Modulation of galactic protons in the heliosphere during the unusual solar minimum of 2006 to 2009

Understand

The last solar minimum activity period, and the consequent minimum modulation conditions for cosmic rays, was unusual.

• The highest levels of galactic protons were recorded at Earth in late 2009 in contrast to expectations.
• Proton spectra observed for 2006 to 2009 from the PAMELA cosmic ray detector on-board the Resurs-DK1 satellite are presented together with the solutions of a comprehensive numerical model for the solar modulation of cosmic rays.
• The model is used to determine what mechanisms were mainly responsible for the modulation of protons during this period, and why the observed spectrum for 2009 was the highest ever recorded.