TABLE 650.— ELEMENTS AND CONSTANTS OF ATMOSPHERIC 615 

 ELECTRICITY* 



The elements of atmospheric electricity show variations, both regular and irregular. 

 Over land the irregular variations are very pronounced and the regular variations differ 

 notably from place to place, in marked contrast to the corresponding characteristics over 

 the ocean. Therefore, and because of the wider and more uniform geographical distribution 

 of ocean observations, it seems best to give the greater weight to the ocean data when at- 

 tempting to arrive at values characterizing world-wide conditions. Because of the wide 

 variation from place to place in the means from land stations, due to local factors, a 

 general mean of these is of questionable significance. Hence it seems better to indicate 

 the extremes of station means in the case of elements for which the data are sufficiently 

 abundant. 



Certain disparities, which will be found between published tables of ocean data, arise 

 largely from the inclusion of more recent data. 



Of the atmospheric-electric elements the potential gradient has been the most exten- 

 sively observed. The sign of the average gradient is everywhere such as to drive positive 

 ions toward the earth. The periodic variations in this element are of great interest because 

 of their apparent relation with cosmic phenomena. Thus the potential gradient apparently 

 increases with increase in sunspot numbers and varies throughout the year. The maxima 

 in monthly means occur everywhere, with few exceptions, at the time of northern winter, 

 and the corresponding minima occur at the tine of northern summer. The diurnal varia- 

 tion observed over the oceans is everywhere in phase when considered on a common-time 

 basis, except for a minor phase-shift that depends upon the season. This diurnal variation 

 derived from observatories made on the Carnegie during 1915 to 1921, given by the 

 Fourier expression AF/P = 0.15 sin (0 + 186°) +0.03 sin (2(9 + 237°) where is reck- 

 oned at 15° per hour beginning at h Greenwich mean civil time, is in close agreement 

 with that obtained from 1928-1929 observations. 



No general expression that will approximately characterize the diurnal variation over 

 land can be given. These variations determined by local factors are apparently super- 

 imposed upon a variation of the same world-wide character as that found to prevail over 

 the oceans. 



* Tables 650-653 prepared by G. R. Wait, Department of Terrestrial Magnestism, Carnegie Institution 

 of Washington. 



TABLE 651.— IONIC EQUILIBRIUM IN THE ATMOSPHERE 



Equilibrium for atmospheric ionization occurs when q = an 2 + ijiA/ort + ^Nn, where n 

 and N are the number of pairs of small and large ions of one sign and jVo the number of 

 uncharged nuclei ; a, iji, tj 2 , are coefficients of recombination of small ions with small ions, 

 with uncharged nuclei, and with large ions. If for both small and large ions the positive 

 and negative are equally abundant, then No/N = Vi/Vi. When n/N <? 2r) 2 /a, the equilib- 

 rium-condition is expressed by q = )3h ; /3 is designated the diminution-constant; l//3r=0 

 is the "average life"' of a small ion in air which contains an abundance of large ions ; 

 varies inversely as N. 



a: 1.6 X 10- 8 cm 3 /sec 

 *: 5 X 10" a " 

 *: 6X10- 8 " 

 © Over land, 



Average, 30 sec 

 Extremes, 10 to 60 sec 

 Over sea, 230 sec 

 N : Over land, 500 to 50,000 ions/cm 3 

 Aitken nuclei, number per cm 3 : 

 Over open country, up to 10 6 

 Over midocean, about 800 

 In free air, 

 Altitude 1 km 6,000 5 km 50 



3 km 200 8.5 km about 5 



TABLE 652.— CHARGE ON RAIN AND SNOW 



Specific net charge on precipitation : 



Average, 0.5 esu/g 

 Maximum observed, 20 esu/g 



Specific charge on individual raindrops or snowflakes : 



Rain, + 2.7 to — 3.2 esu/g 

 Snow, + 11.6 to — 8.1 esu/g 



SMITHSONIAN PHYSICAL TABLES 



