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Title: Importance of CME Radial Expansion on the Ability of Slow CMEs to Drive Shocks

Abstract

Coronal mass ejections (CMEs) may disturb the solar wind by overtaking it or expanding into it, or both. CMEs whose front moves faster in the solar wind frame than the fast magnetosonic speed drive shocks. Such shocks are important contributors to space weather, by triggering substorms, compressing the magnetosphere, and accelerating particles. In general, near 1 au, CMEs with speed greater than about 500 km s{sup −1} drive shocks, whereas slower CMEs do not. However, CMEs as slow as 350 km s{sup −1} may sometimes, although rarely, drive shocks. Here we study these slow CMEs with shocks and investigate the importance of CME expansion in contributing to their ability to drive shocks and in enhancing shock strength. Our focus is on CMEs with average speeds under 375 km s{sup −1}. From Wind measurements from 1996 to 2016, we find 22 cases of such shock-driving slow CMEs, and for about half of them (11 out of the 22), the existence of the shock appears to be strongly related to CME expansion. We also investigate the proportion of all CMEs with speeds under 500 km s{sup −1} with and without shocks in solar cycles 23 and 24, depending on their speed. Wemore » find no systematic difference, as might have been expected on the basis of the lower solar wind and Alfvén speeds reported for solar cycle 24 versus 23. The slower expansion speed of CMEs in solar cycle 24 might be an explanation for this lack of increased frequency of shocks, but further studies are required.« less

Authors:
; ;  [1]; ;  [2];  [3]
  1. Space Science Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH (United States)
  2. Department of Physics, University of New Hampshire, Durham, NH (United States)
  3. NASA/GSFC and University of Maryland Baltimore County, Greenbelt, MD (United States)
Publication Date:
OSTI Identifier:
22679761
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 848; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALFVEN WAVES; EXPANSION; MASS; SHOCK WAVES; SOLAR CYCLE; SOLAR PARTICLES; SOLAR WIND; SPACE; SUN; VELOCITY

Citation Formats

Lugaz, Noé, Farrugia, Charles J., Winslow, Reka M., Small, Colin R., Manion, Thomas, and Savani, Neel P.. Importance of CME Radial Expansion on the Ability of Slow CMEs to Drive Shocks. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA8EF9.
Lugaz, Noé, Farrugia, Charles J., Winslow, Reka M., Small, Colin R., Manion, Thomas, & Savani, Neel P.. Importance of CME Radial Expansion on the Ability of Slow CMEs to Drive Shocks. United States. doi:10.3847/1538-4357/AA8EF9.
Lugaz, Noé, Farrugia, Charles J., Winslow, Reka M., Small, Colin R., Manion, Thomas, and Savani, Neel P.. Fri . "Importance of CME Radial Expansion on the Ability of Slow CMEs to Drive Shocks". United States. doi:10.3847/1538-4357/AA8EF9.
@article{osti_22679761,
title = {Importance of CME Radial Expansion on the Ability of Slow CMEs to Drive Shocks},
author = {Lugaz, Noé and Farrugia, Charles J. and Winslow, Reka M. and Small, Colin R. and Manion, Thomas and Savani, Neel P.},
abstractNote = {Coronal mass ejections (CMEs) may disturb the solar wind by overtaking it or expanding into it, or both. CMEs whose front moves faster in the solar wind frame than the fast magnetosonic speed drive shocks. Such shocks are important contributors to space weather, by triggering substorms, compressing the magnetosphere, and accelerating particles. In general, near 1 au, CMEs with speed greater than about 500 km s{sup −1} drive shocks, whereas slower CMEs do not. However, CMEs as slow as 350 km s{sup −1} may sometimes, although rarely, drive shocks. Here we study these slow CMEs with shocks and investigate the importance of CME expansion in contributing to their ability to drive shocks and in enhancing shock strength. Our focus is on CMEs with average speeds under 375 km s{sup −1}. From Wind measurements from 1996 to 2016, we find 22 cases of such shock-driving slow CMEs, and for about half of them (11 out of the 22), the existence of the shock appears to be strongly related to CME expansion. We also investigate the proportion of all CMEs with speeds under 500 km s{sup −1} with and without shocks in solar cycles 23 and 24, depending on their speed. We find no systematic difference, as might have been expected on the basis of the lower solar wind and Alfvén speeds reported for solar cycle 24 versus 23. The slower expansion speed of CMEs in solar cycle 24 might be an explanation for this lack of increased frequency of shocks, but further studies are required.},
doi = {10.3847/1538-4357/AA8EF9},
journal = {Astrophysical Journal},
number = 2,
volume = 848,
place = {United States},
year = {Fri Oct 20 00:00:00 EDT 2017},
month = {Fri Oct 20 00:00:00 EDT 2017}
}