Relationship between the equatorial electrojet and global Sq currents at the dip equator region

Nurul Shazana Abdul Hamid,Nurul Shazana Abdul Hamid,Bhaskara Veenadhari,Teiji Uozumi,Huixin Liu,Kiyohumi Yumoto,Jairo Avendaño Sanchez,Akimasa Yoshikawa

doi:10.1186/s40623-014-0146-2

Abstract

The equatorial electrojet (EEJ) is a strong eastward ionospheric current flowing in a narrow band along the dip equator. In this study, we examined the EEJ-Sq relationship by using observations at six stations in the South American, Indian, and Southeast Asian sectors. The analysis was carried out with data on geomagnetically quiet days with Kp ≤3 from 2005 to 2011. A normalization approach was used because it yields more accurate results by overcoming the uncertainties due to latitudinal variation of the EEJ and Sq. A weak positive correlation between the EEJ and Sq was obtained in the Southeast Asian sector, while weak negative correlations were obtained in the South American and Indian sectors. EEJ-Sq relationship is found to be independent of the hemispheric configuration of stations used to calculate their magnetic perturbations, and it also only changed slightly during low and moderate solar activity levels. These results demonstrate that the Southeast Asian sector is indeed different from the Indian and South American sectors, which is indicative of unique physical processes particularly related to the electro-dynamo. Furthermore, we also demonstrate that the definition of the EEJ, that is, the total current or enhanced current, can significantly affect the conclusions drawn from EEJ-Sq correlations.

Highlights

The horizontal magnetic field lines at the equator produce a unique current system like that described below.In the dayside equatorial ionosphere, currents driven by tidal wind through the dynamo mechanism cause an accumulation of charges, which are positive at dawn and negative at dusk terminators, and this results in an eastward electric field, Ey, along the magnetic equator
These correlation coefficients are consistent with the fact that the Sq component was more significant in the total current for both the Southeast Asian and Indian sectors compared to the South American sector
By using the different northern-southern station configurations with the dip equator station located in the western Pacific Ocean, they concluded that the EEJ tends to be negatively correlated with Sq currents measured from stations equatorward of the global Sq current focus

Summary

Introduction

The horizontal magnetic field lines at the equator produce a unique current system like that described below. These correlation coefficients are consistent with the fact that the Sq component was more significant in the total current for both the Southeast Asian and Indian sectors compared to the South American sector (see Figure 4). We performed the analysis using different station pairs in the Southeast Asian sector along the 210° chain to investigate whether this northern (N)-southern (S) hemisphere (by referring to dip equator) configuration affects the results obtained. The location of these stations is shown in the map on the left panel of Figure 6. We are not sure about the exception in the year 2010 in the Southeast Asian sector as the result might not be significant because of the big data gap for the first six months

Findings

Discussion

Conclusion