ANGEOAnnales GeophysicaeANGEOAnn. Geophys.1432-0576Copernicus GmbHGöttingen, Germany10.5194/angeo-33-1173-2015Combined effects of concurrent Pc5 and chorus waves on relativistic electron dynamicsKatsavriasC.ckatsavrias@phys.uoa.grhttps://orcid.org/0000-0002-0604-697XDaglisI. A.https://orcid.org/0000-0002-0764-3442LiW.DimitrakoudisS.GeorgiouM.TurnerD. L.PapadimitriouC.Department of Physics, National and Kapodistrian University of Athens, Athens, GreeceDepartment of Physics, Aristotle University of Thessaloniki, Thessaloniki, GreeceDepartment of Atmospheric and Oceanic Sciences, UCLA, California, USAInstitute for Astronomy, Astrophysics, Space Applications & Remote Sensing, National Observatory of Athens, Penteli, GreeceThe Aerospace Corporation, El Segundo, California, USAC. Katsavrias (ckatsavrias@phys.uoa.gr)25September2015339117311819June201526August201512September2015This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from https://angeo.copernicus.org/articles/33/1173/2015/angeo-33-1173-2015.htmlThe full text article is available as a PDF file from https://angeo.copernicus.org/articles/33/1173/2015/angeo-33-1173-2015.pdf
We present electron phase space density (PSD) calculations as well as
concurrent Pc5 and chorus wave activity observations during two intense
geomagnetic storms caused by interplanetary coronal mass ejections (ICMEs)
resulting in contradicting net effect. We show that, during the 17 March
2013 storm, the coincident observation of chorus and relativistic
electron enhancements suggests that the prolonged chorus wave activity seems
to be responsible for the enhancement of the electron population in the outer
radiation belt even in the presence of pronounced outward diffusion. On the
other hand, the significant depletion of electrons, during the 12 September
2014 storm, coincides with long-lasting outward diffusion driven by the
continuous enhanced Pc5 activity since chorus wave activity was limited both
in space and time.
The relativistic electron population in the outer radiation belt is extremely
variable – especially during periods of enhanced geomagnetic activity.
During such times, it is continually subjected to loss and acceleration
processes, which compete and can deplete, enhance or cause little (or no) effect on the electron population .
The mechanisms responsible for the acceleration or loss can be generally
divided into two categories: adiabatic or reversible changes (e.g.,
DST
effect) and non-adiabatic or irreversible changes.
Concerning the non-adiabatic relativistic electron acceleration two
mechanisms act (usually) together: (i) inward radial diffusion and (ii)
local acceleration via wave–particle interactions through whistler mode
chorus waves. For inward radial diffusion, electrons in the plasma sheet
represent a source of high phase space density (PSD), and when the third
adiabatic invariant is broken these particles can diffuse inwards in radial
distance, gaining energy in the process . For
in situ acceleration by wave–particle interactions, substorm injections and
enhanced convection are responsible for providing a seed population of tens
to a few hundreds keV electrons which can then be accelerated to higher
energies, of the order of ≈ MeV, as they interact with lower band
chorus waves inside the outer belt . Some of these injected
particles can also generate plasma waves responsible for gyro-resonant
acceleration of electrons to relativistic energies
. As shown by
chorus emissions are often substorm dependent and chorus emissions are
generally enhanced when substorm activity is enhanced. Moreover, the
equatorial chorus is strongest in the lower band during active conditions in
the region 3<L<7, between 23:00 and 13:00 MLT, consistent with keV
electron injection from substorms near midnight and subsequent drift around
dawn to the dayside.
Non-adiabatic (true) losses, on the other hand, are believed to be dominated
by two mechanisms: (i) rapid scattering into the atmospheric loss cones
(drift or bounce) via wave–particle interactions due to plasmaspheric hiss, electromagnetic ion cyclotron
(EMIC) or chorus waves and (ii) magnetopause shadowing
combined with outward radial transport .
Recently, combined electron precipitation observations
and simulations to show that EMIC waves were able to affect the low pitch
angle electrons in the outer belt, but not the core of the electron
distribution during the 11 October 2012 event. In addition,
showed that in the absence of additional energization,
plasmaspheric hiss was responsible for continuous losses of electrons inside
the plasmasphere during the time period 22 December 2012 through 13 January
2013.
showed that the majority of non-adiabatic losses of outer
radiation belt electrons with energies above 300 keV during the main phase of
the 6 January 2011 geomagnetic storm were not lost to the atmosphere but to
Earth's magnetopause through magnetopause shadowing and subsequent rapid
outward radial transport. Even in the case of limited compression of the
magnetosphere, showed that there is a clear correlation
between electron PSD dropouts and the solar wind pressure pulse, owing to a
combination of magnetopause shadowing and outward radial diffusion. The
latter can be achieved under the presence of ULF waves, a regularly occurring
phenomenon, which can violate the third invariant condition and allow for
electron radial diffusion .
In this work we attempt an assessment of selected mechanisms (substorm
injections and wave–particle interactions via chorus and Pc5 waves) that
contribute to the variability of the electron population in the outer
radiation belt. To that end, we examine the PSD in phase space coordinates as
well as wave activity (ULF Pc5 and whistler chorus) to compare and contrast
the evolution of equatorial mirroring, relativistic and sub-relativistic
electron population throughout Earth's outer radiation belt for two different
geomagnetic storms: one storm resulting in an overall enhancement (17 March
2013) and the other resulting in depletion (12 September 2014) of the PSD
throughout the outer belt.
Data selection and methodology
We use electron differential fluxes from the Magnetic Electron Ion
Spectrometer (MagEIS) Medium M75 and High instruments ,
on board the Van Allen Probes. Fluxes are converted to PSD for fixed first
and second adiabatic invariants for a range of values and K<0.05G1/2RE (equatorial mirroring electrons with pitch angles 90 ±∼ 15∘) by applying the method described by
using magnetic field measurements from the fluxgate
magnetometers of Van Allen Probes . The use of PSD at
fixed phase space coordinates (PSCs) allows us to both track particles and to
identify regions and times when the adiabatic assumption breaks down
(injection events, fast loss events), and therefore to automatically
filter out the so-called DST effect. All values of the
invariants K and L∗ were calculated at each measurement point using the
magnetospheric field model (TS05). In addition,
magnetic field measurements from the fluxgate magnetometers of RBSP (3 min resolution) as well as ground measurements obtained from SuperMAG
collaboration were used to determine the average Pc5 power. A continuous
wavelet transform with the Morlet wavelet as the basis function has been
applied to analyze them in the time–frequency domain .
Prior to the time–frequency analysis using wavelet transforms, a high-pass
Butterworth filter with a cut-off frequency of 0.9 mHz was applied to obtain
the wavelet power spectra covering the Pc5 frequency range (typically between
2 and 7 mHz). To quantify the temporal evolution of ULF wave activity,
we calculated the weighted sum of the wavelet spectrum over Pc5 wave
frequencies. The ULF wave-derived diffusion coefficients are then obtained
from the aforementioned ground and in situ measurements.
have demonstrated that the electric term is dominant over the magnetic one,
over a wide range of parameters. Nevertheless, the magnetic term is more
easily calculated from satellite data, since variations of |B| correspond
to compressional waves, and |B| is easily measured; and relative
changes in the value of DLLB are qualitatively, if not quantitatively,
similar to changes in the value of DLLE. Therefore, we calculate
DLLB for indicative values of μ, under the simplifying assumption
that the whole ULF power falls in wave mode 1. The reason that
increasing the wave m value does not significantly affect the magnetic field
diffusion coefficient is because increasing m also increases the resonant
wave frequency and at higher wave frequencies the magnetic field PSD is much
lower . On the other hand, we have obtained DLLE from
the IMAGE (International Monitor for Auroral Geomagnetic Effects)
and CARISMA (Canadian Array for Realtime
Investigations of Magnetic Activity) magnetometer
array data using the mapping method of . That method is
restricted to daytime measurements and relies on ground stations that do not
always match the location of the spacecraft in question. However, they are
useful in providing a more accurate estimation of the total diffusion
coefficient, whenever concurrent measurements are available.
Moreover we infer chorus wave amplitudes from the ratio of precipitating and
trapped electron fluxes over the energy of 30–100 keV (measured by POES
satellites) applying the method described by . In this way we
can estimate the chorus wave intensity in broad MLT coverage, which cannot be
obtained from in situ chorus wave measurements by equatorial satellites
alone. Supplementary measurements of 1 min averaged values of solar wind
speed, pressure and interplanetary magnetic field (IMF) as well as geomagnetic indices SYM-H and AL from the
NASA/OMNI database
http://omniweb.gsfc.nasa.gov/
are also
considered.
Detailed event analysisEnhancement event
An overview of the 16–18 March 2013 period of interest is shown in Fig. a–c. An interplanetary coronal mass ejection (ICME) on 17 March (arrival time at 05:00 UT)
increased the solar wind speed from its quiet values to approximately 750 km s-1 and dynamic pressure to approximately 16 nPa while the IMF magnitude
reached 21 nT. Pressure gradually decreased to the pre-storm levels by
midnight UT of the same day while speed gradually decreased by the end of
the recovery phase on 18 March. The strongly southward IMF (≈ 20 h
duration) associated with the ICME caused an intense storm (SYM-H index
reached -130 nT) and an interval of enhanced substorm activity (AL reached
-2100 nT) for the rest of day 17 until the beginning of the recovery phase.
During 18 March there is no substorm activity or pressure enhancements. In
Fig. d we show calculations of the magnetopause and
plasmapause location using the models of and
, respectively. Clearly the location of the magnetopause
starts at a distance of L∼11 and reaches L∼6 during the main
phase of the storm while it recovers to pre-storm distances afterward. The
plasmapause exhibits a similar behavior; it starts at L∼4, while it
moves to L∼3 during the main and recovery phase of the storm and then
it recovers to slightly lower than the pre-event levels on 19 March.
Right after the storm sudden commencement (SSC) and the beginning of the
substorm activity, the global chorus amplitudes increase by more than 1
order of magnitude for all L shells (Fig. e). This
enhanced chorus activity lasts until the end of the main phase of the storm
– which coincides with the end of the substorm activity – and decreases to
the pre-storm levels during the recovery phase. This is consistent with the
results of , who showed the dependence of
chorus activity on substorm injections.
ULF wave activity, calculated from the magnetic field measurements of the Van
Allen Probes in the nightside magnetosphere, shows similar behavior (Fig. f). There is an enhancement of Pc5 power up to 3 orders of
magnitude right after the SSC that lasts until the beginning of the recovery
phase of the storm. The subsequent decrease of Pc5 activity to the pre-storm
levels coincides with the gradual decrement of dynamic pressure and solar
wind speed. This is consistent with the theory of generation of ULF waves
due to instabilities (e.g., Kelvin–Helmholtz) at the flanks
of the magnetosphere. and proposed that
fluctuations in the geomagnetic field produced by ULF waves may cause
adiabatic radial diffusion of the radiation belt electrons. As a consequence
the diffusion coefficients (Fig. g) are enhanced up to 3
orders of magnitude during the main phase of the storm for the whole outer
belt (3.5<L<6.5) and gradually drop to the pre-storm levels. The
enhancement of radial diffusion is the same for the dayside magnetosphere as
well (Fig. h–i); diffusion coefficients are enhanced up
to 3 orders of magnitude during the main phase of the storm and then return
to the pre-storm level values.
(a–d) Values of solar wind parameters and geomagnetic indices with
1 min resolution, during the time period 16–18 March 2013. Top to
bottom: average IMF and its z component (Bz), solar wind speed and dynamic
pressure, geomagnetic indices SYM-H and AL, models of magnetopause
and plasmapause location. (e) Chorus
wave intensity averaged over all MLTs based on the POES electron
measurements. (f) Pc5 power from RBSP for the nightside magnetosphere
(22:00 < MLT < 04:00). (g) Averaged values of DLLB corresponding to RBSP
magnetic field measurements at the nightside magnetosphere
(22:00 < MLT < 04:00). (h) Pc5 power for the dayside magnetosphere obtained from
ground observations (06:00 < MLT < 11:00). (i) Averaged values of DLLE
at the dayside magnetosphere (06:00 < MLT < 11:00) obtained from the CARISMA
and IMAGE ground magnetometer arrays. The vertical dashed lines circumscribe
the main phase of the storm.
Time profiles of PSD for fixed adiabatic invariants are shown in Fig. . Each point is defined as the average PSD calculated from RBSP A
and B after a binning in L∗ values. As shown, the overall net
effect of the storm is enhancement of the electron population but there are
slight differences depending on the electrons' energy. The population with
μ=100 MeV G-1 (panel a) increases right after the SSC. By the afternoon
of 17 March, PSD has reached its maximum (up to 4 orders of magnitude) that
coincides with the maximum of substorm activity. After the beginning of the
recovery phase of the storm, PSD remains enhanced until the end of the storm.
We note that there seems to be a dependence of the enhancement on the
L shell; enhancement is more pronounced for lower L shells and, in addition,
PSD is almost decreased to the pre-storm levels for L=5.25. The 300 MeV G-1
electron population (panel b) shows similar behavior except the enhancement
is simultaneous for all L shells. The 600 and 900 MeV G-1 population show
different behavior. Right after the SSC there is a PSD depletion (up to
an order of magnitude) that coincides with the maximum compression of the
magnetopause, which is the result of magnetopause shadowing . After
the depletion there is a sudden enhancement of PSD that reaches its maximum
value at the end of the main phase of the storm (a few hours later than the
lower μ population). Again, PSD remains enhanced until the end of the
storm. We note that the dependence of the enhancement on L shell is not
apparent in the high μ population (as μ increases the enhancement is
more or less of the same order of magnitude).
Nightside PSD time profiles obtained from RBSP flux measurements for
fixed adiabatic invariants during the 16–18 March time period. Each panel corresponds to
different value of μ (100, 300, 600 and 900 MeV G-1 respectively) and each color curve
to different value of L∗. The vertical dashed lines circumscribe the main phase of the
storm.
Depletion event
An overview of the 11–13 September 2014 period of interest is shown in Fig. a–c. There is a high-speed stream that caused a
≈10 h (00:00–10:00 UT on 12 September) increase of speed
(up to 450 km s-1) and pressure (up to 10 nPa) as well as some sporadic
substorm activity but no storm (the minimum SYM-H index reached -20 nT).
After a 3 h quiet period an ICME arrives at 15:00 UT of 12 September. Solar wind speed is increased from
its quiet values to approximately 750 km s-1 and dynamic pressure to approximately 20 nPa while the IMF magnitude
reached 30 nT. The strongly southward IMF associated with the ICME caused a
short-lived but intense storm (SYM-H index reached -100 nT) and an
approximately 2 h interval of enhanced substorm activity (AL reached
-1200 nT) at the end of day 12. Speed gradually decreases on 13 September but
never reaches the pre-storm levels. In addition, strong fluctuations of
pressure are present during the whole recovery phase of the storm, yet there is no sign
of substorm activity. The location of the magnetopause (panel d) starts at a
distance of L∼10 and reaches L∼6 during the main phase of the
storm while it recovers to larger than the pre-storm distances afterwards.
The plasmapause exhibits a similar behavior; it starts at L∼4, while it
moves to L∼3 during the main phase of the storm and then it recovers to
pre-event levels on 14 September.
The global chorus amplitudes are increased less than 1 order of magnitude
(Fig. e), and the enhancement is very limited both in space
(3.5<L<5.5) and time (only during the minimum SYM-H). This enhancement
coincides with the strong but also limited in time (a couple of hours)
substorm activity indicating once again the dependence of chorus intensity on
substorm injections.
ULF wave activity in the nightside magnetosphere shows completely different
behavior (Fig. f). There is an enhancement of Pc5 power
caused by a high-speed stream during the beginning of 12 September but Pc5
recover to the previous levels. With the arrival of the ICME in the
afternoon, we observe an enhancement of more than 3 orders of magnitude (at
all L shells). This enhancement is weakened during the storm recovery phase
(up to 2 orders of magnitude); still, Pc5 power remains high, compared to the
pre-storm levels, even at the end of the storm. This coincides with the fact
that both solar wind speed and pressure are still enhanced during the
recovery phase of the storm. As a consequence the diffusion coefficients
(Fig. g) are enhanced up to 3 orders of magnitude during
the main phase of the storm while the enhancement persists for L>4 during
the recovery phase. The enhancement of radial diffusion is almost the same
for the dayside magnetosphere (Fig. h–i); diffusion
coefficients are enhanced up to 3 orders of magnitude during the main phase
of the storm and then show sporadic and weak enhancements above the
pre-storm levels.
Same as Fig. during the time period 11–13 September
2014.
Time profiles of PSD for fixed adiabatic invariants are shown in Fig. . The overall net effect of this storm is completely different,
depending on the electrons' energy. The population with μ=100 MeV G-1
(panel a) increases right after the SSC and before midnight of 13 September;
PSD for high L shells has reached its maximum that coincides with the
maximum of substorm activity. After the beginning of the recovery phase of
the storm, PSD for L∗<4.5 remains enhanced until the end of the storm
while PSD for L∗>4.5 recovers to the pre-storm levels. We note that the
dependence of the PSD enhancement on the L shell appears in both events. As
we move to higher values of μ the behavior of the electron population is
completely different. The 300 MeV G-1 electron population (panel b) shows an
enhancement during the maximum chorus activity (main phase of the storm) and
a depletion for L∗>4.5 right before the beginning of the recovery phase
of the storm. By the end of the recovery phase, the electron population at
high L shells has returned to the pre-storm levels while the low L shell
population shows slight enhancement. For the higher μ electron population
the aforementioned depletion is more abrupt and deep (especially for higher
L shells) and the net effect of the storm is depletion and very slow
recovery of PSD that exceeds the time interval of this study.
Same as Fig. for the 11–13 September 2014 time period.
Discussion
In order to study the contribution of different mechanisms to the outer
radiation belt dynamics we chose to investigate the impact of ICMEs. The
reason for that is that ICMEs drive a variety of magnetospheric processes
that are relevant for radiation belt dynamics. They have a high solar wind
speed and much larger ULF wave power than their surroundings. There are also
indications that fluctuating IMF and Pdyn that are associated with ICMEs
can enhance substorm occurrence and thus chorus wave activity
.
Both examined events exhibited intense storms (as indicated by the SYM-H
index) caused by the arrival of an ICME. The pressure pulse was high enough
to compress the magnetosphere to low L shells in both cases, but there are
pronounced differences that connect the solar wind–magnetic field–waves–electron population chain of events. During the March 2013 storm, the
z component of the IMF was continuously negative for more than 18 h and
produced an equivalent time interval of intense substorm activity
while speed and pressure gradually and smoothly decreased to the pre-storm
levels. On the other hand, during the September 2014 storm the strong
southward component of the IMF lasted for approximately 4 h and produced
an equivalent interval of substorm activity while speed and pressure
showed intense fluctuations during the recovery phase of the storm. During
both recovery phases no substorm activity was present.
During the first storm, pronounced wave activity (both chorus and Pc5) at all
L shells during the main phase was exhibited while there was no activity at
all during the recovery phase. The latter coincides with the absence of
substorm activity as well as the absence of fluctuations and the gradual
decrement of speed and pressure on 18 March. The second storm exhibited very
limited (in time and space) chorus activity, due to the short-lived main
phase and substorm activity, but long-lasting Pc5 activity due to the
continuously enhanced and fluctuating solar wind speed and pressure. The
latter is consistent with the statistical study of , who showed, over a
21-month period, that ULF wave activity (in the range of Pc4–5)
is strongly correlated with solar wind speed and pressure in 4–9 RE.
The net effect of the two storms was completely different and moreover
dependent on the energy of the electrons. The March 2013 event suggests
that the intense series of substorms and the associated generation of chorus
waves are the mechanisms that lead to enhancement of the electron population.
This is consistent with the results of and .
In detail, the low μ electron population was enhanced right after the
beginning of the substorm activity while a few hours later higher energy
electrons reached the maximum values of PSD. This result (amongst others in
the literature) is a verification of the scenario proposed by
in which substorm- and shock-related injections are
responsible for the access of energetic electrons (approximately hundreds of keV) to the
outer belt and the generation of chorus activity. These seed electrons are
accelerated by chorus waves to even higher (relativistic) energies. We note
that the electron acceleration occurs even though the Pc5 activity was
pronounced (and comparable to the chorus activity) and outward diffusion, as
indicated by the diffusion coefficient calculations, was present. Moreover,
electron PSDs remain enhanced even during the storm recovery phase. This
coincides with the absence of significant activity both in the solar wind
(speed, pressure and IMF) and inside the magnetosphere (AL index and waves).
On the other hand, observations of the September 2014 event suggest
that the outward diffusion driven by the pronounced and long-lasting Pc5
activity was, possibly, the dominant mechanism for >300 MeV G-1 electron PSD
depletion. In detail, the low μ electron population was enhanced right
after the beginning of the short-lived substorm activity due to the
shock/substorm-related injections. Furthermore, the intense substorm
injection (during the main phase of the storm) drove chorus wave activity
which, consequently, was also short-lived. Nevertheless, despite their short
duration, chorus waves efficiently accelerated at 4.25<L<5 to
relativistic energies (μ>300 MeV G-1). During the recovery phase of the
storm, the >300 MeV G-1 electron population is depleted. This depletion
coincides with the absence of significant chorus wave activity and the
enhanced Pc5 power. We note that, as explained below, outward diffusion
seems to be the only mechanism (combined with magnetopause shadowing or not)
able to cause such a pronounced depletion of the >300 MeV G-1 electron
population.
Alternative loss mechanisms could be the scattering of the >300 MeV G-1
electron population into the loss cone via wave–particle interactions due to
plasmaspheric hiss or EMIC waves. However, have shown
that EMIC waves are able to affect only ultra-relativistic electrons at
higher latitudes but not the equatorial mirroring population examined here.
Moreover, the activity of plasmaspheric hiss is limited mostly inside the
plasmapause , which was compressed up to L=3 during both of
the events. Even if the plasmapause were located at higher L shells,
hiss-driven electron precipitation has a timescale from ≈1 day to
tens of days depending on energy
and not a few hours. In addition, this depletion is consistent with the
results of , who showed that non-adiabatic losses on 25 June
2008 event occurred over a timescale of 1–4 h.
Conclusions
In this work we attempt an assessment of selected mechanisms that
contribute to the variability of the electron population in the outer
radiation belt. To that end, we examine the PSD in phase space coordinates
as well as wave activity (ULF Pc5 and whistler chorus) to compare and
contrast the evolution of equatorially mirroring, relativistic and
sub-relativistic electron population throughout Earth's outer radiation belt
for two different geomagnetic storms: (a) one storm that exhibited pronounced
chorus and Pc5 wave activity for the same time interval and resulted in an
overall enhancement of the electron population (16–18 March 2013) and (b)
another that exhibited short-lived chorus wave activity but pronounced and
long-lasting Pc5 wave activity which resulted in depletion of the >300 MeV G-1 electron population (11–13 September 2014) throughout the outer
belt. All of this evidence leads us to the following conclusions:
There is a 300 MeV G-1 threshold in μ that separates not only the source of relativistic electron
population inside the outer belt after the arrival of a prominent pressure pulse but also the mechanisms
that contribute to its variability. Electrons below this limit are accelerated due to substorm/shock
injections regardless of the net effect of various mechanisms on higher μ electrons while electrons
above this threshold are accelerated locally by interactions with chorus waves.
Concerning the >300 MeV G-1 electrons, the comparison of the two events shows that during
similar intervals of pronounced chorus and Pc5 wave activity, the relative effect is higher for chorus waves (i.e., the chorus-driven acceleration exceeds the Pc5-driven losses).
Finally, it is the long-lasting Pc5 power enhancements (with absence of chorus wave activity)
that lead to PSD depletion of the >300 MeV G-1 electron population via outward diffusion.
A future statistical study with a large-enough number of events is necessary in order to verify the aforementioned results.
Acknowledgements
This research has been co-financed by the European Union (European Social
Fund – ESF) and Greek national funds through the Operational Program
Education and Lifelong Learning of the National Strategic Reference Framework
(NSRF) – Research Funding Program: Thales. Investing in knowledge society
through the European Social Fund. We are thankful to the THEMIS and RBSP–ECT
teams, NASA's OMNI and NGDC for online data access and data analysis tools.
RBSP–ECT data and analysis software are made available at the
http://www.rbsp-ect.lanl.gov through funding by JHU/APL contract no. 967399
under NASA's Prime contract no. NAS5–01072. The analysis at UCLA was
supported by the NASA grants NNX11AD75G, NNX11AR64G, NNX13AI61G, NNX14AI18G,
and NNX15AF61G, and the Air Force Young Investigator program. The topical editor B. Mauk thanks J. Bortnik and one anonymous referee for help in evaluating this paper.
References
Baker, D. N. and Daglis, I. A.: Radiation belts and ring current, in Space Weather – Physics and Effects,
edited by: Bothmer, V. and Daglis, I. A., 173–202, Springer Verlag, Berlin, 2007.Balasis, G., Daglis, I. A., Georgiou, M., Papadimitriou, C., and
Haagmans, R.: Magnetospheric ULF wave studies in the frame of Swarm mission: A
time-frequency analysis tool for automated detection of pulsations in
magnetic and electric field observations, Earth Planets Space,
65, 1385–1398, 10.5047/eps.2013.10.003, 2013.Blake, J. B., Carranza, P. A., Claudepierre, S. G., Clemmons, J. H., Crain Jr., W.
R., Dotan, Y., Fennell, J. F., Fuentes, F. H., Galvan, R. M., George, J. S.,
Henderson, M. G., Lalic, M., Lin, A. Y., Looper, M. D., Mabry, D. J., Mazur, J. E.,
McCarthy, B., Nguyen, C. Q., O'Brien, T. P., Perez, M. A., Redding, M. T., Roeder, J.
L., Salvaggio, D. J., Sorensen, G. A., Spence, H. E., Yi, S., and Zakrzewski,
M. P.: The Magnetic Electron Ion Spectrometer (MagEIS) Instruments Aboard
the Radiation Belt Storm Probes (RBSP) Spacecraft, Space Sci. Rev., 179,
383–421, 10.1007/s11214-013-9991-8, 2013.Bortnik, J., Cutler, J. W., Dunson, C., and Bleier, T. E.: An automatic wave
detection algorithm applied to Pc1 pulsations, J. Geophys. Res.,
112, A04204, 10.1029/2006JA011900, 2007.Boyd, A. J., Spence, H. E., Claudepierre, S. G., Fennell, J. F., Blake, J. B.,
Baker, D. N., Reeves, G. D., and Turner, D. L.: Quantifying the radiation belt
seed population in the 17 March 2013 electron acceleration event,
Geophys. Res. Lett., 41, 10.1002/2014GL059626, 2014.Chen, Y., Friedel, R. H. W., Reeves, G. D., Onsager, T. G., and Thomsen, M. F.:Multisatellite determination of the relativistic electron phase space density
at geosynchronous orbit: Methodology and results during geomagnetically quiet
times, J. Geophys. Res., 110, A10210,
10.1029/2004JA010895, 2005.Chen, Y., Friedel, R. H. W., Reeves, G. D., Cayton, T. E., and Christensen, R.:
Multi–satellite determination of the relativistic electron phase space
density at geosynchronous orbit: An integrated investigation during
geomagnetic storm times, J. Geophys. Res., 112, A11214,
10.1029/2007JA012314, 2007.Elkington, S. R., Hudson, M. K., and Chan, A. A.: Resonant acceleration and
diffusion of outer zone electrons in an asymmetric geomagnetic field, J.
Geophys. Res., 108, A1116, 10.1029/2001JA009202, 2003.Fälthammar, C. G.: Effects of time–dependent electric fields on
geomagnetically trapped radiation, J. Geophys. Res., 70,
2503–2516, 10.1029/JZ070i011p02503, 1965.Hietala, H., Kilpua, E. K. J., Turner, D. L., and Angelopoulos, V.: Depleting
effects of ICME–driven sheath regions on the outer electron radiation belt,
Geophys. Res. Lett., 41, 2258–2265, 10.1002/2014GL059551, 2014.Horne, R. B., Thorne, R. M., Glauert, S. A., Albert, J. M., Meredith, N. P., and
Anderson, R. R.: Timescale for radiation belt electron acceleration by
whistler mode chorus waves, J. Geophys. Res., 110, A03225,
10.1029/2004JA010811, 2005.Jaynes, A. N., Li, X., Schiller, Q. G., Blum, L. W., Tu, W., Turner, D. L., Ni, B.,
Bortnik, J., Baker, D. N., Kanekal, S. G., Blake, J. B., and Wygant, J.: Evolution
of relativistic outer belt electrons during an extended quiescent period,
J. Geophys. Res., 119, 9558–9566, 10.1002/2014JA020125, 2014.Kim, K. C., Lee, D. Y., Kim, H. J., Lyons, L. R., Lee, E. S., Ozturk, M. K., and
Choi, C. R.: Numerical calculations of relativistic electron drift loss
effect, J. Geophys. Res., 113, A09212,
10.1029/2007JA013011, 2008.Kim, K. C. and Lee, D. Y.: Magnetopause structure favorable for radiation
belt electron loss, J. Geophys. Res., 119, 5495–5508,
10.1002/2014JA019880, 2014.Kletzing, C. A., Kurth, W. S., Acuna, M., MacDowall, R. J., Torbert, R. B.,
Averkamp, T., Bodet, D., Bounds, S. R., Chutter, M., Connerney, J., Crawford, D.,
Dolan, J. S., Dvorsky, R., Hospodarsky, G. B., Howard, J., Jordanova, V., Johnson, R.
A., Kirchner, D. L., Mokrzycki, B., Needell, G., Odom, J., Mark, D., Pfaff Jr., R.,
Phillips, J. R., Piker, C. W., Remington, S. L., Rowland, D., Santolik, O., Schnurr, R.,
Sheppard, D., Smith, C. W., Thorne, R. M., and Tyler, J.: The Electric and
Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on RBSP,
Space Sci. Rev., 179, 127–181, 10.1007/s11214-013-9993-6, 2013.Li, W., Ni, B., Thorne, R. M., Bortnik, J., Green, J. C., Kletzing, C. A., Kurth, W.
S., and Hospodarsky, G. B.: Constructing the global distribution of chorus,
wave intensity using measurements of electrons by the POES satellites and
waves by the Van Allen Probes, Geophys. Res. Lett., 40, 4526–4532, 10.1002/grl.50920, 2013.Li, W., Ni, B., Thorne, R. M., Ma, Q., Ni, B., Bortnik, J., Baker, D. N.,
Spence, H. E., Reeves, G. D., Kanekal, S. G., Green, J. C., Kletzing, C. A., Kurth, W.
S., Hospodarsky, G. B., Blake, J. B., Fennell, J. F., and Claudepierre, S.
G.: Radiation belt electron acceleration by chorus waves during the 17 March 2013
storm, J. Geophys. Res., 119, 4681–4693, 10.1002/2014JA019945, 2014.Li, X., Baker, D. N., O'Brien, T. P., Xie, L., and Zong, Q. G.: Correlation
between the inner edge of outer radiation belt electrons and the innermost
plasmapause location, Geophys. Res. Lett., 33, L14107,
10.1029/2006GL026294, 2006.Liu, W., Sarris, T. E., Li, X., Ergun, R., Angelopoulos, V., Bonnell, J.,
and Glassmeier, K. H.: Solar wind influence on Pc4 and Pc5 ULF wave activity in
the inner magnetosphere, J. Geophys. Res., 115, A12201,
10.1029/2010JA015299, 2010.Loto'aniu, T. M., Singer, H. J., Waters, C. L., Angelopoulos, V., Mann, I. R.,
Elkington, S. R., and Bonnell, J. W.: Relativistic electron loss due to ultralow
frequency waves and enhanced outward radial diffusion, J. Geophys. Res., 115, A12245, 10.1029/2010JA015755, 2010.Mann, I. R. and Wright, A. N.: Diagnosing the excitation mechanisms of
Pc5 magnetospheric flank waveguide modes and FLRs, Geophys. Res. Lett.,
26, 2609–2612, 10.1029/1999GL900573, 1999.Mann, I. R., Milling, D. K., Rae, I. J., Ozeke, L. G., Kale, A., Kale, Z. C.,
Murphy, K. R., Parent, A., Usanova, M., Pahud, D. M., Lee, E. A., Amalraj, V., Wallis, D.
D., Angelopoulos, V., Glassmeier, K. H., Russell, C. T., Auster, H. U., and Singer, H. J.: The Upgraded CARISMA Magnetometer Array in the THEMIS Era,
Space Sci. Rev., 141, 413–451, 10.1007/s11214-008-9457-6, 2008.Mann, I. R., Murphy, K. R., Ozeke, L. G., Rae, I., Milling, D. K., and Kale, A.:
The role of ultralow frequency waves in radiation belt dynamics,
Geoph. Monog. Series, 199, 69–92,
10.1029/2012GM001349, 2012.Meredith, N. P., Horne, R. B., and Anderson, R. R.: Substorm dependence of
chorus amplitudes: Implications for the acceleration of electrons to
relativistic energies, J. Geophys. Res., 106, 13165–13178,
10.1029/2000JA900156, 2001.Meredith, N. P., Horne, R. B., Iles, R. H. A., Thorne, R. M., Heynderickx, D., and
Anderson, R. R.: Outer zone relativistic electron acceleration associated
with substorm–enhanced whistler mode chorus, J. Geophys. Res.,
107, 1144, 10.1029/2001JA900146, 2002.Meredith, N. P., Horne, R. B., Glauert, S. A., and Anderson, R. R.: Slot
region electron loss timescales due to plasmaspheric hiss and
lightning–generated whistlers, J. Geophys. Res., 112, A08214,
10.1029/2007JA012413, 2007.Ni, B., Shprits, Y., Hartinger, M., Angelopoulos, V., Gu, X., and
Larson, D.: Analysis of radiation belt energetic electron phase space density
using THEMIS SST measurements: Cross-satellite calibration and a case
study, J. Geophys. Res., 116, A03208,
10.1029/2010JA016104, 2011.O'Brien, T. P. and Moldwin, M. B.: Empirical plasmapause models from
magnetic indices, Geophys. Res. Lett., 30, 1152,
10.1029/2002GL016007, 2003.O'Brien, T. P., Lorentzen, K. R., Mann, I. R., Meredith, N. P., Blake, J. B.,
Fennell, J. F., Looper, M. D., Milling, D. K., and Anderson, R. R.: Energization of
relativistic electrons in the presence of ULF power and MeV microbursts:
Evidence for dual ULF and VLF acceleration, J. Geophys. Res.,
108, 1329, 10.1029/2002JA009784, 2003.Ozeke, L. G., Mann, I. R., and Rae, I. J.: Mapping guided Alfvén wave
magnetic field amplitudes observed on the ground to equatorial electric field
amplitudes in space, J. Geophys. Res., 114, A01214,
10.1029/2008JA013041, 2009.Ozeke, L. G., Mann, I. R., Murphy, K. R., Rae, I. J., Milling, D. K., Elkington, S.
R., Chan, A. A., and Singer, H. J.: ULF wave derived radiation belt radial
diffusion coefficients, J. Geophys. Res., 117, A04222,
10.1029/2011JA017463, 2012.Reeves, G. D., McAdams, K. L., Friedel, R. H. W., and O'Brien, T. P.: Acceleration and loss of relativistic electrons during
geomagnetic storms, Geophys. Res. Lett., 30, 1529, 10.1029/2002GL016513, 2003.
Schulz, M. and Lanzerotti, L. J.: Particle diffusion in the radiation
belts, Physics and Chemistry in Space, Berlin, Springer, Germany, 81–85, 1974.Shprits, Y. Y., Thorne, R. M., Friedel, R., Reeves, G. D., Fennell, J., Baker, D.
N.,
and Kanekal, S. G.: Outward radial diffusion driven by losses at
magnetopause, J. Geophys. Res., 111, A11214,
10.1029/2006JA011657, 2006.Shprits, Y. Y., Meredith, N. P., and Thorne, R. M.: Parameterization of
radiation belt electron loss timescales due to interactions with chorus
waves, Geophys. Res. Lett., 34, L11110,
10.1029/2006GL029050, 2007.
Shue, J. H., Song, P., Russell, C. T., Steinberg, J. T., Chao, J. K., Zastenker,
G., Vaisberg, O. L., Kokubun, S., Singer, H. J., Detman, T. R., and Kawano, H.:
Magnetopause location under extreme solar wind conditions, J. Geophys. Res.,
103, 17691–17700, doi:0148-0227/98/98JA-01103, 1998.Tanskanen, E. I.: A comprehensive high-throughput analysis of substorms observed by IMAGE magnetometer network:
Years 1993–2003 examined, J. Geophys. Res., 109, A05220, 10.1029/2003JA010294, 2009.Thorne, R. M., Horne, R. B., Glauert, S., Meredith, N. P., Shprits, Y. Y., Summers,
D.,
and Anderson, R. R.: The Influence of Wave-Particle Interactions on
Relativistic Electron Dynamics During Storms, in: Inner Magnetosphere
Interactions, New Perspectives From Imaging, edited by: Burch, J., Schulz,
M., and Spence, H., AGU, Washington, DC, USA, 159, 101 pp.,
2005. Thorne, R. M., Horne, R. B., Glauert, S., Meredith, N. P., Shprits, Y. Y., Summers,
D.,
and Anderson, R. R.: Evolution and slow decay of an unusual narrow ring
of relativistic electrons near L ∼ 3.2 following the September
2012 magnetic storm, Geophys. Res. Lett., 114, 3507–3511,
10.1002/grl.50627, 2013.Turner, D. L., Shprits, Y., Hartinger, M., and Angelopoulos, V.: Explaining
sudden losses of outer radiation belt electrons during geomagnetic storms,
Nature Physics Lett., 8, 208–212, 10.1038/NPHYS2185, 2012.Turner, D. L., Angelopoulos, V., Li, W., Hartinger, M. D., Usanova, M., Mann, I.
R., Bortnik, J., and Shprits, Y.: On the storm-time evolution of relativistic
electron phase space density in Earth's outer radiation belt, J. Geophys. Res., 118, 2196–2212, 10.1002/jgra.50151, 2013.Turner, D. L., Angelopoulos, V., Li, W., Bortnik, J., Ni, B., Ma, Q., Thorne, R.
M., Morley, S. K., Henderson, M. G., Reeves, G. D., Usanova, M., Mann, I. R.,
Claudepierre, S. G., Blake, J. B., Baker, D. N., Huang, C. L., Spence, H., Kurth, W.,
Kletzing, C., and Rodriguez, J. V.: Competing source and loss mechanisms due
to wave–particle interactions in Earth's outer radiation belt during the 30
September to 3 October 2012 geomagnetic storm, J. Geophys. Res.,
119, 1960–1979, 10.1002/2014JA019770, 2014.Tsyganenko, N. A. and Sitnov, M. I.: Modeling the dynamics of the inner
magnetosphere during strong geomagnetic storms, J. Geophys. Res.,
110, A03208, 10.1029/2004JA010798, 2005.Usanova M. E., Drozdov, A., Orlova, K., Mann, I. R., Shprits, Y., Robertson, M.
T., Turner, D. L., Milling, D. K., Kale, A., Baker, D. N., Thaller, S. A., Reeves, G.
D., Spence, H. E., Kletzing, C., and Wygant, J.: Effect of EMIC waves on
relativistic and ultrarelativistic electron populations: Groundbased and Van
Allen Probes observations, Geophys. Res. Lett., 41,
1375–1381, 10.1002/2013GL059024, 2014.