Epochs Of Solar Activity Research Articles

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.

A comparison of optically measured daytime OH temperatures over the tropics during solar maximum and minimum periods

This paper deals with the variability of optically measured daytime OH temperatures during two different solar activity epochs, over Trivandrum (8.5°N, 76.5°E), a tropical station in India. The data used for the present study span the period of February–March, during the solar maximum year of 2001 and solar minimum year of 2005. The mean daytime temperature (180±5 K) during the 2001 study period was found to be lower than the mean temperature (195±9 K) of the 2005 study period by ~15 K. However, apart from this noticeable shift in mean temperature level, the variabilities in the temperature of both years were strikingly similar. Moreover, the wave periodicities present during these periods were also quite similar. Possible reasons for these observations were investigated in the context of the various forcings that control the energetics of the equatorial mesopause region. The observations presented in this study are unique and reveal a number of newer aspects of the energetics of the tropical mesopause.

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.

Rigidity spectrum of the 27-day variation of the galactic cosmic ray intensity in different epochs of solar activity

We study the temporal evolution of the power rigidity spectrum of the first (27 days) and the second (14 days) harmonics of the 27-day variation of the galactic cosmic ray intensity measured by neutron monitors in the period of 1965–2002. The rigidity spectrum of these variations can be approximated by a power law. We show the rigidity spectra of the first and the second harmonics of the 27-day variation of the galactic cosmic ray intensity have similar time profiles. These spectra are hard ( γ ≈ 0.5 ± 0.1) and soft ( γ ≈ 1.1 ± 0.2) during solar maximum and minimum activity, respectively. We ascribe this to the alternation of the sizes of the modulation regions responsible for the 27-day variation of the galactic cosmic ray intensity in different epochs of solar activity. Especially, the average radial sizes of the modulation regions of the 27-day variation and the heliolatitudinal extension of the heliolongitudinal asymmetry are smaller during solar minimum than during solar maximum. We show also, that the temporal changes of the power rigidity spectra of the first and the second harmonics of the 27-day variation of the galactic cosmic ray intensity are in a negative correlation with the changes of the rigidity spectrum of the corresponding 11-year variation.

Possible dependence between the total solar irradiance and dimethylsulphide

La variabilidad solar es una de las principales influencias naturales del clima terrestre, y que afecta profundamente a los procesos biológicos. Se ha propuesto que algunos de estos procesos biológicos alteran el albedo y por tanto tienen un impacto en el clima. En este trabajo investigamos la relación entre la irradiancia total solar (ITS) y la concentración de Dimetilsulfuro (DMS), que es producido por algas marinas. El DMS se ha mencionado frecuentemente como un forzamiento climático a través de su efecto en las nubes y por tanto en el albedo. En el presente trabajo encontramos que las series temporales de la IST y el DMS muestran una correlación. Para ello utilizamos un esquema probabilístico, la Función de Información Mutua (FIM), que es una medida de la dependencia entre los parámetros de interés. La FIM presenta una dependencia con el ciclo solar: valores mayores aparecen durante épocas de baja actividad solar (épocas de menor IST), mientras que los valores menores se presentan durante tiempos de alta actividad solar (mayor IST). En otras palabras, la dependencia entre IST y DMS es más fuerte durante épocas de actividad solar menor que durante actividad solar mayor.

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.

Features of the 11-year variation of galactic cosmic rays in different periods of solar magnetic cycles

Variations of galactic cosmic ray intensity have been studied based on the neutron monitors and interplanetary magnetic field experimental data for different ascending and descending epochs of solar activity. The dependence of the diffusion coefficient on the cosmic ray particles rigidity R is stronger in the maxima epoch than in the minima epoch of solar activity. For the period of 1977–1981 ( qA > 0) the diffusion coefficient for the minimum epoch is, χ min ∝ R 0.7 ± 0.04 and for the maximum χ max ∝ R 1.3 ± 0.05 ; for the period of 1987–1990 ( qA < 0), χ min ∝ R 0.8 ± 0.05 and χ max ∝ R 1.1 ± 0.04 . The exponents ν y and ν z of the power spectral density of the B y and B z components of the IMF in the region of the frequencies (10 −6– 4 × 10 −6) Hz are larger for the minimum epoch of 1987 ( ν y ≈ 2.0 and ν z ≈ 1.93) than for the maximum epoch of 1990 ( ν y ≈ 1.43 and ν z ≈ 1.27).

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.

Experimental and theoretical investigations of the 11-year variation of galactic cosmic rays

Data of super neutron monitors have been used to study features of the temporal changes of the energy spectrum of the galactic cosmic rays isotropic intensity variations in the various ascending and descending epochs of solar activity (1954–2000) for different solar magnetic cycles (qA > 0 and the qA < 0). Parker's transport equation is numerically solved in order to establish a relationship between the experimentally obtained and theoretically expected energy spectra of.galactic cosmic rays. It is found that the theoretical expected energy spectrum is single valued determined by the dependence of the diffusion coefficient on the rigidity of galactic cosmic rays. The temporal changes of the energy spectrum of galactic cosmic rays isotropic intensity variations from the maxima to the minima epochs of solar activity indicate the radical redistributions of the EAF's fluctuations (irregularities) from the higher frequencies to the lower frequencies. It is concluded that this radical redistributions of the DVIF's fluctuations from the maxima to the minima epochs is one of the general reasons (mechanism) of the 11-year variation of the galactic cosmic rays m 2003 COSPAR.

On the influence of solar activity and the solar magnetic field on the 27-day variation of galactic cosmic rays

The calculated amplitude of the 27-day variation using super neutron monitors data has been compared with changes of the distribution of solar activity on the Sun. Close correlation of the two-peaked pattern of the galactic cosmic rays 27-day variation with changes of the longitudinal asymmetry of the sunspot distribution at the maxima epochs of solar activity has been observed. It is reasonable to assume that drastic changes of the longitudinal asymmetry of solar activity near the solar maximum are reflected in the perturbation of the heliospheric structure, causing the depression of the 27-day modulation. Marked differences between the Sun's magnetic polarity cycles, qA > 0 and qA < 0, were observed in the time profile of the 27-day variation of galactic cosmic rays. The amplitude of the calculated 27-day variation of galactic cosmic rays is not depend on the tilt angles of the heliospheric neutral sheet for both qA > 0 and qA < 0 cycles. The expected amplitude (from theoretical modeling of galactic cosmic rays transport) of the 27-day variation is greater in the qA > 0 than in the qA < 0 solar magnetic cycles being in good agreement with the experimental data for the minima epochs of solar activity.

27-Day variations of galactic cosmic rays and changes of solar and geomagnetic activities

Neutron monitor, solar and geomagnetic activity data have been used to investigate variations of galactic cosmic ray intensity connected with the Sun's rotation for different epochs of solar activity. Behaviors of longitudinal asymmetry of the sunspot distribution, coronal line emission and tilt angles of the heliospheric neutral sheet have been studied. A relationship of the temporal changes of the amplitudes of the 27-day variations of galactic cosmic rays and Kp index of geomagnetic activity with the tilt angles of the heliospheric neutral sheet have been investigated. It is shown that there are no any noticeable relationship between the amplitudes of the 27-day variations of galactic cosmic rays and the tilt angles of the heliospheric neutral sheet for both of the qA > 0 and the qA<0 solar magnetic cycles. At the same time, during the minima and near minima epochs of solar activity the average amplitudes of the 27-day variations of galactic cosmic rays for neutron monitors are about 1.5 times greater for the qA > 0 cycle than for the qA<0 cycle.

The role of drift on the diurnal anisotropy and on temporal changes in the energy spectra of the 11-year variation for galactic cosmic rays

Neutron monitor and interplanetary magnetic field data have been used to study features of the role of drift effect in the temporal changes of the diurnal anisotropy and of the energy spectrum of the 11-year variation of galactic cosmic rays. In order to strictly separate the sectors of the interplanetary magnetic field and its influence on the anisotropy of galactic cosmic rays four solar minima periods (1965, 1976, 1987 and 1997) have been considered. An attempt to separate drift effects in the diurnal anisotropy of galactic cosmic rays, first, due to the gradient and curvature of the regular interplanetary magnetic field, and second, due to the heliospheric neutral sheet has been made. The global survey methods has been used to calculate the components of the three dimensional diurnal anisotropy of galactic cosmic rays based on neutron monitors data. It is shown that there are significant differences between the diurnal anisotropy of galactic cosmic rays found in the reliably established various sectors (duration of each sectors is ≥ 4 days) of the interplanetary magnetic field. The interplanetary magnetic field sector structure effect in the diurnal anisotropy of galactic cosmic rays is assumed to be connected to the heliospheric neutral sheet drift, while 22-year variation of the diurnal anisotropy of galactic cosmic rays is assumed to be connected to drift due to the gradient and curvature of the regular interplanetary magnetic field for different qa > 0 and qA<0 solar magnetic cycles. It is shown that the role of drift in the temporal changes of the energy spectrum of the 11-year variation of GCR is insignificant in both of the qA > 0 and the qA<0 solar magnetic cycles. The temporal changes of the exponent index of the 11-year variation of GCR generally is connected with the various character of the diffusion in interplanetary space for minima and maxima epochs of solar activity.

Features of 27-day variations of galactic cosmic rays and of solar activity

Neutron monitor and solar activity data have been used to investigate the features of the 27-day variation of galactic cosmic rays (GCR) for the last maximum epoch of solar activity (1988–1992). The amplitude of the 27-day variation of GCR significantly diminishes in 1990 coinciding with the sun's polar magnetic field reversal period. The existence of the longitudinal asymmetry of the sunspot areas for the 30–40° heliolatitudinal interval in 1989 coinciding with the first maximum of the 27-day variation of GCR and the asymmetry for the 0–10° heliolatitudinal interval in 1991–1992 corresponding to the second maximum of the 27-day variation of GCR has been revealed. It is assumed that the destruction of the heliolongitudinal asymmetries of the solar wind velocity and of the interplanetary magnetic field strength by merged interaction regions and global merged interaction regions in the heliosphere is the partial cause for the dip in the amplitude of the 27-day variation of GCR during maxima epochs of solar activity.

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.

Characteristics of VHF radiowave scintillations over a solar cycle (1983−1993) at a low-latitude station: Waltair (17.7°N, 83.3°E)

Abstract. The characteristics of VHF radiowave scintillations at 244 MHz (FLEETSAT) during a complete solar cycle (1983–93) at a low-latitude station, Waltair (17.7°N, 83.3°E), are presented. The occurrence of night-time scintillations shows equinoctial maxima and summer minima in all the epochs of solar activity, and follows the solar activity. The daytime scintillation occurrence is negatively correlated with the solar activity and shows maximum occurrence during the summer months in a period of low solar activity. The occurrence of night-time scintillations is inhibited during disturbed days of high solar activity and enhanced during low solar activity.

Features of galactic cosmic ray modulation in different epochs of solar activity

Features of galactic cosmic ray modulation in different epochs of solar activity

Characteristics of VHF radiowave scintillations over a solar cycle (1983–1993) at a low-latitude station: Waltair (17.7°N, 83.3°E)

The characteristics of VHF radiowave scintillations at 244 MHz (FLEETSAT) during a complete solar cycle (1983–93) at a low-latitude station, Waltair (17.7°N, 83.3°E), are presented. The occurrence of night-time scintillations shows equinoctial maxima and summer minima in all the epochs of solar activity, and follows the solar activity. The daytime scintillation occurrence is negatively correlated with the solar activity and shows maximum occurrence during the summer months in a period of low solar activity. The occurrence of night-time scintillations is inhibited during disturbed days of high solar activity and enhanced during low solar activity.