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Galactic cosmic rays as signatures of interplanetary transients

Coronal mass ejections (CMEs), interplanetary shocks, and corotating interaction regions (CIRs) drive heliospheric variability, causing various interplanetary as well as planetary disturbances. One of their very common in-situ signatures are short-term reductions in the galactic cosmic ray (GCR) flux (i.e. Forbush decreases), which are measured by ground-based instruments at Earth and Mars, as well as various spacecraft throughout the heliosphere (most recently by Solar Orbiter). In general, interplanetary magnetic structures interact with GCRs producing depressions in the GCR flux. Therefore, different types of interplanetary magnetic structures cause different types of Forbush decreases, allowing us to distinguish between them. We recently developed and employed two different analytical models to explain CME-related and CIR-related Forbush decreases, using an expansion-diffusion and the convection-diffusion approaches, respectively. We used observation-based generic CME and CIR profiles as the theoretical background for the models and tested the models on various case studies. Moreover, the CME-related Forbush decrease model (ForbMod, Dumbovic et al., 2018 ; 2020) is brought one step further, as it also considers the energy dependance of the detector with which the measurements are made. ForbMod is tested through model-to-observations comparison to analyse to how many CMEs it is applicable and could ultimately provide a helpful tool to analyse Forbush decreases. With new modelling efforts, as well as observational analysis we are one step closer in utilizing GCR measurements to provide information on interplanetary transients, especially where other measurements (e.g. plasma, magnetic field) are lacking.

Sun, Heliosphere, coronal mass ejection, corotating interaction regions, forbush decreases, galactic cosmic rays

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