Heliospheric modulation of cosmic ray protons : Role of enhanced perpendicular diffusion during periods of minimum solar modulation

The effect of enhanced perpendicular diffusion in the polar regions of a simulated heliosphere seems required in drift models for the modulation of galactic cosmic rays in order to find a latitude dependence of cosmic ray protons in the inner heliosphere that is compatible with Ulysses observations. This effect was studied in detail to establish how important it is and to understand the role it plays in global cosmic ray modulation, particularly during minimum modulation periods. After searching through a large parameter space, it was found that enhanced perpendicular diffusion was indeed necessary to obtain compatibility with observations in the inner heliosphere, especially during A > 0 magnetic field polarity epochs (e.g., from 1990 to ∼2000). This approach, however, also increased the radial dependence during this epoch. Switching to A 0 and A < 0 solar minimum modulation periods.

[1]  John W. Bieber,et al.  Numerical Investigation of Perpendicular Diffusion of Charged Test Particles in Weak Magnetostatic Slab Turbulence , 2000 .

[2]  G. Zank,et al.  An evaluation of perpendicular diffusion models regarding cosmic ray modulation on the basis of a hydromagnetic description for solar wind turbulence , 1999 .

[3]  Joe Giacalone,et al.  The Transport of Cosmic Rays across a Turbulent Magnetic Field , 1999 .

[4]  L. Fisk,et al.  Mechanisms for Latitudinal Transport of Energetic Particles in the Heliosphere , 1999 .

[5]  C. K. Saikia,et al.  Seismic source and structure estimation in the western Mediterranean using a sparse broadband network , 1999 .

[6]  M. Hattingh,et al.  Toward a Realistic Diffusion Tensor for Galactic Cosmic Rays , 1998 .

[7]  J. Lockwood,et al.  Intensities of anomalous and galactic cosmic rays in the outer heliosphere near the heliospheric equator in 1987 and during the period from 1994 to 1996 , 1997 .

[8]  M. Potgieter.  Heliospheric modulation of galactic electrons: Consequences of new calculations for the mean free path of electrons between 1 MeV and ∼10 GeV , 1996 .

[9]  L. Fisk.  Motion of the footpoints of heliospheric magnetic field lines at the Sun : Implications for recurrent energetic particle events at high heliographic latitudes , 1996 .

[10]  S. Suess,et al.  Ulysses solar wind plasma observations from pole to pole , 1995 .

[11]  D. Mccomas,et al.  The underlying magnetic field direction in Ulysses observations of the southern polar heliosphere , 1995 .

[12]  M. Hattingh,et al.  Steady-state drift-dominated modulation models for galactic cosmic rays , 1995 .

[13]  J. Phillips,et al.  Ulysses solar wind observations to 56° south , 1995 .

[14]  M. Potgieter,et al.  The simulation of complete 11 and 12 year modulation cycles for cosmic rays in the heliosphere using a drift model with global merged interaction regions , 1995 .

[15]  J. Simpson,et al.  Ulysses out-of-ecliptic observations of “27-day” variations in high energy cosmic ray intensity , 1995 .

[16]  M. Potgieter,et al.  The modulation of cosmic rays in the high latitude heliosphere: A computer simulation , 1995 .

[17]  H. Sierks,et al.  Propagation of jovian electrons in and out of the ecliptic , 1993 .

[18]  Jiasheng Chen,et al.  Cosmic-ray anisotropies and gradients in three dimensions , 1993 .

[19]  J. Lockwood,et al.  On the interplanetary cosmic ray latitudinal gradient , 1992 .

[20]  M. Potgieter,et al.  The simulated features of heliospheric cosmic-ray modulation with a time-dependent drift model. I - General effects of the changing neutral sheet over the period 1985-1990 , 1992 .

[21]  M. Potgieter,et al.  A time-dependent drift model for the long-term modulation of cosmic rays with special reference to asymmetries with respect to the solar minimum of 1987 , 1990 .

[22]  M. Potgieter,et al.  Interplanetary cosmic ray radial gradients with steady state modulation models , 1989 .

[23]  M. Potgieter,et al.  A drift model for the modulation of galactic cosmic rays , 1985 .

[24]  J. Jokipii,et al.  Effects of drift on the transport of cosmic rays. VI - A three-dimensional model including diffusion , 1983 .

[25]  L. Fisk.  Solar modulation of galactic cosmic rays, 4. Latitude-dependent modulation , 1976 .

[26]  E. Parker,et al.  Stochastic aspects of magnetic lines of force with application to cosmic-ray propagation. , 1969 .

[27]  S. Ferreira.  Comparison of a Two- and Three-Dimensional Drift Model , 1999 .

[28]  J. Kota.  Cosmic-ray Modulation and the Structure of the Heliospheric Magnetic Field , 1999 .

[29]  B. Heber,et al.  The heliospheric Modulation od Cosmic ray Electrons: Rigidity Dependence of the perpendicular Diffusion Coefficient , 1999 .

[30]  M. Potgieter.  The heliospheric modulation of galactic cosmic rays: The role of perpendicular diffusion enhanced in the polar regions of the heliosphere , 1999 .

[31]  J. Giacalone.  Particle Drifts in a Fluctuating Magnetic Field , 1999 .

[32]  R. B. Mckibben.  Three-dimensional Solar Modulation of Cosmic Ray and Anomalous Components in the Inner Heliosphere , 1998 .

[33]  B. Heber,et al.  The modelling of the latitude dependence of cosmic ray protons and electrons in the inner heliosphere , 1997 .

[34]  C. Steenberg,et al.  An alternative approach to the modeling of anomalous cosmic ray intensities in the heliosphere , 1997 .

[35]  B. Heber,et al.  Spatial variation of >40 MeV/n nuclei fluxes observed during the Ulysses rapid latitude scan , 1996 .

[36]  H. Moraal,et al.  3. Steady state drift solutions of the transport equation , 1996 .

[37]  M. Potgieter,et al.  Long-term Cosmic-Ray Modulation along the Ulysses Trajectory: A Numerical Simulation , 1995 .

[38]  J. Jokipii,et al.  3-D Distribution of Cosmic Rays in the Outer Heliosphere , 1995 .

[39]  John W. Bieber,et al.  Proton and Electron Mean Free Paths: The Palmer Consensus Revisited , 1994 .

[40]  M. Potgieter,et al.  The Simulation of Base-line Cosmic-Ray Modulation for the Ulysses Trajectory , 1993 .

[41]  J. Jokipii,et al.  The polar heliospheric magnetic field , 1989 .

[42]  Eugene N. Parker,et al.  THE PASSAGE OF ENERGETIC CHARGED PARTICLES THROUGH INTERPLANETARY SPACE , 1965 .