locations and in most cases are rather 

 irregular, probably due to large year-to- 

 year variability for given months. Since 

 only twelve years are represented, stand- 

 ard deviations were not computed for these 

 data. 



REPRESENTATIVENESS OF INDICES 



Zonal wind indices based on pressure 

 gradients in the region of the northern 

 hemisphere westerlies have been widely 

 applied in meteorology to indicate signifi- 

 cant aspects of air circulation. While 

 the Westerly index defined in this report 

 is not strictly zonal, it is nearly so and 

 represents wind components near the axis 

 of the mean maximum westerly flow. 



Since this axis may shift north or 

 south from its normal position in indivi- 

 dual months it was considered important to 



test the sensitivity of the Westerly index 

 used here to fluctuations in the maximum 

 intensity of Westerly geostrophic winds 

 over the North Pacific. 



Accordingly, a procedure was adopted 

 in which values of the "maximum westerly 

 components" were obtained by extending the 

 line through the two points defining each 

 location in the Westerly index (3-6) north 

 and south, respectively, to 55° and 30" N. 

 latitude. By successive trials, the maxi- 

 mum pressure difference along each line was 

 determined across a distance equal to 300/ 

 (sine of latitude) nautical miles. Monthly 

 values so obtained for the period 1946-57 

 are tabulated in table 6 (page 104). The 

 column labeled "DSP" (displacement) shows 

 whether the maximum value occurred south 

 (S), north (N) or at the same latitude (X) 

 as the fixed locations shown in figure 1 

 (page 3). 



The maximum pressure differences 

 obtained at the four locations on each 



J 

 s 



DEC JAN FEB MAR APR MAY JUN JUL AUG SEPT OCT NOV DEC 



Figure 5g, h. --Grand monthly means of ,)ressure differences 

 for period 1926-57. (g) Alaska index; (h) Inland Index. 

 The vertical lines drawn through each point extend one 

 standard deviation above and below the monthly mean 

 values. 



2r 



- 



J I I L 



-v^- 



J I L 



DJFMAMJJASOND 



MONTH 



igure 6. --Pressure differences representing "cross-current" 

 wind components at locations 3a-6a averaged by 

 month for period 1946-57. 



