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Cosmic ray induced ionization (CRII) is an important factor of outer space influences on atmospheric properties. Variations of CRII are caused by two different processes – solar activity variations, which modulate the cosmic ray flux in interplanetary space, and changes of the geomagnetic field, which affects the cosmic ray access to Earth. Migration of the geomagnetic dipole axis may greatly alter CRII in some regions on a time scale of centuries and longer. Here we present a study of CRII regional effects of the geomagnetic field changes during the last millennium for two regions: Europe and the Far East. We show that regional effects of the migration of the geomagnetic dipole axis may overcome global changes due to solar activity variations.
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Advances in
Geosciences
Regional cosmic ray induced ionization and geomagnetic field
changes
G. A. Kovaltsov1and I. G. Usoskin2
1Ioffe Physical-Technical Institute, St. Petersburg, Russia
2Sodankyl¨
a Geophysical Observatory (Oulu Unit), University of Oulu, Finland
Received: 16 October 2006 – Revised: 4 December 2006 – Accepted: 27 February 2007 – Published: 13 August 2007
Abstract. Cosmic ray induced ionization (CRII) is an im-
portant factor of outer space influences on atmospheric prop-
erties. Variations of CRII are caused by two different pro-
cesses – solar activity variations, which modulate the cos-
mic ray flux in interplanetary space, and changes of the geo-
magnetic field, which affects the cosmic ray access to Earth.
Migration of the geomagnetic dipole axis may greatly alter
CRII in some regions on a time scale of centuries and longer.
Here we present a study of CRII regional effects of the ge-
omagnetic field changes during the last millennium for two
regions: Europe and the Far East. We show that regional
effects of the migration of the geomagnetic dipole axis may
overcome global changes due to solar activity variations.
1 Introduction
Presently, there are numerous arguments suggesting that so-
lar magnetic variability affects the global climate in different
aspects and on different time scales (see, e.g., de Jager, 2005;
Haigh, Lockwood and Giampapa, 2005; Versteegh, 2005).
An important factor affecting the terrestrial environment is
the flux of cosmic rays permanently impinging on the Earth.
In particular, galactic cosmic rays (CR) form the dominant
source of ionization in the atmosphere, especially the tropo-
sphere. Variations of the cosmic ray flux lead to significant
changes in the cosmic ray induced ionization (CRII), which
in turn may modulate processes related to the formation of
clouds (e.g. Ney, 1959; Svensmark, 2000; Carslaw et al.,
2002). There is much evidence for a significant correlation
between the cosmic ray flux and low cloud cover on a global
scale during the last 20 years (e.g., Marsh and Svensmark,
2000; Pall´
e Bago and Butler, 2000). On the other hand, the
relation between CRII and cloud coverage is not uniform and
Correspondence to: I. G. Usoskin
(ilya.usoskin@oulu.fi)
has a clear geographical pattern – strong correlations are lim-
ited to several large areas (e.g., the Northern Atlantic and Eu-
rope, the Far East, and the circum-Antarctic region), where
cloud formation conditions may be more sensitive to CRII
variations (Pall´
e et al., 2004; Usoskin et al., 2004a). There-
fore, changes of CRII in these regions can produce a larger
effect on the cloud cover and thus on the climate than global
CRII variations.
The cosmic ray flux, and the ensuing CRII, are modulated
by several processes. The most obvious is solar modulation
which leads to the well-known 11-year cycle in CR inten-
sity but also causes long-term variations (e.g., Usoskin et al.,
2003; Solanki et al., 2004). On the other hand, local CRII
is defined by the flux of CR which can access a given loca-
tion on the Earth. Variations of the local CR flux are caused
not only by the overall modulation of CR by solar activity
but also by changes of the local geomagnetic rigidity cutoff
(the minimum rigidity of CR needed to access the location).
The latter is defined by both the global dipole moment of
the geomagnetic field and by the geomagnetic latitude of the
site (details are discussed in Sect. 2), which vary with time
because of the magnetic axis migration (Kudela and Bobik,
2004; Shea and Smart, 2004a,b).
Most of the earlier studies consider possible climatic ef-
fects of either solar activity or cosmic ray flux at the Earth’s
orbit (e.g., Shaviv, 2005; Usoskin et al., 2005a). However,
the local variations of CRII in some locations may be domi-
nated on long time scales, centennial and longer, not by these
global processes but by geomagnetic field changes. In this
paper we consider such CRII variations in two regions in the
Northern Hemisphere with the highest correlation between
cloud formation and CRII – Europe and the Far East – and
estimate the role of geomagnetic field variations on atmo-
spheric ionization for the last millennium.
Published by Copernicus Publications on behalf of the European Geosciences Union.
32 G. A. Kovaltsov and I. G. Usoskin: Cosmic Ray Induced Ionization
0
500
1000
1500
0
5
10
15
3
4
5
6
CRII (ion pairs / cm3 sec atm)
φ
(MV)
PC (GV)
Fig. 1. Cosmic ray induced ionization of the atmosphere at an alti-
tude of 3km (depth 700g/cm2) as a function of the geomagnetic
cutoff rigidity Pcand modulation potential φ.
2 Cosmic Ray Induced Ionization
The ionization rate in the atmosphere can be represented in
the following form:
Q(x, φ , Pc)=X
iZ
Tc,i
Ji(T , φ ) Yi(x ,T ) dT , (1)
where the summation is performed over different ith species
of CR (protons, αparticles, heavier species), Yi(x, T ) is
the ionization yield function (the number of ion pairs pro-
duced at altitude xin the atmosphere by one CR particle of
the ith type with kinetic energy T– see Usoskin et al. (2004b,
2006a)), Ji(T , φ ) is the differential energy spectrum of the i-
th species of GCR that is defined by the modulation potential
φwhich depends on the solar activity level (see Caballero-
Lopez and Moraal, 2004; Usoskin et al., 2005b). Integration
is over the kinetic energy Tabove Tc,i , which is kinetic en-
ergy corresponding to the local geomagnetic rigidity cutoff
Pc. The value of Pccan be approximately computed using
St¨
ormer’s approximation (Elsasser et al., 1956):
Pc1.9×Mcos4λG,(2)
where Pcis the vertical geomagnetic cutoff in GV, Mis the
dipole moment of the geomagnetic field expressed in 1025
Gauss cm3, and λGis the local geomagnetic latitude. λGcan
be calculated from local geographical coordinates (λ;φ) and
the coordinates of the magnetic pole (λP;φP)
sinλG=sin λP×sin λ+cos λP×cos λ×cosPφ)(3)
Thus one can see from Eq. 1 that the local CRII depends on
both the level of solar activity (quantified via the modulation
potential φ) and on local parameters of the geomagnetic field
1000 1200 1400 1600 1800 2000
8
9
10
11
1000 1200 1400 1600 1800 2000
0
200
400
600
800
1000 1200 1400 1600 1800 2000
0
2
4
6
8
0 90 180 270 360
75
80
85
90
b)
M [1025 Gauss cm3]
MM W S D
Md)
c)
φ
[MV]
Years
PC (GV)
Far East
Europe
a)
1000 1200
1500
1800
2000
N. Latitude
Longitude
Fig. 2. Changes during the last millennium: (a) Migration of the ge-
omagnetic pole; (b) Dipole moment; (c) Geomagnetic cutoff rigid-
ity in Europe (geographical 50N 0E) and Far East (geographical
45N 140E); (d) Modulation potential (decadal averages). Let-
ters denote the Medieval maximum (MM) as well as the Wolf (W),
Sp¨
orer (S), Maunder (M) and Dalton (D) minima of solar activity.
(quantified via the geomagnetic rigidity cutoff Pc). The de-
pendence of CRII (computed by the method of Usoskin et al.
(2006a)) on the values of Pcand φis shown in Fig. 1 for an
altitude of about 3km (atmospheric depth 700 g/cm2). The
range shown in the figure covers a range of realistic values of
φ(from the Maunder minimum up to very high solar activity
with φ1500 MV) and Pc(from poles up to equatorial cutoff
of 15GV).
Adv. Geosci., 13, 31–35, 2007 www.adv-geosci.net/13/31/2007/
G. A. Kovaltsov and I. G. Usoskin: Cosmic Ray Induced Ionization 33
3 Geomagnetic field and solar activity changes during
the last millennium
The geomagnetic field changes in time, due to the varying
dipole moment Mand to geomagnetic pole migration. The
latter leads to a varying geomagnetic latitude λGfor a given
geographical location. The dipole moment was gradually de-
creasing during the last millennium (see Fig. 2b) by nearly
1/3 of its value. Here we use data of the geomagnetic re-
constructions by Bloxham and Jackson (1992) and Hongre
et al. (1998) before 1900 and the IGRG/DGRF model after
1900. Changes of the dipole axis were quite rapid during the
last millennium (see Fig. 2a), so that the northern (magnet-
ically southern) pole migrated from the Severnaya Zemlya
archipelago circa 1000 AD to Northern Greenland nowadays,
i.e., by around 180in geographical longitude.
Both Mand λGdefine the local geomagnetic cutoff
(Eq. 2). The pole migration may greatly modify the value of
Pcin some locations, particularly in mid-latitudes, leading to
significant variations of Pcand thus CRII in these regions.
Solar activity was also changing greatly during the last
millennium affecting the variability of the cosmic ray flux,
and thus CRII. Fig. 2d shows time profile of the heliospheric
modulation φ(Solanki et al., 2004) reconstructed from data
on the cosmogenic isotope 14C measured in tree rings. Note
that 14C is globally mixed in the atmosphere before depo-
sition in a natural archive and therefore is affected by the
dipole moment (which has been taken into account by the
reconstruction of φ) but is insensitive to the dipole axis mi-
gration. It is notable that the solar activity was significantly
lower in the past than during the last few decades (Usoskin
et al., 2003; Solanki et al., 2004), which implies that global
CRII would have been higher in the past.
4 Effects in CRII
In order to study the effects of geomagnetic-field changes,
we consider in detail two regions: the European region (in-
cluding the East-North Atlantic affected by the Gulf stream)
with its centre at geographical 50N 0E and the Far East
region with its centre at 45N 140E. We note that these re-
gions correspond to areas where the CRII may strongly affect
low cloud formation (Usoskin et al., 2006b; Voiculescu et
al., 2006). Therefore, variations of the CRII in these regions
may be relevant for climate changes. Long-term changes of
the geomagnetic cutoff in these regions are shown in Fig. 2c.
One can see that these changes are quite dramatic, by more
than a factor of two: Pcchanged between 1.9 and 4.7 GV
in Europe and between 3.2 and 7.2GV in the Far East. The
corresponding changes in the geomagnetic latitude were be-
tween 45and 55and 35and 50, respectively, but Pc
changes include also changes of M.
Using the computed changes in the local geomagnetic
rigidity cutoff Pc(see Fig. 2c) and the reconstructed solar
1000 1200 1400 1600 1800 2000
90
100
110
120
130
1000 1200 1400 1600 1800 2000
90
100
110
120
130
CRII (%)
A) Europe
B) Far East
CRII (%)
Years AD
Fig. 3. Decadal averaged cosmic ray induced ionization (solid
curves) at 3km altitude (700g/cm2depth) in Europe (geographi-
cal 50N 0E) and the Far East (geographical 45N 140E). Dot-
ted curves correspond to hypothetical variations if there were no
changes in the geomagnetic field, i.e. changes are attributed to only
solar activity variations. All curves were normalized to the period
1990–2000 (4.82 and 4.13 ion pairs cm3s1atm1for Europe
and the Far East, respectively), which is depicted by the dashed
line.
modulation of galactic CR (Fig. 2d), and applying the CRII
model (Fig. 1), we have calculated the expected changes in
CRII in the two selected regions, which are shown as solid
curves in Fig. 3. These changes include both solar activity
and geomagnetic field changes. In order to disentangle so-
lar and geomagnetic field changes in the CRII variations, we
have also computed CRII changes caused only by solar ac-
tivity changes (dotted line in Fig. 3), i.e., assuming that the
geomagnetic field did not change but remained the same as
now.
In the European region, the absolute maximum of the CRII
occurred during the Maunder minimum with the ionization
rate being 20% higher than nowadays (Fig. 3a). During the
Medieval maximum (ca. 1200AD) the CRII level was very
similar to the modern level. This pattern resembles global
climatic reconstructions: Medieval warming followed by the
Little Ice age and then the Modern warming (see, e.g., Eddy,
1977). Here we note that it still a matter of intense debate
whether these pronounced climatic features were regional
(related to European regions) or global. On the other hand,
these CRII variations were largely affected by geomagnetic
changes, e.g., the CRII would have been 10% higher 800
www.adv-geosci.net/13/31/2007/ Adv. Geosci., 13, 31–35, 2007
34 G. A. Kovaltsov and I. G. Usoskin: Cosmic Ray Induced Ionization
years ago than now if there were no changes in the geomag-
netic field. This implies that the long-term changes in CRII
in Europe were mostly defined by the migrating geomagnetic
pole before 1500AD rather than by solar activity variations.
The situation is quite different in the Far East. The changes
of CRII would be small, within 10%, if the geomagnetic field
was the same as now (Fig. 3b). However, the full span of
CRII changes is estimated to be as large as 30% between ca.
1300 and the modern epoch. Moreover, the CRII rate was
25% higher during the Medieval maximum than now, due to
changes in the geomagnetic rigidity cutoff (see Fig. 2c). This
is contrary to the pattern for the European region.
From this study we can conclude that local CRII variations
may be largely affected by geomagnetic field changes, and
not only by the global modulation of the CR flux by solar
activity.
5 Conclusions
The Earth’s climate is not formed/modulated uniformly over
the globe, but is mostly determined by conditions in some
specific key regions, which in turn affect larger regions or
global climate features. Thus, the global climate can be af-
fected via changes of not only global atmospheric or ocean
parameters, but also via local changes if they are related to
such key regions. Here we have considered an important at-
mospheric parameter, the cosmic ray induced ionization, in
two regions in the Northern Hemisphere – the European re-
gion and the Far East region – during the last millennium.
We have shown that CRII variations in these two regions are
dominated by changes caused by the migration of the geo-
magnetic pole, which exceed those variations due to solar
activity changes.
We note that the migration of the magnetic pole during the
last millennium, which caused significant effects in cosmic
ray induced ionization variations in some regions, was not
exceptional. Actually, it can be regarded as a minor excur-
sion (about 2000km or 18of a great circle during the mil-
lennium). There is evidence for more dramatic excursions of
the geomagnetic axis, even for historical times. For example,
the magnetic pole could have migrated for more that 90of a
great circle during the so-called “Sterno-Etrussia” geomag-
netic excursion around 700 BC (Dergachev et al., 2004). The
corresponding changes in local CRII must then be dramatic
and may result in strong regional effects.
It is important to realize that temporal variations of the in-
solation at any location on Earth are defined by the variabil-
ity of the solar irradiance and thus are synchronous all over
the globe. On the other hand, regional changes in CRII can
be affected not only by the varying flux of galactic cosmic
rays but also by geomagnetic field changes, that may exhibit
very particular regional features. Accordingly, studies of re-
gional effects may shed new light on debates concerning a
particular mechanism responsible for the solar variability–
climate link – cosmic rays or solar radiance (Haigh, 1996;
Tinsley, 1996; Yu, 2002; Kristjansson et al., 2004; Carslaw
et al., 2002; Haigh, Lockwood and Giampapa, 2005).
We conclude that local effects in variations of the cosmic
ray flux, which may dominate over the globally averaged
changes in some locations, should be taken into account in
long-term studies of solar-terrestrial relations.
Acknowledgements. Suomalainen Tiedeakatemia (Vilho, Yrj¨
o and
Kalle V¨
ais¨
al¨
a Foundation), the Academy of Finland, and Russian
Academy of Sciences (Project #30) are thanked for financial
support.
Edited by: N. Crosby and M. Rycroft
Reviewed by: two anonymous referees
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Presented here is a review of present knowledge of the long-term behavior of solar activity on a multi-millennial timescale, as reconstructed using the indirect proxy method. The concept of solar activity is discussed along with an overview of the special indices used to quantify different aspects of variable solar activity, with special emphasis upon sunspot number. Over long timescales, quantitative information about past solar activity can only be obtained using a method based upon indirect proxies, such as the cosmogenic isotopes \(^{14}\)C and \(^{10}\)Be in natural stratified archives (e.g., tree rings or ice cores). We give an historical overview of the development of the proxy-based method for past solar-activity reconstruction over millennia, as well as a description of the modern state. Special attention is paid to the verification and cross-calibration of reconstructions. It is argued that this method of cosmogenic isotopes makes a solid basis for studies of solar variability in the past on a long timescale (centuries to millennia) during the Holocene. A separate section is devoted to reconstructions of strong solar energetic-particle (SEP) events in the past, that suggest that the present-day average SEP flux is broadly consistent with estimates on longer timescales, and that the occurrence of extra-strong events is unlikely. Finally, the main features of the long-term evolution of solar magnetic activity, including the statistics of grand minima and maxima occurrence, are summarized and their possible implications, especially for solar/stellar dynamo theory, are discussed.
... В работе [Shea and Smart, 2004] показано, что вариации ГКЛ за счет изменения геомагнитного поля (и, соответственно, жесткости обрезания) за последние 400 лет, по величине сопоставимы с модуляцией ГКЛ в течение 11-летнего солнечного цикла (в среднем по расчетам за последние четыре солнечных цикла). Согласно [Kovaltsov and Usoskin, 2007] Velinov et al. , 2005;. Usoskin et al., 2005;Kovaltsov and Usoskin, 2007]; 2) связь между ГКЛ, ОСО и вековой вариацией геомагнитного поля неоднозначна. ...
... Согласно [Kovaltsov and Usoskin, 2007] Velinov et al. , 2005;. Usoskin et al., 2005;Kovaltsov and Usoskin, 2007]; 2) связь между ГКЛ, ОСО и вековой вариацией геомагнитного поля неоднозначна. Таким образом, контроль геомагнитного поля над интенсивностью ГКЛ, с одной стороны, и корреляция ОСО и ГКЛ с другой, требует механизма, посредством которого ГКЛ может оказывать влияние озон, и в первую очередь на область, где его концентрация максимальна, т.е. ...
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О связи климатических параметров с магнитным полем Земли сообщают многие авторы. Однако отсутствие механизма такой связи является препятствием для расширения таких исследований. На основании инструментальных наблюдений выявлена пространственно-временная связь основных структур в геомагнитном поле, полях приземной температуры и давления, а также озона и удельной влажности вблизи тропопаузы. Предлагается один из возможных механизмов – цепочка причинно-следственных связей: 1.) модуляция интенсивности и глубины проникновения галактических космических лучей ГКЛ в атмосфере Земли геомагнитным полем; 2.) изменение плотности озона вблизи тропопаузы под воздействием ГКЛ; 3.) изменение температуры вблизи тропопаузы вследствие высокой поглощающей способности озона; 4.) изменение статической устойчивости высокой тропосферы, и соответствено удельной влажности, вследствие изменения температуры тропопаузы; 5.) усиление/ослабление парникого еффекта водянной пары сопровождаемое потеплением/похолоданием климата.
... This reduction is now known as FD (Forbush Decrease), which is a consequence of heliospheric storms and very often observed simultaneously with a geomagnetic storm. All these three kinds of perturbations: in the solar wind, in the magnetosphere and on the flux of cosmic rays are closely interrelated and caused by the same active processes on the sun [48][49][50][51]. ...
... Çíà÷èòåëüíî ìåíüøå ðàáîò ïîñâÿùåíî ñâÿçè ãëàâíîãî ãåîìàãíèòíîãî ïîëÿ , ãåíåðèðóåìîãî â ÿäðå Çåìëè (âðåìåííûå ìàñøòàáû îò 10 8 ñ), è êëèìàòà (íàïðèìåð, [Gallet et al., 2003[Gallet et al., , 2005Bakhmutov, 2006;Kovaltsov, Usoskin, 2007;Usoskin et al., 2009;Kerton 2009;Áàõìóòîâ è äð., 2011;Kitaba et al., 2013]). Ðåãóëÿðíûå èíñòðóìåíòàëüíûå íàáëþäåíèÿ êàê ìàãíèòíûõ, òàê è êëèìàòè÷åñêèõ ïàðàìåòðîâ ðåäêî ïðåâûøàþò 100 ëåò, ïîýòîìó è êîððåëÿöèè ìåaeäó íèìè â ìàñøòàáàõ íåñêîëüêèõ ïîñëåäíèõ äåñÿòèëåòèé ñ÷èòàþòñÿ íàèáîëåå äîñòîâåðíûìè. ...
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Analysis of main geomagnetic field (from IGRF model) and climatic parameters (near surface air temperature and surface pressure) allows us to determine their variability and spatial-time relations between them during 20 century. Integral characteristics and dynamics of the above parameters in latitudinal band 40-700N have been investigated, applying one and the same approach. This gives us the possibility to reveal their global and regional characteristics – the differences and similarities between them. Three distinct periods of the spatial-temporal distribution of geomagnetic field intensity have been determined, that could be connected to corresponding periods of mean near surface air temperature evolution during the 20-th century: (1) initial global warming (1911-1943); (2) stabilization (end of 1940s- middle1970s); (3) secondary global warming (middle of 1970s-2000s). There is a good correspondence between geomagnetic field, near surface air temperature and pressure spatial distributions during the 20-th century. The high coefficient of similarity between integral spatial distributions of geomagnetic field intensity F and surface air temperature T (RFT) = -0.83 is quite unexpected. It indicates that relations between them could hardly be a random connection. If there is a causal relation between them, it obviously should be in the direction: geomagnetic filed influence on the temperature and/or surface pressure. The main problem in this case is that the mechanisms of magnetic filed influence on climatic parameters are less investigated and poorly understood. In this paper geomagnetic field is considered to be a first element of the causal chain of processes relating it with Earth’s climate. A brief review of resent understanding of solar - geomagnetic field influence on climate shows that the main role in this process is played by galactic cosmic rays. Results presented here are basement for the second part of this paper, where the causal link of the processes connecting geomagnetic field with galactic cosmic rays, ozone and water vapour near the tropopause (with their influence on the radiation balance of the planet and consequently on climate) is thoroughly analysed.
... Various studies indicate, however, that the mechanism may have significant climatic influence when differentiated according to latitude, season, and atmospheric altitude (Yu and Luo, 2014). Importantly, the Svensmark process appears to work best at middle latitudes, where sufficient suitable stratified clouds, liquid cloud droplets, and suitable quantities of cosmic rays exist (Kovaltsov and Usoskin, 2007; Laken et al., 2010; Svensmark, 2000, 2003; Pallé et al., 2004; Usoskin et al., 2004). For key regions, Voiculescu and Usoskin (2012) documented a persistent response of clouds to cosmic rays over the entire studied time interval (1984e2009), indicating a real link. ...
Chapter
Millennial-scale climate variability is a globally well-established Holocene phenomenon described for all oceans and continents. Cycles are known from upper, middle, and lower latitudes, encompassing all climate zones from the Arctic to the tropics. The amplitude of the observed temperature fluctuations is often more than 1°C and thus has a similar or even greater range than the warming that has occurred since the Little Ice Age. Furthermore, many of these Holocene, natural climate fluctuations show the same level of abruptness as the 20th-century warming. A common characteristic of many of the documented millennial climate fluctuations is their good match with solar activity changes, as well as a North Atlantic climate record by Bond et al. (2001). Besides solar activity changes, internal millennial ocean cycles may have contributed to the observed climate oscillations. Both solar and internal climate system autocyclical drivers are not yet fully implemented in the current climate models, which still do not manage to reproduce the variable Holocene climate development. Yet successful hindcast capability is generally considered a prerequisite that qualifies models to be used for modeling of future climate. This chapter reviews Holocene millennial-scale climate fluctuations as reported in 64 papers worldwide. Future research needs to attempt a detailed correlation of the existing Holocene climate curves, complemented by additional data sets filling gaps in currently poorly documented regions. A good understanding of global Holocene millennial- and centennial scale climate variability and its possible solar forcing is required as a calibration basis for a new generation of climate models that should have the objective to reliably reproduce past climate change before attempting detailed future simulations.
... In (Shea and Smart, 2004), it is shown that the GCR variations due to the changes in the geomagnetic field (and, therefore, the geomagnetic cutoff hardness) during the past 400 years are commensurate with the GCR modulation during the 11 year cycle (averaged over the previous four last solar cycles). According to (Kovaltsov and Usoskin, 2007), the regional variations in the GCR intensity caused by the drift of the geo magnetic pole can be even stronger than the deviations associated with the changes in solar activity. ...
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