Whistler wave properties and their occurrence during the Parker Solar Probe's 1st and 2nd encounter

Abstract : We present the analysis of narrow-band whistler wave signatures observed between the lower-hybrid and half of the electron cyclotron frequency during the 1st and 2nd encounters of Parker Solar Probe (PSP). These whistlers are identified using the band-pass filter data from the Digital Fields Board on the PSP. We find that nearly 85% of the whistlers are observed for less than three seconds consecutively, the probability of occurrence of long-consecutive (> 60 s) whistler intervals are rare. Using both the peak and mean band-pass filter data we show that whistler waves occur intermittently and the majority of the whistlers are of low amplitudes and occur for a short period (< 0.1 s). We investigate the dependence of the occurrence of whistlers and their amplitudes with respect to different proton and electron plasma parameters and with respect to magnetic field deflections. Several of the observed whistler features are in line with the previous Helios observations. We infer that the slower the velocity of the wind is, the higher the occurrence of whistlers is.