Continuous measurement of current in air and possible relation with intense earthquake

Known as the global circuit, atmospheric ionic current (AIC) is flowing into the ground. In this study, the potential, Vm, of an electrode placed outside under open air was measured continuously using an electrometer with its voltage measuring mode. Vm should be a product of AIC flowing into the electrode and the input impedance of the electrometer. This measuring system, instead of direct measurement of AIC, was used to avoid noises caused by commercial power lines, motors, and other electronic devices. It also measures sudden change of atmospheric electric field. This is also an important feature. Daily time evolution of Vm is normally periodical, after sunset until sunrise Vm stays small, then it increases gradually, reaching a peak around noon followed by a gradual decrease in the evening. Occasionally different signals were observed, especially a few weeks prior to an intense earthquake. Vm was increased several weeks prior to a major earthquake, especially Vm was high in the midnight. It should be noted that, about 40 min prior to a very intense earthquake in north part of Japan in March 11, 2011, Vm showed sudden decrease. This decrease is related with the reported increase of electron density in ionosphere around the epicenter. The increased number of electron may produce ionic space charge in stratosphere, that could be measurable by this system. The abnormal behavior of Vm could be precursory phenomenon of an intense earthquake