27 day variation of cosmic rays along with interplanetary parameters

Abstract

The linkages between solar activity and the earth's climate have been suggested and the 11-year cycle in solar activity evident in sunspot numbers is the most examined example of periodicity in previous studies, no quantitative evidence indicating a relationship for tropospheric phenomena has been found for a short period. The Sun is characterized by solar activity and solar wind (dynamical extension of solar corona) changing in time and having the asymmetrical distributions with the heliolongitudes in general. Owing to the rotation of the Sun there are observed the periodicity of 25-26 days (sidereal period) among the large range of the quasi-periodic changes of different parameters of solar activity and solar wind as viewed from the arbitrary point of the interplanetary space; the same periodicity as viewed from the Earth equals 27-28 days (sinodial period). It is accepted that the periodicities of solar and geomagnetic activities, solar wind, galactic cosmic rays and other parameters characterizing the solar-terrestrial relationships connected with the Sun's rotation are called the 27-day variations, instead this periodicity can be slightly different. The observed modulation of galactic cosmic ray intensity on time and spatial scales contains information regarding their transport in the helios- phere. We used the data of cosmic ray neutron monitor as well as interplanetary parameters to identify the correlation between their 27-day variations. The 27-day variation of cosmic ray intensity is found to linearly correlated with the interplanetary magnetic field strength (B), the north south component (Bz) of the interplanetary magnetic field vector and the product of the solar wind speed (V) times B (V x B). The cross correlation function of the 27-day cosmic ray variation versus the solar wind speed shows a negative correlation. However, the 27-day variation of cosmic rays is correlated with the variation in both the x- and y- components of inter- planetary magnetic field. The most significant 27-day variations of CR were found not to correlate with those of other solar indices.