Detrending GOLD FUV Data to Reveal Equatorial Plasma Bubble Structures

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.