Preferential Amplification of Rising Versus Falling Frequency Whistler-Mode Signals

Wednesday, 17 December 2014
Justin Li1, Vijay Harid1, Maria Spasojevic1, Mark Golkowski2 and Umran Inan1,3, (1)Stanford University, Stanford, CA, United States, (2)University of Colorado Denver, Denver, CO, United States, (3)Koc University, Istanbul, Turkey
Analysis of ground-based ELF/VLF observations of injected whistler-mode waves from the 1986 Siple Station experiment indicate a distinct preference for the magnetospheric amplification of rising frequency-time ramps over descending frequency-time ramps. In examining conjugate region receptions of ±1 kHz/sec frequency ramps, we find that the rising ramps generate a total power that is on average 1.9 times higher than that of falling frequency ramps when both are observed within a given transmission. Also, in 17% of receptions, only the rising frequency ramps are observed, and the descending ramps are below the detectable signal level. Using a narrowband Vlasov-Maxwell numerical simulation, we explore the preferential amplification of rising ramps due to differences in the linear growth rate as a function of frequency and the onset and duration of nonlinear phase trapping. These results contribute to the understanding of magnetospheric wave amplification and the formation of structured rising elements in chorus.