| Name: | Yogesh . |
| Affiliation: | Physical Research Laboratory |
| Conference ID : | ASI2023_39 |
| Title : | Helium abundance in Stream Interaction Regions - insights |
| Authors : | Yogesh (1,2), D. Chakrabarty (1), N. Srivastava (3)
1. Physical Research Laboratory, Ahmedabad-380009, India
2. Indian Institute of Technology, Palaj, Gujarat 382355, India
3. Udaipur Solar Observatory, Physical Research Laboratory, Ahmedabad-380009, India |
| Mode of Presentation: | Oral |
| Abstract Category : | Sun and the Solar System |
| Abstract : | The Helium abundance (AHe = nHe/nH*100 %) varies significantly in different layers of the Sun. The photospheric value of AHe is 8% but it remains 4-5% in solar corona. AHe varies in the timescale of the solar cycle. Further, it also gets significantly enhanced at smaller time scales when interplanetary coronal mass ejections (ICMEs) pass through interplanetary (IP) medium. In the past, the variation in helium abundance (AHe) corresponding to the ambient solar wind, ICMEs etc., have been addressed to throw new insights into the physical processes. However, the changes in AHe in the IP medium due to the interaction of different solar wind streams have not received adequate attention. In this talk, we will discuss the variation in AHe in the stream interaction region (SIR) based on the measurements from the first Lagrangian point (L1) of the Sun-Earth system. It is shown that SIRs can modify the AHe abundance in the IP medium on some occasions, although the degree of enhancements on those occasions are usually not as significant as seen during the passage of ICMEs. It is suggested that the pitch angle of alphas and protons and the difference between their velocities play important roles in changing AHe inside SIRs. Importantly, the fast wind regions of SIRs show higher modification in the AHe than in the slow wind regions. The occurrence frequency of alpha particles having higher pitch angles in the fast wind region is found to be higher than that of the protons. The work suggests that the differential velocity and pitch angle distribution of alphas and protons play important roles in determining the AHe enhancement inside SIRs. The changes in the AHe variation in SIRs during solar cycle 23 and 24 will also be discussed. |
