1
Supplement to “Forecasting and Remote Sensing Outer-belt Relativistic
2
Electrons from Low-Earth-Orbit”
3
4
Yue Chen, Geoffrey D. Reeves, Gregory S. Cunningham, Robert J. Redmon, and Michael
5
Henderson
6
7
Correspondence to: cheny@lanl.gov
8
9
This supplement includes materials that are relevant but not essential to presenting the
10
main conclusions. First we validate the chorus wave proxy using recent Van Allen Probes
11
data, and then we examine measurements of >100 keV electrons from POES MEPED E2
12
channel in detail. Next, by deriving pseudo POES data from pitch-angle resolved Van
13
Allen Probes MagEIS observations and comparing to original POES data, we are able to
14
confirm that the observed cross-energy cross-pitch-angle coherence is real and not due to
15
MeV electron contamination on POES instruments. At last, we show how the electron
16
phase space density radial distributions observed by Van Allen Probes vary over time and
17
then evaluate the role of the magnetopause boundary and radial diffusion.
18
1
19
1. Validation of the Chorus Wave Proxy Method
20
The chorus wave proxy method developed in Chen et al. [2014a] is tested using long-term
21
Van Allen Probes observations from 2012 Oct. to 2014 Dec. Besides confirming the one-
22
to-one temporal correlation, we quantitatively validated the proxy method taking
23
advantage of the two probes. Within each 4.5 h time bin, we first derive the fitting
24
parameter P by comparing Van Allen Probe-A chorus wave observations to POES
25
precipitation at the conjunctive (L, MLT) positions as defined by Equ (1) of Chen et al.
26
[2014a], then validate the method by applying the same P parameter to POES data so as to
27
compare with chorus wave observations from Probe-B at other conjunctive (L, MLT)
28
positions. One such example is shown in Figure S1. Indeed, the PE value for Probe-A (i.e.,
29
an in-sample test) is 0.37 and the PE for Probe-B (out-of-sample test) is 0.11 for this 3-
30
month period. In comparison, PE values using empirical averaged, three-Kp categorized
31
chorus distributions from CRRES data are ~ -1.2 for both satellites during the same period.
32
33
2. POES E2 Measurements within the Period
34
NOAA POES satellites have circular sun-synchronous orbits (altitude ~800-850 km,
35
inclination ~98o) with a period of ~102 min. The Space Environment Monitor-2 (SEM-2)
36
on board each 3-axis stabilized POES spacecraft contains 2 solid-state detector
37
telescopes—one oriented to view in the anti-Earth-center direction (i.e., the 0o telescope)
38
and the other to view at about 90o to the first (i.e., the 90o telescope)—to measure
39
electrons in 3 energy ranges (E1, 0.03-2.5 MeV, E2, 0.1-2.5 MeV and E3, 0.3-2.5 MeV).
40
2
41
Figure S2 presents details of NOAA-15 E2 (>100 keV) data during the period. Panel A
42
replots the same ratio curve as in Figure 1E, and Panel B shows the count rates from the
43
90o telescope (blue) compared to 1 MeV fluxes from MagEIS (red). The green vertical
44
lines mark the spikes in Panel A, and it can be seen that the leading edge of each spike in
45
Panel A always corresponds to a simultaneous increment in >100 keV electrons in Panel B,
46
while significant dropouts of 1 MeV electrons may (e.g., events 3 and 9) or may not (e.g.,
47
events 5 and 11) be coincidental. By comparing the timings and amplitudes of both
48
increments and dropouts, we conclude that it is the increments of >100 keV precipitation
49
instead of the dropouts in MeV electrons that is the main contributor to the formation of
50
leading edge of most spikes observed in the ratio curve.
51
52
Figure S2-D compares the 90o telescope data (black) to the 0o telescope data (gray, timed
53
by 20). Although the one-to-one correlation can be seen for the sudden increments in the
54
two populations, electron levels measured by the 0o degree always recede much more
55
quickly to the instrument back ground level of ~1 cnt/s. This is mainly due to the fact that
56
in the outer belt the 0o telescope measures electrons well within the loss cone while the
57
90o telescope mostly measures near and/or across the loss cone. Thus the higher flux
58
levels for the larger pitch angles allow the 90o telescope to register more dynamic
59
signatures. Indeed, much less dynamics are recorded by the 0o telescope of the E3 channel
60
with even higher energy (not shown here). Due to these reasons, we chose to use POES
61
measurements from the 90o telescope in this study, which provide more information to the
62
predictive filters.
63
3
64
3. Ruling out the Possibility of MeV Electron Contaminations on POES MEPED E2
65
and E3 Channels
66
The MagEIS instruments on board Van Allen Probes are believed to provide the cleanest
67
electron observations on radiation belts that are often taken as the “gold standard”. Thus,
68
using the level-3 pitch-angle resolved data from Van Allen Probes, we are able to derive
69
the expected electron intensities at POES altitudes (called pseudo POES data here)
70
following the methods described in Chen et al. [2014b]. As the example shown in Figure
71
S3, since the dynamics shown in the pseudo data (Panel A) agree well with those in
72
original POES E3 data (Panel B) particularly at L-shells between ~3.5 – 5.0, we believe
73
MeV electrons have no significant effects on POES MEPED electron channels, and thus
74
the cross-energy cross-pitch-angle discussed in the main text must be real. The difference
75
in CR values between two panels are caused by errors from various sources, including
76
such as mapping from the magnetic equator to low-altitudes, limited pitch-angle resolution
77
for electrons near the loss-cone from Van Allen Probes’ near equatorial orbits, and no
78
consideration of angular effects from MEPED’s wide opening angles. However, the
79
difference in the absolute values in Panels A and B are not our concern for this study since
80
we only need to compare how the pseudo data and real data vary over time. In addition,
81
we also compare NOAA-15 data in two different MLT zones (predawn and afternoon) and
82
see very different electron intensities (not shown here). Considering MeV electrons should
83
have no MLT-dependence, the observed significant MLT-dependence in POES MEPED
84
E2 and E3 channels provides another evidence supporting POES electron measurements
85
used here should be reliable.
86
4
87
4. Electron Radial Distributions and the roles of Magnetopause Shadowing and
88
Radial Diffusion
89
Here we evaluate the effects of Magnetopause shadowing and radial diffusion in the
90
observed outer-belt electron dynamics. Figure S4-A plots the temporally evolving electron
91
phase space density (PSD) radial distributions in the same period. In this plot electrons
92
have the 1st adiabatic invariant µ=550MeV/G and the 2nd adiabatic K=0.03G0.5RE, which
93
correspond to ~1MeV energy and ~45o equatorial pitch angle at L=4.6. The white symbols
94
in Panel A mark the peak PSD positions in radial distributions, which are mostly at > ~5.5
95
but sometimes move to as low as ~4.5. This is consistent from previous PSD studies by
96
Chen et al. [2010] and Turner et al. [2012] that both show persistent PSD peaks exists at L
97
between ~5-6 and negative PSD gradients at larger L-shells using THMEIS data. This
98
suggests that 1 MeV electrons at L=4.6 are generally inside the PSD peak no matter
99
during the loss or energization times. Therefore, the PSD peaks at larger L-shells and
100
positive PSD radial gradients at L between 3.5 -5 do not favor outward radial diffusion,
101
and thus the effects of magnetopause can be deemed unimportant for the dropouts of MeV
102
electrons in this region; similarly, since persistent PSD peaks exists at L~5-6 instead of the
103
outside of radial belt boundary, the role of magnetopause/plasma sheet can also be deemed
104
insignificant for the energization of MeV electrons at L between 3.5-5.
105
106
However, during MeV electron energization, it is possible that the inward radial diffusion
107
from PSD peaks to smaller L-shells contributes to the cross-energy cross-pitch-angle
108
coherence. Although quantifying the contribution of radial diffusion needs simulations
109
from sophisticated models and thus is beyond the scope of this study, we may still do
5
110
some quantitative evaluations. Using the empirical Kp-driven DLL from Brautigam and
111
Albert [2000], we can estimate the time needed for a signature of new MeV electrons to
112
propagate from beyond L=5 to L=3.5 through diffusion. Using the max Kp values during
113
the period (Panel B), we can calculate the characteristic time ∫3.5 2𝐷 𝑑𝐿 to be >1.0 day
114
with Kp =5 or >1.8 day with Kp=4. However, from the lag times for maximum CC for
115
each L-shell in Figure 2, we know the lag-time difference for L-shells within 3.5 – 5 is
116
<~10 h which is less than half of the diffusive time scales. In addition, we neither see the
117
expected lag-time dependence due to inward radial diffusion—the time lag should
118
increase significantly with decreasing L-shells—in the CC plots. Therefore, based upon
119
above evaluations, we conclude that it is unlikely for the inward radial diffusion to
120
dominate the time lags observed in the cross-energy cross-pitch-angle coherence.
5
𝐿
𝐿𝐿
121
122
123
References
124
Brautigam, D.H. and J.M. Albert (2000), Radial diffusion analysis of outer radiation belt
125
electrons during the October 9, 1990, magnetic storm, J. Geophy. Res., 105, A1, 291-
126
309
127
Chen, Y. et al. (2014a), Global time-dependent chorus maps from low-Earth-orbit electron
128
precipitation and Van Allen Probes data, Geophys. Res. Lett., 41,
129
doi:10.1002/2013GL059181
130
Chen, Y. et al. (2014b), REPAD: An empirical model of pitch-angle distributions for
131
energetic electrons in the Earth’s outer radiation belt, J. Geophys. Res., 119,
132
doi:10.1029/2013JA019431
6
133
Chen, Y., G. Reeves, and R. Friedel (2010), On the role of transition region in controlling
134
the outer radiation belt dynamics: A survey of in-situ observations, Fall AGU Meeting,
135
SM33C-1920, San Francisco, CA, December 2010
136
Turner, D.L., V. Angelopoulos, Y. Shprits, A. Kellerman, P. Cruce, and D. Larson (2012),
137
Radiation distributions of equatorial phase space density for outer radiation belt
138
electrons, Geo. Res. Lett., 39, L109101, doi: 10.1029/2012GL051722
7
139
140
141
142
143
144
145
146
147
Figure S1 Validation of the chorus wave proxy method in a 3-month period. A)
Observed chorus wave amplitudes by Van Allen Probe-A, B) proxy chorus waves derived
from POES precipitating >30 keV electrons along Van Allen Probe-a trajectory, and C)
ratios between proxy values and observations. Colors from orange to dark gray indicate
good agreements. D) Dst (black) and AE (gray) indices. E, F, G) Validations using Van
Allen Probe-B data in the same format. All data are binned by 4.5 h and 0.2 in L.
8
148
149
150
151
152
153
154
155
156
Figure S2 Count rates (CRs) for >100 keV electrons measured by NOAA-15 at L=4.6
within the same ~260 day period as in Figure 1. A) Ratios between CRs for
POES >100 keV electrons and RBSP 1MeV electron fluxes (replotted from Figure 1E). B)
Time series of >100 keV CRs (blue) compare to 1MeV electron fluxes (red). C) Dst
(black) and Kp (gray) indices. D) CRs for locally trapped (black) and precipitating
(gray) >100keV electrons measured at low altitude by NOAA-15. Here precipitating CRs
are timed by 20 to bring the curve close to that of locally trapped population.
9
157
158
159
160
161
162
163
Figure S3 Testing possible MeV electron contaminations on POES MEPED E3
electron channel. A) Pseudo >300 keV electron observations at POES altitude, derived
from RBSP-a MagEIS pitch-angle resolved data, are sorted by L-shell and time. The time
period is the same as in Figure 1. B) Original POES E3 data in the same format. The two
black lines in both panels mark L=3.5 and 5.
10
164
165
166
167
168
169
170
171
172
Figure S4 Electron radial PSD distributions vary with time (Panel A) and magnetic
activity (B, black for Dst and gray for Kp). Here electrons have the 1st adiabatic
invariant µ=550MeV/G and the 2nd adiabatic K=0.03G0.5RE, which correspond to ~1MeV
energy and ~45o equatorial pitch angle at L=4.6. White symbols in Panel A mark the
maximum PSD locations with L-shells between 3 – 6. Green vertical lines are identical to
those in Figure S2 indicating the spikes of in the ratios between >100 keV precipitating
and 1 MeV trapped electrons.
11