Survey of Annual Fluctuation in Total Geomagnetic Intensity Observations
Mitsuharu NISHIMURA, Shin ARITA, Takashi MORIYAMA, Masahiko HASHIMOTO, Masashi SUGAWARA, Norihisa ISHIDA and Hiroshi HASEGAWA
Annual fluctuations in total magnetic intensity are observed at the continuous total geomagnetic intensity station (79F) at the Memambetsu branch. To identify the causes of this fluctuation, we measured outdoor air temperature and underground temperatures (at depths of 0.1, 0.5, and 1 m) near 79F in order to clarify their relationship with the fluctuations in total geomagnetic intensity. The results of this survey revealed that the annual fluctuations have a high correlation with the underground temperatures near the ground surface. We also conducted a magnetic survey in an area of the Memambetsu branch including 79F, and we found that the magnetic gradient near 79F was considerably greater in the east?west direction (10 nT/m) than that in the north?south direction. We therefore concluded that the annual fluctuations at 79F are caused by local variations in the magnetic field around the station that result from temperature changes.