We analyze the time-variation of cosmic ray intensity during the periods when large and sudden disturbances occur and last for several days. We consider periods when there are sudden decreases of ≥5% ...in the galactic cosmic ray (GCR) intensity records. For the analysis, in addition to cosmic-ray intensity data, we utilize several solar wind plasma and field parameters. Time variation of changes in GCR intensity have been compared with simultaneous changes in solar wind plasma and field parameters, in order to gain insight about the physical processes responsible for large-amplitude cosmic ray disturbances. We utilize not only data about changes in the magnitude of some of the plasma and magnetic field parameters but also the parameters which provide information about the turbulent or quite (non-turbulent) nature of the parameters. Moreover, we also utilize the magnitude of a number of plasma and field parameters and their various products, during cosmic ray decrease of various magnitudes. The magnitudes of various plasma and field parameters and their various products including some newly tried products are subjected to correlation analysis with the magnitude of cosmic-ray decreases. We identify plasma and field parameters and their products which best correlates with cosmic-ray decreases. We provide an empirical relation that can be useful to estimate the amplitude of Forbush decreases using interplanetary plasma and field observations. Our results provide further insight about the physical processes playing important role during large cosmic ray disturbances in the heliosphere. Our results further demonstrate that large-amplitude Forbush decreases in GCR intensity occur due to passage of enhanced and turbulent magnetic field structure, consistent with the model that Forbush decreases are mainly due to scattering of cosmic ray particles by enhanced turbulent magnetic field regions in the heliosphere.
A study is performed of phases of solar cycle minima in sunspots, the heliosphere, and the intensity of Galactic cosmic rays (GCRs). Times of maximum GCR intensity in the minima of the last five ...cycles (including the current one), corresponding main heliospheric factors, and relationships between them are determined. The dependence of the near-Earth GCR proton spectrum on heliospheric factors of their linear trend in the minima of solar cycles 21/22, 22/23, and 23/24 (1987, 1997, 2009) is calculated and analyzed with emphasis on the behavior of crossover energy for successive minima.
Effects on galactic cosmic rays (GCRs) of several heliospheric factors during the minimum phases of the sunspot cycles are studied. Times of maximum GCR intensity are determined for the last five ...sunspot minima, including the present one, together with the corresponding main heliospheric factors important for the modulation of GCRs in the heliosphere. The quantitative relation between these factors and the solar magnetic field is studied with the poloidal magnetic field of the Sun considered as a governing factor for many heliospheric characteristics during sunspot minima. The dependence of GCR proton spectra on these heliospheric factors for the last five sunspot minima 21/22–24/25 is calculated and discussed. Special attention is paid to the energy at which spectral cross-overs occur for consecutive minima, related to the changing polarity of the heliospheric magnetic field. The long-term observational series on GCR proton modulation at the Earth are considered with respect to the energy of these cross-overs.
The observation of galactic cosmic ray (GCR) Helium isotopes (3He2 and 4He2) at the Earth had been done precisely with the PAMELA and AMS02 space detectors and reported from July 2006 to December ...2007 and from May 2011 to May 2017, respectively. These observations span time frames that include solar maximum activity and the magnetic field reversal epoch. A comprehensive, three-dimensional numerical modulation model for the transport of GCRs in the heliosphere is utilized to simulate the modulation of galactic Helium isotopes from the end of the minimum activity in the previous A < 0 cycle, through solar maximum, and toward minimum activity in the current A > 0 cycle. A particular objective is to reproduce the main features of the 3He2 to 4He2 ratio observed at rigidities between 2.15 GV and 15.3 GV. We find that the model reproduces the apparent single power law rigidity of this ratio and its time dependence in good agreement with observations. The simulated results indicate that in addition to the significant change of particle drift with solar activity, the rigidity dependence of the diffusion coefficients below 4 GV change differently before solar maximum activity than afterwards. This influences the unfolding of the modulation of GCRs with changing solar activity differently when they have different very local interstellar spectra and mass-to-charge ratios.
We study the role of galactic cosmic ray (GCR) variability in influencing the rainfall variability in Indian Summer Monsoon Rainfall (ISMR) season. We find that on an average during ‘drought’ (low ...ISMR) periods in India, GCR flux is decreasing, and during ‘flood’ (high ISMR) periods, GCR flux is increasing. The results of our analysis suggest for a possibility that the decreasing GCR flux during the summer monsoon season in India may suppress the rainfall. On the other hand, increasing GCR flux may enhance the rainfall. We suspect that in addition to real environmental conditions, significant levitation/dispersion of low clouds and hence reduced possibility of collision/coalescence to form raindrops suppresses the rainfall during decreasing GCR flux in monsoon season. On the other hand, enhanced collision/coalescence efficiency during increasing GCR flux due to electrical effects may contribute to enhancing the rainfall. Based on the observations, we put forward the idea that, under suitable environmental conditions, changing GCR flux may influence precipitation by suppressing/enhancing it, depending upon the decreasing/increasing nature of GCR flux variability during monsoon season in India, at least. We further note that the rainfall variability is inversely related to the temperature variation during ISMR season. We suggest an explanation, although speculative, how a decreasing/increasing GCR flux can influence the rainfall and the temperature. We speculate that the proposed hypothesis, based on the Indian climate data can be extended to whole tropical and sub-tropical belt, and that it may contribute to global temperature in a significant way. If correct, our hypothesis has important implication for the sun - climate link.
•Under suitable environmental conditions changing GCR flux influence precipitation.•Decreasing GCR flux may suppress the rainfall.•Increasing GCR flux may enhance the rainfall.•Rainfall and Temperature variabilities are inversely related at least in ISMR season.
The regions of interaction between solar wind streams of different speed, known as corotating interaction regions, form an almost constantly existing structure of the inner heliosphere. Using ...observational data on the main characteristics of the heliosphere, important for GCR modulation, and the results of 3D MHD modeling of corotating interaction regions, and Monte Carlo simulation of recurrent GCR variations, we analyze the importance of the corotating interaction regions for longitude-averaged characteristics of the heliosphere and GCR propagation, and possible ways for simulating long-term GCR intensity variations with respect to the corotating interaction regions.
•Influence of solar variability on the Indian climate has been studied.•Indian climate appears to be influenced by solar variability.•Mechanism for Sun–climate relationship may be related solar ...polarity also.
We use Indian temperature data of more than 100years to study the influence of solar activity on climate. We study the Sun–climate relationship by averaging solar and climate data at various time scales; decadal, solar activity and solar magnetic cycles. We also consider the minimum and maximum values of sunspot number (SSN) during each solar cycle. This parameter SSN is correlated better with Indian temperature when these data are averaged over solar magnetic polarity epochs (SSN maximum to maximum). Our results indicate that the solar variability may still be contributing to ongoing climate change and suggest for more investigations.
Solar wind-magnetosphere coupling, its causes and consequences have been studied for the last several decades. However, the assessment of continuously changing behaviour of the sun, plasma and field ...flows in the interplanetary space and their influence on geomagnetic activity is still a subject of intense research. Search for the best possible coupling function is also important for space weather prediction. We utilise four geomagnetic indices (ap, aa, AE and Dst) as parameters of geomagnetic activity level in the earth's magnetosphere. In addition to these indices, we utilise various solar wind plasma and field parameters for the corresponding periods. We analyse the geomagnetic activity and plasma/field parameters at yearly, half-yearly, 27-day, daily, 3-hourly, and hourly time resolutions. Regression analysis using geomagnetic and solar wind data of different time resolutions, over a continuous long period, and at different phases of solar activity (increasing including maximum/decreasing including minimum) led us to suggest that two parameters BV/1000 (mVm−1) and BV2 (mVs−1) are highly correlated with the all four geomagnetic activity indices not only at any particular time scale but at different time scales. It probably suggests for some role of the fluctuations/variations in interplanetary electric potential, its spacial variation i.e., interplanetary electric field BV (mVm−1) and/or time variation BV2 (mVs−1), in influencing the reconnection rate.
•Search for best possible solar wind-magnetosphere coupling function.•Geomagnetic activity and plasma/field parameters analysed.•Long-period data of different time resolutions analysed.•Parameters BV and BV2 are highly correlated with geomagnetic activity indices.•Important implications for solar-terrestrial physics and space weather forecast.
Precision measurements of the Z = 2 component in cosmic radiation provide crucial information about the origin and propagation of the second most abundant cosmic ray species in the Galaxy (9% of the ...total). These measurements, acquired with the PAMELA space experiment orbiting Earth, allow to study solar modulation in details. Helium modulation is compared to the modulation of protons to study possible dependencies on charge and mass. The time dependence of helium fluxes on a monthly basis measured by PAMELA has been studied for the period between July 2006 to January 2016 in the energy range from 800
MeV/n
to ~ 20
GeV/n
.
The PAMELA experiment with magnetic spectrometer operated almost ten years on board of the Resurs DK1 satellite. The satellite was launched on 15 June 2006 on polar orbit with an inclination of 70° ...and an altitude of 350-610 km. The spectrometer continuously measured charged cosmic ray particles in wide energy range from about 50 MeV up to several TeV. In this work the spectra of electrons and positrons averaged over one year were obtained from July of 2006 until January 2016, i.e. from the end of 23th and at the beginning of 24th solar cycle including the period of interplanetary magnetic field polarity reversal. These precise long duration time-dependent measurements of the electron and positron spectra are important to estimate possible contributions of exotic cosmic ray sources such as dark matter annihilation or decay.
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