Cosmic ray intensity variations during 0200-0700 UT, August 5, 1972

Venkatesan, D.; Mathews, T.; Lanzerotti, L. J.; Fairfield, D. H.; Bostrom, C. O.

doi:10.1029/ja080i013p01715

Cited by 18 publications

(10 citation statements)

References 10 publications

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“…Pomerantz and Duggal [1973] report on the ''record-breaking'' Forbush decrease of 4 August 1972 which reduced GCR intensity at the South Pole by 35%, at which time solar wind speed (measured by Pioneer 9 at 0.78 a.u.) jumped above 1200 km/s [Mathews and Lanzerotti, 1973]; IMF increased sharply from 5 to 40 nT [Venkatesan et al, 1975]. The magnetic field configuration of the accompanying shock [Lockwood et al, 1975] led to an intensity decrease in MTs deep underground [Swinson, 1973] and in IC and underground MTs at Yakutsk [Filippov et al, 1973] as well as the multidirectional MTs at Nagoya [Sekido et al, 1973].…”

Section: Forbush Decrease Of August 1972mentioning

confidence: 99%

Cosmic ray detector response to transient solar modulation: Forbush decreases

Ahluwalia

Fikani

2007

J. Geophys. Res.

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[1] The observed modulation of galactic cosmic ray (GCR) intensity, on time and spatial scales, contains information regarding their transport in the heliosphere. One way to extract crucial information from the data is to study the rigidity dependence of modulation. A methodology is described to study the rigidity dependence of the short-term variations in galactic cosmic ray intensity Earth, in terms of the median rigidity of detector response (R m ) to cosmic ray spectrum. We define R m as the rigidity below which lies 50% of detector counting rate. For neutron monitors (NMs), it is easily calculated from the latitude survey obtained at sea level and higher elevations. We compute R m values for some NM sites; solar cycle dependence for them is shown to be small. Their practical utility is demonstrated in a study of transient cosmic ray solar modulation (Forbush decreases (FDs)), using data published in the literature. We plot the rigidity dependence of the amplitudes of three large Forbush decreases that occurred during the declining phase of three solar cycles (19, 20, and 21). We show that the Forbush decrease amplitude varies inversely with R m over a large range (1 to 300 GV) of GCR rigidities. Thereby, we rule out the existence of a ''transition rigidity'' suggested by Jokipii even for a short-term modulation (large Forbush decreases). We speculate that the force field model may be applicable to large Forbush decreases.

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Section: Forbush Decrease Of August 1972mentioning

confidence: 99%

Cosmic ray detector response to transient solar modulation: Forbush decreases

Ahluwalia

Fikani

2007

J. Geophys. Res.

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“…During the same time interval, the magnetic field increases very much to --100y at Pioneer 9 (Mihalov et al, 1974) and -50y at Explorer 41 (Venkatesan et al, 1975) at the very beginning of this event, and changed direction many times. Later, when the higher velocity solar wind covered the Earth, the magnetic field which by then had returned to lower magnitudes of the order of 40y (HEOS-2) increased again to higher values, which differed from one satellite to the other.…”

Section: Changes In the Interplanetary Mediummentioning

confidence: 99%

“…During the same time period and at Explorer 41 and Prognoz 2 simultaneously the magnetic field magnitude drops from -40y to 103, and after two hours recovers again to 40% Figure 6 (cf. Figure 2 by Yeroshenko et al (1977) and Figure 2 by Venkatesan et al (1975)). Otaola et al (1977b), using a 'Dryer type' double shock ensemble, analysed the propagation of energetic solar protons during the August 1972 events.…”

Section: The Cosmic Ray Increase 3--7 Utmentioning

confidence: 99%

“…In Figure 6 the solar wind velocity from HEOS-2 (-5 min measurements) and Prognoz and Prognoz 2 (hourly values) Zastenker et al (1978), together with the interplanetary magnetic field vector and particle measurements from Explorer 41 (Venkatesan et al, 1975) and a ground based neutron monitor from Calgary. Figure 7 shows solar wind velocity, plasma density and temperature from Prognoz and Prognoz 2.…”

Section: Trapping and Accelerationmentioning

confidence: 99%

“…Data from Explorer 41 (Venkatesan et al, 1975), Prognoz and Prognoz 2 (Zastenker et al, 1976;Yeroshenko et al, 1977) were also used. Explorer 41, HEOS-2, Prognoz and Prognoz 2 were Earth orbiting satellites, i.e.…”

Section: Introductionmentioning

confidence: 99%

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Particle trapping and acceleration during the August 1972 event

Moussas

1980

Sol Phys

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Several features of the August 1972 events are studied using neutron monitor data together with solar wind streamlines calculated on the basis of an approximate kinematic approach. Examination of the evolution of these streamlines shows that the streamline which passes from the Earth undergoes dramatic changes during the main phase of these events. In a few hours this streamline, which was estimated with HEOS-2 solar wind velocity data, was decreased (i.e., compressed) to a total radial extend of 0.2 AU (at the beginning of 5 August), although its initial length was 1 AU. An exact MHD time-dependent solution by Dryer et al. (1978a) gives similar results.The relative cosmic ray increase (3-7 UT, 5 August), immediately after the deep F.d., is attributed to trapping and acceleration of particles between two shock waves. Similar acceleration was found by Pomerantz and Duggal (1974) and Levy et al. (1976) for another cosmic ray increase during this event.The extremely large solar wind velocities during the main phase of the event are not only due to the large energy of the flare but also to the fact that the ambient solar wind was already almost empty because of the sweeping action of previous shock waves.

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Fields and plasmas in the outer solar system

Smith

Wolfe

1979

Space Sci Rev

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The most significant information about fields and plasmas in the outer solar system, based on observations by Pioneer 10 and 11 investigations, is reviewed. The characteristic evolution of solar wind streams beyond 1 AU has been observed. The region within which the velocity increases continuously near 1 AU is replaced at larger distances by a thick interaction region with abrupt jumps in the solar wind speed at the leading and trailing edges. These abrupt increases, accompanied by corresponding jumps in the field magnitude and in the solar wind density and temperature, consist typically of a forward and a reverse shock. The existence of two distinct corotating regions, separated by sharp boundaries, is a characteristic feature of the interplanetary medium in the outer solar system. Within the interaction regions, compression effects are dominant and the field strength, plasma density, plasma temperature and the level of fluctuations are enhanced. Within the intervening quiet regions, rarefaction effects dominate and the field magnitude, solar wind density and fluctuation level are very low. These changes in the structure of interplanetary space have significant consequences for the many energetic particles propagating through the medium. The interaction regions control the access to the inner solar system of relativistic electrons from Jupiter's magnetosphere. The interaction regions and shocks appear to be associated with an acceleration of solar protons to MeV energies. Flare-generated shocks are observed to be propagating through the outer solar system with constant speed, implying that the previously recognized deceleration of flare shocks takes place principally near the Sun. Radial gradients in the solar wind and interplanetary field parameters have been determined. The solar wind speed is nearly constant between 1 and 5 AU with only a slight deceleration of =30 km s -~ on the average. The proton flux follows an r -2 dependence reasonably well, however, the proton density shows a larger departure from this dependence. The proton temperature decreases steadily from 1 to 5 AU and the solar wind protons are slightly hotter than anticipated for an adiabatic expansion. The radial component of the interplanetary field falls off like r -2 and, on the average, the magnitude and spiral angle also agree reasonably well with theory. However, there is evidence, principally within quiet regions, of a significant departure of the azimuthal field component and the field magnitude from simple theoretical models. Pioneer 11 has obtained information up to heliographic latitudes of 16 ~ Observations of the interplanetary sector structure show that the polarity of the field becomes gradually more positive, corresponding to outward-directed fields at the Sun, and at the highest latitudes the sector structure disappears. These results confirm a prior suspicion that magnetic sectors are associated with an interplanetary current sheet surrounding the Sun which is inclined slightly to the solar equator.

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Cosmic ray intensity variations during 0200-0700 UT, August 5, 1972

Cited by 18 publications

References 10 publications

Cosmic ray detector response to transient solar modulation: Forbush decreases

Cosmic ray detector response to transient solar modulation: Forbush decreases

Particle trapping and acceleration during the August 1972 event

Fields and plasmas in the outer solar system

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