Temporal evolution of substorm‐enhanced whistler‐mode waves: Relationship between space‐based observations, ground‐based observations, and energetic electrons

We examine 22 case studies of CRRES satellite observations of substorm‐enhanced whistler‐mode waves. These observations were made close to the geomagnetic equator and between 0200 and 0600 MLT. The frequency of the enhanced whistler‐mode waves is seen to vary strongly with magnetic field strength, and for this reason we plot the data in terms of the equivalent parallel resonant energy of an electron in first‐order cyclotron resonance with a wave of a given frequency. No consistent increase or decrease of the equivalent parallel resonant energy of the substorm‐enhanced whistler‐mode waves with time is seen; rather the typical behavior is that it remains constant with time. We interpret our findings in terms of the injected electron population and resonance ellipses in velocity space. Furthermore, we relate the findings of our study to observations of ducted waves seen on the ground as substorm chorus events (SCEs) and conclude that the frequency dispersion seen in SCEs is dominated by electric field effects.