Abstract During the last three solar cycles and in a wide energy range of galactic cosmic rays both the modulation and the variability of the intensity demonstrate effects related to the Gnevyshev Gap (GG) -a substantial decrease once or twice during the maximum phase of each solar cycle of a parameter that generally varies in phase with the cycle. The GG-effect also manifests itself in the behaviour of both the strength of the average interplanetary magnetic field and the power of its fluctuating component. The energy dependence of the GGeffect in the modulation and in the variability of the cosmic ray intensity was found to be different. The start of the GG-effect in the cosmic ray modulation practically coincides with a change in the energy dependence of the cosmic ray modulation

A I Sladkova

E O Flückiger

G A Bazilevskaya

M B Krainev

M Storini

S A Starodubtsev

V S Makhmutov

CiteSeerX

SH.3.2.19
The Gnevyshev Gap Effect in Galactic Cosmic Rays
M.B. Krainev 1, M. Storini 2, G.A. Bazilevskaya1 ,
E.O. Flückiger3, V.S. Makhmutov1, A.I. Sladkova4, and S.A. Starodubtsev5
1Lebedev Physical Institute RAS, Leninsky Prospect, 53, Moscow, 117924, Russia
2IFSI/CNR, Via del Fosso del Cavaliere, 100, 00133 Roma, Italy
3Physikalisches Institut/University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
4Institute of Nuclear Physics, Moscow State University, Moscow, 119899, Russia
5Institute of Cosmophysical Research and Aeronomy, 677891 Yakutsk, Russia
Abstract
During the last three solar cycles and in a wide energy range of galactic cosmic rays both the modulation
and the variability of the intensity demonstrate effects related to the Gnevyshev Gap (GG) — a substantial
decrease once or twice during the maximum phase of each solar cycle of a parameter that generally varies in
phase with the cycle. The GG-effect also manifests itself in the behaviour of both the strength of the average
interplanetary magnetic field and the power of its fluctuating component. The energy dependence of the GG-
effect in the modulation and in the variability of the cosmic ray intensity was found to be different. The start
of the GG-effect in the cosmic ray modulation practically coincides with a change in the energy dependence
of the cosmic ray modulation.
1 Introduction:
The double-peak structure (DPS) of the maximum phase of the 11-year solar cycle has been a subject of
interest for solar physicists since the investigations made by M. N. Gnevyshev during the 1960s (Gnevyshev,
1963, 1967). Data for more than thirty years showed that DPS manifests itself in many solar and heliospheric
parameters (e.g., Feminella & Storini, 1997; Bazilevskaya et al., 1998, and references therein).
In this paper special attention is paid to the valley between the peaks (we call it the Gnevyshev Gap, or
GG, according to Storini & Pase, 1995) rather than the peaks themselves during the maximum phase of the
solar cycle. We consider that a certain parameterP demonstrates a GG-effect if a) it varies approximately
in phase with the solar cycle and b) it decreases substantially once or twice for short periods of time during
the maximum phase of solar activity. One outstanding feature of the GG-effect on the Sun is that the GG
amplitude is greater for the more energetic parameters (Gnevyshev, 1963, 1967).
A few years ago we found that the GG was a property also of the variability of the galactic cosmic ray
(GCR) intensity in a wide range of characteristic times. This variability can be expressed in terms of the
power spectrum density, the wavelet spectrum or the simple standard deviation (SD) of the daily intensities
with respect to the monthly mean (Storini & Pase, 1995; Bazilevskaya et al, 1995a; Astaf’eva et al., 1997;
Storini et al., 1997). As it is well known the GCR intensity itself varies in a counterphase with the solar cycle.
However, its modulation varies in phase with the solar cycle and demonstrates the GG-effect (Storini, 1995).
Besides, it was noted from long ago (see references in Moraal, 1975, and also Krainev et al., 1983a, 1983b;
Bazilevskaya et al., 1995b) that the temporary change in modulation of GCR intensity during the maximum
phase of each solar cycle strongly depends on the energy of particles. In this paper we discuss GG-effects in
GCR intensity modulation and variability, with special emphasis on their energy dependence, and show that
these effects are also present in the time behaviour of the interplanetary magnetic field, both in its regular and
fluctuating components.
2 Data Processing, Analysis and Discussion:
To analyse the energy dependence of the GG-effect in the GCR modulation and SD we consider the long
time series of the daily counting rates of the neutron monitors at Huancayo/Haleakala (NHu, effective vertical
cutoff rigidity Rc = 13GV ), Rome (NRo; Rc = 6:2GV ) and Climax (NCl; Rc = 3GV ) as well as the balloon
data in the transition maximum in the stratosphere at Murmansk (NMu; Rc = 0:6GV ) (Bazilevskaya et al.,
1991; Bazilevskaya & Svirzhevskaya, 1998, and references therein). Days with particle contribution from the
Sun were excluded from the data series. All the data were monthly averaged and the SD of daily data with
respect to monthly mean was determined. The resulting time series were normalized to the May 1965 count
rate and smoothed on 3–7 month scale.
We define the relative GCR modulation asM  (N(05:1965)  N(t))=N(05:1965)  100;%. In Figure 1
the time profiles of the 7-month smoothed SD (upper panel) and the relative modulation (middle panel) for all
four GCR series and for the last three solar cycles (20–22) are compared with the time profiles of the regular
and fluctuating components of the interplanetery magnetic field (IMF) (lower panel).
For the boundaries of the maximum activity phases we use those reported by Ivanov (1995). Neverthe-
less, the response of the GCRs
to solar changes could be de-
layed by about one year, as
they are sensitive to the con-
ditions in the heliosphere as
a whole. Hence, we looked
for GG-effects in GCRs dur-
ing what we will call the “he-
liospheric maximum phase”
(HMP). Its extent is the one of
Ivanov (1995), prolonged by
one year, and it is shown for
each cycle by vertical dashed
lines in Figure 1. From the
SD trends we observe: (i) the
SD is in phase with the eleven
year cycle, and at neutron mon-
itor energies its amplitude de-
creases with the GCR energy
(the SD for the stratospheric
data is not shown after 1991
because of the relatively poor
statistics); (ii) all SD series
demonstrate the GG-effect (see
arrows and labels). One can
also notice that the relative
amplitudes of GG (AGG
P

(Pb Pg)=Pb  100;%, where
Pb andPg are the values ofP
Figure 1: The time profiles of the 7-month smoothed SD (upper panel), the GCR modulation
(middle panel), the regular strengthB and the power spectrum densityP (f0 = 2  10 6Hz)
of the interplanetary magnetic field (lower panel). The HMP periods are shown by the vertical
dashed lines and the GGs are marked by arrows and labels.
immediately before and at the bottom of the gap, respectively) are approximately the same for all SD series.
For example, for the GG in the cycle 21 theAGGSD = 54.9, 53.3, 53.5, 52.0% and for the GG in the cycle 22
theAGGSD = 51.2, 58.0, 57.7, 52.3% for Murmansk, Climax, Rome and Huancayo, respectively.
Obviously, the modulation of the GCR (middle panel of Figure 1) also follows the solar cycle and there
are gaps (indicated by arrows) during the HMP for all the intensity series considered. Besides, the GGs in
modulation are more narrow than in the SD and the relative amplitude of the gaps inM grows with GCR
energy. For the first GG in the cycle 21 theAGGM = 0.7, 7.7, 23.4, 23.8% and for the GG in the cycle 22 the
AGGM = 10.5, 22.6, 29.2, 26.2% for Murmansk, Climax, Rome and Huancayo, respectively.
The IMF parameter was obtained by using hourly and 5-minute averaged magnetic field intensity, provided
in the ”omni“-files by GSFC. The data were processed to obtain the monthly values of both the mean strength
B and the power spectrum densityP (f) in the frequency range10 6 < f < 10 3Hz (Blackman & Tukey,
1958). The lower panel of Figure 1 shows the behavior of the 7-month smoothedB andP (f0) (f0 = 2 
10 6Hz). It is easily seen that both IMF parameters, relevant for cosmic ray propagation in the heliosphere
— B, describing the regular IMF, andP (f0), relating to its fluctuating component — vary in phase with the
solar cycle and demonstrate the GG-effect (at least in cycles 21 and 22).
To study the energy dependence in the GCR intensity modulation in more detail we, as Krainev (1991),
normalized the 3-month smoothed modulation of Huancayo/Haleakala, Rome and Climax counting rates to
that of Murmansk for the ascending (As) phases of each solar cycle, using a power regression.
In the three panels of Figure 2 the 3-month running means of the GCR modulation normalized
Figure 2: The GCR modulation normalized toMMu for solar cycles 20 (upper panel), 21
(middle panel) and 22 (lower panel). The HMP periods are shown by vertical lines in each
panel.
to MMu(t) are shown sep-
arately for each solar cycle.
Due to the mathematical tech-
nique applied, all four curves
lie very close to each other
during the As–phases of so-
lar cycles. In the descending
(Ds) phases the curves pro-
gressively come apart, indi-
cating a different energy de-
pendence of the GCR mod-
ulation during the Ds-phases,
as found in the past (cf. Po-
pielawska, 1992), after the
high-latitude heliomagnetic
field reversals. During the
HMP the deviations between
the curves are pronounced, the
amplitude of the GG growing
(as it was emphasized from
Figure 1) with the GCR en-
ergy. From Figure 2 we can
also derive that the change in
the energy dependence starts
with the GG-effect but it does
not always return to the previ-
ous dependence with the end
of the GG-effect. In fact, for
cycle 20 a pronounced difference exists between the modulation of high and low energy GCRs up to the end
of 1971, well beyond the GG and HMP. A similar feature was present during the entire HMP of cycle 21, even
in between the gaps. Contrary, during cycle 22 the effects are very localized and practically there is no energy
effect outside the GG.
3 Conclusions:
1. It is evident that the GG-effect — a decrease just in the maximum phase of the 11-year cycle — is definitely
a specific feature both in the GCR modulation and in their variability (SD) in a rather wide energy range
(from several to tens of GeV). For the aim of the GG-effect understanding it is essential that the heliospheric
parameters best related to cosmic ray propagation in the heliosphere — the strength of the regular magnetic
field and the power spectrum density of its fluctuating component — vary in phase with the solar cycle and
demonstrate the GG-effect.
2. The energy dependence of the GG-effect in GCR modulation and variability (SD) seems to be different, the
relative amplitude of the former growing with the particle energy, while that of the latter is energy independent.
3. For all the three cycles considered the start of the GG-effect in the GCR modulation practically coincides
with a change in the energy dependence of the modulation, which may last for some time after the end of the
GG-effect.
4 Acknowledgements
The International Space Science Institute (Bern, Switzerland) is acknowledged for supporting our Gnevy-
shev Gap Investigation. This work was also partly supported by the Russian Foundation for Basic Research,
grants No 98-02-16420, 98-02-31000, 99-02-18222, the Swiss National Science Foundation, Grant NF 20-
050697.97 and by the 1998/99-IFSI/CNR Grant. Thanks are due to the University of Chicago (NSF Grant
ATM 9613963) for the Climax and Huancayo (Haleakala) neutron monitor data and to NASA/Goddard Space
Flight Center for providing the IMF data.
References
Astaf’eva, N.M., et al. 1997, Proc. 25th ICRC (Durban) 7, 337
Bazilevskaya, G.A., et al. 1991, J. Geom. Geoelectr. Suppl. 43, 893
Bazilevskaya, G.A., et al. 1995a, Proc. 24th ICRC (Rome) 4, 572
Bazilevskaya, G.A., et al. 1995b, Adv. Space Res. 16, (9)227
Bazilevskaya, G.A., et al. 1998, in: Medina, J., (ed.), Rayos c´osmicos 98, Proc. 16th ECRS (Alcal´a), 83
Bazilevskaya, G.A., & Svirzhevskaya, A.K. 1998, Space Sci. Rev. 85, 431
Blackman, R.B., & Tukey, J.W. 1958, The Measurement of Power Spectra, Dover, Mineola, N.Y.
Feminella, F., & Storini, M. 1997, A& A 322, 311
Gnevyshev, M.N. 1963, Astron. Zhurn. 40, 401, in Russian (= Soviet Astronomy AJ 7, 311)
Gnevyshev, M.N. 1967, Solar Phys. 1, 107
Ivanov, E.V. 1995, Izv. RAN, ser. phys. 59, 29, in Russian
Krainev, M.B., et al. 1983a, Proc.18th ICRC (Bangalore) 3, 23
Krainev, M.B., et al. 1983b, Proc.18th ICRC (Bangalore) 3, 95
Krainev, M.B. 1991, Izv. Akad. Nauk SSSR, ser. phys. 55, 1942, in Russian
Moraal, H. 1975, Proc 14th ICRC (Munich) 11, 3896
Popielawska, B. 1992, Planet. Space Sci. 40, 811
Storini, M. 1995, Adv. Space Res. 16, (9)51
Storini, M., & Pase, S. 1995, in: Watanabe, T., (ed.), Proc. 2nd SOLTIP Symp., STEP GBRSC News 5,
Special Issue, 255
Storini, M., et al. 1997, Solar Phys. 172, 317


The Gnevyshev Gap Effect in Galactic Cosmic Rays

http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=897558294DDD84E10645C012FD258785?doi=10.1.1.1037.5572&rep=rep1&type=pdf

The Gnevyshev Gap Effect in Galactic Cosmic Rays

Abstract

Similar works

Full text

Available Versions

CiteSeerX