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At least 991 records · Page 55
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NASA NTRS1985

First zonal harmonic component of cosmic ray neutron intensity

Cosmic ray neutron data from the cosmic ray stations from the worldwide network in 1966, 1967 and 1969 are analyzed by means of the three dimensional analysis method by Nagashima. The variations of the north-south anisotropy, which is the first zonal harmonic component obtained from the analysis are studied. The result obtained confirms earlier findings. Relationship of the anisotropy to the interplanetary magnetic field sector polarity is also studied.

Takahashi, H.↗
NASA NTRS1985

The corotating variation of the north-south anisotropy of cosmic rays

Correlation analysis on the relation of the north-south (N-S) anisotropy of cosmic rays, observed by the Nagoya multidirectional meson telescope, with the interplanetary magnetic field (IMP) as well the solar wind velocity within solar Carrington rotation for the period 1971 to 1976 is discussed. It is found that the N-S anisotropy of cosmic rays correlates quite well with the Bx component of the IMF. The correlation coefficient is nearly equal to 0.8.

Xue, S.↗
NASA NTRS1985

A study of periodicities and recurrences in solar activity and cosmic ray modulation

The 154d periodicity was found in the cosmic ray intensity (RE) vs Flares, and some other peaks of coherency in the RC vs aa sub I, that when interpreted as aliased values, might correspond to recurring interplanetary magnetic field structures and solar wind streams. It cannot be excluded, however, that some of the correspondence with aa are of terrestrial origin. This study cannot be considered exhaustive due to the fact that other solar variables, such as polar hole size, are possibly correlated to cosmic ray intensities. However, the number of observations is small so that the interpretation of the results is very difficult.

Attolini, M. R.↗
NASA NTRS1985

Dynamics of two-year cosmic ray variations inferred from the data of spacecraft and stratospheric measurements and from the neutron monitor data in 1959-1981

The two year cosmic ray variations are studied using the spacecraft measurements of 1967 to 1976, the sonde measurements at high latitudes in the stratosphere (Murmansk, Mirny), and the neutron monitor data of 1959 to 1981. The two year variations are most pronounced from 1967 to 1975. An anticorrelation is observed between the two year variations in cosmic rays and in geomagnetic activity.

Charakhchyan, T. N.↗
NASA NTRS1985

Long-term modulation of galactic cosmic rays in high-energy region

The results of continuous registration of the cosmic ray muon intensity on the ground and underground at 7, 20 and 60 m w.e. depths in Yakutsk for 1957 to 1983 are presented. In years of the solar activity maximum in cosmic ray density were found two minima or two-stepped decrease. The second intensity minimum appears to be not the result of the inversion of the general magnetic field of the Sun but caused by the increase of the solar wind speed.

Krivoshapkin, P. A.↗
NASA NTRS1985

Solar tri-diurnal variation of cosmic rays in a wide range of rigidity

Solar tri-diurnal variations of cosmic rays have been analyzed in a wide range of rigidity, using data from neutron monitors, and the surface and underground muon telescopes for the period 1978-1983. The rigidity spectrum of the anisotropy in space is assumed to be of power-exponential type as (P/gamma P sub o) to the gamma exp (gamma-P/P sub o). By means of the best-fit method between the observed and the expected variations, it is obtained that the spectrum has a peak at P (=gamma P sub o) approx = 90 GV, where gamma=approx 3.0 and P sub o approx. 30 GV. The phase in space of the tri-diurnal variation is also obtained as 7.0 hr (15 hr and 23 hr LT), which is quite different from that of approx. 1 hr. arising from the axisymmetric distribution of cosmic rays with respect to the IMF.

Mori, S.↗
NASA NTRS1985

The cosmic ray differential diurnal variation dependences on the zenith angle and the geomagnetic disturbance

Simultaneous and continuous muon measurements in two opposite azimuthal directions under equal zenith angles demonstrated the importance of this method for cosmic ray diurnal variation investigations. Lately these measurements were extended by means of improved telescopes. The obtained cosmic ray diurnal variations were presented as intensity differential curves. Theoretical investigations connected the properties of these curves with some interplanetary spece parameters. The harmonics of these curves were interpreted physically. Some order difference curves were introduced. In earlier works some dependences between the parameters characterizing the first and the second harmonics of the differential intensity curves and the geomagnetic activity were found. Then all measurements were carried out under only one zenith angle. The results of investigations of similar dependences using data of simultaneous measurements under three different zenith angles are presented.

Kavlakov, S.↗
NASA NTRS1985

Solar cycle variations of the anomalous cosmic ray component

The intensity of the anomalous cosmic ray component, consisting of He, N, O, and Ne, has long been known to be especially sensitive to the effects of solar modulation. Following its discovery in 1972, this component dominated the quiet time flux of cosmic ray nuclei below approx. 30 MeV/nucleon during the 1972 to 1978 solar minimum, but then became essentially unobservable at 1 AU with the approach of solar maximum conditions. One recent theoretical model predicts substantial differences in the intensity of the anomalous fluxes from one solar minimum period to the next because of the reversal of the solar magnetic field. Using data from the Caltech experiments on IMP-8 and ICE (ISEE-3), the intensity of anomalous O and He at 1 AU during the years 1972 to 1985 is reported in particular. Whether the anomalous fluxes will return to their 1972-1978 levels, as predicted by spherically symmetric modulation models, or whether they will fail to return to 1 AU, as suggested by modulation models in which gradient and curvature drifts dominate are to be determined. The preliminary analysis of data from 1984 shows that the intensity of 8 to 27 MeV/nucleon O is still more than an order of magnitude below its 1972 to 1978 levels, while the intensity of 25 to 43 MeV/nucleon He is a factor of Approx. 8 below its maximum level in 1977.

Mewaldt, R. A.↗
NASA NTRS1985

The large scale dynamics of the outer heliosphere and the long-term modulation of galactic cosmic rays

The network of cosmic ray observatories reaching across the heliosphere has given new insight into the process of solar modulation, establishing that the decreases occur principally in the outer heliosphere and are produced by interplanetary flow systems; that the hysteresis effects appear to be produced by changes in the rigidity dependence of the diffusion coefficient and that the predicted effects on the cosmic ray gradients associated with the reversal of the solar magnetic field polarity are not observed.

Mcdonald, F. B.↗
NASA NTRS1985

Anomalous short-term increases in the galactic cosmic ray intensity: Are they related to the interplanetary magnetic cloud-like structures?

Thirty-one short-term increases (time duration 24 hours and amplitude up to 5%) in the galactic cosmic ray intensity, occurring inside Forbush decreases events, have been identified over the period 1966 - 1977. These increases are highly anisotropic and occur after the compression region following the shock; the interplanetary medium is characterized by intense ( 10 nT) and higly fluctuating magnetic field B, high velocity, low density and temperature (flare ejecta piston?). These B-fluctuations seem to be ordered variations which could be representative of magnetic clouds. Also the large cosmic ray increase occurring on 17-18 September 1979, belongs to this category of events.

Iucci, N.↗
NASA NTRS1985

Study of dominating parameters of high speed solar plasma streams in relation to cosmic ray and geomagnetic storms

The high speed solar wind streams observed near Earth are generally associated with the solar features, such as solar flares and coronal holes. Past studies of these streams from the two sources have revealed distinctly different effects on cosmic ray intensity, whereas the effect is similar for geomagnetic disturbances. Moreover, the effect of the magnitude of the high speed streams (V) and its rate of increase (dv/dt) has also been a subject of investigation to understand their relative contribution in producing geomagnetic disturbances. From the analysis of some of the fast streams presented here, it is difficult to predict, which one of the two (V, dv/dt) is more effective in producing geo-magnetic disturbances. Further, in most of the cases, no substantial decrease in cosmic ray intensity is observed.

Mishra, B. L.↗
NASA NTRS1985

Observations of cosmic-ray modulations in the fall, 1984

Modulation of cosmic-ray energy spectrum was studied by using the Turku double neutron monitor. The multiplicity region of detected neutrons produced by cosmic ray hadrons in the monitor was divided into seven categories corresponding to mean energies 0.1, 0.3, 1.0, 3.2, 8.6, 21, and 94 GeV of hadrons at sea level. Based on 24-hour frequencies, a statistical analysis showed that modulation of the intensity in all categories occurred during several periods in the fall 1984. The magnitude of the variation was a few per cent.

Torsti, J. J.↗
NASA NTRS1985

The theoretical and experimental investigation of cosmic ray Forbush-effects

The theoretical results of analysis of the expected spatial distributions of density, gradients and anisotropy of cosmic rays, obtained on the basis of the numerical solution of anisotropic diffusion equation in the presence of the disturbances of shock wave type in the interplanetary space are presented. The theoretical calculations on the definition of the energy spectrum and anisotropy of galactic cosmic rays during Forbush effect are compared with the experimental data.

Alania, M. V.↗
NASA NTRS1985

Cosmic ray modulation by high-speed solar wind fluxes

Cosmic ray intensity variations connected with recurrent high-speed fluxes (HSF) of solar wind are investigated. The increase of intensity before the Earth gets into a HSF, north-south anisotropy and diurnal variation of cosmic rays inside a HSF as well as the characteristics of Forbush decreases are considered.

Dorman, L. I.↗
NASA NTRS1985

Cosmic rays 10Be biennal data and their relationship to aurorae and sunspots

The galactic cosmic ray (C.R.) variations which should give information on three dimensional aspects of the heliospheric magnetic fields and on the solar wind, which modulate their influx into the Solar System were studied. In order to decode the information from the C.R. series it is necessary to know the mechanisms through which the modulation is produced. It it clear that a balance of effects with sources at different heliospheric latitudes results in the modulated C.R. intensity. It is found that the modulation of 10Be in polar ice may be due to at least two main contributions: (1) negative and in phase with the Solar flare activity modulating the cosmic ray flux in Forbush-type decreases, and (2) positive in phase with the appearance of large wind streams situated at both polar coronal holes. It is found that the high heliolatitude activity is related to a stable periodicity of 11.1y whereas the low heliolatitude activity contributes to the wondering of the solar cycles.

Attolini, M. R.↗
NASA NTRS1985

When did the average cosmic ray flux increase?

A new 129 to 129 Xe method to obtain cosmic ray exposure ages and to study the average cosmic ray flux on a 10 to the 7th power to 10 to the 8th power year time-scale was developed. The method is based on secondary neutron reactions on Te in troilite and the subsequent decay of 129I, the reaction product to stable 129 Xe. The first measurements of 129 I and 129 Xe in aliquot samples of a Cape York troilite sample are reported.

Nishiizumi, K.↗