico, 1993: An improved real-time global sea surface temperature analysis. J. Climate, 6, 114±119. depth. Data can be viewed online at http://www.pac. Smith, S. D., 1988: Coef®cients for sea surface wind stress, heat ¯ux dfo-mpo.gc.ca/sci/ecobuoys/. If problems of calibration and wind pro®les as a function of wind speed and temperature. and optical fouling can be overcome, the installation of J. Geophys. Res., 93, 15 467±15 472.

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