Modeling of the recurrent Forbush effect of the galactic cosmic ray intensity and comparison with the experimental data

• Published in: Advances in space research Vol. 41; no. 2; pp. 325 - 334
• Main Authors: Wawrzynczak, A., Alania, M.V.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 2008
• Subjects: Forbush effects; Interplanetary magnetic field; Turbulence; Interplanetary magnetic field; Forbush effects; Turbulence
• ISSN: 0273-1177; 1879-1948
• DOI: 10.1016/j.asr.2007.05.017

We study temporal changes of the power law rigidity R spectrum δ D ( R ) D ( R ) ∝ R - γ of the four (2–18 September 1996, 30 September–15 October 1996, 18 March–4 April 2002, and 16 June–4 July 2003) recurrent Forbush effects of the galactic cosmic ray intensity using neutron monitors experimental data and theoretical modeling. We show that the rigidity spectra for all (four) Forbush effects gradually are hardening (the exponent γ decreases) during the decreasing phases of the intensities and then steadily are softening (the exponent γ increases) during the recovery phases. A relationship between the rigidity spectrum exponent γ and the exponent ν of the power spectral density (PSD) of the components of the interplanetary magnetic field in the range of frequency 4 × 10 −6 Hz ⩽ f ⩽ 10 −5 Hz ( PSD ∝ f − V ) is established. During the Forbush effects the exponent ν increases and the exponent γ decreases. We assume that the relationship between the exponent γ and the exponent ν is observed owing to the dependence of the diffusion coefficient K on the galactic cosmic ray particles rigidity R as, K ∝ R α , where α = 2− ν. We develop models (stationary and nonstationary) of the recurrent Forbush effect and show that Parker’s anisotropic diffusion equation is successfully acceptable to describe the features of the recurrent Forbush effect of the galactic cosmic ray intensity. The temporal changes of the rigidity spectrum exponent γ of the Forbush effect of galactic cosmic ray intensity can be successfully used to estimate the temporal evolution of the interplanetary magnetic field turbulence (the exponent ν) for the short period (even less than 1 day), which is not achievable by the in situ measurements of the interplanetary magnetic field.