a set of indices which would reveal fluctua- 

 tions in atmospheric circulation likely to 

 have a significant effect on water movements. 



Tabulation of Indices 



Pressure differences read from each 

 nonthly chart for the period 1926-57 at the 

 36 locations shown in figure 1 (page 3) are 

 listed in table 1 (page 18). Additional 

 sets of pressure differences, read from the 

 charts subsequent to the compilation of 

 table 1, are given in tables 2, 3 and 4 

 (pages 90, 91 and 92). 



Table 2 extends the data of table 1 

 through 1958. Table 3 contains a tabulation 

 of pressure differences read at the supple- 

 mentary locations 26a and 27a (fig. 4). This 

 was done after it was noted, in checking 

 back over the charts, that the points mark- 

 ing locations 26 and 27 frequently straddled 

 low pressure centers or trough lines in the 

 Gulf of Alaska. The pressure differences 

 obtained in such cases would not necessarily 

 be representative of wind strength over the 

 portion of the Alaska current immediately 

 adjacent to the coast. This criticism also 

 applies to locations 26a and 27a which 

 represent pressure gradients entirely over 

 land areas. However, the data obtained for 

 these locations are useful in demonstrating 

 the influence of coastal topography on the 

 positions of pressure systems. This point 

 is discussed further in a later section. 



Table 4 lists pressure differences 

 representing cross-current geostrophic wind 

 components at locations 3a to 6a inclusive 

 (fig. 4). These data, which cover only the 

 twelve year period 1946-57, complement the 

 along-current wind components represented by 

 pressure differences read at locations 3-6. 



The data contained in tables 1-4 were 

 derived as an exploratory means of summariz- 

 ing mean pressure data. Their significance 

 as indices of wind strength in relation to 

 the problem of interaction between sea and 

 atmosphere has not yet been established. 



REGIONAL WIND INDICES 



Analyses have been made on portions 

 of the data to provide some information on 

 seasonal Eind nonseasonal variations in sea 

 level atmospheric circulation. For this 

 purpose, the pressure differences for 



selected locations were averaged to give 

 regional indices of mean geostrophic wind 

 speed both parallel juid perpendicular to the 

 ocean currents. The locations so combined 

 for each regional index are listed below: 



1-6, 9-16, 29 North Pacific Gyre 



The indices have been labeled after appro- 

 priate current systems with two exceptions, 

 the Trade and Westerly. These, representing 

 the regions of the North Equatorial Current 

 and the North Pacific Drift, respectively, 

 are designated by the common names of the 

 prevailing winds in those regions. 



Average pressure differences and 

 monthly anomalies from the 1926-57 means are 

 given for each regional index in table 5 



(page 94). 



Graphs of mean monthly magnitude and 

 variability of the wind indices are shown 

 for certain regions in figure 5 (pages 8 and 

 9). The ordinate of each point gives the 

 mean of the monthly means. The vertical 

 lines extend one standard deviation above 

 and below the mean values. 



These graphs illustrate the differences 

 in seasonal cycles of those indices repre- 

 senting wind components tangential to the 

 major ocean currents. A dominant annual 

 cycle appears in all the curves with the ex- 

 ception of that for the Trade index. Even 

 in this case, spring and summer values tend 

 to be greater than those for fall and winter. 



The seasonal amplitudes of the grand 

 means vary considerably from region to 

 region. For the Trade index it is only two 

 millibars and for the Westerly index, 

 slightly over three millibars. The Alaska, 

 California, Alternate California, Kuroshio 

 and Oyashio indices have amplitude between 

 four and seven millibars. That for the in- 

 land Alaska index exceeds twelve millibars. 



