Frequency and amplitude analysis of chorus emissions observed by GEOTAIL

We try to find the observational evidence of the nonlinear evolution of chorus emissions, by examining their wave form data observed by the GEOTAIL spacecraft. Especially we investigate the relationship between the frequency shift and the amplitude variation of each chorus element. We evaluate statistically the correlation between their frequency sweep rates, frequencies and amplitudes. As a result, a positive correlation is found, which is consistent with the nonlinear growth feature of the chorus emissions obtained in simulation and theory.