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Citation: Makrantoni, P.; Tezari, A.;
Stassinakis, A.N.; Paschalis, P.;
Gerontidou, M.; Karaiskos, P.;
Georgakilas, A.G.; Mavromichalaki,
H.; Usoskin, I.G.; Crosby, N.; et al.
Estimation of Cosmic-Ray-Induced
Atmospheric Ionization and
Radiation at Commercial Aviation
Flight Altitudes. Appl. Sci. 2022,12,
5297. https://doi.org/10.3390/
app12115297
Academic Editor: Francesco Caridi
Received: 9 May 2022
Accepted: 22 May 2022
Published: 24 May 2022
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applied
sciences
Article
Estimation of Cosmic-Ray-Induced Atmospheric Ionization and
Radiation at Commercial Aviation Flight Altitudes
Panagiota Makrantoni 1, Anastasia Tezari 1,2, Argyris N. Stassinakis 1, Pavlos Paschalis 1, Maria Gerontidou 1,
Pantelis Karaiskos 3, Alexandros G. Georgakilas 4, Helen Mavromichalaki 1, *, Ilya G. Usoskin 5,
Norma Crosby 6and Mark Dierckxsens 6
1Athens Cosmic Ray Group, Faculty of Physics, National and Kapodistrian University of Athens,
15784 Athens, Greece; pmakrantoni@phys.uoa.gr (P.M.); anatez@med.uoa.gr (A.T.);
a-stasinakis@phys.uoa.gr (A.N.S.); ppaschalis@phys.uoa.gr (P.P.); mgeront@phys.uoa.gr (M.G.)
2Eugenides Foundation, 17564 Athens, Greece
3Medical Physics Laboratory, Faculty of Medicine, National and Kapodistrian University of Athens,
11517 Athens, Greece; pkaraisk@med.uoa.gr
4DNA Damage Laboratory, Physics Department, School of Applied Mathematical and Physical Sciences,
National Technical University of Athens (NTUA), Zografou, Athens 15780, Greece; alexg@mail.ntua.gr
5Space Physics and Astronomy Research Unit and Sodankylä Geophysical Observatory, University of Oulu,
FIN-90014 Oulu, Finland; ilya.usoskin@oulu.fi
6Royal Belgian Institute for Space Aeronomy, 1180 Brussels, Belgium; norma.crosby@aeronomie.be (N.C.);
mark.dierckxsens@aeronomie.be (M.D.)
*Correspondence: emavromi@phys.uoa.gr
Abstract:
The main source of the ionization of the Earth’s atmosphere is the cosmic radiation that
depends on solar activity as well as geomagnetic activity. Galactic cosmic rays constitute a permanent
radiation background and contribute significantly to the radiation exposure inside the atmosphere.
In this work, the cosmic-ray-induced ionization of the Earth’s atmosphere, due to both solar and
galactic cosmic radiation during the recent solar cycles 23 (1996–2008) and 24 (2008–2019), was studied
globally. Estimations of the ionization were based on the CRAC:CRII model by the University of
Oulu. The use of this model allowed for extensive calculations from the Earth’s surface (atmospheric
depth 1033 g/cm
2
) to the upper limit of the atmosphere (atmospheric depth 0 g/cm
2
). Monte Carlo
simulations were performed for the estimation quantities of radiobiological interest with the validated
software DYASTIMA/DYASTIMA-R. This study was focused on specific altitudes of interest, such as
the common flight levels used by commercial aviation.
Keywords: cosmic rays; ionization; radiation; atmosphere; solar cycle; flight level; aviation
1. Introduction
Cosmic rays are highly energetic particles of extraterrestrial origin. There are two main
components of cosmic rays: galactic cosmic rays (GCRs), which originate from outside of
our Solar System and Solar Energetic Particles (SEPs), which are accelerated during eruptive
processes on the Sun [
1
]. As cosmic rays travel through the interplanetary space and reach
the terrestrial atmosphere, (these rays are named primary cosmic rays), they penetrate by
colliding with nuclei of atoms and ions of the atmosphere, thus creating nucleonic, muonic
and electromagnetic cascades named secondary cosmic rays, as the primary particles are
absorbed inside the atmosphere due to ionization losses. In this way, cosmic rays affect
the physical–chemical properties of the atmosphere, i.e., its ion balance, [
2
,
3
] and may
even affect the regional climate’s variability [
4
]. The Earth’s magnetic field acts as a charge
discriminator and modulates the cosmic ray flux that reaches each location on the Earth.
Since cosmic rays are always present as a natural radiation background, they constitute
a major factor in the ionization of the atmosphere. This process is called cosmic-ray-induced
ionization (CRII). The GCRs affect the CRII by following an 11-year modulation oppositely
Appl. Sci. 2022,12, 5297. https://doi.org/10.3390/app12115297 https://www.mdpi.com/journal/applsci
Appl. Sci. 2022,12, 5297 2 of 14
correlated to the solar activity, i.e., the greater the solar activity, the lower the intensity of
the CRII is. On the other hand, strong fluxes of the unpredictable SEPs produced in solar
flares or coronal mass ejections (CMEs) most likely occur during periods of intense solar
activity and mostly affect the polar regions and high altitudes, where the magnetic field
lines are open and the energetic particles may deposit their energy, even at 20 km a.s.l. It is
noteworthy that GCRs are referred to as the continuous flux of the charged particles which
originate from different sources within the intergalactic space, while SEPs make up the
solar component of cosmic rays, associated with an increase in particle fluxes released in
the interplanetary space after great solar activity. SEPs also create hazards for satellites,
spacecraft, high-altitude aircraft, as well as for the health of air crews and space crews, due
to the enhanced radiation environment SEPs create [5,6].
As cosmic rays contribute to the production of ion pairs, which are involved in several
atmospheric processes, numerous studies indicate that ionization induced by CRs may
affect different climate parameters [
7
,
8
] and so the computation of CRII is considered
necessary. Specifically, the atmospheric ionization may alter the physical and chemical
properties of the atmosphere and affect several processes, such as aerosol and cloud
formation, atmospheric transparency, cloud cover, cyclogenesis and precipitation, especially
in regions of middle and high geographic latitudes. Therefore, several numerical models
were created and validated via comparison with direct observations and measurements of
the CRII, e.g., the Sofia model [
8
,
9
], the Bern model, also called ATMOCOSMIC [
10
,
11
] and
the Oulu model, also called CRAC:CRII [
12
,
13
]. Results from the latter model [
14
] are used
in this work.
Aside from cosmic rays affecting the composition of the atmosphere and contributing
to climate configuration, they may also affect human health [
15
,
16
]. The way that CRII is
modulated and distributed inside the atmosphere affects human exposure to radiation, sug-
gesting that air crew members and frequent flyers of commercial flights should be treated
in a specific way and extra safety measures and necessary regulations should be applied
during their flights. Other than ones referring to the general public, specific regulations and
safety measures do not yet exist for frequent flyers. However, the European Commission,
as well as other entities such as the International Commission on Radiation Units and
Measurements (ICRU) and the International Committee on Radiological Protection (ICRP),
have adopted a series of recommendations and frameworks regarding the determination
of the occupational exposure of aviation crews to cosmic radiation, as well as the most
efficient measures and counteractions to ensure radiation protection [
17
–
19
]. For this rea-
son, several studies on the problem have been performed [
20
–
27
], while various models
and tools have also been developed by the scientific community in cooperation with the
aviation industry. Some of these well-known models are the following: SIEVERT [
28
],
AVIDOS [
29
], NAIRAS [
30
], CARI [
31
], CALVADOS [
32
] SPENVIS [
33
], CRAC:DOSE [
23
]
and PLANETOCOSMICS [10].
Furthermore, ionization also affects the avionic electronic systems during a flight, with
single event effects (SEEs) being a main factor in this [
34
,
35
]. To expand, a single secondary
high-energy atmospheric neutron can collide with a nucleus of the semiconductor, causing
an ionization charge that can affect a semiconductor device. The most common effects of
SEEs are soft errors, firm errors and hard errors that decrease the performance and the
availability of electronic systems. Furthermore, radiation can also affect optical components
(i.e., LEDs, lasers and optical fibers), by changing their optical properties and causing
displacement damage. Usually, the electronic and optoelectronic devices anneal after the
irradiation has stopped but, in some cases, radiation can cause permanent damage [
36
–
38
].
Therefore, it is crucial to estimate the ionization and radiation levels during a flight in order
to be able to maintain reliability standards.
In this work, the CRII was calculated for three different flight levels (FLs): FL310
(
9.45 km
a.s.l. or 31,000 ft), FL350 (10.67 km a.s.l. or 35,000 ft) and FL390 (11.89 km a.s.l. or
39,000 ft). The model used for the aforementioned calculations was the CRAC:CRII model
in its extended version [
12
,
13
]. The CRII for these typical FLs is depicted in ionization
Appl. Sci. 2022,12, 5297 3 of 14
maps (Figure 1), showing the distribution of CRII globally for specific phases of solar cycles
23 and 24 (i.e., solar maxima and minima). More to that, time profiles of the monthly
distribution of CRII for selected magnetic cut-off rigidities for the same FLs during solar
cycles 23 and 24 will be presented.
In addition, a similar study concerning the radiation assessment of occupational
exposure to cosmic rays, specifically the estimation of the ambient equivalent dose rate for
the typical FLs, was performed. For these calculations, the software application Dynamic
Atmospheric Shower Tracking Interactive Model Application (DYASTIMA) [
39
,
40
] of the
Athens Cosmic Ray Group was used. Finally, regarding the investigation in this work, a
combined study was performed and a correlation between these two physical parameters
is shown.
2. Technical Analysis and Data Selection
For the ionization induced by cosmic rays, the CRAC:CRII model of the Oulu Uni-
versity was used—a numerical model that computes the CRII from the sea level to up to
40 km in the atmosphere, for every location on Earth. This model uses the Monte Carlo
CORSIKA tool (v.6.617 August 2007) [
41
], which provides a full development simulation
of an electromagnetic–muon–nucleonic cascade in the atmosphere, as well as the FLUKA
package for the low-energy interactions (v.2006.3b March 2007) [42] and is fully described
in [12,13].
Moreover, concerning calculations of the CRII for specific latitudes, altitudes and
time periods, considering both solar and galactic cosmic rays, the “Cosmic Ray Induced
Ionization: Do-it-yourself kit” (http://cosmicrays.oulu.fi/CRII/CRII.html) (accessed on
5 May 2022
) of the Oulu Cosmic Ray Station was used, and the monthly and annual values
of the modulation parameter Phi (in MV), reconstructed from the ground-based cosmic ray
data, are provided [
43
,
44
]. The modulation parameter corresponds to the local interstellar
spectrum (LIS) of cosmic rays, as provided by [45].
In order to calculate the ambient dose equivalent rate dH*(10)/dt, DYASTIMA was
used [
39
]. Monte Carlo simulations of the secondary cascades taking place in the different
atmospheric layers were performed with this independent GEANT4 software tool
[46–48]
,
which allowed for the determination of several characteristics of the cascade, such as
the energy of the particles and the energy deposits at the different atmospheric layers.
The FTFP_BERT_HP GEANT4 physics list was used, as it adequately describes all pro-
cesses taking place due to secondary cascades. Then, several radiobiological quantities
were calculated with the DYASTIMA-R extension. Specifically, the operational quantity
dH*(10)/dt was estimated by taking into consideration the different radiation weight-
ing factors that corresponded to the different types of secondary cosmic ray particles [
9
].
DYASTIMA/DYASTIMA-R is a validated tool [
40
,
49
,
50
], as it meets the criteria provided
by the ICRU and ICRP documents [
18
,
19
] regarding radiation protection in the aviation
sector. DYASTIMA software was provided through the portal of the Athens Neutron
Monitor Station (A.Ne.Mo.S.) (http://cosray.phys.uoa.gr/index.php/dyastima) (accessed
on 6 April 2022), while a database of selected simulated scenarios is available as a federated
product on the ESA SWE Portal (https://swe.ssa.esa.int/dyastima-federated) (accessed on
6 April 2022).
The required input parameters for performing a simulation with DYASTIMA concern
the characteristics of the planet and its atmosphere, as well as the differential spectrum
of the incoming primary cosmic ray particles at the top of the atmosphere. As far as the
simulations presented in this work are concerned, the atmospheric profile was based on the
International Standard Atmosphere (ISA) model [
51
], while the ISO15390 model was used
for the determination of the primary cosmic ray spectra [
52
]. To take into account the effect
of the geomagnetic field, maps of the cut-off rigidity threshold values as a function of the
geographic coordinates were used, based on the International Geomagnetic Reference Field
(IGRF) [
53
–
56
]. The magnetic field components were obtained via the National Oceanic and
Appl. Sci. 2022,12, 5297 4 of 14
Atmospheric Administration portal (https://www.ngdc.noaa.gov/geomag/) (accessed on
24 March 2022).
3. Results
In this work, a study of cosmic-ray-induced ionization, computed via the CRAC:CRII
model [
12
,
13
], along with the estimated ambient dose equivalent rate computed via the
validated software DYASTIMA/DYASTIMA-R [
39
,
40
], was performed globally during the
last two solar cycles (23 and 24) and focused on specific altitudes that corresponded to the
most common commercial flight levels: FL310 (9.45 km a.s.l.), FL350 (10.67 km a.s.l.) and
FL390 (11.89 km a.s.l.).
More specifically, the CRII at FL390 during the solar minima and solar maxima of solar
cycles 23 and 24 is presented in Figure 1, globally, via ionization maps. Figure 1a depicts the
CRII map that corresponds to the minimum of solar cycle 23 (in the year 1996), Figure 1b
depicts the CRII map that corresponds to the maximum of solar cycle 23 (in the year 2001),
Figure 1c depicts the CRII map that corresponds to the minimum of solar cycle 24 (in the
year 2009) and Figure 1d depicts the CRII map that corresponds to the maximum of solar
cycle 24 (in the year 2014). Comparing these four maps, it is clear that the ionization rate
during the solar minima was greater than the ionization rate during the solar maxima of
both cycles. This is due to the fact that the CRII followed the behavior of the cosmic ray
intensity and was positively correlated with them, while it negatively correlated with the
solar activity. In other words, the greater the solar activity, the lower the intensity of the
CRII is [57–59].
Moreover, when comparing the solar minima and maxima of solar cycles 23 and 24, it
is obvious that the CRII had greater values during solar cycle 24 than that of solar
cycle 23,
which was well expected, since solar cycle 24 is characterized as a relatively quiet solar cycle,
unlike solar cycle 23, where the solar activity was greater. The minimum and maximum
values for CRII and dH*(10)/dt obtained during this work for these specific time periods
are presented in Table 1. Regarding the geographic coordinates, it was observed that,
globally, the maximum ionization rate was found in polar regions while, at lower latitudes,
the ionization rate reached minimum. This was due to the magnetic field of the Earth and
the geomagnetic cut-off rigidity (Rc) that corresponded to each location, from
0 GV
in polar
regions to up to 17 GV in equatorial regions. The lower the geomagnetic cut-off rigidity
(Rc), the more cosmic rays penetrated the magnetosphere and the atmosphere of the Earth;
the CRs then ionized the atmosphere and created various effects [
51
]. Both the CRII and
estimated ambient dose equivalent rate maps were generated based on the rigidity map
of [53–56].
Figure 1. Cont.
Appl. Sci. 2022,12, 5297 5 of 14
Figure 1.
Maps of the CRII rate (ion pairs/(g*s)) at FL390: (
a
) during the minimum of solar cycle 23;
(
b
) during the maximum of solar cycle 23; (
c
) during the minimum of solar cycle 24; (
d
) during the
maximum of solar cycle 24.
Appl. Sci. 2022,12, 5297 6 of 14
Table 1.
Minimum and maximum values of CRII and the estimated ambient dose equivalent rate
during the minimum and maximum of solar cycles 23 and 24 at FL390.
YEARS
CRII (Ion Pairs/(g*s)) dH*(10)/dt (µSv/h)
Minimum
Values
×104
Maximum
Values
×104
Minimum
Values
Maximum
Values
1996 (SC23 min) 3.6 12.0 1.22 6.83
2009 (SC24 min) 3.7 13.6 1.24 7.05
2001 (SC23 max) 3.4 9.1 1.18 5.49
2014 (SC24 max) 3.5 11.0 1.19 5.50
With regard to the radiation exposure, the ambient dose equivalent rate at FL390
during the solar minima and solar maxima of solar cycles 23 and 24 is presented in
Figure 2
. A behavior similar to that of CRII was noticed. Greater values of the dH*(10)/dt
were observed in the polar regions (Rc = 0–2 GV) and lower values near the equator
(
Rc = 15–17 GV
), for both solar minima and maxima conditions. This was due to the depen-
dence of the radiation levels at the atmospheric layers on the cosmic ray intensity [
40
,
60
].
As expected, the radiation exposure was greater during the solar minima compared to the
solar maxima, due to the negative correlation between the solar activity and the intensity of
the incoming cosmic ray particles. Greater values of dH*(10)/dt were also observed during
the extended solar minimum in 2009 for both polar and equatorial regions, as compared to
those observed during 1996. The observed differences can be characterized as relatively
small, since the primary spectrum model used as input for the respective computations
provided the estimation of the galactic component and did not take into account any SEPs
which took place during this time period.
Figure 2. Cont.
Appl. Sci. 2022,12, 5297 7 of 14
Figure 2.
Maps of the estimated ambient dose equivalent rate (
µ
Sv/h) at FL390: (
a
) during the
minimum of solar cycle 23; (
b
) during the maximum of solar cycle 23; (
c
) during the minimum of
solar cycle 24; (d) during the maximum of solar cycle 24.
Time profiles of the yearly values of the CRII and the ambient dose equivalent rate
from the year 1996 to the year 2019 (covering the last two solar cycles) are presented in
Figures 3and 4. Four different geomagnetic cut-off rigidity values were selected: 0.1 GV
for the polar region (Figure 3a), 3.1 GV (Figure 3b), 8.5 GV, which corresponded to the
middle geographic latitudes and specifically Athens, Greece (Figure 4a) and 14.9 GV for the
equatorial region (Figure 4b). The results are provided for the three different atmospheric
altitudes which corresponded to the usual flight levels of the commercial aircraft: FL310
(9.45 km a.s.l.), FL350 (10.67 km a.s.l.) and FL390 (11.89 km a.s.l.).
The CRII and dH*(10)/dt values for this time period and for all flight levels can be
found in the Supplementary Material. It is interesting that both the CRII (left axis, blue lines)
and ambient dose equivalent rate (right axis, red lines) followed a long-term modulation,
specifically an 11-year one, at all the aforementioned locations, the same way the GCR
intensity did [
59
–
61
], since the radiation exposure of aircraft crews was directly linked to
the intensity of the cosmic radiation. Furthermore, comparing the time profiles of the three
different FLs, it is obvious that the higher the aircraft flew, the higher the CRII and the
estimated ambient dose equivalent rates were, since the shielding effect of the atmosphere
was reduced and thus the radiation exposure of the aircrew and frequent flyers was higher.
It was also observed that the difference among the values at the three FLs was greater as
one reached lower rigidities, e.g., polar regions, and became smaller as one reached higher
rigidities, e.g., equatorial regions. Since the magnetic field was weaker and more permeable
in the polar regions, it allowed even primary cosmic ray particles of lower energies to reach
the surface of the Earth, resulting in higher levels of cosmic radiation, unlike in the lower
Appl. Sci. 2022,12, 5297 8 of 14
geographic latitudes where the magnetic lines were almost parallel to the Earth’s surface,
and therefore provided effective shielding.
Figure 3.
Yearly distribution of CRII rate (left axis, blue lines) and ambient dose equivalent rate (right
axis, red lines) at three different flight levels (FL310, FL350, FL390), for the time period 1996–2019:
(a) at a polar region with cut-off rigidity 0.1 GV; (b) a region with cut-off rigidity 3.1 GV.
Concerning the CRII, once again, it is noted that during all phases of solar cycle 24,
which was a less active solar cycle, the values were greater than those of the respective
phases of solar cycle 23, when the solar activity was intense. However, this difference
became very small as we moved towards the equatorial regions, which showed that the
solar activity mostly affected low-rigidity regions.
More precisely, the CRII decreased by 5.6% near the poles and 24.2% near the equator
during SC23 and by 5.4% and 19.1% during SC24, respectively. Similarly, the dependence
of the dH*(10)/dt on the solar cycle was most evident near the poles (Rc = 0.1 GV) and,
to a lesser extent, near the equator (Rc = 14.9 GV), due to the geomagnetic field shielding,
which reflected particles of lower energies. In addition, the dH*(10)/dt decreased by 3.3%
near the poles and 19.6% near the equator during SC23 and by 4.1% and 22% during
SC24, respectively.
Finally, the correlation between the yearly distribution of the CRII and the estimated
ambient dose equivalent rate for all four rigidities mentioned above (0.1 GV, 3.1 GV, 8.5 GV
Appl. Sci. 2022,12, 5297 9 of 14
and 14.9 GV), for all three FLs (FL310, FL350 and FL390), from 1996 to 2019, is illustrated
in Figure 5. It is of great importance that a positive correlation between the two physical
quantities was observed, with the correlation coefficient being R
2
= 0.97. This confirms
that the cosmic-ray-induced ionization of the Earth’s magnetosphere contributed to the
radiation deposited at different locations and altitudes. The data of Figures 3and 4are
given as Supplementary Material.
Figure 4.
Yearly distribution of CRII rate (left axis, blue lines) and ambient dose equivalent rate (right
axis, red lines) at three different flight levels (FL310, FL350, FL390), for the time period 1996–2019:
(a) at a region with cut-off rigidity 8.5 GV; (b) an equatorial region with cut-off rigidity 14.9 GV.
Appl. Sci. 2022,12, 5297 10 of 14
Figure 5.
Scatter plot of the yearly distribution of the CRII and the ambient dose equivalent rate for
the time period 1996–2019 for FL310, FL350, FL390.
4. Discussion and Conclusions
In this study, the estimated CRII rate and ambient dose equivalent rate distribu-
tions all over the globe were presented for the most common commercial flight levels
(FL310, FL350 and FL390) during the recent two solar cycles 23 and 24 (1996–2019). For
the calculation of the CRII and the dH*(10)/dt, the CRAC:CRII model of Oulu Univer-
sity [
12
,
13
] and the DYASTIMA/DYASTIMA-R software [
39
,
40
] were used, respectively.
The distribution of both physical quantities was initially depicted in the maps, where the
values during the minima and maxima of solar cycles 23 and 24 (for FL390) were illus-
trated for the entire Earth and all the cut-off rigidities (0–17 GV). The maximum values
were observed during the solar minima and at polar regions (approximately 7
µ
Sv/h
at FL390), while the minimum values during the solar maxima and at the equatorial re-
gions were approximately 1.2
µ
Sv/h at FL390, due to the anticipated anticorrelation of
the cosmic ray intensity with the solar activity, as well as due to the shielding of the ge-
omagnetic field. Furthermore, a comparison between solar activity and ionization can
be presented. Using the average sunspot number (ASN) as a measure of solar activity
(
8 for 1996
, 180.3 for 2001, 8.4 for 2009 and 114 for 2014), we can get the following ratios:
ASN2001/ASN2014 = 1.58
and
ASN1996/ASN2009 = 0.95
. By calculating the corresponding
rations for the maximum values of CRII at FL390 for the same timestamps, we get the fol-
lowing results:
CRII2001/CRII2014 = 0.83
and
CRII1996/CRII2009 = 0.88
. According to these
results, it is clear that as the solar activity increased, the ionization decreased as expected.
Additionally, different dynamics were observed between solar cycles 23 and 24, due
to the difference in solar activity during these two solar cycles which is indicated in Table 1.
Concerning the different FLs, it can be concluded that the higher the FL, the higher the CRII
and the radiation exposure of aircrews and frequent flyers, since the provided shielding
of the atmosphere was reduced in higher atmospheric altitudes. Comparing the CRII and
dH*(10)/dt calculations for the four different rigidities/latitudes (0.1 GV, 3.1 GV, 8.5 GV
and 14.9 GV), for all three FLs during the entire period 1996–2019, it was noted that the
correlation was positive, with the correlation coefficient R2= 0.97.
From the above analysis, we conclude that both tools gave significant results and can
be used in order to study the effect of the ionization and radiation induced by cosmic rays
on the environment, space weather, climate change [62,63] and human health [15,22].
Specifically, advances in technology during the last few decades have made air travel-
ing more accessible to everyone. This has led to an increase in the number of flights as well
Appl. Sci. 2022,12, 5297 11 of 14
as an increase in flight altitude, since commercial aircraft are obliged to travel at higher
altitudes due to elevated air traffic. The tools mentioned above are of great importance
for the assessment of the health effects of the occupational exposure of aviation crews to
radiation due to the permanent galactic radiation background. They are also useful for
assessing the health effects of potential additional exposure due to sporadic events which
cause elevated radiation (such as SEPs and GLEs) [
24
,
64
] and radiation clouds (which are
regional radiation enhancements possibly due to photons, GCR and outer-belt relativistic
electrons), where the ambient dose equivalent rates are significantly increased [65].
Furthermore, all the extracted results have a great impact on ensuring properly
shielded avionic electronic systems, which depends on the levels of ionization and ra-
diation. High ionization levels may cause severe malfunctions in semiconductor parts,
decreasing the performance and the reliability of the electronic systems. An accurate
estimation of such levels would help prevent hardware failures and software errors.
A detailed study of extreme events may contribute to the updating of safety measures
and regulations, as well as to the updating of air traffic flow and capacity management, by
taking into consideration the respective occupational exposure conditions. An extension
of this work is planned in order to include more scenarios, i.e., different input parameters
regarding the spectrum of incoming particles based on experimental data (such as the ones
provided in [
5
,
6
]), more FLs, actual flight plans and extreme events such as SEPs and GLEs.
Supplementary Materials:
The following supporting information can be downloaded at: https:
//www.mdpi.com/article/10.3390/app12115297/s1. Table S1. CRII and dH*(10)/dt values for
cut-off rigidities 0.1GV, 3.1GV, 8.5GV and 14.9GV over the years 1996–2019.
Author Contributions:
Conceptualization, P.M. and A.T.; data curation, P.M., A.T. and A.N.S.;
formal analysis, A.N.S.; investigation, P.M. and A.T.; methodology, M.G.; resources, P.M., A.T. and
A.N.S.; software, P.P. and I.G.U.; supervision, H.M.; project administration, P.M. and A.T.; validation,
H.M. and P.K.; writing—original draft preparation, P.M., A.T. and A.N.S.; writing—review and
editing, H.M., N.C., M.D. and A.G.G. All authors have read and agreed to the published version of
the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement:
The datasets generated and/or analyzed during the current study are
available from the corresponding author on reasonable request.
Acknowledgments:
This work is supported by the ESA Space Safety Programme’s network of
space weather service development and pre-operational activities and supported under ESA Con-
tract 4000134036/21/D/MRP, in the context of the Space Radiation Expert Service Centre. The
European Neutron Monitor Services research is funded by the ESA SSA SN IV-3 Tender: RFQ/3-
13556/12/D/MRP. A.Ne.Mo.S is supported by the Special Research Account of Athens University
(70/4/5803). I.G.U. acknowledges partial support from the Academy of Finland (projects ESPERA
No. 321882
). Thanks are due to the Special Research Account of the University of Athens for sup-
porting the Cosmic Ray research. Thanks are also due to the Oulu Cosmic ray colleagues for kindly
providing cosmic ray data as well as the cosmic-ray-induced ionization model.
Conflicts of Interest: The authors declare no conflict of interest.
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