Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsh11c1128b&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SH11C-1128
Physics
2104 Cosmic Rays, 2139 Interplanetary Shocks
Scientific paper
The Fisk model of the heliospheric magnetic field (HMF) has proven to be quite difficult to implement in three-dimensional numerical modulation codes. To overcome certain difficulties, we have developed a divergence-free hybrid HMF, which is a Fisk HMF at mid-latitudes, but changes to a Parker HMF in the solar equatorial plane and above the solar poles. Although this field will under-estimate the effects of the Fisk field, its use should give some insight into the effect of an HMF with a periodic meridional and azimuthal components on cosmic-ray modulation. To study the properties of this hybrid field, we solve the three-dimensional steady-state TPE in a system corotating with the Sun, using spherical coordinates in an ADI numerical scheme which covers the entire heliopshere. In this paper we investigate 27-day recurrent variations of both protons and electrons with our model. We find that the amplitude of these variations is directly proportional to the latitudinal gradient in the intensity, in agreement with observational studies. Moreover, we find that this relation becomes less clear if drift effects are reduced in the model. We also consider variations in the magnitude of the components of the HMF observed by the Ulysses spacecraft during its 1994/5 Fast Latitude Scan. Based on a theoretical analysis which predicts a long-term variation in the azimuthal component of the Fisk field, we searched for such variations in Ulysses magnetic field data. Our preliminary analysis shows quasi-periodic variations with periods of the order of several times the solar equatorial rotation period.
Burger R. A.
de Jager Ocker C.
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