Charge sign dependent recurrent modulation of galactic cosmic ray electrons and protons: Implications from Ulysses.
B. Heber
Max-Planck-Institut für Aeronomie, Germany
J.B. Blake
The Aerosspace Corporation, Los Angeles, CA 90009, USA
G. Wibberenz, V. Bothmer, Horst Kunow
Inst. für Exp. und Angew. Physik, Universität Kiel, Ohlshausenstr. 40-60, 24118 
Kiel, Germany
M.S. Potgieter and R.A. Burger
Space Research Unit, School of Physics, Potchefstroom
University for CHE, 2520 Potchefstroom, South Africa

In the 1950's Simpson and coworkers showed that recurrent cosmic ray variations, as they were first observed by Forbush, could be attributed to dynamic phenomena in the interplanetary medium. Since measurements of space probe in the interplanetary space became available it has been known that associated with the occurrence of recurrent fast and slow solar wind streams, interacting which each, other recurrent variations in the cosmic ray nuclei flux are observed. As pointed out recently by Jokipii and co workers recurrent modulation for positively and negatively charged particles may be different. In the time interval extending from July 1992 to July 1994, Ulysses on it's journey to high heliographic latitudes registered ~20 stable and long-lasting Corotating Interaction Regions (CIRs). In this work we use data from the Cosmic Ray and Solar Particle Investigation Kiel Electron Telescope (COSPIN/KET) instrument on board Ulysses to study the recurrent variation of 2.5~GV electrons and protons.
We find that 1) electrons are periodically modulated, 2) the periodicity of ~29 is longer than the period of ~26 days for protons, and 3) the amplitude is generally larger than the one observed for protons.