Postdoctor HE Hongqing and his teacher WAN Weixing provide a direct analytical formula as a function of parameters concerning the physical properties of solar energetic particles (SEPs) and solar wind to directly and quickly determine the parallel mean free path of SEPs with adiabatic focusing.

Since all of the quantities in the analytical formula can be directly observed by spacecraft, this direct method would be a very useful tool in space weather research. As applications of the direct method, they investigate the inherent relations between the parallel mean free path and various parameters concerning physical properties of SEPs and solar wind. Comparisons of parallel mean free paths with and without adiabatic focusing are also presented.

Figure 1. Parallel mean free path of SEPs as a function of the radial distance. (Image by HE)

Figure 2. Parallel mean free path of SEPs as a function of particle rigidity. (Image by HE)

He & Wan. A Direct Method to Determine the Parallel Mean Free Path of Solar Energetic Particles with Adiabatic Focusing. The Astrophysical Journal. 2012, 747-1-38, doi:10.1088/0004-637X/747/1/38 (Download Here)