Statistical analysis of hiss wave spectrum from the

Statistical analysis of hiss wave spectrum from the EMFISIS wave data Wen Li, R. M. Thorne, J. Bortnik, C. A. Kletzing, W. S. Kurth, and G. B. Hospodarsky Motivation + Objective Ø Previous statistical results are limited due to frequency coverage (> 100 Hz) and lack of polarization properties. Ø Unusually low frequency hiss (~20 Hz) is reported [Li et al. , 2013]. Ø Evaluate hiss wave frequency spectrum at various L and MLT using 2 -year of EMFISIS wave data.

Global distribution of hiss wave amplitudes over 20 -4000 Hz AL*: the minimum AL in previous 3 hours. Statistical analysis § 2012/10/01− 2014/ 07/01 from both Probe A and B §Survey-mode WFR data with 6 sec resolution §Hiss Bw is calculated over 204000 Hz in the high density region (> 30 /cc). • Hiss Bw is stronger on the dayside than that on the nightside. • Hiss Bw is activity dependent, with stronger (weaker) wave amplitudes on the dayside (nightside) with increasing geomagnetic activity.

Frequency spectrogram of Bspec during quiet times AL*: the minimum AL in previous 3 hours. §The peak frequency tends to decrease with increasing L-shell. §Bspec over 04 -20 MLT is slightly larger than that over 20 -24 MLT.

Frequency spectrogram of Bspec during modest times §Bpsec is larger compared to quiet times over 04 -20 MLT. §Significant wave power extends below 100 Hz over 04 -20 MLT particularly at L > 3.

Frequency spectrogram of Bspec during active times §Peak wave frequency tends to decrease with increasing L-shell over 08 -20 MLT. §Bspec is larger (smaller) compared to that during weaker activities over 04 -20 MLT (20 -04 MLT). §The wave intensity < 100 Hz becomes even stronger during active conditions.

Observed hiss Bspec vs. the previously used Gaussian wave spectrum 12 -16 MLT Previously adopted hiss wave distribution: [e. g. , Lyons et al. , 1972; Summers et al. , 2007; Shprits et al. , 2009; Subbotin et al. , 2010; Thorne et al. , 2013; Ni et al. , 2013, 2014] §Observed hiss peak wave frequency is smaller than the previously used Gaussian spectrum §Hiss peak frequency becomes smaller at larger L-shells §Bspec is larger at higher frequencies (> 1. 2 k. Hz) compared to previous hiss model.

Daa of previous and new hiss wave model at L = 3 and 12 -16 MLT

With new opportunities § Increase the statistical significance of hiss frequency spectrum model by including more data during the declining phase of the solar cycle § Multi-point observation will allow us to resolve the evolution of hiss wave spectrum simultaneously at various MLTs § CUBESAT electron measurements at the conjugate low altitudes will quantify hiss-driven electron precipitation at various MLTs Science question: What is the evolution of plasmaspheric hiss frequency spectrum and intensity at various MLTs in individual events? 2016/03/25 4 RE

Evidence of plasmaspheric hiss originated from chorus: Coordinated Van Allen Probes and THEMIS observations Wen Li, L. Chen, J. Bortnik, R. M. Thorne, V. Angelopoulos, C. A. Kletzing, W. S. Kurth, and G. B. Hospodarsky Motivation + Objective Ø Ray tracing simulations suggest that plasmaspheric hiss is originated from chorus waves. Ø However, the direct evidence of showing this correlation is very limited due to the difficulty of capturing this coordinated observation. Ø Using coordinated observation from Van Allen Probes and THEMIS, we evaluate the correlation between plasmaspheric hiss and chorus.

Coordinated event between THEMIS and RBSP THEMIS • THEMIS (9 -10 RE): Chorus • RBSP (5 -6 RE): Hiss 2014 -02 -02 (20: 40 – 21: 40 UT) TH-E 200 -600 Hz RBSP-B

RBSP THEMIS During the burst period of THEMIS 200 -600 Hz 1 2

Correlation coefficients between chorus and Hiss 1 2 • The highest correlation (> 0. 7) is obtained over 220 -400 Hz with a time delay of ~6 -12 sec in both periods.

Ray tracing simulation (~300 Hz) • Simulated time delay of rays to propagate from chorus location into hiss location is ~12 s, roughly consistent with observed time delay between chorus and hiss emissions. ~12 s • This also supports that chorus waves observed at 9 -10 RE, where chorus is previously considered to be unlikely to propagate into the plasmasphere, are newly found to be capable of being the source of plasmaspheric hiss.

With new opportunities 2016/01/29 2015/10/31 §Multi-point observation 2016/01/29 will allow us to capture more coordinated events showing potential chorushiss correlation. Chorus hiss 2017/11/30 §Requirements: ²Dayside ²Some SAT: outside pp ²Some SAT: inside pp 2017/07/31 ²In the similar MLT ²Fast-survey mode Science Question: When, where, and how often is plasmaspheric hiss originated from chorus?