Study of field?￠????aligned current (FAC), interplanetary electric field component ( E y ), interplanetary magnetic field component ( B z ), and northward ( x ) and eastward ( y ) components of geomagnetic field during supersubstorm

摘要

A dominant process by which energy and momentum are transported from the magnetosphere to the ionosphere is known as field?￠????aligned current (FAC). It is enhanced during magnetic reconnection and explosive energy release at a substorm. In this paper, we studied FAC, interplanetary electric field component ( E y ), interplanetary magnetic field component ( B z ), and northward ( x ) and eastward ( y ) components of geomagnetic field during three events of supersubstorm occurred on 24 November 2001, 21 January 2005, and 24 August 2005. Large?￠????scale FAC, supposed to be produced during supersubstorm (SSS), has potentiality to cause blackout on Earth. We examined temporal variations of the x and y components of high?￠????latitude geomagnetic field during SSS, which is attributed to the FACs. We shall report the characteristics of high?￠????latitude northward and eastward components of geomagnetic field variation during the growth phase of SSS by the implementation of discrete wavelet transform (DWT) and cross?￠????correlation analysis. Among three examples of SSS events, the highest peak value of FAC was estimated to be ~19????????Am ?￠????2 . This is shore up with the prediction made by Parks (1991) and Stasiewicz et al. (1998) that the FACs may vary from a few tens to several hundred ????Am ?￠????2 . Although this peak value of FACs for SSS event is much higher than the average FACs associated with regular substorms or magnetic storms, it is expedient and can be expect for SSS events which might be due to very high density solar wind plasma parcels (PPs) triggering the SSS events. In all events, during growth phase, the FAC increases to extremely high level and the geomagnetic northward component decreases to extremely low level. This represents a strong positive correlation between FAC and geomagnetic northward component. The DWT analysis accounts that the highest amplitude of the wavelet coefficients indicates singularities present in FAC during SSS event. But the amplitude of squared wavelet coefficient is found to be different from each other, which might be due to the solar wind PPs of different density triggering the SSS events. The cross?￠????correlation analysis suggests that the perturbation on geomagnetic northward component at high latitude during SSS strongly correlates with the fluctuation pattern of FAC density. Hence, the FAC is the primary sources for the eastward?￠????westward magnetic field perturbations at high latitude.