Geomagnetic plasma probe for solar wind

Magnetograms from Alibag reveal that the range Δ H of the daily variation of the horizontal component is negatively correlated with the minimum value ΔHmin, during a day. This relationship is largely unaffected by the degree of geomagnetic disturbance and holds good during all phases of the 11-year cycle of solar activity. From the nature of the relationship between ΔH and ΔHmin. it is concluded that the daily variation of the geomagnetic field at a low latitude station outside the influence of the equatorial electroject must be regarded as largely due to a weakening of the ambient field on the night side rather than an enhancement of the field on the day side due to ionospheric currents. There exists a good correlation between (ΔH)2 and the kinetic energy density of the solar wind in interplanetary space measured by IMP-1 satellite. It is suggested that ΔH is largely the result of the partial ring currents related to the convective drift of the plasma from the tail of the magnetosphere. Moreover, using the relationships established during the IMP-1 period, the annual mean kinetic energy density of solar wind for geomagnetically quiet days for the past 11-year cycle is estimated, treating the earth as a plasma probe

Study of the anisotropy of cosmic rays with narrow angle telescopes

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Meteorological and extra-terrestrial causes of the daily variation of cosmic ray intensity

The daily variations of total cosmic ray intensity and the intensities of meson and electron components have been studied at Alimedabad with vertical geiger counter telescopes. The influence of meteorological factors on these variations has been examined, and it has been found that appropriate barometric coefficients for correcting the cosmic ray intensities can be obtained from a consideration of the semidiurnal components of the variations. The barometric coefficients for the three intensities are βr = -4.2% percm.Hg, βM = -2.4% percm.Hg. βK = -14.0% percm.Hg. The cosmic ray intensity variations are corrected with the appropriate coefficients for the daily variation of barometric pressure. No significant variation is then left in the electron intensity, implying that variations of this component are mostly caused by the mass absorption effect with a variation of barometric pressure. In total intensity and in meson intensity, on the other hand, there is a significant residual variation of about ·3% in amplitude. This is mainly diurnal in character with a maximum at 0900 hours I.S.T. Reasons are given for concluding that the meson residual variation is not primarily caused by either the diurnal variation of temperature in the atmosphere or of geomagnetic elements. It is finally concluded that the bulk of the meson residual diurnal variation is extra-terrestrial in origin and is caused by continuous solar emission of cosmic ray particles. This conclusion is discussed in terms of the interpretation of omnidirectional and unidirectional measurements of the diurnal variation by other workers. A connection between changes in the amplitude and the hour of maximum of the diurnal variation has been suggested

A solar flare type increase in cosmic rays at low latitudes

During the hour following the big solar flare on 23-2-1956, an average increase of +5.7 ± 0.8% has been observed in meson intensity measured with standard telescopes at Ahmedabad, Kodaikanal and Trivandrum. This is the first report of a significant solar flare type increase in cosmic rays near the geomagnetic equator. If the increase is due to solar protons travelling in approximately direct paths, the energy of the protous must extend from about 35-67.5 Bev. It is estimated that the average flux of such protons is approximately equal to 1.5 times the flux of general cosmic ray intensity in the same energy range. During the hour, the sun is estimated to have emitted more than 1028 protons of about 50 Bev energy

Variations of intensity and anisotropy of cosmic rays measured at the geomagnetic equator

A study of cosmic ray intensity variations has been conducted during 1956–57 at the equatorial mountain station of Kodaikanal, using a standard neutron monitor. The data have been examined to look for the relationship between the day-to-day changes of intensity, the variance of bi-hourly deviations, the occurrence of large bi-hourly deviations at different hours of the day and the associated parameters of the daily variation. The results are related to the electromagnetic state of interplanetary space as determined by streams of solar matter in the neighbourhood of the earth, carrying with them frozen magnetic fields. Comparison is made with the model elaborated by Dorman. The principal conclusions are as follows: (1) Day-to-day changes of intensity involve increases as well as decreases with respect to a base intensity for the period in question. (2) The daily variation of intensity of local neutrons, at an equatorial mountain station during 1956–57, has often a large diurnal as well as a semi-diurnal component. (3) On days of high geomagnetic disturbance, the daily variation exhibits abrupt changes indicative of the source being situated at a distance shorter than the range of the geomagnetic field. On geomagnetically quiet days, the daily variation has a form consistent with its being related to an anisotropy in interplanetary space. On days of moderate geomagnetic disturbance, the daily variation has changeable characteristics. (4) Correlated day-to-day changes of mean intensity and daily variation have been confirmed. For geomagnetically disturbed days, the semidiurnal component is greater than the diurnal component for increases of intensity, and conversely for decreases of intensity. (5) An examination of the time series of Cp for high intensity and for low intensity indicates the presence of a component of the frozen magnetic field in the direction of the solar dipole field. However, during the period of observation the solar dipole field and the sunspot field were in the same direction. Therefore, the results obtained cannot be considered either to confirm or refute the possibility of beams carrying sunspot fields with them

Short-period fluctuations of cosmic ray intensity at the geomagnetic equator and their solar and terrestrial relationship

By using power spectrum analysis on the μ meson intensity records of a high counting rate instrument (106 counts/min) operated at Chacaltaya, Bolivia, it has been possible to identify the presence of cosmic ray fluctuations of 15 to 19 and 25 to 28 cycles per hour (cph). These frequencies were found at a 99% level of significance in the average of 1034 three-hour samples extending from November 1965 to June 1966. Comparison with Pioneer 6 measurements (Ness et al., 1966) indicates that the magnetosheath field, at a distance of about 10 earth radii (RE), and the interplanetary magnetic field show peaks in spectral density that correspond closely (though not identically) with peaks in muon intensity. It is most plausible that these cosmic ray fluctuations are caused by the fluctuations of geomagnetic field corresponding to an amplitude of about 20 γ in the dipole magnetic field. Magnetic field measurements conducted in the magnetosphere by Explorer 6 (Judge and Coleman, 1962) and Explorer 12 (Patel and Cahill, 1964) show similar oscillations. Recent observations by ATS 1 confirm the presence of magnetic oscillations of similar frequencies at about 6 RE . These frequencies are also found in the geomagnetic micropulsations observed at the surface of the earth. The integrated power of cosmic ray oscillations in the frequency range of 6 to 30 cph has been studied at various periods, and its solar-terrestrial relationship is examined. The association of observed frequencies in cosmic rays with frequencies in the solar photosphere and the interplanetary magnetic field, as well as the resonance frequencies of the magnetosphere, are discussed

Time variations of directional cosmic ray intensity at low latitudes. I. Comparison of daily variation of the intensity of cosmic rays incident from East and West

A study has been conducted at Ahmedabad during 1957 and 1958 of the time variations of meson intensity incident from east and west at 45° to the vertical. A characteristic difference of about 6 h in the diurnal time of maximum for the east and west directions is observed to occur on many days and this has been interpreted as signifying an anisotropy of primary radiation caused by a source outside the influence of the geomagnetic field. However, there are many days on which the daily variation has a maximum near noon for both directions. On such days the predominant influence is that of a local source situated within the influence of the geomagnetic field. The local source is associated with geomagnetically disturbed days. Long-term changes in the daily variation are found to be similar for the east, vertical and west directions

Changes of solar anisotropy and of the intensity of cosmic radiation

Solar and terrestrial relationships of the changes of anisotropy have been studied, and theories have been advanced to explain the creation of the anisotropy by a modulation of cosmic-ray intensity incident at particular directions. The results of the investigation presented are of a preliminary character and indicate certain tentative conclusions which can be drawn from the analysis of data from narrow-angle telescopes operated over a period of eleven months in 1956. One of the most important conclusions is that there is a definite correlation between day to day changes of anisotropy and the daily mean intensity