Journal of the Meteorological Society of Japan. Ser. II
Online ISSN : 2186-9057
Print ISSN : 0026-1165
ISSN-L : 0026-1165
On the Diurnal Yariation of Earth-current Potential Gradient on Calm and Disturbed Days, at the Kakioka Magnetic Observatory
T. Yosimatu
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1936 Volume 14 Issue 7 Pages 323-328


The main part of the variation recorded every day of earth-magnetism. or earth-current may be generally supposed to be an intermixed result by all agencies from the sun of which ultraviolet light is said by some authors to cause the diurnal variation and charged or neutral corpuscular rays mainly to relate to the occurrence of the disturbance. Then the disturbance must deform the diurnal variation of usual days. To know this effect of the disturbance of earth-current, we constructed the Difference-Curve_??_[Diurnal Variation on Disturbed Days]-[Diurnal Variation on Calm Days] for the east-component-larger variation direction at this place-in the period of Sept. 1932 to Dec. 1934.
The Difference-Curve-call it the Curve for short hereafter-is obviously a single oscillation against the double one of the diurnal variation, having max. at about midnight and min. at early afternoon when the westward current is taken as positive. The portion from the negative part of the Curve to the positive part; that is, from day to night, is steeper than the opposite portion. The transition points between the negative and positive parts of the mean Curve in the full period are 5.0h and 18.5h (135° E. M. H.) which are about 40 minutes earlier, or later than the sun-rise and sun-set on the ground at Tokyo. This may suggest some relationships between the solar effect upon the upper air, say ionized layers, and the charge of the diurnal variation on disturbed days.
A seasonal variation of the Curve is seen by the largest amplitude in Summer (May, June, July, Aug.) and smallest in Winter (Nov., Dec., Jan., Feb.), while the diurnal variation has the max. amplitude in Spring (Mar., Apr., Sept.. Oct.) at this place.
Next, supposing the most disturbed interval of each disturbed day is T hours, of which N hours belong to the night part (18h to 6h) of the day, we classify the disturbed days into two cases;
The Curve of (ii) has a smaller amplitude with 70% of that of (i), and a small phase difference which decided conclusion desires more data. This result means in the other words that the diurnal variation on days having many hours of disturbance in the night part of the days is not so differed from that on calm days, compared with that of disturbed days of which larger part of the disturbed hours belong to the daytime.
The similar Curve for 1933 of earth magnetic horizontal component shows also a single wave such as at some other places, and the same value of R=amp of the Curve/amp. of the diurnal variation on calm days=0.7with that of earth-current for the same days, but larger phase difference compared that of the diurnal variation on calm days.
he vector difference between the resultant diurnal variation current on calm and disturbed days are calculated for 1934 and expressed by a fish-bone figure. Its absolute value and the angle θ between the diurnal variation current on calm days and this difference current are also shown. This result seems to show that the effect in daytimes by the disturbance upon the diurnal variation is somewhat differ from that in night part.
The interpretation of the resuls is not so easy in the present state, but the author proposes a possible suggestion th_??_t the main cause of the effect of the disturbance obtained above may not be hidden so far outside the earth's atmosphere, but in the upper parts of the ionized regions, of which lower part, for example the E-layer, is now supposed to be the main domain of the diurnal variation on calm days. The ionization of the supposed parts may be greatly increased in the mean state on the disturbed days by some agencies from the sun, w_??_ether radiations, or corpuscles may they be; and also hea_??_el or dissociated by the sun's radiation, inducing an anomalous current variation.

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