Transcript Statistical analysis of hiss wave spectrum from the EMFISIS wave data

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
 Previous statistical results are limited due to frequency
coverage (> 100 Hz) and lack of polarization properties.
 Unusually low frequency hiss (~20 Hz) is reported [Li et
al., 2013].
 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 kHz) compared
to previous hiss model.
Daa of previous and new hiss
wave model
at L = 3 and 12-16 MLT
Daa (new) - Daa (pre)
Difference =
Daa (pre)
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
 Ray tracing simulations suggest that plasmaspheric hiss
is originated from chorus waves.
 However, the direct evidence of showing this correlation
is very limited due to the difficulty of capturing this
coordinated observation.
 Using coordinated observation from Van Allen Probes
and THEMIS, we evaluate the correlation between
plasmaspheric hiss and chorus.
Coordinated event
between THEMIS
and RBSP
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
Correlation coefficients between chorus and Hiss
•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
2017/11/30
Multi-point observation
2016/01/29 will allow us to capture
more coordinated events
showing potential chorushiss correlation.
2017/07/31
Requirements:
Dayside
Some SAT: outside pp
Some SAT: inside pp
In the similar MLT
Fast-survey mode
Science Question:
When, where, and how
often is plasmaspheric
hiss originated from
chorus?