Minimum Epoch Of Solar Activity Research Articles

The Algorithm of the Two Neutron Monitors for the Analysis of the Rigidity Spectrum Variations of Galactic Cosmic Ray Intensity Flux in Solar Cycle 24

The method of the two neutron monitors was used to analyze the parameters of the rigidity spectrum variations (RSV) of galactic cosmic ray intensity (GCR) flux in solar cycle 24 based on the data from the global network of neutron monitors. This method is an alternative to the least squares method when there are few monitors working stably in a given period, and their use in the least squares method is impossible. Analyses of the changes in exponent γ in the RSV of GCR flux from 2009 to 2019 were studied. The soft RSV (γ = 1.2–1.3) of the GCR flux around the maximum epoch and the hard RSV (γ = 0.6–0.9) around the minimum epoch of solar activity (SA) is the general feature of GCR modulation in the GeV energy scale (5, 50), to which neutron monitors were found to correspond. Therefore, various values of the RSV γ in the considered period show that during the decrease and increase period of SA, the essential changes in the large-scale structure of the heliospheric magnetic field (HMF) fluctuations/turbulence take place. The exponent γ of the RSV of the GCR flux can be considered a significant parameter to investigate the long-period changes in the GCR flux.

Theoretical and Experimental Studies of the Rigidity Spectrum of the 27-Day Variation of the Galactic Cosmic Ray Intensity in Different Epochs of Solar Activity

We consider the recent, very exceptional, 11-year cycle (2003 – 2009) of solar activity and confirm that the relative amplitude in rigidity spectrum, δD(R)/D(R), which can be approximated by a power law in rigidity R, of the first three harmonics of the 27-day variation of the galactic cosmic ray (GCR) intensity is hard in the maximum and soft in the minimum epochs of solar activity, as was found by neutron monitor data for the period of 1965 – 2002. This property is seen not only in separate minimum and maximum epochs but in individual intervals of a solar Carrington rotation as well: There exist many individual intervals of solar rotation when the expected rigidity spectrum of the 27-day variation of the GCR intensity indeed is hard in the maximum epoch of solar activity and is soft in the minimum epoch. We then construct a three-dimensional model of the 27-day variation of the GCR intensity based on Parker’s transport equation, by implementing in situ measurements of the changes in heliographic longitude of the solar wind velocity and interplanetary magnetic field for different epochs of solar activity.

Three dimensional model of the interplanetary magnetic field and 27-day variation of the galactic cosmic ray intensity

We present a model of the 27-day variation of the galactic cosmic ray (GCR) intensity for three dimensional (3-D) heliosphere with the heliolongitudinal and heliolati- tudinal dependent radial solar wind speed for the period of 1995 - minimum epoch of solar activity (A > 0). In the present model we implement heliolongitudinal asymmetry of solar wind velocity reproducing as the sum of first and sec- ond harmonics depending on the heliolatitudes and the reg- ular part of the solar wind velocity (V0) changing versus he- liolatitudes in accord to in situ measurements of the Ulysses spacecraft. We show that the range of changes of the sum of the first and second harmonics of the 27-day variation of the GCR intensity for Kiel neutron monitor is little less than expected from the modelling, however, they are comparable. equations with the heliolongitudinally dependent solar wind velocity reproducing in situ observations. In spite, in situ measurements are an unique information which should be considered as a basic data in any type of modelling. This paper is a continuation of study presented in Alania et al. (2010) tending to construct a 3-D model of the 27-day vari- ation of the GCR intensity being able in certain scope to

Dependence of the 27-day variation of cosmic rays on the global magnetic field of the Sun

We show that the higher range of the heliolongitudinal asymmetry of the solar wind speed in the positive polarity period (A>0) than in the negative polarity period (A<0) is one of the important reasons of the larger amplitudes of the 27-day variation of the galactic cosmic ray (GCR) intensity in the period of 1995–1997 (A>0) than in 1985–1987 (A<0). Subsequently, different ranges of the heliolongitudinal asymmetry of the solar wind speed jointly with equally important corresponding drift effect are general causes of the polarity dependence of the amplitudes of the 27-day variation of the GCR intensity. At the same time, we show that the polarity dependence is feeble for the last unusual minimum epoch of solar activity 2007–2009 (A<0); the amplitude of the 27-day variation of the GCR intensity shows only a tendency of the polarity dependence. We present a three dimensional (3-D) model of the 27-day variation of GCR based on the Parker’s transport equation. In the 3-D model is implemented a longitudinal variation of the solar wind speed reproducing in situ measurements and corresponding divergence-free interplanetary magnetic field (IMF) derived from the Maxwell’s equations. We show that results of the proposed 3-D modeling of the 27-day variation of GCR intensity for different polarities of the solar magnetic cycle are in good agreement with the neutron monitors experimental data. To reach a compatibility of the theoretical modeling with observations for the last minimum epoch of solar activity 2007–2009 (A<0) a parallel diffusion coefficient was increased by ∼40%.

27-day variations of the galactic cosmic ray intensity and anisotropy in the minimum of the 23rd solar activity cycle

We study the 27-day variations of the solar wind velocity, galactic cosmic ray (GCR) intensity and anisotropy in the last minimum epoch of solar activity (2007–2009, A<0). The average amplitude of the 27-day variation of the galactic cosmic ray anisotropy (A27A) in the current minimum epoch of solar activity (2007–2009, A<0) is lesser than in previous positive polarity period as it is expected from the drift theory. So, polarity dependence rule for the 27-day variation of the GCR anisotropy is fully kept. It is a universal principle for the amplitudes of the 27-day variation of the GCR anisotropy. At the same time, the average amplitude of the 27-day variation of the GCR intensity (A27I) remains at the same level as for previous minimum epoch 1995–1997 (A>0) showing by the same token an violation of its polarity dependence rule established earlier. We assume that this phenomenon could be generally related with the well established 27-day variation of the solar wind velocity being in anti-correlation with the similar changes of the 27-day variation of the GCR intensity. Generally, a character of the heliolongitudinal asymmetry of spatial large-scale structure of the solar wind velocity (SWV) established in the recent minimum epoch, preferentially pronounces in the behavior of the 27-day variation of the GCR intensity than anisotropy. The formation of the 27-day variation of the GCR anisotropy preferentially takes place in a restricted disk like local vicinity in the helioequatorial region, whilst the 27-day variation of the GCR intensity is formed in the global three dimensional vicinity of the heliosphere.

On the Relationship of the 27-day Variations of the Solar Wind Velocity and Galactic Cosmic Ray Intensity in Minimum Epoch of Solar Activity

We study the relationship of the 27-day variations of the galactic cosmic ray intensity with similar variations of the solar wind velocity and the interplanetary magnetic field based on observational data for the Bartels rotation period # 2379 of 23 November 2007 – 19 December 2007. We develop a three-dimensional (3-D) model of the 27-day variation of galactic cosmic ray intensity based on the heliolongitudinally dependent solar wind velocity. A consistent, divergence-free interplanetary magnetic field is derived by solving Maxwell’s equations with a heliolongitudinally dependent 27-day variation of the solar wind velocity reproducing in situ observations. We consider two types of 3-D models of the 27-day variation of galactic cosmic ray intensity, i) with a plane heliospheric neutral sheet, and ii) with the sector structure of the interplanetary magnetic field. The theoretical calculations show that the sector structure does not significantly influence the 27-day variation of galactic cosmic ray intensity, as had been shown before, based on observational data. Furthermore, good agreement is found between the time profiles of the theoretically expected and experimentally obtained first harmonic waves of the 27-day variation of the galactic cosmic ray intensity (with a correlation coefficient of 0.98±0.02). The expected 27-day variation of the galactic cosmic ray intensity is inversely correlated with the modulation parameter ζ (with a correlation coefficient of −0.91±0.05), which is proportional to the product of the solar wind velocity V and the strength of the interplanetary magnetic field B (ζ∼VB). The high anticorrelation between these quantities indicates that the predicted 27-day variation of the galactic cosmic ray intensity mainly is caused by this basic modulation effect.

A model of the long period Galactic Cosmic Ray variations

We develop a two-dimensional (2-D) time dependent model of the long period variation of Galactic Cosmic Ray (GCR) intensity. Besides the well-known fundamental processes responsible for the modulation of GCR intensity, we implement the following in the model: the parameters characterizing temporal changes in the exponent ν of the Power Spectral Density (PSD) of the Interplanetary Magnetic Field (IMF) turbulence, the modulus B of the IMF, the tilt angle δ of the Heliospheric Neutral Sheet (HNS), and changes in the drift effect of the GCR particles upon solar activity. We assume that the drift effect of the GCR particles has the maximal value in the minimum epoch of solar activity, when drift dominates, and that it has the minimal value in the maximum epoch, when diffusion dominates. We show that an acceptable compatibility is maintained for the period between 1976 and 1987 (solar cycle #21), when the expected temporal changes in the GCR particle density are shifted, as regards the temporal changes of the smoothed experimental data on the GCR intensity, for 18 months. We consider a delay time ∼18 months as an effective delay time caused by the combined influence of all parameters implemented in the 2-D model. We also conclude that one of the important indicators of the compatibility of the experimental data (1976–1987) and 2-D time dependent modeling of the long period variations of the GCR intensity is the high correlation between the temporal changes of the rigidity spectrum exponents γ calculated from theoretical model and the experimental data.

The rigidity spectrum of the harmonics of the 27-day variation of the galactic cosmic ray intensity in different epochs of solar activity: 1965–2002

We study temporal changes of the rigidity ( R) spectrum of the harmonics of the 27-day variation of the galactic cosmic ray (GCR) intensity using neutron monitors (NM) data for the period 1965–2002. We show that the rigidity spectrum of the third harmonic (9 days) of the 27-day variation of the GCR intensity changes in a similar way as the spectra of the first and second harmonics, being hard in the maximum epochs and soft in the minimum epochs of solar activity. We ascribe this finding to the alternation of the sizes of the modulation regions of the 27-day variation of the GCR intensity in different epochs of solar activity. The average size of the vicinity of the corotating interaction regions, causing the 27-day variation of the GCR intensity, is less in the minimum epochs than in the maximum epochs of solar activity. A vicinity of the corotating interaction regions of larger size involves in modulation higher rigidity particles of GCR than the vicinity of smaller size; thus, this statement can be considered as one of the reasons leading to the hardening of the rigidity spectrum of the harmonics of the 27-day variation of the GCR intensity in maximum epochs compared with minimum epochs of solar activity. We also show that the temporal changes of the power rigidity spectrum of the third harmonic of the 27-day variation of the GCR intensity are negatively correlated with the rigidity spectrum of the 11-year variation of the galactic cosmic ray intensity. We found a recurrence in the temporal changes of the amplitudes of the first harmonic of the 27-day variation of the GCR intensity and in some parameters of solar activity and solar wind.

On relation of the long period galactic cosmic rays intensity variations with the interplanetary magnetic field turbulence

We study a relationship of the exponent γ of the rigidity R spectrum δD(R)D(R) of the galactic cosmic rays (GCR) intensity variations δD(R)D(R)∝R-γ and the exponent νy of the power spectral density (PSD) of the By component of the interplanetary magnetic field (IMF) (PSD=Pf-νy, where P is power and f is frequency) in the range of the frequency f ≈ 4 × 10−6–10−5 Hz. For this purpose we use data of neutron monitors and the IMF in the period of 1967–2002. We show that the rigidity spectrum of the long-period variations of the GCR intensity is hard in the minimum epochs of solar activity (γ ≈ 0.6) when the exponent νy of the PSD of the IMF is higher (νy ≈ 1.9), and is soft in the maximum epochs (γ ≈ 1.2), when the exponent νy is relatively lower (νy ≈ 1.4). We ascribe these features to the essential rearrangement of the structure of the IMF turbulence during the 11-year cycle of solar activity assuming that the IMF turbulence is homogeneous and isotropy for time scales τ > 1 day. We reveal the relationships among rigidity spectrum exponent γ, exponent νy and the power P of the PSD of the IMF turbulence in different epochs of solar activity. We suppose that the changes of the structure of the IMF turbulence versus solar activity (manifesting in the changes of the exponent γ of the rigidity R spectrum of the GCR intensity variations) is one of the important reasons of the 11-year variation of the GCR intensity for the rigidity of the GCR particles, to which neutron monitors are respond.

27-day variations of the galactic cosmic ray intensity and anisotropy

We study the 27-day variations of the galac- tic cosmic ray (GCR) intensity and three dimensional (3-D) anisotropy in different polarity periods of the solar magnetic cycle. We found that the larger amplitudes of the 27-day vari- ations of the galactic cosmic ray anisotropy and intensity in the minimum epochs of solar activity for the A> 0 polarity period than for the A 0 polarity period. The 27-day variation of the GCR 3-D anisotropy has a sporadic character; it appears and disappears as wave packages (wave oscillations) with an average duration of 4-6 solar rotations. We found that the rigidity R power law spectrum of the am- plitudes (A27) of the 27-day variation of the GCR intensity (A27/R ) is hard ( = 0.54± 0.11) in the A> 0 polar- ity period (1996-1997) and is soft ( = 0.95± 0.12) in the A< 0 period (1986-1987).

New index of long-term variations of galactic cosmic ray intensity

We find that the soft rigidity spectrum of the Galactic Cosmic Ray (GCR) intensity variations for the maximum epoch and the hard rigidity spectrum for the minimum epoch calculated based on the neutron monitors experimental data (1960–2002) are related with the various dependence of the diffusion coefficient on the GCR particle’s rigidity for different epoch of solar activity. This dependence is stronger in the maximum epoch than in the minimum epoch of solar activity, and is provided by the essential temporal rearrangements of the structure of the Interplanetary Magnetic Field (IMF) turbulence from the maxima to minima epoch of solar activity. We also show that the rigidity spectrum of GCR intensity variations is harder for the effective rigidities ∼(10–15) GV (by neutron monitors data), than for the effective rigidities ∼(25–30) GV (by neutron monitors and muon telescopes data). A general scenario of GCR modulation versus solar activity is settled on the essential temporal rearrangements of the structure of the IMF turbulence. Therefore, the temporal changes of the power law rigidity spectrum exponent can be considered as a vital (new) index to explain the 11-year variations of the GCR intensity. We assume that ∼(70–80)% of the changes of the amplitudes of the 11-year variations of GCR intensity is related with the changes of the IMF turbulence versus solar activity.

On statistical relationship of solar, geomagnetic and human activities

Data of galactic cosmic rays, solar and geomagnetic activities and solar wind parameters on the one side and car accident events (CAE) in Poland on the other have been analyzed in order to reveal the statistical relationships among them for the period of 1990–2001. Cross correlation and cross spectrum of the galactic cosmic ray intensity, the solar wind (SW) velocity, K p index of geomagnetic activity and CAE in Poland have been carried out. It is shown that in some epochs of the above-mentioned period there is found a reliable relationship between CAE and solar and geomagnetic activities parameters in the range of the different periodicities, especially, 7 days. The periodicity of 7 days revealed in the data of the CAE has the maximum on Friday without any exception for the minimum and maximum epochs of solar activity. However, the periodicity of 7 days is reliably revealed in other parameters characterizing galactic cosmic rays, SW, solar and geomagnetic activities, especially for the minimum epoch of solar activity. The periodicity of 3.5 days found in the series of CAE data more or less can be completely ascribed to the social effects, while the periodicity of 7 days can be ascribed to the social effect or/to the processes on the Sun, in the interplanetary space and in the Earth's magnetosphere and atmosphere.

The Sun's total irradiance: Cycles, trends and related climate change uncertainties since 1976

A composite record of the Sun's total irradiance compiled from measurements made by five independent space‐based radiometers since 1978 exhibits a prominent 11‐year cycle with similar levels during 1986 and 1996, the two most recent minimum epochs of solar activity. This finding contradicts recent assertions of a 0.04% irradiance increase from the 1986 to 1996 solar minima and suggests that solar radiative output trends contributed little of the 0.2°C increase in the global mean surface temperature in the past decade. Nor does our 18‐year composite irradiance record support a recent upward irradiance trend inferred from solar cycle length, a parameter used to imply a close linkage in the present century between solar variability and climate change.