Correlation Analysis Between Banded Chorus and Electron Density Enhancement Using Van Allen Probes Data

The generation mechanism of banded chorus is still debated. One hypothesis invokes the frequency‐dependent ducting of whistler waves by a localized density enhancement, where the lower band propagates ducted while the upper band is unguided. The present study extracts the background density structures during banded chorus activities and investigates the correlations between them. We find that (a) half of the banded chorus events are associated with small peak‐to‐base density irregularities (the ratio ); (b) only 28% of the banded chorus events occur with localized enhancements (by contrast, 14% for no‐gap chorus), with radial extents 10–600 km and peak‐to‐base ratios ; and (c) for these 28% events occurring with localized enhancements, no strong correlation between lower band chorus and the parameters of the density enhancements is found. We also find that most of the lower‐band waves in our banded chorus events can be considered being ducted by these localized moderate‐to‐large density structures and that the use of geometric optic theory can be justified for them. We conclude that although the banded chorus occurrence is somewhat favored with moderate‐to‐large density ducts, the lack of strong interpretable correlation between them calls for a more comprehensive theoretical framework aided by improved plasma density measurements.