Characteristics of negative values of polar cap index as an indicator of reversed convection

概要

論文の詳細を見る
The polar cap (PC) index sometimes shows negative values in the summer hemisphere. The Hall current induced by reversed convection causes the negative values of PC index. This means that the negative PC is an indicator of reversed convection in the polar cap of the summer hemisphere. Using the northern PC index (PCN) for 1995 to 1999, we have statistically examined the occurrence characteristics of negative values of PCN. The results of our data analysis show that a negative value of PCN frequently occurs when the solar zenith angle is less than 75° and when the IMF BY and BZ are positive. These results are consistent with those obtained by the previous studies. Further, we found that the occurrence of negative PCN increases with solar wind electric field projected onto the GSM YZ plane (ET), if the clock angle is less than 60° When the clock angle is from 60 to 80°, the occurrence of negative PCN increases with ET in the cases when ET is less than 4 mV/m, and decreases with increasing ET in the cases of ET greater than 4 mV/m. Further, the occurrence of negative PCN increases with increasing magnitude of IMF projected onto the GSM YZ plane (BT) and decreases with increasing solar wind velocity. These results suggest that the occurrence of reversed convection in the polar cap is not a simple function of IMF clock angle. Their occurrences are also controlled by the magnitude of BT and solar wind velocity.
国立極地研究所の論文