Solar activity,in which there is an explosive release of magnetic energy in the solar atmosphere,is one of the most spectacular manifestations of space plasma activity.Non-potential,free magnetic energy is accumulated by the interaction between plasma and magnetic fields in the photosphere and sub-photospheric layer.In the photosphere and lower solar atmosphere,plasma is only partially ionized and there is three-species(or three-fluid)plasma.Cowling conductivity should therefore be considered in explaining solar observations.On the other hand,the explosive release of magnetic energy is believed to be caused by magnetic reconnection in the corona,where plasma is fully ionized and essentially collisionless.However,for collisionless plasma,we seem to have no precise quantitative description or formulation of its conductivity.To physically understand magnetic reconnection in collisionless plasma is an important task in making further progress in solar activity studies.This article discusses the plasma perspective of solar activity studies.The discussion begins with solar observations,and then,an analysis of the plasma problems that we face and need to better understand.
