Modulation Of Cosmic Ray Intensity Research Articles

Modulation of Cosmic Ray Intensity along with Interplanetary Causes and Solar Activity Parameters during Solar Cycle 24

Modulation of Cosmic Ray Intensity along with Interplanetary Causes and Solar Activity Parameters during Solar Cycle 24

Statistical relationship of cosmic ray intensity modulation with coronal mass ejections and solar flare index indices

Statistical relationship of cosmic ray intensity modulation with coronal mass ejections and solar flare index indices

Testing the impact of coronal mass ejections on cosmic-ray intensity modulation with algorithm selected Forbush decreases

ABSTRACT The relationship between coronal mass ejections (CMEs) and Forbush decreases (FDs) has been investigated in the past. But the selection of both solar events are difficult. Researchers have developed manual and automated methods in efforts to identify CMEs as well as FDs. While scientists investigating CMEs have made significant advancement, leading to several CME catalogues, including manual and automated events catalogues, those analyzing FDs have recorded relatively less progress. Till date, there are no comprehensive manual FD catalogues, for example. There are also paucity of automated FD lists. Many investigators, therefore, attempt to manually select FDs which are subsequently used in the analysis of the impact of CMEs on galactic cosmic-ray (GCR) flux depressions. However, some of the CME versus FD correlation results might be biased since manual event identification is usually subjective, unable to account for the presence of solar-diurnal anisotropy which characterizes GCR flux variations. The current paper investigates the relation between CMEs and FDs with emphasis on accurate and careful Forbush event selection.

Intensity of galactic cosmic rays in the early sun epoch

The process of heliospheric modulation of intensity of galactic cosmic rays is investigated by solving the transport equation. The spatial-energetic distribution of cosmic rays in the present epoch and in the past is analyzed. It is demonstrated that the particle density and the energy density of cosmic rays in the Solar System in the distant past were much lower than the corresponding current values. The cosmic ray intensity modulation in the early heliosphere was especially strong in the case of low-energy particles.

The Solar Polar Field in the Cosmic-Ray Intensity Modulation

In this work the modulation of galactic cosmic-ray intensity based on solar and heliospheric indices for the solar cycle 23 (1996-2008), is studied. In previous works a number of different indices such as the sunspot number, the CME-index, the interplanetary magnetic field and the heliospheric current sheet tilt were selected to be the most appropriate ones in order to describe the cosmic ray intensity of 10 GV observed by the network of neutron monitors. The new approach is an extension of this study to the influence of the solar magnetic field parameters, such as the mean magnetic field and the polar magnetic field, on the cosmic ray (CR) modulations. Using the wavelet analysis method a major periodicity of about 20-21 years was confirmed in the solar magnetic field data, indicating the existence of the solar magnetic cycle in CR variations. The best empirical relation of the cosmic ray modulation taking into account the sunspot number, the CME-index, the mean solar magnetic field and the solar polar field was improved significantly: a relative root mean square deviation (RMSD) between the observed and the calculated cosmic ray intensity values is found to be 8.7% instead to the previous one of about 10%.

Cosmic Ray and Geomagnetic Response to High Speed Solar Wind Streams

The study of cosmic ray intensity and geomagnetic response have been carried out with the data registered by ground based and satellite data on 24-hour scale during 1996, 2000 and 2008 which corresponds to solar minimum of solar activity cycle 23 during 1996 and 2008 followed by a solar maximum in the year of 2000. The minimum of solar activity cycles are characterized by different polarity of the north pole of the sun’s magnetic field as the polarity reversal occurs during 2000. The results presented in this paper indicate that cosmic ray intensity and geomagnetic field is highly disturbed during the passage of these streams at Earth. The average time-profile of the decrease in cosmic ray intensity produced by streams associated with coronal holes and solar flares during the maximum epoch of solar activity cycle 23 is explained in terms of existing models of solar modulation of cosmic rays. The comparison of modulation features during the different magnetic conditions i.e. during 1996 & 2008 shows that drift effects are less dominant in the short-term modulation of cosmic rays. These results indicate that the solar wind streams are playing an important role in the transient modulation of cosmic ray intensity.

Solar and climate influences on ice core 10Be records from Antarctica and Greenland during the neutron monitor era

Cosmogenic 10Be in polar ice cores is a primary proxy for past solar activity. However, interpretation of the 10Be record is hindered by limited understanding of the physical processes governing its atmospheric transport and deposition to the ice sheets. This issue is addressed by evaluating two accurately dated, annually resolved ice core 10Be records against modern solar activity observations and instrumental and reanalysis climate data. The cores are sampled from the DSS site on Law Dome, East Antarctica (spanning 1936–2009) and the Das2 site, southeast Greenland (1936–2002), permitting inter-hemispheric comparisons. Concentrations at both DSS and Das2 are significantly correlated to the 11-yr solar cycle modulation of cosmic ray intensity, rxy=0.54 with 95% CI [0.31; 0.70], and rxy=0.45 with 95% CI [0.22; 0.62], respectively. For both sites, if fluxes are used instead of concentrations then correlations with solar activity decrease. The strength and spectral coherence of the solar activity signal in 10Be is enhanced when ice core records are combined from both Antarctica and Greenland. The amplitudes of the 11-yr solar cycles in the 10Be data appear inconsistent with the view that the ice sheets receive only 10Be produced at polar latitudes. Significant climate signals detected in the 10Be series include the zonal wave three pattern of atmospheric circulation at DSS, rxy=−0.36 with 95% CI [−0.57; −0.10], and the North Atlantic Oscillation at Das2, rxy=−0.42 with 95% CI [−0.64; −0.15]. The sensitivity of 10Be concentrations to modes of atmospheric circulation advises caution in the use of 10Be records from single sites in solar forcing reconstructions.

Galactic Cosmic Ray Modulation and the Last Solar Minimum

In this work the galactic cosmic ray modulation in relation to solar activity indices and heliospheric parameters during the years 1996 – 2010 covering solar cycle 23 and the solar minimum between cycles 23 and 24 is studied. A new perspective of this contribution is that cosmic ray data with a rigidity of 10 GV at the top of the atmosphere obtained from many ground-based neutron monitors were used. The proposed empirical relation gave much better results than those in previous works concerning the hysteresis effect. The proposed models obtained from a combination of solar activity indices and heliospheric parameters give a standard deviation < 10 % for all the cases. The correlation coefficient between the cosmic ray variations of 10 GV and the sunspot number reached a value of r=−0.89 with a time lag of 13.6±0.4 months. The best reproduction of the cosmic ray intensity is obtained by taking into account solar and interplanetary indices such as sunspot number, interplanetary magnetic field, CME index, and heliospheric current sheet tilt. The standard deviation between the observed and calculated values is about 7.15 % for all of solar cycle 23; it also works very well during the different phases of the cycle. Moreover, the use of the cosmic ray intensity of 10 GV during the long minimum period between cycles 23 and 24 is of special interest and is discussed in terms of cosmic ray intensity modulation.

Multi-parametric effect of solar activity on cosmic rays

The long-term modulation of cosmic ray intensity (CRI) by different solar activity (SA) parameters and an inverse correlation between individual SA parameter and CRI is well known. Earlier, it has been suggested that the concept of multi-parametric modulation of CRI may play an important role in the study of long-term modulation of CRI. In the present study, we have tried to investigate the combined effect of a set of two SA parameters in the long-term modulation of CRI. For this purpose, we have used a new statistical technique called “Running multiple correlation method”, based on the “Running cross correlation method”. The running multiple correlation functions among different sets of two SA parameters (e.g., sunspot numbers and solar flux, sunspot numbers and coronal index, sunspot numbers and grouped solar flares, etc.) and CRI have been correlated separately. It is found that the strength of multiple correlation (among two SA parameters and CRI) and cross correlation (between individual SA parameter and CRI) is almost similar throughout the period of investigation (1955–2005). It is also found that the multiple correlations among various SA parameters and CRI is stronger during ascending and descending phases of the solar cycles and it becomes weaker during maxima and minima of the solar cycles, which is in accordance with the linear relationship between SA parameters and CRI. The values of multiple correlation functions among different sets of SA parameters and CRI fall well within the 95% confidence interval. In the view of odd-even hypothesis of solar cycles, the strange behaviour of present cycle 23 (odd cycle), as this is characterized by many peculiarities with double peaks and many quiet periods (Gnevyshev gaps) interrupted the solar activity (for example April 2001, October–November 2003 and January 2005), leads us to speculate that the solar cycle 24 (even cycle) might be of exceptional nature.

Long-term modulation of cosmic ray intensity in relation to sunspot numbers and tilt angle

A detailed correlative analysis between sunspot numbers (SSN) and tilt angle (TA) with cosmic ray intensity (CRI) in the neutron monitor energy range has been performed for the solar cycles 21, 22 and 23. It is found that solar activity parameters (SSN and TA) are highly (positive) correlated with each other and have inverse correlation with cosmic ray intensity (CRI). The ‘running cross correlation coefficient’ between cosmic ray intensity and tilt angle has also been calculated and it is found that the correlation is positive during the maxima of odd cycles 21 and 23. Moreover, the time lag analysis between CRI and SSN, and between CRI and TA has also been performed and is supported by hysteresis curves, which are wide for odd cycles and narrow for even cycles.

Statistical considerations in superposed epoch analysis and its applications in space research

Superposed epoch analysis is often used to demonstrate an effect or a periodicity. This method of analysis was originally proposed by Chree (Some phenomena of sunspots and of terrestrial magnetism at Kew observatory. Philosophical Transactions Royal Society London Series A 212, 75) and applied for studying the time variation of geophysical data. In its first application, Chree reported a 27-day periodicity (recurrence tendency) in geomagnetic data. Since then this method of analysis is being used in several disciplines either for testing the relationship between two diverse phenomena or to search for periodicities in the data. In addition to cosmic ray physics, various fields of research in which this method of analysis is often used include solar, magnetospheric, heliospheric, ionospheric and atmospheric physics as well as astrophysics and meteorology/climatology etc. Although a powerful method, an appropriate procedure to test the level of significance (statistical reality) of the obtained results is still lacking. This is highly desirable as, in the absence of a suitable test, a spurious/undesirable signal may appear as a ‘genuine’ effect. This paper describes two techniques with application, one based on t-test and other on F-test, to test the significance level of results obtained on the basis of superposed epoch (Chree) analysis. Since most of the data acquired in atmosphere and space show a solar cycle variation, an appropriate procedure is also described for the data transformation (removal of solar cycle variation) before subjected to test a ‘genuine’ effect. To highlight the necessity for removal of solar cycle effect, a comparison of the results of significance test, before and after the data transformation, is also presented. Although these techniques are applicable to solar/astrophysical/heliospheric/magnetospheric/ionospheric/atmospheric/meteorological data, the procedure is illustrated using cosmic ray data. Details of the procedure to test the Forbush-decrease effect in cosmic ray intensity observed due to passage of interplanetary shocks, are discussed. Test results by two statistical procedures, one based on t -test and another based on F -test, are also compared in this paper. The effectiveness of interplanetary shocks on transient modulation of cosmic rays is studied and tested by both techniques. Both the techniques lead to similar conclusions. It is demonstrated, using both the techniques, that the effect of interplanetary shocks on transient modulation of cosmic ray intensity is statistically significant only due to the shocks whose sudden commencement amplitude exceeds certain limits.

Transient Modulation of Cosmic Ray Intensity: Role of Magnetic Clouds and Turbulent Interaction Regions

Two distinct regions of shock-associated magnetic clouds, (i) magnetically turbulent regions formed due to interaction between magnetic cloud and ambient magnetic field i.e. turbulent interaction region (TIR), and magnetically quiet region called magnetic cloud have been considered separately and correlation of interplanetary plasma and field parameters, magnetic field strength (B) and solar wind speed (V), with cosmic ray intensity (I) have been studied during the passage of these two regions. A good correlation between B and I and between V and I has been obtained during the passage of sheath when the magnetic field is high and turbulent, while these correlation have been found to be poor during the passage of magnetic clouds when the field is strong and smooth. Further, there is a positive correlation between enhancement in field strength and its variance in the sheath region. These results strongly support the hypothesis that most Forbush decreases are due to scattering of particles by region of enhanced magnetic turbulence. These results also suggest that it will provide a better insight if not the magnetic field enhancement alone but in addition, the nature of magnetic field enhancement is also considered while correlating the field enhancements with depressions in cosmic rays.

Shock Orientations, Magnetic Turbulence and Forbush Decreases

We have studied the effects of quasi-parallel and quasi-perpendicular shocks on the transient modulation of cosmic-ray intensity. Interplanetary magnetic field strength, its variance and solar wind velocity during their passage have also been considered for the analysis in this work. It has been demonstrated that magnetically turbulent quasi-parallel shocks are much more effective in producing Forbush decreases in cosmic-ray intensity than the non-turbulent quasi-perpendicular shocks. From these results it is inferred that turbulence in the shock environment is an important factor in causing Forbush decreases by scattering particles due to magnetic field fluctuations. Results presented in this study provide more specific information about structures responsible for Forbush decreases, physical processes mainly responsible for this phenomenon and the possibility of predicting the likely occurrence of Forbush decreases from observations in space.

The influence of transient solar-wind events on the cosmic-ray intensity modulation

We have studied the behavior of cosmic rays observed by three stations during a time of high-speed solar-wind (HSSW) events. These stations cover the median rigidity range 16-164 GV. The influence of the IMF (interplanetary magnetic field) associated with HSSW has also been studied. Our analysis covers the period 1967-1986. Both the cosmic-ray intensity and geomagnetic activity are enhanced by coronal-mass-ejection events. The IMF magnitude and fluctuation are responsible for the depression of cosmic-ray intensity during HSSW events. This depression is rigidity dependent. Low-energy cosmic rays suffer more intensity depression. The rigidity spectrum of the cosmic-ray intensity decreases is dependent upon the phase of the solar cycle. It was steeper during the period 1979-1980. The power exponent is dependent upon the magnetic state of the solar cycle in support of the prediction of the drift model. PACS Nos.: 96.50Ci, 96.40-z

The influence of transient solar-wind events on the cosmic-ray intensity modulation

The influence of transient solar-wind events on the cosmic-ray intensity modulation

Study and effect of magnetic clouds on the transient modulation of cosmic-ray intensity

Data of cosmic-ray intensity from the Calgary Super Neutron Monitor and interplanetary plasma and field data are divided into three groups corresponding to the magnetic clouds preceded by shocks, followed by interaction region and clouds without any such association, observed during the period 1967–1982. A superposed epoch analysis of these data, in addition to the field variance data, have been performed. The results suggest the hypothesis that the Forbush decreases are caused by the scattering of particles in the region of enhanced turbulence, observed during the passage of shocked plasma (i.e., sheath) between the shock front and the magnetic cloud.

Time-evolution of cosmic-ray intensity modulation

Application of analyzing time-series into trigonometric series allows the investigation of cosmic-ray intensity variations in a wide periodicity range from a few months to 10 or even more years. By this technique, the amplitude and the phase of all observed fluctuations can be given. For this purpose, cosmic-ray data of five ground-based neutron-monitor stations for the time interval 1964–1985 have been analyzed.

Solar activity and modulation of the cosmic ray intensity

A transfer function F between a measure of the solar activity S and the 11‐year cosmic ray intensity modulation Io‐I is determined for the two sunspot cycles 19 and 20. For S we used the monthly occurrence of major flares, all flares, sunspots and ssc's. In agreement with D. J. Hatton [1980] and G. A. Bowe and D. J. Hatton [1982], we find a well‐behaved transfer function for both major flares and all flares. It is a damped pulse with duration of 16 and 13 months for the major flares and all flares, respectively. These figures are significantly longer than that of 10 months obtained by Bowe and Hatton.

Cosmic-ray 13 day oscillation and two-sector interplanetary magnetic field

The cosmic-ray intensity modulation observed at the boundary crossing of the interplanetary magnetic-field sector structure is related with the about 13 day oscillation during the years 1973 and 1974 when the magnetic field presents two sectors.

Observation of pronounced isotropic variations of cosmic ray intensity during August–September 1979

A study of the cosmic ray intensity data from high‐latitude stations reveals an isotropic variation of ∼30‐day periodicity and a peak‐to‐peak amplitude of 10% during the two months August–September 1979. Such an unusual modulation of cosmic ray intensity has not been observed before. It is clear that the variation is worldwide and in view of no significant north‐south asymmetry, we have to visualize the modulation region responsible for the effect to be extremely large. The rigidity spectra of the variation is found to be similar to that of Forbush decreases. The results are discussed in terms of solar activity. No obvious physical mechanism is readily seen, to account for this intensity variation.