Luo, X (reprint author), Chinese Acad Sci, SIGMA Weather Grp, Natl Space Sci Ctr, State Key Lab Space Weather, Beijing 100190, Peoples R China.
; Luo, X (reprint author), North West Univ, Ctr Space Res, ZA-2520 Potchefstroom, South Africa.
National Natural Science Foundation of China [41231068, 41304137, 41531073, 41504132, 11575203]
; Specialized Research Fund for State Key Laboratories
; post-doctoral programme of the North-West University in South Africa
; South African National Research Foundation (NRF) [87820, 68198]
; NASA [NNX14AJ53G, NNX15AN72G]
; US National Science Foundation [CNS 09-23050]
英文摘要:
Based on the reduced diffusion mechanism for producing Forbush decreases (Fds) in the heliosphere, we constructed a three-dimensional (3D) diffusion barrier,. and by incorporating it into a stochastic differential equation (SDE) based time-dependent, cosmic-ray transport model, a 3D numerical model for simulating Fds is built and applied to a period of relatively quiet solar activity. This SDE model generally corroborates previous Fd simulations concerning the effects of the solar magnetic polarity, the tilt angle of the heliospheric current sheet (HCS), and cosmic-ray particle energy. Because the modulation processes in this 3D model are multi-directional, the barrier's geometrical features affect the intensity profiles of Fds differently. We find that both the latitudinal and longitudinal extent of the barrier have relatively fewer. effects on these profiles than its radial extent and the level of decreased diffusion inside the disturbance. We find,. with the 3D approach, that the HCS rotational motion causes the relative location from the observation point to the HCS to vary, so that a. periodic pattern appears in the cosmic-ray intensity at the observing location. Correspondingly, the magnitude and recovery time of an Fd change, and. the recovering intensity profile contains oscillation as well. Investigating the Fd magnitude variation with heliocentric radial distance, we find that the magnitude decreases. overall. and,. additionally, that the Fd magnitude exhibits an oscillating pattern as the radial distance increases, which coincides well with the wavy profile of the HCS under quiet solar modulation conditions.
