Research On Special Structures In The Slow Solar Wind

Space weather is increasingly receiving national attention,and it may have profound effects on astronaut health,space-based and ground-based electronics,etc.Solar activity and solar wind are important factors affecting space weather.Solar wind can usually be divided into two fast and slow winds.Compared with fast wind,the origin and evolution of slow solar wind are still debated.In this paper,we investigate the abnormal low-density structure and Alfvénicity characteristics in the slow solar wind by using multi-satellite observations,case studies,statistical studies,and the construction of relevant solar wind models.We hope this study can shed some light on the origin and evolution of the slow solar wind by analyzing the special structure and phenomena in the slow solar wind.During the period of solar activity minimum,the number of solar sunspots and large solar eruption events is greatly reduced,the global solar magnetic field topology is nearly a simple dipole structure.Most solar wind detected near Earth are in an unperturbed state and can be roughly divided into fast and slow according to the speed while the fast wind originated from the polar coronal holes and the slow wind from the low latitude region.The fast and slow wind can interact with each other to form the corotating interaction region and stream interface which separates the dense slower wind with sparse faster wind.We found an abnormally low density event embedded in the compressed part of CIR using the data from ACE,WIND and twin STEREO.Except the speed,most of the properties of the event are similar to the fast wind behind the stream interface.By considering the position of the spacecraft and speed,we reconstruct the spatial structure of the event and found that the boundary is almost parallel with the event's magnetic field.The magnetic field of the event is perpendicular to the parker spiral and combining the pitch angle distribution of the suprathermal electrons,the field has a roll back topology.All these information conclusively suggest that the origin of the low density region is similar to the fast wind.By using the two-step mapping techniques,we found the footpoint of the event is in the small coronal hole region near an active region.We also report another similar event in the ascending phase of the solar activity.We also make comparison the properties between the two events and the typical transient events.We make further analysis about the Alfvénic properties of the small coronal hole originated event and found that the Alfvénicity is lower than expected.The small coronal hole originated wind usually reported with high Alfvénicity.Considering the Alfvénic fluctuation as the Alfvén wave superposed on the ambient solar wind,the speed between the co-originated plasma and Alfvén wave are differ in speed.We assumed that the low Alfvénicity of the small coronal hole event is attribute to the propagation effect.We then calculated the propagation of small coronal hole winds and Alfvén waves using a simple two-dimensional solar wind model;the results show that the Alfvén waves are separated from the co-originated plasma during the propagation,leading to small coronal hole winds with low Alfvénicity and ordinary slow winds with high Alfvénicity.This result qualitatively explains the properties of the small coronal hole winds and Alfvénic slow wind with normal slow wind properties.This study provides a new insight into the origin of the slow solar wind mystery.The Main Innovation Points in this Dissertation:· First discover the density anomaly structure in the compressed solar wind· Using multi-satellites data to analysis the density anomaly structure and confirmed the small coronal hole origin wind· Analysis the Alfvénic property of the small coronal hole origin wind and build a simple model to explain the reduced Alfvénicity...