The unusual cosmic ray variations in July 2005 resulted from western and behind the limb solar activity

Abstract

One of the most interesting and unusual periods of the recent solar activity was July 2005. Despite the fact that it was a late declining phase of the 23rd solar cycle, generally a time of solar quiescence, that period was marked by extreme activity. The main events occurred at the invisible side of the Sun and did not reveal significant consequences in the Earth or near the Earth. However, cosmic ray variations testify to the high power of these events. A rather unusual Forbush effect was observed starting from July 16, 2005. It was characterized by very large cosmic ray anisotropy, the magnitude and direction of which are in accordance with a western powerful source. Usually in such a case when the main interplanetary disturbance is far in the west, the Forbush effect is absent or it is very small and short lasting. In July 2005 a rare exclusion was observed which may testify to the giant decrease of 10 GV cosmic ray density (quite possible >=30%, indicating an unusually high cosmic ray gradient) to the west from the Sun–Earth line. In this work, a description of the July 2005 situation as well as the results of the convection- diffusion treatment with space cosmic ray gradients is presented. Some general remarks concerning extreme western solar events and their impact on cosmic rays are also discussed.