Characteristics of the Expansion of Magnetic Funnels in Solar Quiet Regions

Via the potential field extrapolation of the observed photospheric magnetic field, the structure of the photospheric magnetic fields above solar quiet regions is renewed. As revealed by the result, below 20 Mm the open magnetic lines exhibit many obvious small funnel structures. These funnels expand with height and at the height of about 20 Mm they combine into large funnel structures. By a systematic study of the tendency of change of the cross section areas of funnels, it is discovered that the cross section areas of funnels in solar quiet regions expand approximately linearly. The velocity of expansion of magnetic funnels at rather low altitudes (< 20 Mm) is larger than that at high altitudes (> 20 Mm). This phenomenon has important significance for the two-dimensional numerical simulations of the origin of solar wind and the mass flow in magnetic loops. At the same time it is found that the number of closed magnetic lines decreases in the form of exponential function.