Variation with solar cycle of the diurnal variation of cosmic rays underground

The cosmic-ray diurnal variation has been observed with scintillator telescopes at a depth of 40 m.w.e. at Chacaltaya, Bolivia, since the last solar maximum, and at the same depth near Albuquerque, New Mexico, since the last solar minimum. During the solar maximum from 1958 to 1960 the amplitude of the diurnal variation was 0.3% for the Chacaltaya telescopes, but at solar minimum early in 1965 it was as low as 0.05%. Since that time, the amplitude has been steadily increasing, and it is now between 0.1% and 0.2% at both the Bolivia and the New Mexico stations.The telescopes measure the cosmic-ray flux from the north, south, east, and west directions, as well as from the vertical; and the various observed times of the diurnal maximum for these directions confirm the extraterrestrial nature of the anisotropy. The maximum occurs at approximately 15 h local solar time in the vertical telescopes. A study of the asymptotic directions of these telescopes for differing primary energies, and of the behavior of the phases of the diurnal variation at the two stations, gives indications of the energies of the primary particles responsible for the diurnal variation. The results are compared with the models of Axford and of Ahluwalia and Dessler.

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Cosmic rays, aerosol formation and cloud-condensation nuclei: sensitivities to model uncertainties

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-4001-2011 ◽

2011 ◽

Vol 11 (8) ◽

pp. 4001-4013 ◽

Cited By ~ 37

Author(s):

E. J. Snow-Kropla ◽

J. R. Pierce ◽

D. M. Westervelt ◽

W. Trivitayanurak

Keyword(s):

Cosmic Rays ◽

Solar Minimum ◽

Solar Maximum ◽

Cloud Condensation Nuclei ◽

Cosmic Ray ◽

Organic Aerosol ◽

Test Cases ◽

Primary Emissions ◽

Cosmic Ray Flux ◽

Aerosol Properties

Abstract. The flux of cosmic rays to the atmosphere has been reported to correlate with cloud and aerosol properties. One proposed mechanism for these correlations is the "ion-aerosol clear-air" mechanism where the cosmic rays modulate atmospheric ion concentrations, ion-induced nucleation of aerosols and cloud condensation nuclei (CCN) concentrations. We use a global chemical transport model with online aerosol microphysics to explore the dependence of CCN concentrations on the cosmic-ray flux. Expanding upon previous work, we test the sensitivity of the cosmic-ray/CCN connection to several uncertain parameters in the model including primary emissions, Secondary Organic Aerosol (SOA) condensation and charge-enhanced condensational growth. The sensitivity of CCN to cosmic rays increases when simulations are run with decreased primary emissions, but show location-dependent behavior from increased amounts of secondary organic aerosol and charge-enhanced growth. For all test cases, the change in the concentration of particles larger than 80 nm between solar minimum (high cosmic ray flux) and solar maximum (low cosmic ray flux) simulations is less than 0.2 %. The change in the total number of particles larger than 10 nm was larger, but always less than 1 %. The simulated change in the column-integrated Ångström exponent was negligible for all test cases. Additionally, we test the predicted aerosol sensitivity to week-long Forbush decreases of cosmic rays and find that the maximum change in aerosol properties for these cases is similar to steady-state aerosol differences between the solar maximum and solar minimum. These results provide evidence that the effect of cosmic rays on CCN and clouds through the ion-aerosol clear-sky mechanism is limited by dampening from aerosol processes.

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Cosmic rays, aerosol formation and cloud-condensation nuclei: sensitivities to model uncertainties

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-2697-2011 ◽

2011 ◽

Vol 11 (1) ◽

pp. 2697-2732 ◽

Cited By ~ 1

Author(s):

E. J. Snow-Kropla ◽

J. R. Pierce ◽

D. M. Westervelt ◽

W. Trivitayanurak

Keyword(s):

Cosmic Rays ◽

Solar Minimum ◽

Solar Maximum ◽

Cloud Condensation Nuclei ◽

Cosmic Ray ◽

Organic Aerosol ◽

Test Cases ◽

Primary Emissions ◽

Cosmic Ray Flux ◽

Aerosol Properties

Abstract. The flux of cosmic rays to the atmosphere has been observed to correlate with cloud and aerosol properties. One proposed mechanism for these correlations is the "ion-aerosol clear-air" mechanism where the cosmic rays modulate atmospheric ion concentrations, ion-induced nucleation of aerosols and cloud condensation nuclei (CCN) concentrations. We use a global chemical transport model with online aerosol microphysics to explore the dependence of CCN concentrations on the cosmic-ray flux. Expanding upon previous work, we test the sensitivity of the cosmic-ray/CCN connection to several uncertain parameters in the model including primary emissions, Secondary Organic Aerosol (SOA) condensation and charge-enhanced condensational growth. The sensitivity of CCN to cosmic rays increases when simulations are run with decreased primary emissions, but show location-dependent behavior from increased amounts of secondary organic aerosol and charge-enhanced growth. For all test cases, the change in the concentration of particles larger than 80 nm between solar minimum (high cosmic ray flux) and solar maximum (low cosmic ray flux) simulations is less than 0.2%. The change in the total number of particles larger than 10 nm was larger, but always less than 1%. The simulated change in the column-integrated Ångström exponent was negligible for all test cases. Additionally, we test the predicted aerosol sensitivity to week-long Forbush decreases of cosmic rays and find that the maximum change in aerosol properties for these cases is similar to steady-state aerosol differences between the solar maximum and solar minimum. These results provide evidence that the effect of cosmic rays on CCN and clouds through the ion-aerosol clear-sky mechanism is limited by dampening from aerosol processes.

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Ulysses COSPIN observations of cosmic rays and solar energetic particles from the South Pole to the North Pole of the Sun during solar maximum

Annales Geophysicae ◽

10.5194/angeo-21-1217-2003 ◽

2003 ◽

Vol 21 (6) ◽

pp. 1217-1228 ◽

Cited By ~ 56

Author(s):

R. B. McKibben ◽

J. J. Connell ◽

C. Lopate ◽

M. Zhang ◽

J. D. Anglin ◽

...

Keyword(s):

Cosmic Rays ◽

Solar Maximum ◽

Cosmic Ray ◽

Energetic Particles ◽

Solar Energetic Particles ◽

Polar Regions ◽

The Sun ◽

The South ◽

The North ◽

Inner Heliosphere

Abstract. In 2000–2001 Ulysses passed from the south to the north polar regions of the Sun in the inner heliosphere, providing a snapshot of the latitudinal structure of cosmic ray modulation and solar energetic particle populations during a period near solar maximum. Observations from the COSPIN suite of energetic charged particle telescopes show that latitude variations in the cosmic ray intensity in the inner heliosphere are nearly non-existent near solar maximum, whereas small but clear latitude gradients were observed during the similar phase of Ulysses’ orbit near the 1994–95 solar minimum. At proton energies above ~10 MeV and extending up to >70 MeV, the intensities are often dominated by Solar Energetic Particles (SEPs) accelerated near the Sun in association with intense solar flares and large Coronal Mass Ejections (CMEs). At lower energies the particle intensities are almost constantly enhanced above background, most likely as a result of a mix of SEPs and particles accelerated by interplanetary shocks. Simultaneous high-latitude Ulysses and near-Earth observations show that most events that produce large flux increases near Earth also produce flux increases at Ulysses, even at the highest latitudes attained. Particle anisotropies during particle onsets at Ulysses are typically directed outwards from the Sun, suggesting either acceleration extending to high latitudes or efficient cross-field propagation somewhere inside the orbit of Ulysses. Both cosmic ray and SEP observations are consistent with highly efficient transport of energetic charged particles between the equatorial and polar regions and across the mean interplanetary magnetic fields in the inner heliosphere.Key words. Interplanetary physics (cosmic rays) – Solar physics, astrophysics and astronomy (energetic particles; flares and mass ejections)

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Latitudinal and radial variation of >2 GeV/n protons and alpha-particles at solar maximum: ULYSSES COSPIN/KET and neutron monitor network observations

Annales Geophysicae ◽

10.5194/angeo-21-1295-2003 ◽

2003 ◽

Vol 21 (6) ◽

pp. 1295-1302 ◽

Cited By ~ 9

Author(s):

A. V. Belov ◽

E. A. Eroshenko ◽

B. Heber ◽

V. G. Yanke ◽

A. Raviart ◽

...

Keyword(s):

Magnetic Field ◽

Cosmic Rays ◽

Neutron Monitor ◽

Solar Minimum ◽

Latitudinal Gradient ◽

Solar Maximum ◽

Cosmic Ray ◽

Galactic Cosmic Rays ◽

Alpha Particles ◽

Polar Regions

Abstract. Ulysses, launched in October 1990, began its second out-of-ecliptic orbit in September 1997. In 2000/2001 the spacecraft passed from the south to the north polar regions of the Sun in the inner heliosphere. In contrast to the first rapid pole to pole passage in 1994/1995 close to solar minimum, Ulysses experiences now solar maximum conditions. The Kiel Electron Telescope (KET) measures also protons and alpha-particles in the energy range from 5 MeV/n to >2 GeV/n. To derive radial and latitudinal gradients for >2 GeV/n protons and alpha-particles, data from the Chicago instrument on board IMP-8 and the neutron monitor network have been used to determine the corresponding time profiles at Earth. We obtain a spatial distribution at solar maximum which differs greatly from the solar minimum distribution. A steady-state approximation, which was characterized by a small radial and significant latitudinal gradient at solar minimum, was interchanged with a highly variable one with a large radial and a small – consistent with zero – latitudinal gradient. A significant deviation from a spherically symmetric cosmic ray distribution following the reversal of the solar magnetic field in 2000/2001 has not been observed yet. A small deviation has only been observed at northern polar regions, showing an excess of particles instead of the expected depression. This indicates that the reconfiguration of the heliospheric magnetic field, caused by the reappearance of the northern polar coronal hole, starts dominating the modulation of galactic cosmic rays already at solar maximum.Key words. Interplanetary physics (cosmic rays; energetic particles) – Space plasma physics (charged particle motion and acceleration)

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Solar Wind Effects on the Transport of 3–10 MeV Cosmic‐Ray Electrons from Solar Minimum to Solar Maximum

The Astrophysical Journal ◽

10.1086/376869 ◽

2003 ◽

Vol 594 (1) ◽

pp. 552-560 ◽

Cited By ~ 18

Author(s):

S. E. S. Ferreira ◽

M. S. Potgieter ◽

D. M. Moeketsi ◽

B. Heber ◽

H. Fichtner

Keyword(s):

Solar Wind ◽

Solar Minimum ◽

Solar Maximum ◽

Cosmic Ray ◽

Wind Effects

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PERIODICAL FLUCTUATION STUDIES OF COSMIC-RAY DIURNAL VARIATIONS DURING THE QUIET-SUN PERIOD 1962–64

Canadian Journal of Physics ◽

10.1139/p67-220 ◽

1967 ◽

Vol 45 (8) ◽

pp. 2733-2748 ◽

Cited By ~ 1

Author(s):

Masahiro Kodama

Keyword(s):

Diurnal Variation ◽

Solar Minimum ◽

Counting Rate ◽

Solar Rotation ◽

Rotation Period ◽

Cosmic Ray ◽

Diurnal Variations ◽

Statistical Studies ◽

Periodic Fluctuations ◽

Recurrence Tendency

Statistical studies of periodic fluctuations of the cosmic-ray diurnal variation have been performed, using neutron and meson component data obtained by the high-counting-rate cosmic-ray monitors at Deep River. The data cover an interval from May 1962 to October 1964, a period of descending solar activity ending near the solar minimum. It is shown that a 27-day recurrence tendency of the amplitude of the diurnal variation occasionally appears as well as shorter recurrent variations, ranging from one-half to one-sixth of the solar rotation period. The correlations of these fluctuations with some typical solar and terrestrial indices are examined in order to search for possible origins of the shorter recurrent variations. A possible connection with the Kp index exists.

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The North–South Anisotropy and the Radial Density Gradient of Galactic Cosmic Rays at 1 AU

Publications of the Astronomical Society of Australia ◽

10.1017/s1323358000020191 ◽

1995 ◽

Vol 12 (2) ◽

pp. 153-158 ◽

Cited By ~ 1

Author(s):

D. L. Hall ◽

M. L. Duldig ◽

J. E. Humble

Keyword(s):

Cosmic Rays ◽

Diurnal Variation ◽

Density Gradient ◽

Cosmic Ray ◽

Ecliptic Plane ◽

Galactic Cosmic Rays ◽

Radial Density ◽

Sidereal Time ◽

Direction Parallel ◽

The North

AbstractThe radial density gradient (Gr) of Galactic cosmic rays in the ecliptic plane points outward from the Sun. This indicates an increasing density of cosmic ray particles beyond the Earth’s orbit. Due to this gradient and the direction of the Sun’s interplanetary magnetic field (IMF) above and below the IMF wavy neutral sheet, there exists an anisotropic flow of cosmic ray particles approximately perpendicular to the ecliptic plane (i.e. in the direction parallel to BIMF × Gr). This effect is called the north–south anisotropy (ξNS) and manifests as a diurnal variation in sidereal time in the particle intensity recorded by a cosmic ray detector. By analysing the yearly averaged sidereal diurnal variation recorded by five neutron monitors and six muon telescopes from 1957 to 1990, we have deduced probable values of the average rigidity spectrum and magnitude of ξNS. Furthermore, we have used determined yearly amplitudes of ξNS to infer the magnitude of Gr for particles with rigidities in excess of 10 GV.

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Simulation of field-aligned H<sup>+</sup> and He<sup>+</sup> dynamics during late-stage plasmasphere refilling

Annales Geophysicae ◽

10.5194/angeo-26-1507-2008 ◽

2008 ◽

Vol 26 (6) ◽

pp. 1507-1516 ◽

Cited By ~ 19

Author(s):

J. Krall ◽

J. D. Huba ◽

J. A. Fedder

Keyword(s):

Diurnal Variation ◽

Late Stage ◽

Solar Minimum ◽

Solar Maximum ◽

Density Ratio ◽

Neutral Winds ◽

Order Of Magnitude ◽

Density Ratios

Abstract. The refilling of the plasmasphere for 3≤L≤4 following a model storm is simulated over long times (days) using the NRL ionosphere code SAMI2 (Sami2 is Another Model of the Ionosphere). Refilling is dependent on the supply of topside H+ and He+ ions with the result that H+ refilling rates decrease and He+ refilling rates generally increase with increasing F10.7 index. Both early- and late-stage refilling are affected by net ion flows from the warmer to the colder geomagnetic hemisphere. When these flows are strong, the ability of the "winter helium bulge" to increase He+ refilling rates is suppressed. When neutral winds are not included, refilling rates fall, typically by a factor of two. In most cases, late-stage He+ refilling is proportional to H+ refilling, with typical He+/H+ density ratios of 2% for solar minimum and 10% for solar maximum. For high values of F10.7, He+ refilling exhibits a strong diurnal variation so that the He+/H+ density ratio varies by as much as a factor of two during late-stage refilling. Finally if the plasmasphere is left undisturbed, the H+ density can refill for as long as five weeks at L=3 and ten weeks at L=4, with saturation densities nearly an order of magnitude greater than typical observed densities. This confirms that the plasmasphere at these L values rarely obtains saturation.

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