Modulation loops, time lag and relationship between cosmic ray intensity and tilt of the heliospheric current sheet
Department of Physics, Aligarh Muslim University, Aligarh 202 002, India e-mail: firstname.lastname@example.org
2 Department of Physics, Hindustan Institute of Technology, Greater Noida, India e-mail: email@example.com
Accepted: 26 January 2007
Aims.We study certain aspects of the solar modulation of galactic cosmic ray intensity during different solar activity cycles and in different polarity states of the heliosphere.
Methods.We plotted modulation loops between the cosmic ray intensity and the tilt angle of the heliospheric current sheet during three solar activity cycles 21, 22 and 23 and obtained the area of modulation loops. The time lag between the tilt angle and the cosmic ray intensity in odd, even solar activity cycles and during 0, 0 polarity states of the heliosphere are determined using correlation analysis. Rate of intensity decrease with tilt angle during different solar and magnetic cycles are estimated from best fit method.
Results.Marked differences during the two odd and the one even solar cycles, as well as during different polarity states of the solar magnetic field ( 0 and 0) are found. We observe variations in finer features of modulation loops obtained using one, three, six and twelve rotation averaged data. We find that the time lag in even cycle (22) is much different from that in odd cycles (21, 23). Moreover, considerable difference in time lags are also observed during 0 and 0 polarity states of the heliosphere. We also find that the cosmic ray intensity decreases at much faster rate (and with better correlation) with increase in tilt angle during 0 than 0, indicating stronger response to the tilt angle changes during 0. These results are discussed in the light of 3D modulation models including the gradient and curvature drifts and the tilt of the heliospheric current sheet.
Key words: cosmic rays / Sun: activity / solar wind / solar-terrestrial relations
© ESO, 2007