Yu. R. Rivin and L. I. Gromova
Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation, Troitsk, Russia
The current knowledge on plasma flows from the Sun (these flows will below be called solar wind, the definition being broader than the Parker [1976] definition which referred to the plasma flow related only to the corona hydrodynamical expansion into the interplanetary space: quiet solar wind with a velocity of 300 km s ^{-1} ) shows that the flows are rather complicated formations which are influenced by the variations of the large-scale solar magnetic fields including the cyclic variation with T 11 years. The variation of the annual dynamical parameters of the solar wind (SW) and also "frozen" into it interplanetary magnetic field (IMF, B_{I} ) are below analyzed from these positions. The relation (different for different parameters) between the cyclic variations of the solar magnetic fields and interplanetary medium parameters is demonstrated, and some features of the experimental data in the King catalogue which complicate their analysis are indicated.
Figure 1 |
Figure 2 |
(1) |
where V const, and in the following consideration the main attention should be paid only to analyzes of V and n.
Figure 3 |
Figure 1b shows (smoothed by the same L ) curves of the annual values of: (1) the Wolf numbers ( W ) as the characteristic of the cyclic variation of the toroidal component of the solar magnetic field ^{1}B generated above the basic of the convective zone, and (2) the magnitude of the radial component of the large-scale magnetic field B_{R}, ^{2}B generated within the basis of the convective zone, and the field of the Sun as a star |B_{s}| which plays a determining role in processes in the interplanetary medium. Obridko and Rivin [1996] and Rivin [1998a, 1998b, 1999a, 1999b] discussed these characteristics in detail and called the former and latter fields dipole and quadrupole, respectively. A complete comparison of the cycles of these magnetic fields with the interplanetary medium parameters is difficult because of the short series of observations (2-3 cycles). However to distinguish cycles of various fields, the difference in their amplitude modulation was taken into account: for B_{R} the amplitude of cycle 22 is several times lower than the amplitude of cycle 21, for W and B_{s} the amplitudes in both cycles are approximately equal, or the amplitude of B_{s} is even slightly higher in cycle 22. These differences and also the phase variations are used in the interpretation below.
Figure 4 |
Figure 5 |
1. In the main dynamical parameters of SW there exists a ~11-year cycle which is mainly in antiphase to the cyclic variations of B_{R} . Its amplitude decreases in n and V from cycle 20 to cycle 22 and the spectral amplitude exceeds by several times the amplitudes of other harmonics including the harmonics with T 22 years.
2. The cycle with T 11 years in the data on V is additionally shifted in phase by 2-3 years (it lags) relative the cycle of B_{R} , that is, by ~3-4 years relative to the W cycle. Its spectral amplitude for 3 cycles is ~20 km s^{-1} and that is only slightly higher than s .
3. The properties of the ~11-year cycle in n till the beginning of the 1970s are considerably different from the properties of the following two cycles (on the n-W plane in Figure 3 the data for the years before the beginning of the 1970s form such a point distribution which is approximated by a straight line having essentially different coefficients than those for the following cycles). That requires individual consideration of this parameter before and after the years indicated. It is possible that this difference is the cause of the distortion of the n and nV spectra in Figure 3. The cycle of the plasma density according to the data from 1971 (practically after the doubtful interval) occurs strictly in antiphase to the B_{R} cycle without any delays. Its approximate average amplitude is 0.5-1 cm ^{-3} that is close to s as in case of the SW velocity.
Hence some properties of the n and V cycles (properties 1-3) correspond to the properties of the cycles of the ^{2}B magnetic field. However, it is possible that the correlation is still more informative at the n-W plane than at the n- B_{R} plane.
More than 30 years ago Severnyy [1966] suggested that the interplanetary magnetic field is a continuation of the total magnetic field of the Sun B_{s} into the interplanetary space and proposed observations of this solar field as a field of a star for diagnostics of IMF variations. The modern experimental data on the |B_{z}| and B_{s} 11-year cycles support this suggestion.
Figure 6 |
Figure 7 |
Figure 7 shows variations of the modules of the IMF vector and components and also variations of the solar magnetic fields. Here the identity of the variations of the vector and its components with the variations of B_{s} is already visually seen.
Figure 8 |
1. The amplitude attenuation of the cyclic variation of the modulus of the total magnetic field of the Sun near the Earth is a factor of 2 10^{4}.
2. The amplitude of the ~11-year cycle of IMF increases from cycle 20 to cycle 22 and is approximately equal in cycles 21 and 22 (even is slightly higher in the latter), this fact being principally different from the amplitude modulation of the V and n cycles.
3. No phase shifts between the B_{I} and B_{s} cycles were discovered.
4. The cyclic variation of the modulus of the total magnetic field of the Sun ( B_{s} ) is the main source of the cyclic variation of IMF.
5. The variations of the initial annual values of B_{I} and its components do not contain explicitly expressed cyclisity with T 11-22 years. The best correlation is detected between the phase of the total solar magnetic field variation with the B_{y} component of the interplanetary magnetic field.
6. The scatter of points relative the approximating line in Figure 8 has a tendency to be lower in the middle part of the cycle and to increase in the epochs of its extremes.
The cyclic variation of B_{s} contains a superposition of the |^{1}B| and |^{2}B| magnetic fields; the |^{1}B_{s}| input prevails in the amplitude variations and the |^{2}B_{s}| input is manifested in the phase shift of the B_{s} cycle relative the W cycle by 1-2 years [Rivin, 1998b, 1999a, 1999b]. The corresponding properties of the cyclisity of the solar magnetic fields are "inherited" by the modulus of the interplanetary magnetic field, that is, the variations of B_{I} with T 11 years are on the whole identical to similar variations of B_{s} . At the same time the variations of the B_{y} and B_{x} (the latter in antiphase) components of the initial IMF correspond to the variations of B_{s}.
It is principally important and in some way unexpected that the cyclic variations of the two main dynamic parameters of SW, probably first, differ from the variations of B_{I} and, second, have somewhat different properties: the phase of the V cycle is shifted by ~3 year relative the phase of the W cycle, whereas the phase of the n cycle coincides with the phase of the |^{2}B_{s}| magnetic field cycle. Probably, this difference indicates similar but slightly different formation sources of the cycles of these two parameters. At the same time the amplitude attenuation of the cycles of both parameters shows that probably the field |^{2}B_{s}| influences each of them more than the |^{1}B_{s}| field, that is, the plasma has a much deeper origin.
Annual mean values of n before the early 1970s are systematically underestimated by 3-4 cm ^{-3}. It follows from the " n-W " plot (Figure 4) that this underestimation is not caused by random errors. It is not yet clear whether it manifests a systematic error in the n determination in King catalogue for the corresponding year or has some physical sense. The results of this paper correct partially the assumptions (made by Rivin [1989] earlier) on the cyclisity nature of the interplanetary medium parameters varying with T 11 years.
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