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We report our investigation on the detection and classification of equatorial plasma bubble (EPB) structures in the Global-scale Observations of the Limb and Disk (GOLD) far ultraviolet (FUV) data. We have developed a novel technique for detrending the nighttime GOLD FUV irradiance data, which helps reveal large-scale field-aligned depletions associated with EPBs. The data detrending technique is a two-dimensional generalization of the rolling-barrel data detrending technique [Pradipta et al., 2015] that operates in one dimension. In this case, the rolling barrel is replaced with a rolling ball with two degrees of freedom to navigate across a two dimensional uneven terrain defined by the nighttime GOLD FUV irradiance data. The inferred baseline irradiance and the detrended irradiance data are subsequently transformed into geomagnetic coordinate in order to trace the position of the equatorial ionization anomaly (EIA) crests and the shape of EPB depletions. In the data analysis, the detected EPB depletions may appear either straight or curved with an inverse-C shape, depending on the solar local time. Zonal drift velocities of the detected EPBs are deduced based on sequential frames of GOLD FUV observation data. Afterwards, the computed EIA and EPB traces are transformed back from geomagnetic into geographic coordinate for realistic comparison with the original GOLD FUV observation data., {"references":["Pradipta, R., Valladares, C. E., and Doherty, P. H. (2015), An effective TEC data detrending method for the study of equatorial plasma bubbles and traveling ionospheric disturbances, J. Geophys. Res. Space Physics, 120, 11,048–11,055, https://doi.org/10.1002/2015JA021723"]}

Magnetic storms cause significant disturbances in the middle- and low-latitude ionosphere through penetration electric fields, disturbance dynamo electric fields, and neutral winds and composition changes. Understanding the interplay of different processes is critical for understanding storm-time ionospheric electrodynamics. In this study, we analyze ionospheric data measured by multiple satellites and ionospheric radars during intense magnetic storms and address the following important issues in ionospheric dynamics. (1) Long-lasting penetration electric fields are identified. The eastward penetration electric field is dominant in the equatorial ionosphere for 10-14 hours during continuous southward interplanetary magnetic field (IMF) and cause increase of 100-200 m/s in the equatorial vertical ion drift. (2) Strong subauroral polarization streams (SAPS) occur in the dusk-evening sector during the main and recovery phases of the magnetic storm and penetrate to equatorial latitudes without obvious time delay, leading to the generation of large westward plasma drifts of 200-300 m/s at all middle and low latitudes. (3) The topside ion density measured by the DMSP satellites is increased by a factor of 5-10, and these density enhancements last for 12 hours or longer, indicating the enhanced equatorial fountain effects caused by penetration electric fields. (4) A new type of ionospheric ion density oscillations with a period of ~6 hours is identified, which is different from travelling ionospheric disturbances and longitudinal wave-4 structure. This study provides new insight into storm-time ionospheric electrodynamics at middle and low latitudes., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)