###### Abstract  
Studies on counter-electrojet currents (CEJ) using ground data revealed that this current could occur simultaneously among locations that are less than 30\({}^{\circ}\) longitude apart. In our work, the symmetricity of CEJ variation between the west and east of Southeast Asia, separated by \(\sim\)25\({}^{\circ}\), 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. CEJ; solar activity level; season; Southeast Asia; solar cycle 24 202220220220220220220220220220220220220220220220220220220220220220220222022022202220222022220222202  
geomagnetic conditions. For example, CEJ during quiet days could be driven by changes in the atmospheric tides that dominate the global wind system at ionospheric heights [4,5]. The variability for both CEJ and EEJ events are dependent on the variation in local time, longitude, seasonal dependence, lunar cycles, magnetic activity, and solar activity [6, 7, 8, 9, 10, 11, 12]. The CEJ study has been gradually expanded to a global scale through the integration of ground, satellite, and ionospheric measurements. Over a large longitudinal separation range, the variability of CEJ showed that morning occurrence dominated more than afternoon globally, except for the Indian sector. The highest occurrence rate was recorded in the Brazilian sector than elsewhere [10]. CEJ occurrence might not take place simultaneously on the same day if the longitude separation was less than 30\({}^{\circ}\)[13, 14, 15], but a study in the Indian sector revealed more simultaneous occurrences between \(\sim\)15\({}^{\circ}\) separations after 1500 LT [16]. On the other hand, a study on the EEJ-Sq (solar quiet) relationship demonstrated an uncommon behavior in Southeast Asia when compared to India and America, due to the disturbance in dynamo regions [17]. These aforementioned works motivate and present an opportunity to preliminarily examine the symmetricity of CEJ variation between the insular (east) and peninsular (west) of Southeast Asia that are separated within 30\({}^{\circ}\) longitude before a comprehensive study can be conducted as a continuation thereof. Moreover, detailed studies of CEJ, especially in the western part of Southeast Asia, are limited as only data from the east were primarily utilized in past studies [8,10,18]. Although it is widely accepted that CEJ must occur between 06:00 and 18:00 LT, the determination of the local time interval is not generally agreed upon as it usually depends on the study focus, region, and CEJ occurrences themselves. For instance, an initial study that introduced the local time interval used the following classification for African and Indian sectors: morning (06:00-08:00 LT), noon (11:00-12:00 LT), afternoon (13:00-14:00 LT), and evening CEJ (15:00-18:00 LT) [19].