## 1. Introduction

[2] Space weather research is of growing importance to the scientific community and can affect human activities. Interplanetary coronal mass ejections (ICMEs, including their shocks) and vast structures of plasma and magnetic fields that are expelled from the Sun outward through the heliosphere are now known to be a key causal link between solar eruptions and major interplanetary and geomagnetic disturbances [*Dryer*, 1994]. In order to realistically reflect the properties of three-dimensional CME propagation, the numerical research of three-dimensional background solar wind has become one of key problems that have to be solved for modeling space weather events.

[3] CMEs and their interplanetary consequences (ICMEs) represent different aspects of the same phenomenon responsible for large geomagnetic storms [*Gosling*, 1990]. Because of the great complexity, each aspect has typically been investigated separately. This approach is useful for revealing the basic underlying physics; however, a complete picture requires a comprehensive model of all of the processes considered together. Successful merging of two-dimensional and three-dimensional magnetohydrodynamic (MHD) coronal and heliospheric models has been reviewed and performed by *Dryer* [1974, 1975, 1982, 1994], *Dryer* [1998], *Usmanov and Dryer* [1995], *Wu et al.* [1997, 1999], *Odstrcil et al.* [2002a, 2004a], and *Manchester et al.* [2005]. The coronal simulation conducted by *Odstrcil et al.* [2002a] started from an initial potential magnetic field and spherically symmetric Parker solar wind. The plasma density and the temperature at the boundary were given as constants, and the radial velocity was determined at each time step by solving the gas characteristic equations. In the work by *Odstrcil et al.* [2002b], the coronal model, whose domain extends from the photosphere up to 30 Rs, was based on the three-dimensional resistive MHD equations that were solved by a semi-implicit finite difference scheme using staggered values, while the heliospheric model, whose domain extends from 30 to 275 Rs, was based on the three-dimensional ideal MHD equations that were solved by an explicit finite difference Total Variation Diminishing/Lax-Friedrichs (TVD/LF) scheme using cell-centered values. The output from the coronal model consisted of a temporal sequence of MHD flow parameters, which were used as a boundary condition for the heliospheric model. An alternative procedure that included a three-dimensional kinematic approach for shock arrival prediction procedures was described by *Fry et al.* [2001, 2003].

[4] *Usmanov et al.* [2000] also used a global axisymmetric MHD solar wind model with WKB Alfvén waves, which were simulated by combining a time relaxation numerical technique in the two-dimensional solar corona region (1–22 Rs) with a marching-along-radius method in the outer region (22 Rs-10 AU). In the coronal region, they assumed the initial state of the magnetic field as a dipole, and the hydrodynamic variables were given by a Parker-type solution of the one-dimensional HD equations [*Parker*, 1963]. Once a steady state solution in the inner region was obtained, a slice of the solution at the interface between the two regions interface (22 Rs) was used as the inner boundary condition to start integration throughout the outer region [*Usmanov*, 1993; *Usmanov and Dryer*, 1995; *Usmanov et al.*, 2000]. Their global steady state axisymmetric MHD model successfully reproduced quantitatively the observations made by Ulysses during its first fast latitude traversal in 1994–1995 [*Usmanov and Dryer*, 1995; *Usmanov et al.*, 2000].

[5] The large-scale structure of solar wind observed by Ulysses near solar minimum was also simulated by*Feng et al.* [2005] by using the three-dimensional numerical MHD model. Their model combined the TVD Lax-Friedrich scheme and MacCormack II scheme and divided the computational domain into two regions as follows: one from 1 to 22 Rs and the other from 18 Rs to 1 AU. On the basis of the observations of the solar photospheric magnetic field and an addition of the volumetric heating [*Suess et al.*, 1996; *Wang et al.*, 1998] to MHD equations, the large-scale bimodal solar wind (i.e., fast and slow wind) structure mentioned above was reproduced by using the three-dimensional MHD model, and their numerical results were roughly consistent with Ulysses’ observations. Their simulation showed that the initial magnetic field topology and the addition of volume heating could govern the bimodal structure of solar wind observed by Ulysses and also demonstrated that the three-dimensional MHD numerical model used by them was efficient in modeling the large-scale solar wind structure.

[6] *Riley et al.* [2001; see also *Linker et al.*, 1999] proposed an empirically driven global MHD model of the solar corona and inner heliosphere. They used the output of the coronal solution directly to provide the inner boundary condition of the heliospheric model. In modeling the solar corona they specified at the lower boundary the radial component of the magnetic field *B*_{r} based on the observed line-of-sight measurements of the photospheric magnetic field. Uniform characteristic values were used for the plasma density and temperature. Initial estimates of the field and plasma parameters were found from a potential field model and a Parker transonic solar wind solution [*Parker*, 1963], respectively. Their results showed that the simulations reproduced the overall large-scale features of the observations during the “whole Sun month” (August/September 1996), although the specified lower boundary conditions were very approximate.

[7] The self-consistent, time-dependent initial and boundary conditions with solar rotation, on the basis of observation results, will play a very important role in three-dimensional background solar wind numerical model, and the work devoted to this aspect is still at its initial stage. In this paper, on the basis of the observation of the solar magnetic field and K-coronal brightness, the self-consistent structures on the source surface are established with the help of MHD equations at 2.5 Rs according to the global distribution of coronal mass output’s flux *F*_{m} (density *ρ* × speed *v*) by *Wei et al.* [2003]. By using the self-consistent source surface structures as initial and boundary conditions, we have successfully developed a three-dimensional magnetohydrodynamic (MHD) regional combination numerical model [*Feng et al.*, 2005] of background solar wind, from the source surface of 2.5 Rs to near the Earth’s orbit (215 Rs) and beyond. This model includes solar rotation and volumetric heating. Once a steady state solar wind is produced, we use a CME model as input into the inner boundary of 2.5 Rs. The dynamical interaction of a CME with the background solar wind flow between 2.5 and 215 Rs (1 AU) is investigated. Observations of the 6–12 January 1997 Sun-Earth connection event are used as a test for our numerical simulation. A brief description of the observations is given in section 2. The three-dimensional MHD regional combination numerical model of background solar wind, which includes self-consistent initial and boundary conditions, is described in section 3. The three-dimensional numerical simulation of CMEs is given in section 4. Numerical results and comparisons with the observations are presented in section 5. Finally, the concluding remarks are given in section 6.