Charge sign dependent recurrent modulation of galactic cosmic
ray electrons and protons: Implications from Ulysses.
J.B. Blake
The Aerosspace Corporation, Los Angeles, CA 90009, USA
G. Wibberenz, V. Bothmer
Inst. f"ur Exp. und Angew. Physik, Universit"at 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.