References

ANGEO

Annales Geophysicae

ANGEO

Ann. Geophys.

1432-0576

Copernicus Publications

Göttingen, Germany

10.5194/angeo-31-2163-2013

Statistical study of foreshock cavitons

Kajdič

¹ Blanco-Cano

https://orcid.org/0000-0001-7171-0673

² Omidi

³ Meziane

⁴ Russell

C. T.

https://orcid.org/0000-0003-1639-8298

⁵ Sauvaud

J.-A.

¹ Dandouras

https://orcid.org/0000-0002-7121-1118

¹ Lavraud

Institut de Recherche en Astrophysique et Planétologie, University of Toulouse, UMR5277, CNRS, Toulouse, France

Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, México D. F., México

Solana Scientific Inc., Solana Beach, CA, USA

Physics Department, University of New Brunswick, Fredericton, Canada

Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA, USA

06 12 2013

31 12 2163 2178

2013

This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/

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The full text article is available as a PDF file from https://angeo.copernicus.org/articles/31/2163/2013/angeo-31-2163-2013.pdf

In this work we perform a statistical analysis of 92 foreshock cavitons observed with the Cluster spacecraft 1 during the period 2001–2006. We analyze time intervals during which the spacecraft was located in the Earth's foreshock with durations longer than 10 min. Together these amount to ~ 50 days. The cavitons are transient structures in the Earth's foreshock. Their main signatures in the data include simultaneous depletions of the magnetic field intensity and plasma density, which are surrounded by a rim of enhanced values of these two quantities. Cavitons form due to nonlinear interaction of transverse and compressive ultra-low frequency (ULF) waves and are therefore always surrounded by intense compressive ULF fluctuations. They are carried by the solar wind towards the bow shock. This work represents the first systematic study of a large sample of foreshock cavitons. We find that cavitons appear for a wide range of solar wind and interplanetary magnetic field conditions and are therefore a common feature upstream of Earth's quasi-parallel bow shock with an average occurrence rate of ~ 2 events per day. We also discuss their observational properties in the context of other known upstream phenomena and show that the cavitons are a distinct structure in the foreshock.

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