Abstract
Total electron content measurements given by the global navigation satellite system (GNSS) have successfully presented results to capture the signatures of equatorial plasma bubbles. In contrast, the correct reproduction of plasma depletions at electron density level is still a relevant challenge for ionospheric tomographic imaging. In this regard, this work shows the first results of a new tomographic reconstruction technique based on GNSS and radio-occultation data to map the vertical and horizontal distributions of ionospheric plasma bubbles in one of the most challenging conditions of the equatorial region. Twenty-three days from 2013 and 2014 with clear evidence of plasma bubble structures propagating through the Brazilian region were analyzed and compared with simultaneous observations of all-sky images in the 630.0 nm emission line of the atomic oxygen. The mean rate of success of the tomographic method was 37.1%, being more efficient near the magnetic equator, where the dimensions of the structures are larger. Despite some shortcomings of the reconstruction technique, mainly associated with ionospheric scintillations and the weak geometry of the ground-based GNSS receivers, both vertical and horizontal distributions were mapped over more than 30° in latitude, and have been detected in instances where the meteorological conditions disrupted the possibility of analyzing the OI 630 nm emissions. Therefore, the results revealed the proposed tomographic reconstruction as an efficient tool for mapping characteristics of the plasma bubble structures, which may have a special interest in Space Weather, Spatial Geodesy, and Telecommunications.
Highlights
Ionospheric plasma bubbles are large-scale structures of density depletion in the Earth’s ionosphere
Several works have conducted an analysis based on ionosondes measurement, such as Rastogi [10] by reporting seasonal variations of Equatorial Spread F, Saito and Maruyama [11] by studying the day-to-day variability of plasma bubbles, and Wang et al [12] by using concurrent ionosonde observations with other instruments to correlate the occurrence of scintillations with plasma bubbles
Radio scintillation measurements enabled the monitoring of plasma bubbles in the level of signal fluctuations [22], which makes it possible to capture the occurrence of plasma bubbles [23] and their signatures [24], even in the Brazilian area [25,26]
Summary
Ionospheric plasma bubbles are large-scale structures of density depletion in the Earth’s ionosphere. Previous works have shown clear evidence of equatorial plasma bubbles at TEC level [31,32] by comparing the airglow images with the Vertical TEC (VTEC) parameter obtained with GNSS observations These VTEC values have intrinsic shortcomings, due to the approximation of the ionosphere as a thin shell with a constant height at about 350–450 km above the Earth’s surface. Considering that the spatial variability and evolution of ionospheric plasma bubble irregularities is a topic of major interest in the Brazilian region [36], we present here the possibilities of a new tomographic method for imaging plasma depletions at electron density level. Since the tomographic reconstruction provides three-dimensional representations, the performance of the tomographic algorithm is investigated for analyzing the plasma bubble vertical structures
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