atmospheric effects and sidereal variations of eas
TRANSCRIPT
Atmospheric effects and sidereal variations of EAS1
N. N. EFIMOV, D. D. KRASILNIKOV, S. I. NIKOLSKY, AND F. K. SHAMSUTDIXOVA Institrcte of Cosinophysical Research and Aeronomy, Yakutsk Branch, Siberian Department,
Academy of Sciences, U.S.S.R.
Received June 21, 1967
The results of observations, made during 1959-64, on intensity variations of EAS of mean sizes 1.4 x 104 to 1.4 x 105 particles at sea level are reported. Variations of shower size caused b y fluctuations in pion decay have been observed and these correlate with density variations in the atmosphere. The corrected sidereal rate shows no evidence for anisotropy of the arrival directions of showers.
The apparatus for continuous EAS observa- tions at sea level that we used is described elsewhere (Krasilnikov et al. 1962). The ex- perimental data on which this paper is based are given in Table I, where the following notation is used: C(3; 1.0; 3.8) indicates a threefold coincidence between G-M counter groups of area 1.0 m' each and separation 3.S in ("local EAS detector"); C(6; 1.0; 57) indicates sixfold coincidences between two local EAS detectors situated 57 m from one another; N is the mean size of EAS in charged particles; f and n are the mean rate and the total number of showers analyzed, respec- tively.
The geometrical effect of the atmosphere's density change is determined by the height variation of level ho - 100 mb (ho is the pressure at the observation level), using our height coefficients an calculated earlier (Kra- silnikov et al. 1962), a,(which is the tempera- ture equivalent of L Y E ) , and a,,, the observed barometric coefficient.
I11 Fig. 1, using the mean-monthly values obtained with five-year observations, is shown the EAS intensity dependence (with baro- metric correction) upon H7fo-loo, which is the height in meters of the layer of the atmosphere havinu xessure ho - 100 mb. The heights of 0.1 other isobaric levels change with the same phase as that of the ho-100 mb level, but the amplitude of their variation increases with altitude. At Yakutsk the seasonal change of
IPresented at the Tenth International Conference on Cosmic Rays, held in Calgary, June 19-30, 1967, EAS-13,24.
FIG. 1. Seasonal change of the height of the layer with pressure ho - 100 nlb and EAS intensity.
the height of the 500-mb pressure layer is 600 m, and that of the 100-mb is 1 200 m.
It is seen that with an increase in H7~~-lOo (that is with a rise in temperature and fall in density of the atmosphere above the observa- tion station) the intensity of showers, re- corded with a local EAS detector, falls steeply while for C(6; 1.0; 57) the dependence be- comes flatter and even changes sign at large values of H7fo-100. This effect of atmospheric density may be explained as the effect of decay of pions: with a decrease in the atmo- spheric density, the probability of pion decay increases, and this leads to a decrease in the shower's observed size.
In Fig. 2, are plotted EAS intensity varia- tions during the passage of a cyclone (see also Krasilnikov et al. 1964). The cyclone's period is of interest in this case. The tempera- ture changes in the atmosphere above the 700- mb level generally have a sign opposite to
Canadian Journal of Physics. Volulne 46. S84 (1968)
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EFIMOV ET AL.: SIDEKEAL V.ARIATIOSS OF EAS
TABLE I The experimental data characteristics
that observed in the lower third of the atmo- effect of the layers of the atmosphere above sphere. The results show that after correc- the 700-mb level. This indicates that the trans- tioils for barometric and local (temperature verse momenta of pions with energy 1011-1012 in near-earth layer) geometric effects, a resi- eV, generated at heights of 4 6 km, influence dual variatioil in the shower detection rate the lateral distribution of EAS particles at sea is obser~~ed. This latter effect is the geometric level.
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FIG. 2. EAS intensity variations during the passage of a cyclone. Subscripts H and h refer to corrections for height and pressure. The horizontal scale represents a period of cyclone passage (in arbitrary units).
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CANADIAN JOURNAL OF PHYSICS. VOL. 46. 1968
TABLE I1
Diurnal variations of pressure 7 ~ 0 , surface temperature T o , and EAS intensity without correc- tions. A, and t , are the amplitude and maximum time of the first harmonic, respectively
Solar time Sidereal time
A1 (%) t~ (h) -41 (%I tl (h)
In investigations of sidereal variations the usual temperature corrections should not be used, because diui-nal changes in the atmo- sphere have the special feature that diurnal temperature variations at the earth's surface are earlier in phase and larger in amplitude than those in higher layers (Efimov 1967; Efimov et al. 1966).
In this paper the barometric coefficient a,, is the usual one (see Table I ) , but the temperature coe5cient and phase shift, with which it must be used, are determined from the solar-diurnal variations given in Table 11.
From the solar-diurnal variation of pressure and using ah, we find the barometric correc- tion vector. Subtracting it from the solar- diurnal variation vector of EAS density, we have the expected temperature correction vec- tor. By comparison of the latter with the solar- diurnal variation temperature vector the temperature coefficient p, and the phase shift T between these two vectors are determined: -0.08% per "C and 2 h for C(3; 1.0; 3.8) and 0.08% per "C and 4 h for C(6; 1.0; 57). (Both types of EAS selection demonstrate the delay of the temperature vector. )
Further, using a,,, P,, and .r we find the vector sum from the intensity sidereal varia- tion vector (Table 11), and thus, at last, the
true vector of EAS sidereal variation. The results are given in Table 111.
TABLE I11 Amplitude and nlaximunl time of the first harnlonic of true sidereal EAS intensity variations according to the data for the period August 1959 to July 1964 a t Yalcutsk
Thus, primary cosmic rays with energy Eo -. 1014-1015 eV are found to be isotro~ic since any anisotropy that exists must have a first- harmonic amplitude of less than 0.1%.
REFERENCES
EFIMOV, N. N. 1967. Geomagnetizm i Aeronomiya. I n press.
EFIMOV, N. N., KRASILNIXOV, D. D., and SHAMSUT- DINOVA, F. K. 1966. Izv. Akad. Nauk SSSR (Trudy vsesoyuznoi konferentsii po kosmiches- kim lucham, Alma-Ata) . I n press.
KRA~ILNJXOV, D. D., ATAKOVA, M. M., EFIMOV, N. N., NIFONTOV, M. M., and SHAMSUTDINOVA, F. K. 1964. Kosmicheskie luchi i problemy kosmo- fiziki, str. 111, Novosibirsk.
KRASILNIKOV, D. D., EFIMOV, N. N., and NIFONTOV, M. A. 1962. J. Phys. Soc. Japan ( Suppl. A-I11 ), 17, 230.
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