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Studies on counter-electrojet currents (CEJ) using ground data revealed that this current could occur simultaneously among locations that are less than 30° longitude apart. In our work, the symmetricity of CEJ variation between the west and east of Southeast Asia, separated by ~25°, was preliminarily examined according to its types: morning (MCEJ) and afternoon (ACEJ). Since most of the past studies had overlooked the occurrence after dusk, the monitoring period was also extended from 18:00 to 21:00 LT, namely, the post-sunset depletion (PSD). The magnetometer station in Davao, Philippines (DAV) and Langkawi, Malaysia (LKW) were chosen to represent the east and west parts. The EEJ index (i.e., EUEL) over the periods of the solar cycle 24 (2008–2018) was utilized specifically during magnetically quiet days (Kp < 3). As the result, both parts symmetrically showed that MCEJ and ACEJ were positively and negatively correlated with the F10.7 index. Contrarily, MCEJ and ACEJ were asymmetrically prominent in the east and west. CEJ types also varied symmetrically with the season, especially for MCEJ and ACEJ (at high level), prominent during Equinox and J-solstice. Post-sunset depletion (PSD) in both parts was symmetrically solar activity independent, as no correlation with the F10.7 index was observed in the extended observation. PSD that varied symmetrically with season was also solar activity independent, except in the east during Equinox, where it was negatively correlated with the F10.7 index. Our finding also revealed that PSD was prominent during Equinox, except for the high level in the west part.

A negative decrement in geomagnetic data in equatorial region is not necessarily cause by the well-known counter electrojet, CEJ but it is also can be affected by solar activity such as a solar flare. Relying on this matter, we did a comparison between CEJ and unusual solar flare effect called as SFE* on geomagnetic data before introducing several types of CEJ that can be extracted from EUEL index. This study used ground data from MAGDAS network located in Langkawi (LKW) with 1-minutes resolution during solar cycle 24 and applied EUEL index. From the results, it is crucial to ensure the minimum duration of EUEL depletion is within an hour because less than an hour depletion could be possibly cause by solar activity. Four interval of time that has been introduced in our study composed of several types of CEJ which are morning CEJ, afternoon CEJ and evening CEJ, with additional the controversial CEJ occurrence which is night CEJ. We also successfully demonstrated a rare CEJ occurrence that associated with solar flare effect using EUEL index.

Sistem arus di ionosfera khatulistiwa terdiri daripada elektrojet khatulistiwa (EEJ) dan suria senyap (Sq). Arus EEJ merupakan satu jalur arus yang mengalir ke arah timur sepanjang kawasan dip khatulistiwa. Arus Sq pula adalah gegelung arus yang mengalir di hemisfera utara dan selatan bumi pada arah yang bertentangan. Kajian ini bertujuan untuk menganalisis kesan aktiviti matahari terhadap profil latitud sistem arus, khususnya di kawasan Asia Tenggara. Data yang digunakan dalam kajian ini merangkumi data geomagnet daripada lima stesen magnetometer dalam rangkaian MAGDAS iaitu stesen Muntinlupa (MUT), Cebu (CEB), Davao (DAV), Manado (MND) dan Pare Pare (PRP). Keamatan arus EEJ yang paling tinggi adalah pada waktu tengah hari sekitar 1000 dan 1100 LT semasa solar minimum dan kajian ini telah menganalisis sistem arus daripada 1000 hingga 1400 LT. Analisis menunjukkan bahawa ribut geomagnet yang berlaku pada 23 April 2008 adalah disebabkan oleh letusan jirim korona (CME) yang memberikan peningkatan kepada nilai arus pada hari tersebut. Peningkatan yang ketara dapat dilihat pada arus di stesen hemisfera selatan, iaitu stesen MND dan PRP. Berdasarkan analisis yang dilakukan, ia turut mendapati bahawa ribut geomagnet memberikan peningkatan kepada nilai arus walaupun di luar waktu puncak. Selain itu, profil arus ini turut dibandingkan dengan profil arus pada hari senyap iaitu pada

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