Nonlinear Processes in Geophysics www.nonlin-processes-geophys.net 1023-5809 1607-7946 6 3/4 1999 10.5194/npg-6-235-1999 http://www.nonlin-processes-geophys.net/6/235/1999/ http://www.nonlin-processes-geophys.net/6/235/1999/npg-6-235-1999.html http://www.nonlin-processes-geophys.net/6/235/1999/npg-6-235-1999.pdf 235 242 0000-00-00 Energetic particle cross-field diffusion: Interaction with Magnetic Decreases (MDs) B. T. Tsurutani G. S. Lakhina D. Winterhalter J. K. Arballo C. Galvan R. Sukurai Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA Indian Institute of Geomagnetism, Colaba, Mumbai/Bamobay, India Magnetic field Decreases (MDs) are detected in the heliospheric polar regions. The MDs have minimum spatial scales sizes of 25 proton thermal gyroradii, and are typically bounded by tangential or rotational discontinuities. The distribution of the magnitudes of the decreases within AIDs is a continuum, with the smallest decreases being most frequent in occurrence. The largest decreases can be 80% of the ambient field. The thickness distribution is also a continuum, and is shown to be independent of the field magnitude decrease. Charged particle interactions with the MDs lead to particle guiding center displacements and hence particle cross-held diffusion. We develop a diffusion model to apply to energetic ion interactions with MDs using the MD properties described in this paper. One specific day of data is used to illustrate that the particle cross-field diffusion will be extremely rapid due to such interactions.