Can a nightside geomagnetic Delta H observed at the equator manifest a penetration electric field?

摘要

abstract_textpA prompt penetration electric field (PPEF) usually manifests itself in the form of an equatorial ionospheric electric field being in correlation with a solar wind electric field. Due to the strong Cowling conductivity, a PPEF on the dayside can be inferred from Delta H (H), which is the difference in the magnitudes of the horizontal (H) component between a magnetometer at the magnetic equator and one off the equator. This paper aims to investigate the performance of H in response to a PPEF on the nightside, where the Cowling conductivity is not significant. We first examine the strongest geomagnetically active time during the 20 November 2003 superstorm when the Dst drops to -473nT and show that the nightside H can indeed manifest a PPEF but with local time dependence and longitude dependence. We then examine a moderately active time by taking advantage of the multiple-penetration event during 11-16 November 2003 when the Dst remains greater than -60nT. During this event, a series of PPEF pulses recorded in Peru, Japan, and India form a database, allowing us to examine PPEF effects at different local times and longitudes. The results show that (1) the nightside H was caused by attenuation of the effects of the polar electric field with decreasing latitude; (2) the nightside H can manifest a PPEF at least in the midnight-dawn sector (0000-0500 LT), but not always; and (3) the magnitude of the nightside H in the midnight-dawn sector in Peru is on average only 1/18 of that of the dayside H in response to a given PPEF./p/abstract_text