FISHERY BULLETIN: VOL. 70, NO. 3 



anomalous cold air and sea advection from the 

 north. 



Figure 3. which relates surrounding values to 

 the diamond at lat 20°N, long 170°W, instead 

 of demonstrating the east-west (trough-ridge) 

 teleconnections described in connection with Fig- 

 ures 1 and 2, focuses on north-south telecon- 

 nections. These relationships were first pointed 

 out by Walker and Bliss (1930) in studies of the 

 North Pacific Oscillation, and later expanded by 

 Willett, Bodurtha, and staff (1949)/ Lorenz 

 (1951), and O'Connor (1969). The upper sec- 

 tion of Figure 2 shows that 700-mb heights are 

 strongly negatively correlated between lat 20°N 

 and 50°N, implying a north-south half-wave 

 length of some 30° latitude. 



A large part of this negative correlation is as- 

 sociated with "blocking" situations (low zonal 

 index patterns) wherein anticyclones are found 

 near the Aleutians contemporaneously with cy- 

 clones near Hawaii (Kona Storms). In the re- 

 verse case, abnormally strong Aleutian Lows are 

 usually accompanied by strong subtropic anti- 

 cyclones (high zonal index patterns). 



The middle portion of Figure 3, while showing 

 large-scale coherence around the diamond, indi- 

 cates that the area of negative correlation lies 

 farther south in the SST pattern than in the 

 700-mb pattern, so that little correlation exists 

 between SST anomalies at lat 50°N and lat 20°N 

 in the central North Pacific. Probably this small 

 degree of correlation implies a much more com- 

 plex mechanism than wind-driven advection and 

 heat exchange, or that sea-level anomalies in 

 these situations are not well prescribed by the 

 700-mb anomalies. Also, the diamond lies out- 

 side the zone of major influence of the westerlies. 



Although there is a strong tendency for North 

 Pacific SST anomaly patterns to have compen- 

 sating large pools of warm and cold water, it 

 should not be assumed that the mean tempera- 

 ture anomaly of the entire North Pacific is zero. 

 Figure 4 shows that the mean SST for the entire 



SSToM ENTIRE NORTH PACIFIC (NORTH OF ZCN) 



' Willett, H. C, F. T. Bodurtha, and Staff. 1949. 

 Final report of the Weather Bureau - M.I.T. extended 

 forecasting project for the fiscal year July 1, 1948-June 

 30, 1949. Mass. Inst. Technol., Cambridge, Mass., 109 p. 

 ("Memorandum of Understanding" with the U.S. Weath- 

 er Bureau.) [Processed.] 



vUrfA. 



■■^aaIA- 



WSSFWSSFW W W 



'47 48 '49 '50 '51 



'52 '53 '54 '55 '56 '5? '56 '59 '60 '61 '62 '63 '64 '65 66 '67 68 



Figure 4. — Departures of mean sea-surface temperature 

 (°F) from the 1947-66 averages over the entire North 

 Pacific, north of lat 20°N. 



North Pacific (north of lat 20°N) varies over a 

 range of about 2°F in extreme seasons, and as 

 much as 1°F in extreme years I Assuming nor- 

 mal atmospheric parameters, a 1°F change would 

 imply a difference in heat of evaporation of 47.8 

 X 10^° cal., equivalent to the evaporation of 8.14 

 X 10'^ g of water or about 23.4 cm of water over 

 the entire North Pacific. The oceanic mean SST 

 anomalies are highly correlated with the area 

 occupied by positive signs of the SST anomalies 

 (r = 0.84) . Thus, the North Pacific mean anom- 

 aly is often determined not by the domination 

 of some extreme values but by the vast extent 

 of major anomalous areas. For example, dur- 

 ing the extreme negative SST anomaly of fall 

 1964 and extreme positive anomaly of summer 

 1967 (see Figure 4) 14% and 73% respectively 

 of the North Pacific had positive signs. Large 

 areal anomalies of this sort arise from the fact 

 that the sea has a much greater persistence than 

 the atmosphere (Namias and Born, 1970). 

 Jfence, large warm or cold pools in one area, 

 such as the western Pacific, are apt to resist 

 rapid change over a month or even a season, 

 while the eastern Pacific may be undergoing 

 more rapid response. This differential rate of 

 response may be due to a more shallow thermo- 

 cline in one area of the Pacific than another and/ 

 or more vigorous atmospheric circulation 

 changes. 



These almost ocean-wide extremes of SST are 

 naturally transitory, because their space scale 

 is not compatible with modal long-wave atmos- 

 pheric patterns, so that ultimately compatible 

 patterns must be restored. 



The high positive correlation between mean 

 SST over the entire North Pacific and percent 

 of the total area occupied by positive signs may 



616 



