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Journal of Atmospheric and Solar-Terrestrial Physics 179 (2018) 251–260
Contents lists available at ScienceDirect
Journal of Atmospheric and Solar-Terrestrial Physics
journal homepage: www.elsevier.com/locate/jastp
South-Atlantic Anomaly magnetic storms effects as observed outside the
International Space Station in 2008–2016
T
Tsvetan P. Dachev
Space Research and Technology Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str. Block 1, 1113, Sofia, Bulgaria
A R T I C LE I N FO
A B S T R A C T
Keywords:
Inner radiation belt
South-Atlantic anomaly
Proton flux
Relativistic electrons
ISS
Space radiation
Two Liulin type spectrometers performed measurements of the energetic particles flux outside the International
Space Station (ISS) in 3 long-term periods between 2008 and 2016. The linear regression analysis is performed of
1053 averaged per day South-Atlantic anomaly (SAA) proton flux measurements from the daily Dst index. The
data reveal that the SAA flux dependence from the Joule heating in the high latitudes and respectively from the
neutral atmosphere density, isn't observed only in the time of the magnetic storms. This is a permanent, continues process influencing the SAA fluxes all the time. The data, obtained during the two magnetic storms in
2010 and to powerful storms of March and June 2015, were used to find and classify the following short-term
magnetic storm effects: 1) The SAA proton flux maximum and area show strong decrease during the main phase
of the magnetic storms. The protons losses can be caused by the collisions with the storm-enhanced neutral
oxygen atoms. This hypothesis is proved by a comparison with the prediction by the NRLMSISE-00 model global
neutral Oxygen density; 2) Increase of the proton flux, in the presence of solar energetic protons, is observed
during the storm sudden commencements (SSC); 3) An enhanced flux of relativistic electrons is recorded in SAA
during the recovery phase of the magnetic storms at L-values higher than 1.7. They migrate from the outer
radiation belt. Their presence was proved by the analysis of the energy deposition spectra.
1. Introduction
The current paper analyses the short-term geomagnetic storm effects of the inner radiation belt (IRB) in the region of the SAA. Energetic
particles fluxes data are obtained with two Liulin type (Dachev et al.
(2015a) Bulgarian-German radiation risk radiometers-dosimeters (R3D)
(Dachev et al., 2002; Häder and Dachev, 2003; Häder et al., 2009),
mounted outside the ISS during 3 European Space Agency (ESA) EXPOSE facility (Dachev et al., 2012a, 2015b; 2017a) missions, as follows:
• R3DE instrument was installed in Expose-E facility (Rabbow et al.,
•
•
2012) outside ESA Columbus module of the ISS. The flux data
covered the time interval between February 22 2008 and September
1, 2009 (Dachev et al., 2012).
Expose-R facility (Rabbow et al., 2015), hosted the R3DR instrument
(Dachev et al., 2015b) in the period from March 11, 2009 to August
20, 2010 outside of the Russian “Zvezda” module.
R3DR2 instrument measured the flux in the EXPOSE-R2 platform
(Rabbow et al., 2017) outside of the Russian “Zvezda” module from
October 24, 2014 to January 11, 2016 (Dachev et al., 2017a,
2017b). The R3DR2 instrument is the same as the one that flew in
the EXPOSE-R facility from 2009 to 2010. The latter was named
R3DR. The instrument in the EXPOSE-R2 platform has the extension
R2 to distinguish between the data from the previous mission.
1.1. Long-term IRB variations
The IRB fluxes and dose rates are much stable in comparison with
the large and fast dynamics of the ORB fluxes and dose rates (Dachev,
2017). The IRB variations can be split in 2 cases: 1) long-term variations
connected with the solar activity and 2) short-term variations, connected with the geomagnetic activity.
The solar cycle variation in the SAA was first observed by Nakano
and Heckman (1968). Huston et al. (1998) also found it examining the
anticorrelation relationship between the F10.7 flux and the SAA proton
flux using data from the TIROS/NOAA spacecraft.
Dachev et al. (1999) observed the long-term variations in the “MIR”
space station SAA data with LIULIN instrument, too. The peak value of
the flux and dose rate in the SAA at L∼1.4 increased gradually by a
factor of 2 between 1991 and 1994 at an altitude of 410 km. The increase was attributed to the decrease of the atmospheric density during
the declining phase of the solar activity, which is due to the lower rate
of heating of the upper atmosphere when the solar ultraviolet (UV) and
extreme ultraviolet (EUV) radiation diminishes during solar minimum.
E-mail address: tdachev@bas.bg.
https://doi.org/10.1016/j.jastp.2018.08.009
Received 9 May 2018; Received in revised form 6 August 2018; Accepted 14 August 2018
Available online 16 August 2018
1364-6826/ © 2018 Elsevier Ltd. All rights reserved.
Journal of Atmospheric and Solar-Terrestrial Physics 179 (2018) 251–260
T.P. Dachev
photodiodes and behind the aluminum wall of the instruments and are
therefore not visible.
The R3D instruments are a Liulin type (Dachev et al. 2002, 2015a)
deposited energy spectrometers containing: one semiconductor detector
(Hamamatsu S2744-08 PIN diode) 2 cm2 area, 0.3 mm thick), one
charge-sensitive preamplifier (AMPTEC, A225F type), 2 microcontrollers and a serial interface of RS422 toward the EXPOSE facility.
A pulse analysis technique is applied to obtain of the deposited energy
spectrum, which further is used for the calculation of the absorbed dose
and the flux in the silicon detector. The two microcontrollers, through
specially developed firmware, manage the units.
A system international (SI) determination of the dose is used to
calculate the absorbed dose in the silicon detector. The SI dose is the
energy in Joules deposited in one kilogram of a matter. The following
equation relates the dose to energy loss and detector mass:
Qin et al. (2014) performed statistical analyses based on reasonable
Gaussian fits, using proton flux data measured by NOAA 15 from 1999
through 2009. They found that the variation of the peak proton flux in
the SAA anticorrelated with that of F10.7 during the solar cycle. They
also found it while examining the anticorrelation relationship between
the F10.7 radio flux phase lag of 685 days between the solar F10.7 flux
and the proton flux decrease.
Malakhov et al. (2015) analyzed the proton fluxes with energies
E > 80 MeV for L-shells 1.14–1.16 (B/B0 = 1.0–1.07), measured with
PAMELA and ARINA instruments of the Resurs-DK1 satellite at a constant 573 km altitude between 2009 and 2014. They found a clear
maximum in the proton fluxes in 2009, coinciding with 23th solar activity minimum.
1.2. Short-term IRB variations
255
D (Gy ) =
A relatively very small number of papers reported IRB proton flux
decreases during magnetic storm.
Looper et al. (2005) described that: “after the 29 October 2003, at
the approximately 600 km altitude of SAMPEX, the usual belt of the
energetic protons (above 19 MeV) around L = 2 almost completely
disappeared, recovering only after several months”. They also observed
the appearance of a new belt of ultrarelativistic (above 10 MeV) electrons, centered on L = 2.
Zou et al. (2015) observed proton losses at the outer boundary of the
inner radiation belt, which can be explained by the field line curvature
scattering mechanism. They mention that the decrease of the proton
flux and SAA area of the central part of the SAA is probably caused by
the enhanced neutral atmospheric density during geomagnetic storms.
∑ Ni Ei MD−1
i=1
(1)
where MD is the mass of the detector in kg, Ni is the number of the
pulses registered in channel “i”, Ei is the deposited energy (in Joules,
known through the calibration of the detector) corresponding to
channel “i”.
According to the formulae (1) the dose rate is a function of the count
rate in the 256 channels or totally a function of the flux. In many of our
previous publications, concerning the R3DE/R/R2 data, the dose rates
were analyzed, while in this paper the main studied variable is the flux.
The linear dependence between the dose and flux rate allow using
qualitatively the previously obtained trends in the dose rate to make a
consideration for the trends in the flux.
The semiconductor detectors of the R3D instruments was mounted
below of 0.3 g cm2 total shielding from the front side. The calculated
required kinetic energy of particles arriving perpendicular to the detector was 0.835 MeV for electrons and 19.5 MeV for protons.
Recently, Dachev (2017) and Dachev et al. (2017a) published a
comprehensive description of the R3DR2 instrument and its calibration.
Therefore, we will skip those details. R3DE and R3DR instruments are
identical to the R3DR2.
2. Material and methods
A total of 14 different space instruments were developed, qualified
and used in different space missions between 1988 and 2017 (Dachev
et al., 2015a) by the scientist from the Solar-Terrestrial Physics Section,
Space Research and Technology Institute, Bulgarian Academy of Sciences (SRTI-BAS). Data from 3 experiments are presented here. These
are the R3DE/R/R2 instruments mounted outside ISS in 3 different
mission of the ESA EXPOSE facility between 2008 and 2016. More than
600,000 10-s resolution data with SAA flux measurements are analyzed
to reveal the geomagnetic storm effects.
Fig. 1 shows the external view of R3D instruments mounted on the 3
EXPOSE facilities. The R3D instruments are small-dimension
(76 × 76 × 36 mm), low-mass (0.17 kg) automatic devices that measure solar electromagnetic radiation in four channels and ionizing radiation in 256 channels. In Fig. 1, the small circles on the surface in the
central part of the R3D instruments show the four solar visible-and UVradiation photodiodes. (The data from these diodes are not addressed in
this paper.) The ionizing radiation detectors are located below the
3. Results for the geomagnetic storm effects observed with R3D
instruments
Our first observation of the flux and the dose rate short-term decrease in the SAA maximum, during magnetic storm, was performed
with the LIULIN instrument on “Mir” Space Station during the famous
magnetic storm on March 24, 1991. The prestorm SAA flux inside of the
station was at the maximal flux level of 25–30 cm−2 s−1, while the
average per day flux level was 10–12 cm−2 s−1. The SSA average fluxes
decrease down to 7-8 cm−2 s−1 in the period March 25–30, 1991. This
coincides with the main and recovery phase of the magnetic storm. On
Fig. 1. a/b/c. External view of the R3D instruments (in the upper left corner of the pictures) as
mounted on the ESA EXPOSE facilities. (The
EXPOSE-R2 picture (Fig. 1c) was taken by the
Russian cosmonauts G. Pedalka and M. Kornienko on August 15, 2015 during an examination of the facility outside the Russian “Zvezda”
module.) (Picture credit ESA/RKA).
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Journal of Atmospheric and Solar-Terrestrial Physics 179 (2018) 251–260
T.P. Dachev
31 March, the SAA flux recovered to the prestorm levels.
It is curious, that the flux and the dose rate decrease on March 25,
1991 was first presented, but not commented, in Fig. 3 in the presentation by T. Dachev in 1997 (Dachev, 1997). The presentation was
focused on the “new” belt characterization, and we failed to report the
details of the storm induced decrease in the SAA maximum.
and STS-124 missions. For STS-126, STS-119, and STS-127, the drop
was also 80 cm−2 s−1 from an average level of 160 cm−2 s−1. The
Space Shuttle dockings with the ISS create strong decreases in the
maximal flux values due to the additional shielding effect of the space
shuttle body on the R3DE detector. (Dachev et al., 2011a). Berger et al.
(2017) concluded that the ISS attitude rotation at 180° is the main
reason for the decrease in the SAA dose rate during the Shuttle dockings.
The simultaneous analysis (Dachev, 2013) of the ascending/descending SAA dose rate maxima, obtained by three Liulin type instruments, two of which were far away from the Space Shuttle body,
showed that the flux decrease, generated by the additional shielding
provided by the 78 tons Shuttle body, is the main reason. The ISS attitude rotation at 180° is with secondary influences. Only calculations,
taking into account the 3D mass distribution around the examined instrument data can really answer which processes and at which level
form the observed flux and doses rate decreases.
A very small daily Dst index variations, in the range of −10 to
−20 nT, are observed during the R3DE mission, as expected for the
time with a very low solar activity. The two small magnetic storms with
daily Dst values below −40 nT observed on March 9 and July 22, 2009
coincide with Space Shuttle dockings and the further short-term analysis of SAA flux behavior during the storm is impossible. The long-term
dependence of the R3DE SAA average per day flux is presented in
Fig. 6a.
3.1. Radiation sources selection procedures
The following three primary radiation sources were expected and
recognized by the data selection procedures designed for the R3D instruments:
(i) Globally distributed primary Galactic Cosmic Rays (GCR) particles
and their secondary products;
(ii) Protons in the SAA region of the IRB;
(iii) Relativistic electrons and/or bremsstrahlung in the high latitudes
of the ISS orbit, where the ORB is situated.
The first selection procedure was described by Dachev et al. (2012).
During the measurements with the R3DR2 instrument few solar energetic particles (SEP) events were observed. That is why the selection
procedure was upgraded (Dachev et al. (2017a). As a results the SEP
source was recognized in the ISS data (Dachev et al. (2016). Together
with the real SEP particles, a low flux of what were likely to be mostly
secondary particles (SP) (protons, neutrons and heavier than H+ ions),
some of them associated with detector interactions, were also found in
the data.
Dachev et al. (2017a) and Dachev (2017) published a comprehensive explanation of the R3D instruments radiation sources selection
procedures, so here we will omit these descriptions.
3.3. Geomagnetic storm effects observed with R3DR instrument outside the
ISS in 2009–2010
The measurements with the R3DR instrument in the EXPOSE-R
platform outside the Russian Zvezda module of the ISS (Dachev et al.,
2015b) were carried out in the period March 2009–August 2010.
Dachev (2013) compared the data between the middle of March and
middle of June 2009, obtained simultaneously by the R3DE and R3DR
instruments. The main findings were the higher dose rates, produced by
the SAA proton and the ORB electron sources in the R3DR instrument.
The explanation of this result is connected with the fact that the R3DR
instrument was less shielded by the surrounding construction elements
of the Russian Zvezda module than the R3DE instrument. The latter was
surrounded by heavy construction elements of the EuTEF platform and
the European Columbus module (pls. see Fig. 2 in Dachev (2013)). The
GCR dose rate, measured with the R3DE instrument, was larger than the
dose rate observed by the R3DR instrument and the explanation is
connected with the fact that the heavily shielded surrounding of R3DE
instrument produces a larger amount of secondaries, interpreted as GCR
particles.
Because of a failure of the computer, connecting the external facility
to the ISS and the ground, no data were retrieved in the three large time
spans: June 24- December 28, 2009, January 21 -February 18, 2010 and
March 12-March 21, 2010 (Rabbow et al., 2015). The data in 2009 were
characterized by a very low solar activity. The Ap index contained the
3.2. Geomagnetic storm effects observed with the R3DE instrument outside
the ISS in 2008–2009
The measurements with the R3DE instrument in the EXPOSE-E
platform outside the Columbus module of the ISS (Dachev et al., 2012)
were carried out in the period February 2008–September 2009. Unfortunately, this period is characterized by a very low solar and geomagnetic activity in the minimum between the 23 and 24 solar activity
cycles (https://www.swpc.noaa.gov/products/solar-cycle-progression).
Dachev et al. (2012) in Fig. 4 presented the trends in the R3DE SAA
dose rate and the protons energy. It is necessary to add that relatively
low average hourly and daily dose rates were observed in the period
February–June 2008. They were generated by the low flux values at the
low station altitudes in the range of 350–365 km. The increase of the
station altitude up to 365–375 km after June 21, 2008 led to an increase
of the average dose rates and flux rate up to 22 to 27 cm−2 s−1.
The main feature, seen in the R3DE data was that during the five
space shuttle docking times the SAA maximal fluxes fall down by
80 cm−2 s−1 and reach an average level of 65 cm−2 s−1 for the STS-123
Fig. 2. The short-term geomagnetic storm variations of the SAA parameters as observed by R3DR instrument in the period March 22- April 21, 2010.
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Journal of Atmospheric and Solar-Terrestrial Physics 179 (2018) 251–260
T.P. Dachev
Fig. 3. The short-term geomagnetic storm variations of the SAA parameters as observed by the R3DR instrument in the period July 21-August 21, 2010.
differences is that as the R3DR detector is located on the left side of the
ISS “Zvezda” module opposite the ISS vector of velocity. It is shielded
heavily by the “Zvezda” module body on the descending orbits from
west to east drifting inner belt protons, when the ISS was in the nominal
“XVV”
orientation
(http://spaceflight.nasa.gov/station/flash/iss_
attitude.html). This explanation is well illustrated for the R3DR instrument data in slides No 7 and 29 by Dachev et al. (2011b), available
on-line at http://www.wrmiss.org/workshops/sixteenth/Dachev.pdf).
The procedure of docking of the STS-131 requires a rotation of the
ISS velocity vector at 180°. That is why the SAA structures of the
maxima in Fig. 2 are rotated, starting from 7 to 8 April 2010 when the
descending orbits maximal fluxes is larger than the ascending in the
whole period of docking till April 16–17, 2010. The return to the
nominal regime of orientation with another rotation of the ISS at 180°
happens after the undocking of the STS-131 on April 17–18, 2010.
The analysis of the average per day flux variations (the red line) in
Fig. 2 shows that during the prestorm period the levels are the highest
with values of about 32–35 cm−2 s−1. The main phase conditions decreases the average flux down to 26 cm−2 s−1 on 6 April 2010. The
period of the STS-131 docking is characterized with a wide minimum
(Dachev et al., 2011a); Berger et al. (2017)) with an average value of
25 cm−2 s−1. The undocking of the Shuttle, during the period of the
recovery phase, returns the average flux levels to the values of
28–34 cm−2 s−1.
minimal observed values at the end of 2009 (https://www.swpc.noaa.
gov/products/solar-cycle-progression).
Because of all the circumstances described in the previous paragraph, we only analyze the R3DR average daily flux in SAA along with
the Dst index for the period from March 24 to August 16, 2010.
The Dst behavior, during the R3DR mission, shows that there are 4
magnetic storm-like disturbances around: April 7 with a minimal value
of −47 nT, May 5 with −44 nT, May 31 with −34 nT and around
August 4 with a minimal value of −57 nT. Only 2 of them on April 7
and August 4, 2010 caused clearly visible response in the average flux.
Fig. 2 presents the short-term SAA flux variations (blue points) by
the date and UT. The Dst index (black curve), the average per day flux
(red line and points) and the maximal observed per day flux (magenta
line) in the period from March 22 to April 21, 2010 are plotted also.
Each of the variables is plotted against the right and left vertical axes
with the same color as the variables.
It is seen that during the period March 22-April 3 the flux (blue
points) forms 2 bar-like structures of maximums, which contain maximum of 9 and minimum of 6 crossing of the SAA region. The first barlike structure of few bars is produced during the descending orbit
crossings of the SAA region. The next bunch of bars with higher maximal fluxes is generated during the ascending orbit crossings of the SAA
region.
The simplest explanation of the ascending/descending flux value
Fig. 4. a: The 3-dimensional L-value versus time plot of
the observed by R3DR2 instrument maximal in the bin
SAA and ORB flux rate in cm−2 s−1. The data are plotted
against the color bar in the upper-right part of the figure.
Fig. 4b: The 3-dimensional L-value versus time plot of the
observed by R3DR2 instrument average in the bin SAA
flux rate in cm−2 s−1. The data are plotted against the
color bar in the lower-right part of the figure. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this
article.)
254
Journal of Atmospheric and Solar-Terrestrial Physics 179 (2018) 251–260
T.P. Dachev
Fig. 5. A long-term correlation of the R3DR2 instrument SAA averaged per day flux and the daily Dst index between October 24, 2014 and January 11, 2016.
3.4. Geomagnetic storm effects observed with the R3DR2 instrument outside
the ISS in 2014–2016
3.4.1. Overview of the Earth radiation belts in the period October 24,
2014–January 11, 2016
Fig. 4a presents a 3-dimensional L-value versus time plots of the
maximal observed ORB and IRB flux rates in cm−2 s−1 against the color
bar in the upper-right part of the figure. Data between October 24, 2014
and January 11, 2016 are plotted independently by the type of the
source. It may be considered that the ORB relativistic electrons flux
variations, with energy more than 0.835 MeV, are plotted in the L range
2.4–6. The IRB greater than 19.5 MeV proton flux variations are plotted
in the L range 1–2.4. The plotted values are the maximal observed per
day per bin flux values. The bins, with size of 0.02 L-value units, are
organized in a 442 daily vertical bars that are plotted against the date
and thus form the 3-dimensional plot.
The maximal flux bins in Fig. 4a cover the whole L-values range
from 1 to 6 in the Southern hemisphere. In the Northern hemisphere the
flux data bins are extended only up to L = 4.7 due to the Earth magnetic field hemisphere asymmetries. This explain the borderline seen in
Fig. 4a at L = 4.7 and the smaller population of the bins in the L range
between 4.7 and 6.
The disturbances recorded between 9:16:14 and 12:28:11 UTC on
January 14, 2015 in both panels are generated in 59 spectra with high
count rates and respectively flux rate in 5 channels: 242, 243, 253, 254
and 256. The counts number in channel 253 are fixed for all occurrences at 13,138 counts. The signals (not noise) are distributed over the
2.5 orbits and disappear. There is no explanation of the nature of the
signals.
The following peculiarities and geomagnetic storm effects are seen
in Fig. 4 panels:
Fig. 6. The long-term dependences of the SAA averaged per day flux by the
daily Dst index for the EXPOSE/E/R/R2 missions.
The moderate magnetic storm on the August 5, 2010 produces another short-term decrease of the SAA flux, seen in Fig. 3. Same variables
are plotted in Fig. 3 as in Fig. 2.
The average per day flux before the storm was at a level of
39–40 cm−2 s−1. During the storm on August 5–7, 2010 the average per
day flux falls down to levels of 31–33 cm−2 s−1. After the storm in the
period August 11–20, the average per day flux returns to the prestorm
levels of 39–40 cm−2 s−1. The relatively higher fluxes in Fig. 3, in
comparison with the fluxes in Fig. 2, have to be explained with the
higher altitude (368 km) of the SAA measurements in August. The
March–April 2010 measurements were performed at the altitudes of
359–361 km. The magenta line in Fig. 3 of the maximal flux, measured
during the period, shows very similar features as the average per day
flux.
• Fig. 4a:
- The measured by the R3DR2 instrument ORB flux rates in the
range 3.3–11,814 cm−2 s−1 with an average value of 85 cm−2 s−1
dominate the IRB flux rates, which are in the range
0.15–304 cm−2 s−1 with an average value of 35.9 cm−2 s−1;
- Two periods are clearly verified in Fig. 4a ORB data. In the relatively “quiet” period between October 24, 2014 and the middle of
March 2015, the ORB flux time and space variations are relatively
small and varied in the interval between 1 and 50-60 cm−2 s−1. In
this period, the equatorward boundary of the ORB vary in the
255
Journal of Atmospheric and Solar-Terrestrial Physics 179 (2018) 251–260
T.P. Dachev
•
range took place;
- The “quiet” and disturbed periods in Fig. 4b are also clearly
visible. During the “quiet” period at the beginning of the measurements the poleward boundary of the inner radiation belt extends up to the L = 3. The first strong magnetic storm on March
17, 2015 decreases the IRB poleward boundary down to L = 2.3.
During the months April, May and partly June, the boundary
slowly moves back to the level of L = 2.5. The next strong storm in
June pushes it again down to the level of L = 2.3. In the period
between July and December the boundary extends back to the
value of L = 2.7. The next relatively smaller storm on 21 December brings it down to L = 2.5 again. A very scrupulous comparison between the ORB equatorward and the IRB poleward
boundaries shows that they move simultaneously, in the same
direction, with a different L-value rate.
interval of L-values between 3 and 4 and never penetrate at the Lvalues below 3;
- The strong temporary enhancements of the maximal flux and extension of the ORB maximum down to L = 2.4, presented in the 3D
plot of Fig. 4a, usually takes place in the main phase of the magnetic storm, when the negative value of the Dst is large (Zheng
et al., 2006). In Fig. 4a the daily Dst index variations (http://wdc.
kugi.kyoto-u.ac.jp/index.html) in nT are depicted as white line
against the upper-right vertical axes. During the recovery phase of
the magnetic storms and the substorms, a penetration of the relativistic ORB electrons is observed down to L-value of 1.7. Well
seen is the single day flux enhancement and penetration in the
IRB, connected with the substorm, on July 4, 2015. The IRB was
also populated with a 61 precipitation bands. Dachev (2017) explained this in details).
- After the recovery phase of the magnetic storm, the ORB equatorial boundary moved from about L = 2.4 back to L = 3.0. These
features were repeatedly registered during the storms in March,
June and December 2015. Most of the time, the ORB was with
single maximum distribution in the L profile. After the storms in
March and June, periods with two maxima were registered. The
best example of two maxima L distribution profile, seen in Fig. 4a,
is the period between May 20 and June 20, 2015. The two maxima
L distribution profiles were detected mainly in the southern
hemisphere and are similar to the “third” Van Allen radiation belt
phenomena, recently explained by Mann et al. (2016);
- Similarly to Claudepierre et al. (2017) and Turner et al. (2017), we
recorded the first strong penetration of the relativistic electrons
below L = 2.5 on March 18, 2015. In the period March 18–28 the
lowest boundary of L = 1.7 was reached. Then the relativistic
electrons at a low L disappeared on March 28, 2015. The storm on
June 25, 2015 moved again the fluxes of ORB relativistic electrons
at L-values below 2 and they are clearly seen in Fig. 4a. The ORB
enhancement on July 4, 2015 emphasized them again but at this
case the minimal L-values reached was L = 1.6. Almost all disturbances in the Dst from July 11, 2015 until January 1, 2016
generated a new portion of relativistic electrons in the range of Lvalues between 1.6 and 2. They existed for few days and disappeared until the next Dst disturbance and magnetic substorm.
- The ORB plot in Fig. 4a is very similar to the 1.06 and 1.58 MeV
daily average electron fluxes plots, as observed by MagEIS instrument at the NASA's Van Allen Probes mission (Claudepierre
et al. (2017), Fig. 3).
Fig. 4b:
- The SAA more than 19.5 MeV proton flux variations are plotted in
Fig. 4b in the L range between 1 and 3. The plotted values in the
panel, are the average observed per day per bin flux values. The
bins with a size of 0.02 L-value units are organized in a 442 daily
vertical bars, which are plotted against the date form the 3-dimensional plot.
- The average flux rates in the SAA maximum at the L-values between 1.2 and 1.4 are strongly depend on the altitude of the station, presented with heavy blue line in Fig. 4b against the lowerright axes. The maximum flux values in the period October 24December 24, 2014 are connected with the highest altitudes above
420 km of the station in this period. The wide maximum between
June 2015 and January 11, 2016 is generated not only by the
relative high altitudes but also by the smaller solar activity, which
lowered the neutral atmosphere density and decreased the sink of
the IRB energetic protons;
- A decrease of the IRB fluxes in the whole L-value range is registered during the main phases of the storms on March 17 and June
25, 2015. These SAA flux variations are additionally comprehensively studied in Fig. 7 and Fig. 8;
- During the recovery phases of the magnetic storms a reverse
process of enhancement of the IRB fluxes also in the whole L-value
Our observations before and after the magnetic storm on March 17,
2015 for the first decrease and the next slow movement back to L = 2.7
of the poleward IRB boundary are very similar to the observations and
simulations made by Selesnick et al. (2013) of the effect of the November 2003 magnetic storm on geomagnetically trapped 27–45 MeV
protons observations from a dosimeter on the highly elliptical orbit
HEO-3 satellite (Selesnick et al., 2010). The authors explain the “gradual intensity rise that is interpreted as a direct measurement of the
cosmic ray albedo neutron decay (CRAND) source strength”.
3.4.2. A long-term dependence between the averaged per day IRB flux and
the daily Dst index as observed with the R3DR2 instrument in 2014–2016
Fig. 5 is created to certify the correlation between the SAA proton
flux and the Dst index, previously detected in Fig. 4. Three variables are
plotted in Fig. 5: 1) The daily Dst index in nT is plotted with a black line
against the left vertical axes; 2) The average per day flux is plotted
against the right upper axes with a blue line. It is average value, calculated on the base of in average 572 10-s measurements per day. The
moving average of the average flux, obtained in the period of 2, is
plotted with a heavy red line, which partly smooths out the “oscillating
spikes” (Berger et al., 2017) in the flux rate. The calculated linear fittings of the averaged flux is plotted with red dashed line. 3) The
average altitude of the ISS, obtained at the locations of the SAA flux
measurements, is plotted with a dark-green line against the right-lower
axes. The calculated linear regression of the averaged altitude is plotted
with a dark-green dashed line.
The correlation between the average altitude and the average flux
was already commented in the description of Fig. 4. Here we can add
that the dependence of the SAA flux of the long-term neutral atmosphere density variations is so strong that, despite the slow decrease of
the altitude, the average flux continues to increase towards the end of
the measurements in 2016 because the decrease of the Coulomb sink of
the SAA protons in neutral atmosphere. The altitudinal dependence in
the bottom part of the IRB is a well-known phenomenon that has been
described elsewhere (Filz and Holeman, 1965; Gusev et al., 2003;
Dachev et al., 2015b). Therefore, it will not be discussed further. In
section 4 of the paper, we will return to the dependence of the flux from
the neutral atmosphere.
Fig. 5 confirms the correlation between the averaged flux and the
Dst index. It is seen that virtually any change in the Dst index reflects on
the flux. It is important to emphasize, that the measured minimum
fluxes during the major phases of the magnetic storms in March, June
and December follow the observed minimal values of the Dst index. A
local maximums in the SAA fluxes are also observed during the periods
of the local maximums in the Dst index.
Fig. 6 investigates the direct long-term dependences of the measured with the R3D instruments daily average SAA fluxes from the daily
Dst index variations during the EXPOSE/E/R/R2 mission's. All averaged
data are selected for the periods when the Space Shuttle was not docked
with the ISS and the number of 10-s SAA daily measurements are higher
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Journal of Atmospheric and Solar-Terrestrial Physics 179 (2018) 251–260
T.P. Dachev
Fig. 7. a: The short-term geomagnetic storm variations of the IRB parameters as observed by the R3DR2 instrument in the period March 1-April 1, 2015. Fig. 7b–e are
plots of the flux (blue points) from the L-value for the 4 significant periods during the geomagnetic storm. Fig. 7f presents the deposited energy spectra shapes for the
period June 21–30, 2015 named CGR, ORB, IRB and SEP. These spectra are compared with: 1) the Prest. (Prestorm) spectrum (plotted with a heavy green line),
obtained during the prestorm phase (March 1–10, 2015) in the L range 2.1–2.3 (shown with a green rectangular at Fig. 7b); 2) Recov. (Recovery) spectrum (plotted
with a heavy orange line), obtained during the recovery phase (March 21–31, 2015) in the L range 2.1–2.3 (shown with an orange rectangular at Fig. 7e). The color
lines below the horizontal axes show the continuity of the 4 significant periods. (For interpretation of the references to color in this figure legend, the reader is
referred to the Web version of this article.)
3.4.3. A short-term dependence between the SAA flux and the hourly Dst
index as observed with the R3DR2 instrument in 2014–2916
Fig. 7a presents the short-term SAA flux variations (blue points) in
dependence by the date and the UT. The Dst index hourly values (black
curve), the average per day flux (red line and points) and the maximal
observed per day flux (magenta line and points) in the period from
March 1–31, 2015 are plotted, too. Each of the mentioned above
variables is plotted against the right and left vertical axes with the same
color as the variables. Fig. 7b–e presents 4 L-value distributions of the
flux for the four significant periods during the geomagnetic storm: the
prestorm, the sudden commencement, the main phase and the recovery
phase. The numbers shown in the third title rows for every significant
period are the measured maximal and the average per day SAA flux
values in cm−2 s−1. Fig. 7f presents a comparison of the deposited
energy spectra shapes between “Prestorm” and “recovery phases.
The blue points bar-like structures in Fig. 7a with a 10-s resolution
R3DR2 flux measurements data are similar to the R3DR flux bar
structures in Figs. 2 and 3. The R3DR2 instrument is placed at same
position outside the “Zvezda” module of the ISS, as the R3DR instrument was, that is why the descending orbits bars are smaller than the
ascending orbits bars for all of the time between March 1 and 31, 2015.
This is confirmed in Fig. 7c–d where the narrow ascending orbits
maxima are with a larger flux rates than the wider descending orbits
maxima.
The following main characteristics of the 4 significant periods can
be identified:
than 400. The well seen linear dependence is shown with a heavy blue
dashed line in the 3 panels of Fig. 6.
The shortest line in Fig. 6a presents the R3DE flux data dependence
for 354 days. As already mentioned, a very small daily Dst index variations in the range of 10 to −20 nT are observed during this mission.
This is normal for a period with a very low solar and respectively
magnetic activity. The two small magnetic storms with daily Dst values
below −40 nT, observed on March 9 and July 22, 2009, presents the
smallest observed Dst indexes in Fig. 6a.
Fig. 6b presents the R3DR flux data dependence from the Dst index
for 257 days. The smallest Dst index point of −69 nT was measured on
April 6, 2010. Even smaller hourly Dst variations are well seen in Fig. 2.
The Dst index point with a daily value of −57 nT was observed on
August 4, 2010 and is also is seen in Fig. 3.
Fig. 6c contains the longest data set of 442 days with the R3DR2 flux
dependence from the daily Dst index. The smallest 2 average flux points
in Fig. 6c were observed during the 2 main storms in March and June
2015. More precisely: on 23 June the average flux was 22.8 cm−2 s−1 at
Dst of −133 nT, while on March 18 the average flux was 24.2 cm−2 s−1
at Dst of −105 nT. These points are well visible in Fig. 6c. (The next
part of the paper will present the short term variations, close to the
magnetic storms in March and June 2015).
Fig. 6c reveals that all R3DR2 average flux points follow the linear
approximation. This gives reasonable evidences that the flux dependence from the Dst and respectively from the long-term neutral atmosphere density variations, driven by Joule heating in high latitudes, isn't
observed only in the time of magnetic storms, but is a permanent,
continues process that influences the inner radiation belt fluxes and
dose rates all the time.
• Prestorm phase on 1–10 March 2015 (Fig. 7b):
- The SAA proton flux shows a well-structured maxima at L = 1.35.
Because of the low geomagnetic activity and according to the
plotted in Fig. 4 the flux values extends up to L = 2.7.
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Journal of Atmospheric and Solar-Terrestrial Physics 179 (2018) 251–260
T.P. Dachev
Fig. 8. a: The short-term geomagnetic storm variations of the IRB parameters as observed by the R3DR2 instrument in the period June 11- July 11, 2015. Fig. 8b: A
comparison with the Ap index and predicted by the NRLMSISE-00 neutral Oxygen density. Fig. 8c/d: The global 3D distributions of the measured by the R3DR2
instrument SAA flux (> 40 cm2 s−1) for June 21 and 23, 2015 on the background of the predicted by the NRLMSISE-00 model global 3D distribution of the neutral
Oxygen density.
•
•
•
- The average per day flux (the red line and points) is at a value of
32.8 cm−2 s−1, while the average maximal flux value is at a level
of 243 cm−2 s−1.
The sudden commencement on March 15–16, 2015 (Fig. 7c):
- The flux during the sudden commencement time is similar to the
prestorm distribution but with the largest average per day flux at
value of 35.6 cm−2 s−1, and a maximal flux value of
261 cm−2 s−1. The necessary for the formation of a new IRB belt
solar energetic particles (SEP) (Hudson et al., 1997) were first
observed by the R3DR2 data on 12 March with maximal flux of
14 cm−2 s−1. The next portion of the SEP flux come on March 15.
The largest SEP flux of 23 cm−2 s−1 was observed at 10:03 UT on
March 16. The largest SAA flux of 261 cm−2 s−1 was seen at 02:33
UTC on March 16. It seems that the relative smaller Dst maxima
and the SEP fluxes on March 15–16 were enough effective to
produce a new IRB belt formation before the SSC of 56 nT at 05:00
UTC on March 17, 2015.
The main phase on March 18–19, 2015 (Fig. 7d):
- This period is characterized with a drastic decrease of the average
per day flux down to a value of 22.1 cm−2 s−1, and of the maximal
flux value down to 141 cm−2 s−1. The flux L-shell distribution still
remains similar to the prestorm period distributions.
The recovery phase - March 21–31, 2015 (Fig. 7e):
- The average per day flux and the maximal flux values returns to
the prestorm phase values.
- The poleward boundary of the SAA maximum shortens down to
L = 2.35. As seen in Fig. 7a, the situation remains for 10–15 days.
This has to be explained as “a gradual intensity decay that is interpreted as a direct measurement of the cosmic ray albedo neutron decay (CRAND) source strength” (Selesnick et al., 2010).
Pierrard and Lopez Rosson (2015) observed that after the March
17 event, the extent of the inner belt flux with an energy between
9.5 and 13 MeV is slightly reduced. The latter is bounded up with a
shortening of the inner belt from L = 3.0 to L = 2.8.
- The flux rate above L = 1.9 increases by a factor of 3–4 up to
about 9 cm−2 s−1. As seen in Fig. 4b, the enhances in the flux
above L = 1.9 occur at every recovery phase time interval until the
end of the observations. As already mentioned during the analysis
of Fig. 4a, the enhanced IRB flux in the L-value range between 1.6
and 2.2 is generated by the penetration of the relativistic electrons
from the ORB.
Fig. 7f confirms the presence of the relativistic electrons by a
comparison of the shapes of the deposited energy spectra. The spectra
shapes were comprehensively analyzed in part 3.2 of Dachev et al.
(2017a) that is why we will not describe again the CGR, ORB, IRB and
SEP spectra.
The “Prest.” spectrum (with the green line) in Fig. 7f is obtained by
averaging of 460 spectra, obtained between 1 and 10 March in the Lrange between 2.1 and 2.3 (seen in the green rectangle in Fig. 7b). The
green spectra may be divided at two parts. The shape of the low energy
deposition part, up to the depositing per channel energy of 0.2 MeV, is
similar to the GCR spectrum that is why we consider that this part
consists of high energy GCR particles. The shape of the second part of
the “Prest.” spectrum is similar to the IRB spectrum, obtained in the
maximum of the SAA at L = 1.3. The maximum of this part of “Prest.”
spectrum is moved toward higher deposited energy because the energy
of the IRB protons at 1.9 < L < 2.2 is lower than at L = 1.3 (Sawyer
and Vette, 1976; Dachev, 2009).
The “Recov.” spectrum (with the orange line) in Fig. 7f is obtained
by averaging of 515 spectra, measured between March 21 and 31 in the
L-range between 2.1 and 2.3 (seen in the orange rectangle in Fig. 7e).
The shape of the high energy depositing part of this spectrum is similar
to the “Prest.” spectrum. The shape of the low energy depositing part up
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Journal of Atmospheric and Solar-Terrestrial Physics 179 (2018) 251–260
T.P. Dachev
to 0.2 MeV is completely different than the “Prest.” spectrum. The large
count rates in the low energy depositing channels can be explained only
with the presence of the relativistic electrons. That is why the orange
“Recovery” spectrum is similar to the black ORB spectrum but with a
smaller count rates being measured out of the ORB maximum.
The major conclusion from Fig. 8c/d is: The prestorm SAA maximum fluxes reached 180 cm2 s−1 (Fig. 8c), while the storm main phase
decreased the maximum fluxes down to 130 cm2 s−1 (Fig. 8d). The 3D
SAA > 40 cm2 s−1 flux distribution area, obtained during the prestorm
on June 21, 2015, is larger in comparison with the analogical area
obtained on June 23 during the main phase of the storm. Both observations are similar to the findings of Zou et al. (2015).
The explanation of the observations in Fig. 8c/d is as follows: According to Fuller-Rowell et al. (1994) the geomagnetic storm increases
at high latitudes the Joule heating, which drives a global wind surge,
from both Polar Regions. The surge has the character of a large-scale
gravity wave with a phase speed of about 600 m/s. The surge propagates to the low latitudes and into the opposite hemisphere. In Fig. 8d
the surge is seen as an enhanced density of the neutral Oxygen atoms at
about 10° south latitude. The higher frequency of the Coulomb collision
of protons in the SAA region with oxygen atoms results in a decrease the
SAA proton flux, seen in Fig. 8d, as a smaller 3D flux and a flux distribution area above 40 cm−2 s−1.
4. An attempt to explain the short-term SAA flux decreases with
enhanced protons losses by the Coulomb collisions with the stormenhanced neutral oxygen atoms
Fig. 8a presents the short-term SAA flux variations (the blue points)
in dependence by the date and UT. The Dst index hourly values (the
black curve), the average per day flux (the green line and points), the
maximal observed per day flux (the magenta line and points) and the
SAA proton energy (the red points) from June 11 to July 11, 2015 are
plotted. Each of the mentioned above variables is plotted against the
right and/or left vertical axes with the same color as the variable.
The major event in Fig. 8a is the magnetic storm on 23 June with a
minimal Dst index value of 204 nT at 05:00 UTC on June 23, 2015. As
in the previous short-term effect figures, a well-seen minimum of the
measured flux, the average per day flux and the maximal flux is observed on 23 June. During the 2 substorms on June 26 and July 4, 2015
decreases in the measured flux (the blue points) can be found on June
26 and July respectively. The minimum on June 26 is not confirmed
with a minimum in the average flux. There is not a very-well seen
minimum on 6 July. Also, a well-structured maximum in the neutral
Oxygen density on July 5 is observed. The strong response of the ORB
on July 4 was already discussed in the previous parts of the paper. In
conclusion, we consider that the substorm on July 4, 2015 produces
similar to the major storms effects in the SAA.
Between June 18 and July 6, 2015, the R3DR2 instrument measures
elevated flux of SEP particles (not seen in Fig. 8) with energies higher
than 19 MeV. The maximal SEP flux value of 338 cm−2 s−1 was reached
at 19:23 UTC on June 22, 2015 (Dachev et al., 2016). The elevated SEP
flux and the two SSC-like structures in the Dst variations on June 22 and
July 4 produce well observed enhanced maxima above 250 cm−2 s−1 in
the maximal flux. We will not study the exact morphology of the SSC
events maxima because they are similar to those presented in Fig. 7.
Fig. 8b/c/d aim to investigate the opportunity to explain the main
phase decreases of the SAA flux with the enhanced Coulomb collision
proton losses with enhanced density of the neutral Oxygen atoms,
caused by the upper atmospheric heating at high latitudes (FullerRowell et al. (1994); Sutton et al. (2009); Suresh (2016).
Fig. 8b presents a comparison of the variables in Fig. 8a with the Ap
index and with the predicted by the NRLMSISE-00 model (Picone et al.,
2002) neutral Oxygen density. The latter is calculated in the SPENVIS
(https://www.spenvis.oma.be/help/background/atmosphere/models.
html#MSIS) for a point obtained by averaging of 305 R3DR2 measurements in the SAA maximum with a flux > 190 cm−2 s−1 in the time
span June 11-July 11, 2015. The following average initial NRLMSISE-00 model parameters were used: Altitude = 412.63; Longitude = 51.25°W; Latitude = 31.54°S; Local time (LT) = 5.6 and F10.7
81 day average = 115.78 × 10−22 W m−2 Hz−1, calculated between
May 10 and July, 2015. Fig. 8b reveals that there is a maximum in the
neutral Oxygen density connected with the storm. It is expected that the
Oxygen density maximum has to be on June 23, together with the Ap
index maximum and the SAA flux minimum. Due to the sharp decrease
of the F10.7 values from 135 × 10−22 W m−2 Hz−1, on June 21 down to
110 × 10−22 W m−2 Hz−1 on 23 June the Oxygen density maximum is
predicted on 22 June.
Two global 3D distributions of the measured by the R3DR2 instrument SAA flux (higher than 40 cm2 s−1) June for 21 and 23, 2015 are
presented in Fig. 8c/d. In the background is the predicted by the
NRLMSISE-00 neutral global 3D distribution of the neutral Oxygen
density. The global maps were calculated with the same initial parameters as for the single point.
5. Conclusions
This paper analyses the short-term geomagnetic storm effects of the
inner radiation belt (IRB) in the low Earth orbits (LEO) in the region of
the South Atlantic Anomaly (SAA). The data are obtained in 3 different
periods between 2008 and 2016 at 3 ESA EXPOSE platform missions
outside the ISS.
The main finding in the paper is that the SAA proton flux maximum
in the region of the South-Atlantic Anomaly shows strong decreases
during the main phase of the magnetic storm. This result is obtained by
the detailed analysis of the IRB parameters variations during 4 storms: 2
storms in 2010 and 2 storms in 2015, including the 2 most powerful
storms in March and June 2015.
The correlation between the averaged flux and the Dst index is so
strong that virtually any change in the Dst index reflects in the flux. It is
important to emphasize, that the measured minimum fluxes during the
major phases of the magnetic storms in March, June and December
follow the observed minimal values of the Dst index. Local maximums
in the SAA fluxes are also observed during the periods of the local
maxima in the Dst index.
By a direct analysis of the long-term linear approximation of the
R3D instruments SAA averaged per day flux from the daily Dst index for
the 3 missions it was concluded that a reasonable evidences exists that
the flux dependence from the Dst, and respectively, from the neutral
atmosphere density variations, driven by the Joule heating in the high
latitudes, isn't observed only in the time of magnetic storms, but is a
permanent, continues process, which influences the inner radiation belt
fluxes and dose rates all the time.
Using the predicted by the NRLMSISE-00 model (Picone et al.,
2002) neutral Oxygen density global distribution it was verified that the
higher frequency of the Coulomb collision of protons in the SAA region
with oxygen atoms can cause the decreases in the SAA proton flux and
flux distribution area.
A flux of relativistic electrons, migrating from the outer radiation
belt is observed during the recovery phase of the magnetic storm at the
L-values higher than 1.7. The existence of the energetic electrons in the
other boundary of the inner belt was demonstrated with the analysis of
the depositing energy spectra shape. The latter shows an enhanced
amount of low energy depositing particles (electrons) at the position of
the ORB electrons.
Acknowledgements
The author is grateful to the following colleagues: N. Bankov, B.
Tomov, P. Dimitrov and Y. Matviichuk from Space Research &
Technology Institute at the Bulgarian Academy of Sciences for the cooperation in the development of the R3DR2 spectrometer and for the
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Journal of Atmospheric and Solar-Terrestrial Physics 179 (2018) 251–260
T.P. Dachev
assistance with data analysis; G. Horneck, D.P. Häder, and G. Reitz for
the overall German–Bulgarian cooperation in the Biopan and EXPOSE
projects.
This work was partially supported by Contract No. 4000117692/
16/NL/NDe funded by the Government of Bulgaria through an ESA
Contract under the Plan for European Cooperating States (PECS).
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