Physical Parameters Of The Near-Earth Solar Wind: Dependence On Coronal Sources And Variation With Solar Activity

The solar wind is one of the important medias through which the Sun can influence the space environment near the Earth.Since the solar wind was first measured by Mariner2 in 1962,the acceleration and heating of the initial solar wind are always the significant problems of the solar physics and the space science.The solar wind can usually bedivided into two kinds with its speed,but that is not the only important parameter to describe the characteristics of the solar wind.In order to study the acceleration and heating of the initial solar wind,we can combine the in situ properties of the solar wind and the magnetic structures and plasma properties of its source in the corona to help us understand deeper.Firstly we traced the solar wind back to the its sources with the data of ACE and Wind by two-step mapping technique(Neugebauer et al.1998,2002)Then we identified the coronal sources of the solar wind by PFSS(Potential Field Source Surface)model.Furthermore,We classified the solar wind by three types of the source regions:coronal hole,active region and quiet Sun(Fu et al.2015).After this step,we can get the relationship between the solar wind and the coronal sources.Specifically,we analyzed two aspects of the solar wind:one is the solar wind properties in the solar minimum,especially in the minimum between cycle 23 and 24;the other is the relationship between the properties of the solar wind and its coronal sources.The solar minimum between cycle 23 and 24 is very special.The numbers of the Sunspot and magnetic flux is lower than these in the previous cycles.We find that the velocity of the solar wind in the minimum between cycle 23 and 24 is higher than it in the previous minimum in three types of regions:coronal hole,active region and quiet Sun.These regions play important roles on the fast solar wind in the minimum between cycle 23 and 24.However,the coronal hole had been the major contributor in the previous minimum.Compared with the past observations,the magnetic intensities are stronger and the proton densities are higher in the solar minimum between cycle 23 and 24.We also found that the proton density has a narrow distribution in this solar cycle while the past proton density observations didn' t show that.The solar wind in different regions differs on properties.The solar wind from coronal hole has a wide distribution.The solar wind with high speed,low charge state and low FIP bias is in the center of the coronal hole.The active region has the opposite properties from the coronal hole,and the quiet Sun,The properties of the solar wind from the edge of the coronal hole are similar to those in the active region and quiet Sun.