Propagation of lower-band whistler-mode waves in the outer Van Allen belt: Systematic analysis of 11 years of multi-component data from the Cluster spacecraft
Abstract
Lower-band whistler-mode emissions can influence the dynamics of the outer Van Allen radiation belts. We use 11years of measurements of the STAFF-SA instruments onboard the four Cluster spacecraft to systematically build maps of wave propagation parameters as a function of position.
We determine probability distributions of wave vector angle weighted by the wave intensity. The results show that wave vector directions of intense waves are close to a Gaussian-shaped peak centered on the local magnetic field line.
The width of this peak is between 10 and 20 degrees. The cumulative percentage of oblique waves is below 10-15%.
This result is especially significant for an important class of whistler-mode emissions of lower-band chorus at higher latitudes, well outside their source region, where a simple ray tracing model fails and another mechanism is necessary to keep the wave vectors close to the field-aligned direction. Key Points Lower-band whistler-mode waves influence the outer radiation belt 11 years of wave propagation data from Cluster are analyzed by new methods Wave vector directions of intense waves are mostly field-aligned