Cosmic ray modulation during solar cycle 22: Solar maximum loops at earth and global transients in the heliosphere

Abstract

Neutron monitor data from two pairs of cosmic ray stations, Kiel/Tsumeb and Climax/Huancayo, are used to study the rigidity dependence of solar modulation during the solar activity cycle 22. The long-term decrease of cosmic ray intensity during the ascending phase of cycle 22 is characterized by the same rigidity dependence as for the long-term recovery during the descending phase of cycle 21. This is equivalent to a lack of any significant spectral hysteresis in cosmic ray modulation for both half cycles surrounding the 1987 cosmic ray maximum. The above is true at least for 27-day averages of cosmic ray intemity and at neutron monitor rigidities. In December 1988 the first large Forbush decrease of cycle 22 marked the beginning of increased solar activity which resulted in several prominent interplanetary shocks in 1989-1991. These strong hellospheric disturbances produced global merged interaction regions (GMIRs) which were responsible for large step decreases in cosmic ray intemity seen at all spacecraft throughout the hellosphere, including Voyager 2, Pioneer 10 and 11, as well as Voyager 1. It was found that in the neutron monitor rigidity range, such decreases were followed by rigidity-dependent recoveries. The rigiditydependent recovery manifests itself by formation of hysteresis loops on correlation plots for low-versus high-rigidity cosmic ray intemity changes. The loops, if completed, close approximately at the modulation level from which the corresponding step decrease started. On the other hand, the current long-term cosmic ray recovery (starting from Barrels solar rotation 2162) follows the "normal" rigidity dependence characteristic of both the A>0 recoveries and A<0 decreases/recoveries (where A<0 and A>0 are two different phases of the solar magnetic cycle). All this together confirms the bimodal character of cosmic ray modulation for 1985-1992, the same as found previously for cycles 19-21; the transient modulation (T_--0.5 to -1 year) related to GMIRs is accompanied on recovery by the phenomenon of hysteresis, while the long-term modulation (T>I year) is hysteresis free. The two explanatiom of the phenomenon of spectral hysteresis proposed in the literature, i.e., a time-dependent modulation via convection, diffusion, and drift effects and an acceleration of a normal cosmic ray spectrum in multiple shocks in the outer hellosphere (as proposed by Stoker and Moraal (1986)), are discussed in the context of the presented cosmic ray data. IntroductionOne of the outstanding problems in cosmic ray physics is the identification of processes responsible for the l 1-year variation of galactic cosmic rays. The rapid progress in this field which has taken place in the last several years is related to the availability of information on the solar wind plasma, magnetic field, and energetic particles accumulated from Voyager 1 and 2, Pioneer 10 and 11, and other space probes throughout nearly two solar cycles in the inner and outer hellosphere. Burlaga et al. [1984], using data from Voyager 1 and 2 for 1977-19...

Cross correlation and time-lag between cosmic ray intensity and solar activity during solar cycles 21, 22 and 23

“…Long-term cosmic ray observations by means of neutron monitors now allow us to distinguish modulation effects related to the 22-year solar magnetic cycle from effects due to the 11-year solar activity cycle. Popielawska and others [Pop95] [Pop92] have reported a positive correlation when studying the variations of solar cycles of around 11 years and cycles of magnetic activity of around 22 years using observations of a pair of Climax 1 -Huancayo 2 and confirmed for Kiel 3 -Tsumeb 4 neutron detectors with different cutoff rigidity, latitudes and longitudes, observing a relation of dependence between the variations of solar cycles and magnetic cycles associated with polarity changes of the latter. The final goal was to get an idea about the modulation of cosmic rays and other fundamental characteristics of cosmic rays.…”

Solar Cycle Variation of Cosmic ray Intensity along with Interplanetary and Solar Wind Plasma Parameters

“…Barbara Popielawska [18] used the neutron monitor data from two pairs of cosmic ray stations, Kiel/Tsumeb and Climax/Huancayo, to study the rigidity dependence of solar modulation during the solar activity cycle 22. She noticed that a long-term decrease in the cosmic ray intensity during the ascending phase of cycle 22 is characterized by the same rigidity dependence as for the long-term recovery during the descending phase of cycle 21.…”