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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 36, issue 3 | Copyright
Ann. Geophys., 36, 793-808, 2018
https://doi.org/10.5194/angeo-36-793-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 24 May 2018

Regular paper | 24 May 2018

Statistical analysis of mirror mode waves in sheath regions driven by interplanetary coronal mass ejection

Matti M. Ala-Lahti1, Emilia K. J. Kilpua1, Andrew P. Dimmock2,3, Adnane Osmane2, Tuija Pulkkinen2, and Jan Souček4 Matti M. Ala-Lahti et al.
  • 1Department of Physics, P.O. Box 64, University of Helsinki, Helsinki, Finland
  • 2Aalto University, School of Electrical Engineering, Espoo, Finland
  • 3Swedish Institute of Space Physics, Uppsala, Sweden
  • 4Institute of Atmospheric Physics, Czech Academy of Sciences, Prague, Czech Republic

Abstract. We present a comprehensive statistical analysis of mirror mode waves and the properties of their plasma surroundings in sheath regions driven by interplanetary coronal mass ejection (ICME). We have constructed a semi-automated method to identify mirror modes from the magnetic field data. We analyze 91 ICME sheath regions from January 1997 to April 2015 using data from the Wind spacecraft. The results imply that similarly to planetary magnetosheaths, mirror modes are also common structures in ICME sheaths. However, they occur almost exclusively as dip-like structures and in mirror stable plasma. We observe mirror modes throughout the sheath, from the bow shock to the ICME leading edge, but their amplitudes are largest closest to the shock. We also find that the shock strength (measured by Alfvén Mach number) is the most important parameter in controlling the occurrence of mirror modes. Our findings suggest that in ICME sheaths the dominant source of free energy for mirror mode generation is the shock compression. We also suggest that mirror modes that are found deeper in the sheath are remnants from earlier times of the sheath evolution, generated also in the vicinity of the shock.

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We present a comprehensive statistical analysis of mirror mode waves and the properties of their plasma surroundings in sheath regions driven by interplanetary coronal mass ejection (ICME) to deepen our understanding of these geo-effective plasma environments. The results imply that mirror modes are common structures in ICME sheaths and occur almost exclusively as dip-like structures and in mirror stable stable plasma.
We present a comprehensive statistical analysis of mirror mode waves and the properties of their...
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