Change of the atmospheric electric field around an observation hut by bamboo grove cutting: Estimation using a Field Mill electric field meter
Megumi KAITO, Junpei OOGI, Shingo NAGAMACHI & Takashi OHKAWA
The observed value of the atmospheric electric potential gradient at the Kakioka Magnetic Observatory has decreased since 1990. We hypothesized that the observed values reflected the influence of growth of the bamboo grove around the observation point. We therefore cut bamboo grove of the area surrounding the observation point in 2009. The effect of this cutting was estimated from the results of numerical calculations, which indicated that the observed value should have been 17% greater than the original value since the time before cutting. Furthermore, we expanded the cutting area in the bamboo grove from February to March 2017. Numerical calculations indicated that this cutting would have increased the observed value by 20%. In this study, we made comparative observations with a Field Mill electric field meter at a place not affected by cutting. The Field Mill indicated that the electric potential gradient had increased by 30%. One of the causes of the difference between the numerical calculation result and the comparative observation result seems to be because of the difference between the shape of the bamboo grove used in the numerical calculation and the actual shape. Considering the above, the usefulness of the numerical calculation was confirmed.