Characteristics of hiss-like and discrete whistler-mode emissions

Abstract

The characteristics of hiss-like and discrete (rising and falling tones) whistler-mode waves in the lower-band wave frequency range (0.1-0.5 of equatorial electron gyrofrequency) are investigated using waveform data from nearequatorially orbiting multiple THEMIS spacecraft outside the plasmasphere. Statistical results show that wave polarization properties of hiss-like emissions are similar to rising tones, but are significantly different from falling tones. The magnetic wave amplitudes of hiss-like bands and rising tones are generally larger than those of falling tones. Wave normal angles of broadband hiss-like emissions and rising tones tend to be quasi field-aligned, whereas falling tones are very oblique. Importantly, discrete emissions including rising and falling tones are predominantly observed in the region of low f pe /f ce (the ratio of plasma frequency to electron gyrofrequency), whereas hiss-like bands alone preferentially occur in the region of high f pe /f ce. These important features of hiss-like and discrete whistler-mode emissions should be considered when evaluating their interactions with energetic electrons. © 2012. American Geophysical Union. All Rights Reserved.