Magnetic bright points in the photosphere are the smallest structures that the present observational technique could resolve. They are regarded as a reliable tracer of footpoints of the coronal magnetic ?eld in the photosphere. The energy conversion and transportation caused by the motion of these footpoints is considered as one of the most important energy source of heating the chromosphere and the corona by waves or magnetic reconnection through twist magnetic tubes. The studying of magnetic bright points plays an important role in resolving the century puzzle of the chromosphere and the corona heating. Most of the numerical simulations and observations show that the formation mechanism of the bright points is related to the process of the convective collapse. Namely, magnetic bright points evolve as follows: strong plasma down ?ows in the ?ux tube, magnetic ?eld strengthens, and then magnetic bright points appear. Some simulations and observations revealed that strong down?ows bounce back when they reach the bottom of the ?ux tubes and turn into strong up?ows. The up?ow may develop a shock front that could be energetic enough to bring the chromospheric matter into the corona producing spicules. At the same time the ?ow move upward, the ?ux tube undergoes a kind of instability associated with the convective collapse. The up?owing gas leads the magnetic ?eld in the ?ux tube to weakening, the gas density and the temperature to increasing, and the ?ux tube eventually splits. In theory, Alfv′en waves are found to excite by the oscillation of the ?ux tubes in the photosphere if the footpoints of the ?ux tubes move at a velocity of 1?2 km/s. The Alfv′en wave is invoked in the photosphere and travels upward into the chromosphere and the corona, then dissipates its en- ergy heating the chromosphere and the corona. However, as we have known, the Alfv′en wave has not been detected in the photosphere yet. Whether or not the coronal magnetic ?eld footpoints in the photosphere could move at speed of 1?2 km/s is an important criterion for producing the Alfv′en wave by the ?ux tube motions. Currently, we have known some important facts about the elementary.
修改评论