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  • 1
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    The intensity recovery of Forbush-type decreases as a function of heliocentric distance and its relationship to the 11-year variation (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Recent data indicating that the solar modulation effects are propagated outward in the heliospheric cavity suggest that the 11-year cosmic ray modulation can best be described by a dynamic time dependent model. In this context an understanding of the recovery characteristics of large transient Forbush type decreases is important. This includes the typical recovery time at a fixed energy at 1 AU as well as at large heliocentric radial distances, the energy dependence of the recovery time at 1 Au, and the dependence of the time for the intensity to decrease to the minimum in the transient decreases as a function of distance. These transient decreases are characterized by their asymmetrical decrease and recovery times, generally 1 to 2 days and 3 to 10 days respectively at approx. 1 AU. Near earth these are referred to as Forbush decreases, associated witha shock or blast wave passage. At R equal to or greater than + or - 10 AU, these transient decreases may represent the combined effects of several shock waves that have merged together.
    Keywords: SOLAR PHYSICS
    Type: SH-4.1-9 , 19th Intern. Cosmic Ray Conf - Vol. 4; p 388-391; NASA-CP-2376-VOL-4
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  • 2
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    Energetic solar particle fluxes out to 3 AU during the 7 May 1978 flare event (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Simultaneous solar proton flux measurements on IMP 7 and by the world wide neutron monitor network during the May 7, 1978 flare event led to conclusions that in the energy range from 50 MeV to 10 GeV: (1) the propagation of the flare particles in the interplanetary magnetic field (IMF) between the Sun and the Earth was nearly scatter free; and (2) therefore, the intensity time (IT) profiles of the solar proton fluxes observed at Earth for about one hour after onset represent the solar injection profiles even to energies as low as 50 MeV. Observations of the IMF at Helios A indicate that the IMF was undisturbed between the Sun and Helios A at the time of the May 7, 1978 flare event; and, therefore, the solar particle propagation was also scatter free from the Sun to Helios A.
    Keywords: SOLAR PHYSICS
    Type: SH-3.2-6 , 19th Intern. Cosmic Ray Conf - Vol. 4; p 351-354; NASA-CP-2376-VOL-4
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  • 3
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    Some characteristics of the solar flare event of February 16, 1984 (1985)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: In the morning of February 16, 1984 a solar cosmic ray event (GLE) was recorded by the world wide network of neutron monitors (NM). The counting rate vs. time profile of the Goose Bay NM (geog. lat. = 53.3 deg. N, deog. long. = 299.6 deg E) where the increase is expressed as percent of the counting rate of an equatorial sea level NM is presented. The Goose Bay NM was observed to have the maximum response to the solar particles. Its counting rate vs. time profile exhibits a rapid increase to maximum, has a large amplitude (approx. 170%) and decays rapidly to background in approx. 90 min. In Fig. 1 we also show the counting rate vs. time profile for the Tixie Bay NM (71.6 deg, 128.9 deg) which recorded an increase of only a few percent. Since the NMs at Goose Bay and Tixie Bay have asymptotic viewing directions approx. 180 deg apart in longitude, the anisotropy of the solar particle flux at Earth from these stations.
    Keywords: SOLAR PHYSICS
    Type: SH-3.1-7 , 19th Intern. Cosmic Ray Conf - Vol. 4; p 317-320; NASA-CP-2376-VOL-4
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  • 4
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    Solar activity and modulation of the cosmic ray intensity (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Since its discovery by Forbush (1954), the 11-year cycle modulation of the cosmic ray intensity has been studied extensively. Bowe and Hatton (1982) obtained a well-behaved transfer function F between the solar activity S and the cosmic ray intensity modulation Io-I. They suggested that the 11-year variation for sunspot cycle 20 can be attributed to the modulating effect of solar flare-induced shocks propagating through the heliosphere. The cosmic ray intensity in the absence of solar activity is denoted by Io, while I denotes the observed intensity. Bowe and Hatton infer that the boundary of the heliosphere is located at a distance of 70-90 AU. Since their conclusion is of great importance in understanding the mechanism of the 11-year modulation, the present investigation is concerned with a repetition of their study for two cycles, taking into account the use of a slightly modified method. The obtained results confirm the conclusions reached by Bowe and Hatton that there is a well-behaved transfer function for solar flares.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 4439-444
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  • 5
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    Solar flare proton rigidity spectra deduced from cosmic ray neutron monitor observations (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The solar flare proton rigidity spectra for several flares occurring between 1967 and 1972 have been deduced from the ground level cosmic ray neutron monitor observations. To obtain consistent agreement for all the ground level events (GLEs) analyzed, the specific yield functions of Lockwood and Webber (1967) must be reduced slightly below P = 1.6 GV. The typical spectral indices of solar cosmic rays deduced for GLEs vary from 4 to 6 if the differential spectrum is represented by KP to the minus gamma power. Only occasionally is the spectrum as steep as 8 or 9. The observed spectral index is independent of the magnitude of the integral solar proton flux above 1 GV.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research; 79; Oct. 1
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  • 6
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    Comparison of the solar cosmic ray events on May 7, 1978, and November 22, 1977 (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Neutron monitor data from the IMP 7 and 8 satellites are used in the present analysis of the cosmic ray events of Nov. 22, 1977, and May 7, 1978, in order to determine the energy spectra of the solar protons from 50 MeV to 10 GeV, together with pitch angle distributions, intensity-time profiles, and anisotropy-time profiles. The solar proton energy spectra obtained agree with the overlapping energy range when the pitch angle distribution is taken into account, and it is noted that the energy spectra covering three decades of energy and eight of intensity, together with their time variations, were very similar for the two events. The May 1978 event is important for the study of solar particle acceleration and their subsequent injection into the interplanetary medium. Although the solar proton propagation of the November 1977 event was diffusive, the solar particle injection was also time-extended and energy-dependent.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 769-774
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  • 7
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    Giant transient decreases of cosmic rays in the outer heliosphere in September 1991 (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Large transient decreases over 20 percent were observed above 70 MeV cosmic ray intensity in September 1991, at the three spacecraft, V1, V2, and P10, in the outer heliosphere between 35 and 53 AU. These decreases appear to be related to the intense solar activity occurring in late May and early June, which was responsible for a series of rapid transient decreases at the earth that probably reduced the over 70-MeV intensity by more than 50 percent to the 1owest level ever recorded. Average transit speeds of about 600 to 800 km/s are deduced for the propagation of these transients between the earth and the outer heliosphere. The overall picture of the propagation of these transients is consistent with a massive, almost spherical modulating region moving outward in the heliosphere. The smooth almost exponential recovery of intensities at all three spacecraft for over 160 days after the decrease, and the large total modulation beyond P10 at the time of the decrease, suggest that the modulation boundary is well beyond 53 AU and probably beyond 100 AU.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A5; p. 7821-7825.
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  • 8
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    An observation of a heliospheric magnetic cycle dependence for the integral radial gradient of E above 60 MeV cosmic rays (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The dependence of the integral radial gradient of the cosmic radiation upon the cosmic ray intensity level and heliocentric radial distance is investigated. The magnitude of the integral radial gradient (IRG) from 1982-1990, during a period of negative polarity, is a strong function of the cosmic ray intensity changing from about 1.5 percent/AU at the time of the peak intensity in 1987 to about 3 percent/AU at times of minimum intensity in 1982 and 1990. In the early period studied from 1977 to 1982, during a period of positive polarity, practically no dependence of the magnitude of the IRG on the cosmic ray intensity was found. The gradient remained at about 3 percent/AU during the entire period. It is argued that these specific changes in the behavior of the gradient in opposite polarity cycles are not predicted by either the drift-wavy current sheet or simple diffusion-convection models of the solar modulation. The results are discussed in the context of the present understanding of the causes of the asymmetry in the 11-year modulation cycles.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 15
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  • 9
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    The onset of the new solar modulation cycle in 1987-1988 as a function of heliocentric radius and latitude (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The onset of a new solar modulation cycle were studied in 1987 and 1988, on the basis of data on counting rates of particles with E greater than 60 MeV, observed at the IMP, Voyager (V), and Pioneer (P) satellites. It was found that the decrease at earth was rapid after the intensity maximum in early 1987 and was closely correlated with the increase in the average tilt of the heliospheric current sheet. The initial rapid intensity decrease was found to be related to three small Forbush decreases which are superimposed on a more gradual decrease. By the end of 1988, the intensity decreased by about 40 percent at earth, 30 percent at V2, and 18 percent at P10. This overall decrease was accompanied by an increase in the average integral radial gradient as well as a decrease in the radial dependence of the gradient. The onset of the new solar modulation cycle seems to be related to the complete altering of the solar magnetic structure as observed on the surface of the sun.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 2253-225
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