HR: 0830h
AN: SM31B-1107    [PDF]
TI: Two peaks of Forbush decreases and SSCs in one solar cycle: What causes them?
AU: * Ahluwalia, H S
EM: hsa@stelab.nagoya-u.ac.jp
AF: H.S. Ahluwalia, Physics and Astronomy Department University of New Mexico, 800 Yale Blvd NE, Albuquerque, NM 87131-1156 United States
AU: Kamide, Y
AF: Y. Kamide, Solar Terrestrial Environment Laboratory, Nagoya University Honohara 3-13, Toyokawa, 442-8507 Japan
AB: We have studied the annual frequency distribution of the Forbush decreases (FDs) for three solar cycles (20, 21, 22). Most of them are associated with the fast ICMEs and the SSCs. The frequency varies in step with the solar cycle but the distribution has a notable gap embedded in it, near the maximum of cycle. We show that the gap coincides with the epoch of the solar polar field reversal. There is an indication of an even/odd cycle effect in the frequency distribution of FDs and the associated SSCs. Comparing the FD and SSC frequency distributions with the similar distribution of solar wind electric field, we find that the two peaks in FD and SSC distributions are separated by the Gnevyshev gap. We also show that a large value of the solar wind electric field by itself does not cause a FD to occur unless accompanied by a fast ICME.
DE: 2102 Corotating streams
DE: 2104 Cosmic rays
DE: 2111 Ejecta, driver gases, and magnetic clouds
DE: 2139 Interplanetary shocks
DE: 2162 Solar cycle variations (7536)
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting