Local time variation of the amplitude of geomagnetic sudden commencements (SC) and SC-associated polar cap potential

T Araki,S Tsunomura,T Kikuchi

doi:10.1186/bf03353154

Abstract

Abstract Local time (LT) variations of the averaged H-component amplitude of geomagnetic sudden commencements (SCs) observed at Memambetsu (geomagnetic latitude 35.4°) are derived separately for the summer and winter season. The amplitude was found to be higher at nighttime than daytime in both seasons, and the LT variations showed a good agreement with calculated LT variations of the resultant magnetic field due to a pair of fieldaligned currents (FACs) and ionospheric currents produced by the FACs. The DL- and DP-component of the disturbance field of SC can be separated based on a comparison of the observed and calculated LT variations. A method is introduced by which we can estimate the potential voltage difference associated with the FACs in the polar cap.

Highlights

According to the physical model of geomagnetic sudden commencements (SCs) proposed by Araki (1977, 1994), the disturbance field of SC, Dsc, is given byDsc = DPpi + DLmi + DPmi (1)where pi and mi express the ‘preliminary impulse (PI)’ and ‘main impulse (MI)’, respectively
The DL-field is dominant at low latitudes and is produced mainly by the magnetopause current enhanced after impinging of the interplanetary shock or discontinuity on the magnetosphere
The DPpi- and DPmi-fields, which are dominant at high latitudes, form an adjacent two pulse structure with opposite sense and are produced by a pair of field-aligned currents (FACs) and ionospheric currents (ICs) produced by the FACs so that it is expressed as

Summary

Introduction

According to the physical model of geomagnetic sudden commencements (SCs) proposed by Araki (1977, 1994), the disturbance field of SC, Dsc, is given by. They interpreted the LT variation of the SC amplitude described above by a resultant magnetic field of the FAC that is responsible for DPmi and FAC-produced IC (denoted by ICFAC hereafter). Kikuchi et al (2001) pointed out that the contribution of the magnetic fields due to the FAC for DPpi is important for the interpretation of PPI These researchers calculated LT variations of the H -component PI amplitude due to both the FACs and ICFAC by giving a polar cap potential on the thin shell ionosphere with realistic conductivities, including LT and latitudinal variation and weak auroral enhancement. We show a method to estimate both DLmiand DPmi-field and polar cap potential difference associated with the DPmi-field

Observed and Calculated LT Variation of the Averaged SC Amplitude

Discussion