The solar-wind modulation of cosmic-ray intensity

1968 ◽  
Vol 46 (10) ◽  
pp. S954-S958 ◽  
Author(s):  
S. R. Sreenivasan ◽  
R. H. Johnson
Keyword(s):  
Solar Wind ◽  
Cosmic Rays ◽  
Correlation Coefficient ◽  
Solar Wind Velocity ◽  
Interplanetary Space ◽  
Dominant Role ◽  
Cosmic Ray ◽  
Normal Pattern ◽  
Cosmic Ray Intensity ◽  
Common Basis

It is shown from a consideration of the diffusion of cosmic rays in interplanetary space that the convection of particles by the solar wind is an important effect and hence should be incorporated in all discussions of the propagation of cosmic rays. This provides a common basis for looking at the correlation between relative changes of solar-wind velocity and changes of cosmic-ray intensity. The correlation is shown to be negative and significant. The correlation coefficient is large for a Forbush event, indicating that convection plays a dominant role during the event as contrasted with the normal pattern of changes of cosmic-ray intensity. The 11-year variation of cosmic-ray intensities and the Forbush event receive a natural interpretation on the basis of this discussion.

scholarly journals On the heliolatitudinal variation of the galactic cosmic-ray intensity. Comparison with Ulysses measurements

2003 ◽  
Vol 21 (6) ◽  
pp. 1341-1345 ◽  
Author(s):  
G. Exarhos ◽  
X. Moussas
Keyword(s):  
Solar Wind ◽  
Cosmic Rays ◽  
Interplanetary Space ◽  
Cosmic Ray ◽  
Solar Wind Plasma ◽  
Simple Method ◽  
Cosmic Ray Intensity ◽  
Interplanetary Physics ◽  
Diffusion Convection ◽  
Galactic Cosmic Ray

Abstract. We study the dependence of cosmic rays with heliolatitude using a simple method and compare the results with the actual data from Ulysses and IMP spacecraft. We reproduce the galactic cosmic-ray heliographic latitudinal intensity variations, applying a semi-empirical, 2-D diffusion-convection model for the cosmic-ray transport in the interplanetary space. This model is a modification of our previous 1-D model (Exarhos and Moussas, 2001) and includes not only the radial diffusion of the cosmic-ray particles but also the latitudinal diffusion. Dividing the interplanetary region into "spherical magnetic sectors" (a small heliolatitudinal extension of a spherical magnetized solar wind plasma shell) that travel into the interplanetary space at the solar wind velocity, we calculate the cosmic-ray intensity for different heliographic latitudes as a series of successive intensity drops that all these "spherical magnetic sectors" between the Sun and the heliospheric termination shock cause the unmodulated galactic cosmic-ray intensity. Our results are compared with the Ulysses cosmic-ray measurements obtained during the first pole-to-pole passage from mid-1994 to mid-1995.Key words. Interplanetary physics (cosmic rays; interplanetray magnetic fields; solar wind plasma)

scholarly journals The Galactic cosmic ray intensity at the evolving Earth and young exoplanets

2020 ◽  
Author(s):  
Donna Rodgers-Lee ◽  
Aline Vidotto ◽  
Andrew Taylor ◽  
Paul Rimmer ◽  
Turlough Downes
Keyword(s):  
Solar Wind ◽  
Cosmic Rays ◽  
Cosmic Ray ◽  
Galactic Cosmic Rays ◽  
The Sun ◽  
Cosmic Ray Intensity ◽  
Chemical Signature ◽  
Exoplanetary Systems ◽  
Life On Earth ◽  
Galactic Cosmic Ray

<p>Cosmic rays may have contributed to the start of life on Earth. Cosmic rays also influence and contribute to atmospheric electrical circuits, cloud cover and biological mutation rates which are important for the characterisation of exoplanetary systems. The flux of Galactic cosmic rays present at the time when life is thought to have begun on the young Earth or in other young exoplanetary systems is largely determined by the properties of the stellar wind. </p> <p>The spectrum of Galactic cosmic rays that we observe at Earth is modulated, or suppressed, by the magnetised solar wind and thus differs from the local interstellar spectrum observed by Voyager 1 and 2 outside of the solar system. Upon reaching 1au, Galactic cosmic rays subsequently interact with the Earth’s magnetosphere and some of their energy is deposited in the upper atmosphere. The properties of the solar wind, such as the magnetic field strength and velocity profile, evolve with time. Generally, young solar-type stars are very magnetically active and are therefore thought to drive stronger stellar winds. </p> <p>Here I will present our recent results which simulate the propagation of Galactic cosmic rays through the heliosphere to the location of Earth as a function of the Sun's life, from 600 Myr to 6 Gyr, in the Sun’s future. I will specifically focus on the flux of Galactic cosmic rays present at the time when life is thought to have started on Earth (~1 Gyr). I will show that the intensity of Galactic cosmic rays which reached the young Earth, by interacting with the solar wind, would have been greatly reduced in comparison to the present day intensity. I will also discuss the effect that the Sun being a slow/fast rotator would have had on the flux of cosmic rays reaching Earth at early times in the solar system's life.</p> <p>Despite the importance of Galactic cosmic rays, their chemical signature in the atmospheres’ of young Earth-like exoplanets may not be observable with instruments in the near future. On the other hand, it may instead be possible to detect their chemical signature by observing young warm Jupiters. Thus, I will also discuss the HR 2562b exoplanetary system as a candidate for observing the chemical signature of Galactic cosmic rays in a young exoplanetary atmosphere with upcoming missions such as JWST.</p>

scholarly journals 39. The anisotropy of primary cosmic radiation and the electromagnetic state in interplanetary space

1958 ◽  
Vol 6 ◽  
pp. 377-385
Author(s):  
V. Sarabhai ◽  
N. W. Nerurkar ◽  
S. P. Duggal ◽  
T. S. G. Sastry
Keyword(s):  
Experimental Data ◽  
Cosmic Rays ◽  
Cosmic Radiation ◽  
Interplanetary Space ◽  
Daily Variation ◽  
Cosmic Ray ◽  
The Sun ◽  
Cosmic Ray Intensity ◽  
Daily Variations ◽  
Primary Cosmic Radiation

Study of the anisotropy of cosmic rays from the measurement of the daily variation of meson intensity has demonstrated that there are significant day-today changes in the anisotropy of the radiation. New experimental data pertaining to these changes and their solar and terrestrial relationships are discussed.An interpretation of these changes of anisotropy in terms of the modulation of cosmic rays by streams of matter emitted by the sun is given. In particular, an explanation for the existence of the recently discovered types of daily variations exhibiting day and night maxima respectively, can be found by an extension of some ideas of Alfvén, Nagashima, and Davies. An integrated attempt is made to interpret the known features of the variation of cosmic ray intensity in conformity with ideas developed above.

scholarly journals Low-Amplitude Anisotropic Wave Train Events during Passage of Interplanetary Magnetic Clouds / Mazas Amplitūdas Anizotropiju Viļņu Parādību Secība Starpplanētu Magnētisko Mākoņu Rašanās Laikā

2013 ◽  
Vol 50 (2) ◽  
pp. 68-72
Author(s):  
R. Agarwal ◽  
R.K. Mishra
Keyword(s):  
Solar Wind ◽  
Wind Velocity ◽  
Solar Wind Velocity ◽  
Magnetic Cloud ◽  
Wave Train ◽  
Cosmic Ray ◽  
Magnetic Clouds ◽  
Cosmic Ray Intensity ◽  
The North ◽  
Low Amplitude

The work presents a continuation in the series related to the long-term space observations made by ground-based neutron monitoring stations. The cosmic ray intensity variation is considered as affected by interplanetary magnetic clouds during low-amplitude anisotropic wave train (LAAWT) events. It was observed that the solar wind velocity is higher than normal (> 300 km/s) while the interplanetary magnetic field (IMF) strength is lower than normal on the arrival of magnetic cloud during LAAWT events. The proton density is found to remain significantly low at high solar-wind velocity, which was expected. The north/south component of interplanetary magnetic field turns southward one day before the arrival of cloud and remains in this direction after that. The cosmic ray intensity is found to increase with the solar wind velocity. It is noteworthy that the cosmic ray intensity significantly increases before and 90 h after the arrival of such a cloud, and decreases gradually after its passage. The north/south component of IMF (Bz) is found to significantly correlate with latitude angle (Ө) and disturbance storm time index Dst, whereas the geomagnetic activity index (Ap) significantly anti-correlates with these parameters, decreasing with (Ө) and Dst increasing on the arrival of interplanetary magnetic cloud during LAAWT events.

Two anisotropies of the cosmic-ray particles producing the cosmic-ray diurnal variation

1968 ◽  
Vol 46 (10) ◽  
pp. S828-S830
Author(s):  
Masatoshi Kitamura
Keyword(s):  
Cosmic Rays ◽  
Diurnal Variation ◽  
Interplanetary Space ◽  
Geomagnetic Latitude ◽  
Cosmic Ray ◽  
Diurnal Variations ◽  
Low Energy ◽  
The Other ◽  
Energy Spectra ◽  
Cosmic Ray Intensity

The solar diurnal variations of both meson and nucleon components of cosmic rays at sea level at geomagnetic latitude 57.5° and geomagnetic longitude 0° are analyzed by the model in which two anisotropies of cosmic-ray particles (one of them, Δj1, from about 20 h L.T. and the other, Δj2, from about 8 h L.T. in interplanetary space) produce the solar diurnal variation of the cosmic-ray intensity on the earth.When the energy spectra of Δj1 and Δj2 are represented by [Formula: see text] and [Formula: see text], respectively, where j0(E) is the normal energy spectrum of the primary cosmic rays, it is shown that the evaluation for m1 = 1, 2, m2 = 0 and the cutoffs at 8 and 10 BeV on the low-energy side of spectra of both Δj1 and Δj2 agree well with the observational results at Deep River.

Dependence of cosmic ray intensity on variation of solar wind velocity measured by the GRAPES-3 experiment for space weather studies

2015 ◽  
Vol 91 (12) ◽  
Author(s):  
H. Kojima ◽  
H. M. Antia ◽  
S. R. Dugad ◽  
S. K. Gupta ◽  
P. Jagadeesan ◽  
...  
Keyword(s):  
Solar Wind ◽  
Wind Velocity ◽  
Space Weather ◽  
Solar Wind Velocity ◽  
Cosmic Ray ◽  
Cosmic Ray Intensity

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

2000 ◽  
Vol 78 (4) ◽  
pp. 293-302 ◽  
Author(s):  
I Sabbah
Keyword(s):  
Solar Wind ◽  
Solar Cycle ◽  
Cosmic Rays ◽  
High Speed ◽  
Cosmic Ray ◽  
Power Exponent ◽  
Cosmic Ray Intensity ◽  
Drift Model ◽  
Wind Events ◽  
The Imf

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

Eleven-year modulation of galactic cosmic rays in interplanetary space

1968 ◽  
Vol 46 (10) ◽  
pp. S879-S882 ◽  
Author(s):  
A. N. Chaeakhchyan ◽  
T. N. Charakhchyan
Keyword(s):  
Solar Activity ◽  
Cosmic Rays ◽  
Large Scale ◽  
Interplanetary Space ◽  
Cosmic Ray ◽  
Galactic Cosmic Rays ◽  
Magnetic Clouds ◽  
The Sun ◽  
Cosmic Ray Intensity ◽  
Stationary Level

Almost the whole increase in the cosmic-ray intensity in the stratosphere during the period of decreasing solar activity (1960–64) was composed of a number of individual events occurring at intervals of 6–12 months. This phenomenon is almost entirely due to the corresponding decrease of solar activity (according to the sunspot number).Several interesting cases were found when solar-activity decreases to a new stationary level took place rapidly (within several days). After such events the cosmic-ray intensity gradually increased to reach a stationary level over a period of about two months. The time, tst, during which the cosmic-ray intensity in interplanetary space (after the above-mentioned events on the sun) approaches a stationary value is about 40, 60, and 80 days according to observations in 1961, 1963, and 1964 respectively.Some results have been obtained on the large-scale magnetic "clouds" which modulate the galactic cosmic rays in interplanetary space: (a) The velocity of propagation of these magnetic clouds is [Formula: see text]. According to the data on u and tst the radius of the sphere around the sun, r, within which the cosmic rays are modulated depends little on solar activity and is equal to 10–15 AU. (b) The density of magnetic clouds in space is either independent of the distance to the sun or decreases less rapidly than the inverse square law suggested by conservation of clouds.[Formula: see text]

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