We study the interaction between the Moon and the solar wind through a three-dimensional MHD simulation.Three cases have been discussed in which the interplanetary magnetic field lies at 90,180,and 135 to the solar wi...We study the interaction between the Moon and the solar wind through a three-dimensional MHD simulation.Three cases have been discussed in which the interplanetary magnetic field lies at 90,180,and 135 to the solar wind flow,respectively.A wake with low density and low pressure can always be formed behind the Moon.The plasma temperature and magnetic field are enhanced in the central wake,but the field strength is reduced in the surrounding region.A Mach cone is formed by rarefaction waves emanating from the limb.These rarefaction waves propagate via the fast magnetosonic mode with different velocities in different directions relative to the magnetic field.When the interplanetary magnetic field is not parallel to the solar wind flow,the wake shows some asymmetries,with an acceleration region turning up at the center.Finally,the results are compared with the observations by WIND spacecraft.Our calculations agree reasonably well with the observed values.展开更多
Interaction of the solar wind with the interstellar medium leads to the formation of the heliosphere and termination shock. This article addresses three aspects of the plasma and magnetic field on two sides of the hel...Interaction of the solar wind with the interstellar medium leads to the formation of the heliosphere and termination shock. This article addresses three aspects of the plasma and magnetic field on two sides of the heliopause： （1） The interstellar magnetic field surrounding the heliopause. In the limit of very low plasma β-ratio an analytical solution is obtained for the 3D interstellar magnetic field by means of a line dipole method. The undisturbed magnetic field in the upstream is allowed to have an arbitrary inclination angle. The solution describes the heliosphere as having a blunt-nosed geometry on the upwind side and approaching a cylindrical geometry on the downwind side. The distortion of the magnetic field can penetrate very deep into the interstellar space. （2） Interaction of the interstellar neutral hydrogen with the global solar wind. The ionization process leads to removal of interstellar neutral hydrogen in the heliosphere： on the upwind side, 90% of hydrogen depletion occurs inside 60 AU, the hydrogen density changes rapidly inside 10 AU. A hydrogen cavity forms inside -4 AU; the cavity extends on the downwind side to form a long cavity wake. Outside the cavity and cavity wake, pickup protons are produced, they cause deceleration and heating of the solar wind. The wind speed and temperature also increase steadily with heliolatitude caused by the latitudinal increase in wind speed at the inner boundary. （3） The global geometry of the termination shock. The termination shock has been treated as having a closed geometry in previous heliosphere models. This study presents a new perspective that the global termination shock may have a bow-shaped open geometry. The termination shock forms on the upwind side because the forward motion of the supersonic solar wind is blocked at the blunt-nosed heliopause. However, the heliopause likely to be open on the downwind side; the motion of the supersonic solar wind is unobstructed for shock formation. Thus, the global termination shock likely has an open geometry. On the upwind side the shock flares out and weakens from the nose to its flanks. Eventually, the shock asymptotically reduces to a Mach wave. The supersonic solar wind remains shock free in the heliotail.展开更多
基金supported by National Natural Science Foundation of China(Grant No.40974108)
文摘We study the interaction between the Moon and the solar wind through a three-dimensional MHD simulation.Three cases have been discussed in which the interplanetary magnetic field lies at 90,180,and 135 to the solar wind flow,respectively.A wake with low density and low pressure can always be formed behind the Moon.The plasma temperature and magnetic field are enhanced in the central wake,but the field strength is reduced in the surrounding region.A Mach cone is formed by rarefaction waves emanating from the limb.These rarefaction waves propagate via the fast magnetosonic mode with different velocities in different directions relative to the magnetic field.When the interplanetary magnetic field is not parallel to the solar wind flow,the wake shows some asymmetries,with an acceleration region turning up at the center.Finally,the results are compared with the observations by WIND spacecraft.Our calculations agree reasonably well with the observed values.
文摘Interaction of the solar wind with the interstellar medium leads to the formation of the heliosphere and termination shock. This article addresses three aspects of the plasma and magnetic field on two sides of the heliopause： （1） The interstellar magnetic field surrounding the heliopause. In the limit of very low plasma β-ratio an analytical solution is obtained for the 3D interstellar magnetic field by means of a line dipole method. The undisturbed magnetic field in the upstream is allowed to have an arbitrary inclination angle. The solution describes the heliosphere as having a blunt-nosed geometry on the upwind side and approaching a cylindrical geometry on the downwind side. The distortion of the magnetic field can penetrate very deep into the interstellar space. （2） Interaction of the interstellar neutral hydrogen with the global solar wind. The ionization process leads to removal of interstellar neutral hydrogen in the heliosphere： on the upwind side, 90% of hydrogen depletion occurs inside 60 AU, the hydrogen density changes rapidly inside 10 AU. A hydrogen cavity forms inside -4 AU; the cavity extends on the downwind side to form a long cavity wake. Outside the cavity and cavity wake, pickup protons are produced, they cause deceleration and heating of the solar wind. The wind speed and temperature also increase steadily with heliolatitude caused by the latitudinal increase in wind speed at the inner boundary. （3） The global geometry of the termination shock. The termination shock has been treated as having a closed geometry in previous heliosphere models. This study presents a new perspective that the global termination shock may have a bow-shaped open geometry. The termination shock forms on the upwind side because the forward motion of the supersonic solar wind is blocked at the blunt-nosed heliopause. However, the heliopause likely to be open on the downwind side; the motion of the supersonic solar wind is unobstructed for shock formation. Thus, the global termination shock likely has an open geometry. On the upwind side the shock flares out and weakens from the nose to its flanks. Eventually, the shock asymptotically reduces to a Mach wave. The supersonic solar wind remains shock free in the heliotail.
