Physics & Astronomy ETDs


Roger Ygbuhay

Publication Date



The solution to the transport equation of galactic cosmic rays in the heliosphere is a continuing research problem. Galactic cosmic ray transport is influenced by four physical processes: outward convection due to a magnetized solar wind, inward diffusion along the interplanetary magnetic field line, particle drifts, and adiabatic cooling. Usually one uses simulations to solve for the components of the diffusion tensor applicable to galactic cosmic ray transport in the heliosphere. In this dissertation, I take a data driven approach and use experimental data from 18 neutron monitors of the world-wide network of cosmic ray neutron monitors from 1963 to 2013. These neutron monitors are grouped (NM1 and NM2) by their vertical geomagnetic cut-off rigidities (NM1 < 4.5 GV and NM2 > 4.5 GV). I show the solution to the parameter (alpha) that is the ratio of cosmic ray perpendicular mean free path to the parallel mean free path using neutron monitor data base on the model of hard sphere scattering of cosmic rays in the solar wind plasma and flat heliospheric current sheet. I show my results for the diffusion coefficients, the vector components of the free-space anisotropy in the radial, east-west, and north-south directions as well as the cosmic ray gradients in the radial and transverse directions with respect to the ecliptic plane. I show how these parameters of the transport equation correlate with rigidity, the 11-year solar cycle, and the 22-year solar magnetic cycle. I will also compare my results to the published results from other researchers.

Degree Name


Level of Degree


Department Name

Physics & Astronomy

First Committee Member (Chair)

Dunlap, Dave

Second Committee Member

Skadron, George

Third Committee Member

Gilmore, Mark




cosmic rays, modulation, transport equation, solar cycle, heliosphere

Document Type