Climatology of Plasma Irregularities Using ROTI Index From 2008 to 2023 in East West Asia

Abstract This study investigates characteristics of ionospheric irregularities over the East–West Asian equatorial region using the Rate of TEC Index (ROTI) derived from Global Navigation Satellite System (GNSS) measurements. Data from four stations (GUAM, PIMO, CUSV, and IISC) were analyzed for 2008–2023, covering solar cycle (SC) 24 and the ascending phase of SC 25. While our findings are generally aligned with previous research, this work presents new insights into the complex behavior of ionospheric scintillation in this sector. A key finding is the significant spatial variability in irregularity occurrence, with stations at similar magnetic dip (11–13°) exhibiting varying activity levels. Notable longitudinal asymmetries were also identified, particularly at GUAM, which shows reduced autumnal activity, likely due to local differences in Pre‐Reversal Enhancement (PRE) and magnetic declination. Our study shows a clear daily pattern: scintillation begins after sunset (18:00–19:00 LT), peaks in the late evening (20:00–21:30 LT), and declines by early morning. A slight increase in ROTI is consistently observed just before sunrise at all locations. Temporally, results show dependence on the 11‐year SC and a distinct seasonal pattern, with activity concentrated in equinoctial months. The spring maximum is generally stronger than the autumn one across stations. Finally, although the long‐term trend follows the SC, the relationship is non‐linear. Outliers, such as anomalous activity in 2019, demonstrate that while the Sunspot Number (SSN) is a primary long‐term driver, scintillation is also modulated by short‐term geophysical phenomena.