Chorus source properties that produce time shifts and frequency range differences observed on different Cluster spacecraft

摘要

We present an explanation of frequency range differences and time shifts between corresponding chorus elements of whistler mode chorus which have been recently observed on multiple Cluster spacecraft. We show that a nonmoving or quasi-static source that emits waves in a relatively narrow interval of wave normal angles and that varies both the wave normal angle and frequency during the generation of a single chorus element can reproduce these observations. To validate this model, we perform a ray tracing analysis from a source located close to the geomagnetic equator to simulate the dispersion properties and relative timing of the chorus elements observed at different spacecraft. We demonstrate that the ray tracing simulation leads to patterns which are very similar to those observed.