On the GCR intensity and the inversion of the heliospheric magnetic field during the periods of the high solar activity
aa r X i v : . [ a s t r o - ph . S R ] N ov ND I NTERNATIONAL C OSMIC R AY C ONFERENCE , R
IO DE J ANEIRO T HE A STROPARTICLE P HYSICS C ONFERENCE
On the GCR intensity and the inversion of the heliospheric magnetic fieldduring the periods of the high solar activity K RAINEV
M.B., K
ALININ
M.S.
Lebedev Physical Institute, Russian Academy of Sciences, Moscow, Russia [email protected]
Abstract:
We consider the long-term behavior of the solar and heliospheric parameters and the GCR intensityin the periods of high solar activity and the inversions of heliospheric magnetic field (HMF). The classification ofthe HMF polarity structures and the meaning of the HMF inversion are discussed. The procedure is consideredhow to use the known HMF polarity distribution for the GCR intensity modeling during the periods of highsolar activity. We also briefly discuss the development and the nearest future of the sunspot activity and the GCRintensity in the current unusual solar cycle 24.
Keywords:
GCR intensity, Gnevyshev Gap, energy hysteresis, inversions of the solar and heliospheric magneticfields, solar maxima, unusual solar cycle 24
There are several interesting features in the solar activity,heliospheric characteristics and the GCR intensity in themaximum phase of the solar cycle. First, the sunspot areaand the HMF strength are at their highest levels duringthese periods and both demonstrate the two–peak struc-ture with the Gnevyshev Gap between the peaks (see [1, 2]and references therein). Second, the inversion of the high–latitude solar magnetic fields (SMF) occurs in this phase[3, 4] and it changes the distribution of the HMF polar-ity in the heliosphere. Third, as the GCR intensity in gen-eral anticorrelates with the sunspot area and HMF strength,this intensity is rather low in these periods and it demon-strates the two–gap structure corresponding to the the two–peak structure of the sunspot area and HMF strength withsomewhat different behavior for the low and high energyparticles (the energy hysteresis, see [5, 6] and referencestherein). Note that these phenomena can be very specificin the maximum phase of the current unusual solar cycle(SC) 24.The LPI cosmic–ray group has been studying the com-plex of these phenomena for more than 40 years, tradition-ally connecting the GCR intensity behavior with the SMFinversion (see [7, 8, 9, 10, 11, 6] among others). It is suf-fice to mention that the first papers on the possible SMF in-fluence on the GCR intensity were [7] and [8] dealing withthe energy hysteresis.In this paper we first reanimate an old scenario of ourson the long-term behavior of the solar and heliospheric pa-rameters and the GCR intensity and correlation betweenthem in the periods of high solar activity and the inversionsof the large–scale SMF. Then we discuss the classificationof the HMF polarity structures in order to clarify the mean-ing of the HMF inversion and consider how to model theGCR behavior in these periods. Finally we discuss the de-velopment of the current SC 24 and the maximum sunspotarea and minimum GCR intensity which could be expectedin the near future.
In Fig. 1 the time profiles of all related characteristicsare shown for the last 40 years. The data on the sunspotarea S ss [12], the HMF strength near the Earth B HMF [13] and the SMF characteristics (the quasi–tilt a qt ofthe heliospheric current sheet (HCS), the high–latitudeSMF B polls and the sets of the spherical harmonic co-efficients (cid:8) g l , m , h l , m (cid:9) for the Wilcox Solar Observatory(WSO) model) [14] are used. As a low energy GCR datawe use the results of our stratospheric regular balloonmonitoring (RBM): the difference between the count ratesof the omnidirectional counter in the Pfotzer maximumin Murmansk N MuRBM (cutoff rigidity R c ≈ . N MoRBM ( R c ≈ . T e f f ≈ S ss and B HMF and corresponding double-gap signature in theGCR intensity. This phenomenon was called GnevyshevGap in [1] and was extensively studied (see [2, 6] and ref-erences therein). In [2] we came to the conclusion that thedouble peak structures during solar maxima are due to thesuperposition of the 11-year cycle and quasi-biennial oscil-lations. However, note that the Gnevyshev gaps usually co-incide or occur just after the inversions of the high–latitudeSMF shown in Fig. 1 (b) so there could be some physicalconnection between these two phenomena. In Fig. 1 (c) thequasi–tilt a CS (classic) is shown as well as the four horizon-tal lines illustrating the suggested classification of the peri-ods with respect to the HMF polarity (see next section).Another GCR effect specific for the maximum phaseof solar cycle and also seen in Fig. 1 (d) is the energyhysteresis. The difference between the time profiles of thelow energy intensity and high energy intensity (regressedto the low energy one) clearly demonstrates the magneticcycle. If expressed as a hysteresis loop in the regressionplot, the area of the loop is much greater for the even solarcycle. CR intensity and the inversion of the HMF33 ND I NTERNATIONAL C OSMIC R AY C ONFERENCE , R
IO DE J ANEIRO
Figure 1 : The solar activity, heliospheric parameters andGCR intensity in 1975–2013. The periods of low solaractivity are shaded and the HMF polarity A and the mo-ments of the sunspot maxima are indicated above the pan-els. All data are yearly smoothed. In the panels: (a) the to-tal sunspot area S ss (red) and the HMF strength near theEarth B HMF (blue). The moments of two (for each cycle ex-cept SC 24) Gnevyshev gaps in S ss are shown by the verti-cal dash–dot lines in the panels (a) and (d); (b) the line–of–sign components of the high–latitude photospheric SMF inthe N (red) and S (blue) hemispheres; (c) the HCS quasi–tilt (black) and the classification of the periods with respectto the HMF polarity states (red and blue sections of fourhorizontal lines in the upper part of the panel, see the nextsection); (d) the low energy GCR intensity normalized to100% in 1987 (red) and the high energy intensity (blue) forthe periods of high solar activity regressed to that for thelow energies by the the linear regression in the periods in-dicated by the horizontal blue lines near the time axis.In [9] we isolated two stages in the GCR intensity behav-ior in the maximum phase of solar cycle: 1) the first partof hysteresis connected with the postulated attenuation of B HMF during the HMF inversion and not dependant on thecharge q of the GCR particle and the type of the inversion( (cid:181) dA / dt ) where A is the dominant HMF polarity (the signof B HMFr in the north heliospheric hemisphere); and 2) thesecond part of hysteresis delayed with respect to the firststage by 1–2 years and dependant on the sign of q · dA / dt .Now this scenario looks rather attractive for us if we con-nect the two above stages with two gaps in the double-gapstructure of the GCR intensity and relate the postulated at-tenuation of B HMF with GG in this characteristic for thefirst stage while for the second stage substitute the sign of dA / dt for the sign of A itself (because of the ”dipole” typeof the HMF polarity distribution in this period, see the nextsection).However, note that the magnitude of the discordancebetween the low and high energy GCR intensities during the first gap in the GCR intensity appears to be muchgreater for the even solar cycle 22 than for the odd SC21 and 23 which looks as the dependence on A or, rather, dA / dt during the first stage. Certainly the choice of theregression period is very important and can change thefeatures of the energy hysteresis. On the other hand theabove feature can be due the fact that the reduction of B HMF is also much stronger for the even SC 22 than forthe odd SC 21 and 23.
If we discuss the GCR behavior during the inversion ofthe HMF polarity, we usually keep in mind the reversalof the radial components B polls of the high–latitude large–scale SMF. However, the SMF does not directly influencethe GCR intensity and to understand and model the GCRintensity during such a period one should have some modelon what is going on with the HMF polarity distribution.The main source of our notions on this distribution is theWSO model which can estimate B ssr on the source surface r ss = ( . ÷ . ) r Sun in two variants of the inner bound-ary conditions: fixing from observations B phls (classic) or B phr (radial) photospheric SMF components, see [19] andreferences therein. So calculating B ssr then finding isolines B ssr = N CR = ÷ g , in the sets ofthe spherical harmonic coefficients. So the four cases ofthe HMF polarity distribution for each Carrington rotationwere calculated. The corresponding classification of thetime periods with respect to the HMF polarity distributionare shown as four horizontal lines in the upper part of Fig.1 (c) (classic– g , =
0, classic– g , = g , = g , = B ssr is notproperly estimated in the WSO model, so correspondencebetween the magnitude and shades is not shown in Fig. 2and we discuss only the number and forms of their HCSs.The upper panel of Fig. 2 illustrates the type of the HMFpolarity distribution which we call the ”dipole” type char-acterized by the only and global HCS, that is HCS connect-ing all longitudes. This is the most common type of theHMF polarity distribution ( ≈
80% of all time) both with A < A >
0. Inthe middle panel of Fig. 2 another type of the HMF polaritydistribution is shown which we call the ”transition dipole”type and which is also characterized by the global HCS butbeside it one (as in the middle panel of Fig. 2) or severalother HCSs exist. This type is less common ( ≈ A < A >
0. Finally we call the ”inversion” type the third typeof the HMF polarity distribution illustrated in the lowerpanel of Fig. 2. It is characterized by the absence of theglobal HCS with several nonglobal HCSs (or even none
CR intensity and the inversion of the HMF33 ND I NTERNATIONAL C OSMIC R AY C ONFERENCE , R
IO DE J ANEIRO
Figure 2 : Three main types of the HMF polarity distribu-tion. The thick solid lines are for the HCSs. The color (redfor positive and blue for negative) stands for the HMF po-larity while and its shades designate the magnitude of B ssr .at all which is common for the cases with the monopolespherical harmonic coefficient). This type is also much lesscommon than the ”dipole” type ( ≈ A ; 2) the ”transition dipole” periods limited by theCarrington rotations with this type of the HMF polarity dis-tribution also of the same dominating polarity A ; and 3)the ”inversion” periods limited by the Carrington rotationswith this type. These types of periods are marked by thedifferently colored sections of the horizontal lines in theupper part of Fig. 1 (c): the ”dipole” periods by the darkred (for A >
0) or dark blue ( A <
0) sections; the ”transi-tion dipole” periods by the light red ( A >
0) or light blue( A <
0) sections; and the ”inversion” periods are depicted by the black sections.One can see in Fig. 1 that the ”dipole” period is charac-teristic for the low solar activity and its only HCS can becharacterized by its waviness or quasi–tilt a qt < ≈
40 deg(for the classic variant of the WSO model). The ”transitiondipole” period is characteristic for the intermediate solaractivity and it corresponds to intermediate waviness of theHCS ( ≈ < a qt < ≈
60 deg.), but the quasi–tilt formallydefined as a half of the heliolatitude range of all HSCs isuseless for the calculation of the drift magnetic velocityand the GCR intensity modeling. Finally, the ”inversion”period is characteristic for the periods of maximum solaractivity and the high–latitude SMF inversions and the for-mally defined quasi–tilt ( a qt > ≈
60 deg) is also useless.As can be seen in Fig. 1 (c) for the fast and synchronousin the N– and S–hemispheres SMF inversions (as in SC21) the HMF inversion period is also short, while for theprolonged and nonsynchronous SMF inversions (as in SC22 and 23) the HMF inversion periods are also longer.In general the HMF inversion periods are centered withtheir SMF counterparts and approximately coincide withthe Gnevyshev Gap in the sunspot area and HMF strength.Usually the HMF inversion periods are surrounded bycomparable–sized ”transition dipole” periods. During themain part of solar cycle the HMF polarity distribution is”dipole”–like. This dipole period is asymmetrical with re-spect to the moment t GCRmax of the maximum of the GCR in-tensity, (approximately t GCRmax − < t , years < t GCRmax + . t GCRmax . This fact is importantas the magnetic drift is usually considered significant onlyin the periods around solar minima [18].So for the phase of the low sunspot activity with the”dipole” type of the HMF polarity distribution the GCRintensity can be calculated using the transport equationwith the usual magnetic drift velocity terms (e. g., uti-lizing the tilted-CS model with a tilt a t as a parame-ter) and getting a t as the quasi–tilt a qt from [14]. How-ever, how to get these terms for the high sunspot activityphase with the ”transition dipole” and ”inversion” typesof the HMF polarity distributions, when there are several(or none) HCSs and the formally defined quasi–tilt is use-less? As in [20] the regular 3D HMF can be representedas ~ B ( r , J , j ) = F ( r , J , j ) ~ B m ( r , J , j ) , where ~ B m is theunipolar (or “monopolar”) magnetic field and the HMF po-larity F is a scalar function equal to + − F ( r , J , j , t ) =
0. Then the 3D particle drift velocity is ~ V d = pv / q h (cid:209) × ( ~ B / B ) i , [21], where v and q are theparticle speed and charge, respectively. One can decom-pose the drift velocity into the regular and current sheet ve-locities: ~ V d , reg = pv / q F h (cid:209) × ( ~ B m / B ) i (1) ~ V d , cs = pv / q h (cid:209) F × ( ~ B m / B ) i . (2)So to get the magnetic drift velocities for any type ofthe HMF polarity distribution one needs only F and (cid:209) F or in 2D case F and dF / d J , where F is the HMF polar-ity F averaged over the longitude. All of these quantities( F , (cid:209) F , F , dF / d J ) can be calculated numerically for anycalculated HMF polarity distribution. Note that the funda-mental difference between the global and nonglobal HCS CR intensity and the inversion of the HMF33 ND I NTERNATIONAL C OSMIC R AY C ONFERENCE , R
IO DE J ANEIRO is in the fact that the sign of the radial component of thecurrent sheet drift changes as the particle moves along thenonglobal HCS, so that the connection between the innerand outer heliosphere is blocked.
For the current SC 24 the ”dipole” period ended in thebeginning of 2011. For the classic cases the ”transitiondipole” period ended in the beginning of 2012 while for theradial cases there is no such period. So in the current solarcycle the HMF inversion started well before both the SMFinversion and the first peak in the S ss and B HMF (02.2012;the only peak of the double–peak structure). Neither gapsnor energy hysteresis are observed in the GCR intensity upto now. In the beginning of 2013 we are still in the middleof the HMF inversion. This unusual features of the currentHMF inversion are probably connected with the unusuallylow solar and heliospheric activity in the last two solarcycles.As one can see from panels (a) and (b) of Fig. 1 boththe sunspot and high–latitude solar activity and the HMFstrength are very low during the ascending phase of SC 23and the minimum 23/24 between SC 23 and 24. As a resultthe GCR intensity in the minimum 23/24 is the highestever measured (see [22, 23, 24]) and its current value isstill much higher than in the maxima of the previous solarcycles.However, in the documented history of the solar charac-teristics there were long periods of the high (global max-ima) and low (global minima) sunspot activity [25], andthe cycles of the second half of the last century belong to socalled Modern maximum. As we demonstrated in [26] upto now the sunspot area in SC 24 is much lower than it wasin the cycles of the Modern maximum but much greaterthan in the Maunder and even Dalton minima. In general itcorresponds to the Glaisberg minimum in the first decadesof the last century. Using the regression between the valuesof both characteristics in the first regression points and inthe maximum of the previous solar cycles we managed toestimate the maximum S M ss and minimum J M expectedfor the maximum of SC 24 and came to the conclusion thatin SC 24 the maximum sunspot area can be of the highestvalues for the Glaisberg minimum (SC 14–16). As to theGCR intensity, our upper estimate of J M indicates that inSC 24 the minimum GCR intensity can be slightly higherthan in SC 20, 21, 23.As we stated in [26] up to 2012 the development of SC24 in the N–hemisphere was like in the ”Modern Maxi-mum” (SC 17–23), while that in the S–hemisphere moreclosely resembled the Dalton minimum (SC 5–7). Duringthe last year (2012) the sunspot area in the N–hemispheredecreased while that in the S–hemisphere increased and ifthe sunspot activity in the S–hemisphere overtakes that inthe N–hemisphere during the maximum phase of solar cy-cle (as is often the case) then a lot depends on the activityin the south solar hemisphere in the nearest future.
1. The two–stage scenario of the main characteristic fea-tures of the GCR intensity behavior in the maximum phaseof solar cycle is suggested: 1) the first gap of double–gapstructure and the first part of hysteresis occur during the in- version of the heliospheric magnetic field while 2) the sec-ond gap and the second part of hysteresis proceeds duringthe periods characterized by the ”dipole” type of the HMFpolarity distribution leading to the magnetic cycle in theGCR intensity.2. We isolate three main types of the HMF polarity distri-bution: 1) the ”dipole” type with the only and global HCScharacteristic for the periods of the low solar activity; 2)the ”transition dipole” type with the global HCS and sev-eral other HCSs characteristic for the periods of the inter-mediate solar activity and 3) the ”inversion” type with theabsence of the global HCS characteristic for the periods ofHMF inversion. The simple procedure to get the magneticdrift velocities from the calculated HMF polarity distribu-tion is discussed.3. The comparison of the current solar cycle 24 in thesunspot activity and GCR intensity with the past solar cy-cles shows that sunspot activity corresponds to the Glais-berg minimum in the first decades of the last century whilethe GCR intensity is slightly higher than in previous so-lar cycles. The estimation is made of the sunspot area andGCR intensity expected for the maximum of SC 24. Thenearest future of the SC 24 depends on the activity in thesouth solar hemisphere.
Acknowledgment:
We thank the Russian Foundation forBasic Research (grants 11-02-00095a, 12-02-00215a, 13-02-00585a, 13-02-10006k) and the Program ”Fundamental Proper-ties of Matter and Astrophysics” of the Presidium of the RussianAcademy of Sciences.
References [1] M. Storini and A. Felici, Nuovo Cimento 17C (1994) 697.[2] G.A. Bazilevskaya et al. Solar Phys. 197 (2000) 157-174.[3] R. Howard, Solar Physics 38 (1974) 283.[4] V.I. Makarov and V.V. Makarova, Solar Physics 163 (1996)267.[5] H. Moraal, Proc. 14th ICRC 11 (1975) 3896-3906.[6] M.B. Krainev and G.A. Bazilevskaya, Advances in SpaceResearch 35 (2005) 2124-2128.[7] A.N. Charakhchyan et al., Proc. 13th ICRC 2( 1973)1159-1164.[8] S.N. Vernov et al., proc. 14th ICRC 3 (1975) 1015.[9] M.B. Krainev et al., Proc. 19th ICRC 4 (1985) 481-484.[10] G.A. Bazilevskaya et al., Advances Space Research 9(1995) 227-231.[11] M.B. Krainev et al., Proc. 26th ICRC 7 (1999) 155-158.[12] http://solarscience.msfc.nasa.gov/greenwch.shtml [13] ftp://omniweb.gsfc.nasa.gov/pub/data/omni [14] http://wso.stanford.edu/ [15] G.A. Bazilevskaya, A.K. Svirzhevskaya, Space ScienceReviews 85 (1998) 431-521.[16] Yu.I. Stozhkov et al., Lebedev Physical Institute, Preprint14 (2007)[17] http://helios.izmiran.rssi.ru/cosray/days.htmhttp://helios.izmiran.rssi.ru/cosray/days.htm