A low upper limit on the subsurface rise speed of solar active regions

作者：Birch Aaron C^*; Schunker Hannah; Braun Douglas C; Cameron Robert; Gizon Laurent; Loeptien Bjoern; Rempel Matthias

来源：Science Advances, 2016, 2(7): e1600557.

DOI：10.1126/sciadv.1600557

Magnetic field emerges at the surface of the Sun as sunspots and active regions. This process generates a poloidal magnetic field from a rising toroidal flux tube; it is a crucial but poorly understood aspect of the solar dynamo. The emergence of magnetic field is also important because it is a key driver of solar activity. We show that measurements of horizontal flows at the solar surface around emerging active regions, in combination with numerical simulations of solar magnetoconvection, can constrain the subsurface rise speed of emerging magnetic flux. The observed flows imply that the rise speed of the magnetic field is no larger than 150 m/s at a depth of 20 Mm, that is, well below the prediction of the (standard) thin flux tube model but in the range expected for convective velocities at this depth. We conclude that convective flows control the dynamics of rising flux tubes in the upper layers of the Sun and cannot be neglected in models of flux emergence.

• 出版日期2016-7
• 单位中国科学院国家天文台