During Ulysses’ first rapid pole-to-pole transit from September 1994 to June 1995, its observations showed that middle- or high-speed solar winds covered all latitudes except those between ?20° and +20° nea...During Ulysses’ first rapid pole-to-pole transit from September 1994 to June 1995, its observations showed that middle- or high-speed solar winds covered all latitudes except those between ?20° and +20° near the ecliptic plane, where the velocity was 300―450 km/s. At poleward 40°, however, only fast solar winds at the speed of 700―870 km/s were observed. In addition, the transitions from low-speed wind to high-speed wind or vice versa were abrupt. In this paper, the large-scale structure of solar wind observed by Ulysses near solar minimum is simulated by using the three-dimensional numerical MHD model. The model com- bines TVD Lax-Friedrich scheme and MacCormack II scheme and decomposes the calculation region into two re- gions: one from 1 to 22 Rs and the other from 18 Rs to 1 AU. Based on the observations of the solar photospheric magnetic field and an addition of the volumetric heating to MHD equations, the large-scale solar wind structure mentioned above is reproduced by using the three-dimensional MHD model and the numerical results are roughly consistent with Ulysses’ observations. Our simulation shows that the initial magnetic field topology and the addition of volume heating may govern the bimodal structure of solar wind observed by Ulysses and also demonstrates that the three-dimensional MHD numerical model used here is efficient in modeling the large-scale solar wind structure.展开更多
基金jointly supported by the National Natural Science Foundation of China(Grant Nos.40204010,40374056,40336053 and 49925412)973 Project(Grant No.G2000078405)One-Hundred Talent Project of CAS.
文摘During Ulysses’ first rapid pole-to-pole transit from September 1994 to June 1995, its observations showed that middle- or high-speed solar winds covered all latitudes except those between ?20° and +20° near the ecliptic plane, where the velocity was 300―450 km/s. At poleward 40°, however, only fast solar winds at the speed of 700―870 km/s were observed. In addition, the transitions from low-speed wind to high-speed wind or vice versa were abrupt. In this paper, the large-scale structure of solar wind observed by Ulysses near solar minimum is simulated by using the three-dimensional numerical MHD model. The model com- bines TVD Lax-Friedrich scheme and MacCormack II scheme and decomposes the calculation region into two re- gions: one from 1 to 22 Rs and the other from 18 Rs to 1 AU. Based on the observations of the solar photospheric magnetic field and an addition of the volumetric heating to MHD equations, the large-scale solar wind structure mentioned above is reproduced by using the three-dimensional MHD model and the numerical results are roughly consistent with Ulysses’ observations. Our simulation shows that the initial magnetic field topology and the addition of volume heating may govern the bimodal structure of solar wind observed by Ulysses and also demonstrates that the three-dimensional MHD numerical model used here is efficient in modeling the large-scale solar wind structure.
