Project “Forbush decrease model for expanding CMEs (ForbMod)” aimed to unravel how galactic cosmic rays are influenced by solar storms in the inner solar system (Sun to Mars) by developing a new model and utilizing a number of spacecraft and planetary observation, including those by Mars Curiosity Rover. Our current understanding is that the solar storms, i.e. coronal mass ejections (CMEs), are actually magnetic structures disconnected from its surrounding so that the galactic cosmic rays can only enter inside trough random walk, i.e. diffusion. Since diffusion is slow compared to the speed of initially empty CME while traveling through the interplanetary space, during the passage of the CME over our instruments we observe Forbush decreases, i.e. short-term depressions in the galactic cosmic ray counts. The project generated new knowledge on the properties of galactic cosmic ray decreases by solar storms, which is relevant for space weather, human spaceflight and planetary and exoplanetary atmospheres. The overall objectives were: 1) to use CME observations to constrain the Forbush decrease model and take into account that CME evolves while traveling through interplanetary space, and 2) to compare the modelling results to measurements not only taken from Earth, but also from Mars, recently available with the Mars Curiosity Rover. Both objectives were achieved in the scope of the action, where the analytical Forbush decrease model ForbMod was developed for an arbitrary expansion of a CME and was tested against measurements from near-Earth spacecraft particle detector and Earth ground-based neutron monitors, as well as radiation detector onboard Mars Curiosity Rover. The project results have shown that Forbush decreases can be utilised not only as signatures of CME arrival, but can also provide vital information on CME properties and evolution through combined modelling-observational approach.
