STUDIES IN ATMOSPHERIC ELECTRICITY 



151 



Table 5. Study of conspicuous change in conductivity and air -earth current density on 

 September 9, 1929 in the Pacific Ocean 



Group 



GMT 

 h 



n 

 10-4 esu 



X^„(a) 



10-4 



\+ + X- 

 10-4 esu 



^n 

 104 esu 



^n 

 V/m 



10-V 



Hi 

 10-7 esu 



h^(b) 

 meters 



(1) 



Mean 



1.22 



1.34 



2.56 



0.391 



123 



10.4 



X- X+ X+ + X- py Gu 



10-4 esu 10-4 esu 10-4 esu 104 esu V/M 



(2) 11-12 0.77 0.85 1.62 0.617 188 10.2 



12-13 0.79 0.87 1.66 0.602 180 10.0 



13-14 0.77 0^85 1.62 0.617 188 10^2 



Mean 0.78 0^86 1.63 0.612 185 11.6(c) ip.i 750 



(3) 14-15 0.38 0.42 0.80 1.25 273 7.3 



15-16 0.29 0.32 0.61 1.64 307 6.2 



16-17 0.22 0^24 0.46 2.17 319 4.9 



Mean 0.30 0.33 0.62 1.69 300 12.7(c) g.l 925 



(4) 19-20 0.14 0.16 0.30 3.33 362 3.6 



20-21 0.14 0.16 0.30 3.33 374 3.7 



21-22 0.14 006 0.30 3.33 357 3^^ 



Mean 0J4 0^16 0.30 3.33 364 12.3(c) 3.6 915 



(5) 22-23 0.12 0.14 0.26 3.85 299 2.6 



23-24 0.14 0^16 0.30 3.33 284 2.8 ' 



Mean 0^3 OJ^S 0.28 3.59 292 10.6(c) 2.7 1011 



(a)x+ = 1.10X-. (b)hu = (in - iu)Rn/iu(/°u - Pn). where R^ = 1.11 x 10^ esu, and Pu = ^-^^^ ^ 



104 esu. (c) Values for in assumed from llh to 24h, in accordance with universal-time diurnal- 

 variation characteristics of figure 14. 



approximations to normal values become 11.6, 12.7, 

 12.3, and 10.6. These values of in may be taken with 

 some confidence as correctly representing the current- 

 density values that would have existed on this occasion 

 had not a disturbing element been present. A period of 

 hours rather than days is involved here, unlike the situ- 

 ation in the previously discussed cases, making it pos- 

 sible to establish the values of in with reasonable ac- 

 curacy. In this case, then, the values of in for groups 

 (2) to (5) in table 5 are accepted as known, and the com- 

 putation of appropriate values of hu for these groups is 

 readily accomplished from equation (12). In the compu- 

 tation, the value of Pn was taken as 0.39 x 104 esu, as 

 obtained from group (1) in table 5, and Rn was taken, as 

 before, as 1.11 x 109 esu. The computed values of hu 

 are shown in the last column of table 5. 



Within each group, except (3), in table 5, a certain 

 stability of values of both conductivity and potential-gra- 

 dient will be noted, as if the changes proceeded in defi- 

 nite "steps" through the day. Group (3), the exception, 

 shows continuous change from hour to hour, but the 

 three hours are nevertheless treated as a group. As 

 only negative conductivity was recorded, values of posi- 

 tive and total conductivity for table 5 were computed on 

 the basis that X+/ X- = 1.10. 



The values of h^ for groups (2) to (5) give the inter- 

 esting result that the thickness of the layer in which the 

 disturbing element existed was, except in the first three 

 hours, about 1km, although there was continuous change of 

 potentiahgradient and conductivity over a much longer 

 period. In the first three hours, however, the height ap- 

 pears to have been only seven hundred and fifty meters, 

 and, if the first hour only is considered and the value of 

 in for that hour is taken as 11.3 x 10-7 esu, the value of 

 hu is found to be about five hundred meters. Thus, a 

 wedge-shaped layer appears to have been entered on this 

 occasion, with a "front" five hundred meters high. This 

 front was entered suddenly, because the photographic 

 records of both potential-gradient and conductivity show 

 that the change from normal to disturbed conditions took 

 place in only three or four minutes, commencing at llh 

 05m and ending at llhOSm or 09m. At llhOSm both con- 

 ductivity and potential-gradient had values very close to 

 the average given in table 5 for lOh-llh, and at llh09m 

 both had arrived at the values given as the average for 

 llh-12h. Stable conditions existed before the disturbed 

 region was entered, and were established again, but on a 

 different basis, four minutes later. During the next three 

 hours stable conditions existed within the layer but the 

 layer thickness changed from five hundred to one thousand 



