Practical Applications of GPS Total Electron Content (TEC) Detrending and Mapping Techniques for Studying Equatorial Plasma Bubbles and Midlatitude Irregularities

Abstract

In this work, we present several case examples of ionospheric plasma density depletions and/or irregularities that have been observed over South America and the Caribbean. These plasma density depletions/irregularities were identified in the 2-D geographic maps of detrended TEC values (dTEC = TEC_observed – TEC_smooth.trend) based on the data obtained from 200+ GPS receiver stations in this longitude sector. The dTEC values themselves in this case have been derived numerically using a special GPS TEC data detrending technique described in Pradipta et al. [2015], which is inherently capable of differentiating between depletions and wavelike variations in TEC. We found that the turbulent ionospheric plasma depletions/irregularities over the Caribbean are sometimes simply a further northward extension of equatorial plasma bubbles (EPB) from low-latitude regions over South America. However, on some other occasions they are evidently a form of midlatitude ionospheric plasma phenomena unique to the region, which can occur independently in the absence of any equatorial bubbles in this longitude sector. These “bubblets of the Caribbean” typically have a depth/amplitude ranging from fractions of TECU to several TECU, which is comparable to the amplitude of traveling ionospheric disturbances (TID) induced by acoustic-gravity waves (AGW). However, we must also remark that these midlatitude irregularities/depletions do not show particularly clear/coherent parallel wavefronts commonly seen in classic cases of AGW-induced TID. Finally, we also discuss some ground-based observations as a cross-comparison to the GPS TEC data.