The Recognition Of Magnetic Bright Points In The Solar Photosphere

Magnetic bright points in the photosphere are the smallest structures thatthe present observational technique could resolve. They are regarded as a reli-able tracer of footpoints of the coronal magnetic feld in the photosphere. Theenergy conversion and transportation caused by the motion of these footpointsis considered as one of the most important energy source of heating the chromo-sphere and the corona by waves or magnetic reconnection through twist magnetictubes. The studying of magnetic bright points plays an important role in resolv-ing the century puzzle of the chromosphere and the corona heating. Most ofthe numerical simulations and observations show that the formation mechanismof the bright points is related to the process of the convective collapse. Name-ly, magnetic bright points evolve as follows: strong plasma down fows in thefux tube, magnetic feld strengthens, and then magnetic bright points appear.Some simulations and observations revealed that strong downfows bounce backwhen they reach the bottom of the fux tubes and turn into strong upfows. Theupfow may develop a shock front that could be energetic enough to bring thechromospheric matter into the corona producing spicules. At the same time thefow move upward, the fux tube undergoes a kind of instability associated withthe convective collapse. The upfowing gas leads the magnetic feld in the fuxtube to weakening, the gas density and the temperature to increasing, and thefux tube eventually splits. In theory, Alfvén waves are found to excite by theoscillation of the fux tubes in the photosphere if the footpoints of the fux tubesmove at a velocity of12km s^-1. The Alfvén wave is invoked in the photosphereand travels upward into the chromosphere and the corona, then dissipates its en-ergy heating the chromosphere and the corona. However, as we have known, theAlfvén wave has not been detected in the photosphere yet. Whether or not thecoronal magnetic feld footpoints in the photosphere could move at speed of12km s^-1is an important criterion for producing the Alfvén wave by the fux tubemotions. Currently, we have known some important facts about the elementary structures and the basic features of magnetic bright points. For example, mag-netic bright points have sizes about100-200km and their lifetimes range fromseveral to tens of minutes. Furthermore, their velocities are around12km s^-1on average in the horizontal direction. Especially, some magnetic bright pointswhirl along a logarithm path in granulation lanes, which can trace large scalesswirling down fows. In this paper, we use the region grow algorithm to recognizethe bright magnetic points.