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THEMIS observations of ULF wave excitation in the nightside plasma sheet during sudden impulse events

Shi Q. Q., M. Hartinger, V. Angelopoulos, Q. -. Zong, X. -. Zhou, X. -. Zhou, A. Kellerman, A. M. Tian, J. Weygand, S. Y. Fu, Z. Y. Pu, J. Raeder, Y. S. Ge, Y. F. Wang, H. Zhang, Z. H. Yao, (2012), THEMIS observations of ULF wave excitation in the nightside plasma sheet during sudden impulse events, J. of Geophys. Res. [Space Physics], 118, 284-298, doi:10.1029/2012JA017984

Abstract

Sudden impulses (SIs) are an important source of ultra low frequency (ULF) wave activity throughout the Earth's magnetosphere. Most SI-induced ULF wave events have been reported in the dayside magnetosphere; it is not clear when and how SIs drive ULF wave activity in the nightside plasma sheet. We examined the ULF response of the nightside plasma sheet to SIs using an ensemble of 13 SI events observed by THEMIS (Timed History of Events and Macroscale Interactions during Substorms) satellites (probes). Only three of these events resulted in ULF wave activity. The periods of the waves are found to be 3.3, 6.0, and 7.6 min. East-west magnetic and radial electric field perturbations, which typically indicate the toroidal mode, are found to be stronger and can have phase relationships consistent with standing waves. Our results suggest that the two largest-amplitude ULF responses to SIs in the nightside plasma sheet are tailward-moving vortices, which have previously been reported, and the dynamic response of cross-tail currents in the magnetotail to maintain force balance with the solar wind, which has not previously been reported as a ULF wave driver. Both mechanisms could potentially drive standing Alfvén waves (toroidal modes) observed via the field-line resonance mechanism. Furthermore, both involve frequency selection and a preference for certain driving conditions that can explain the small number of ULF wave events associated with SIs in the nightside plasma sheet.

Authors (sorted by name)

Angelopoulos Fu Hartinger Kellerman Shi Weygand Zhang Zhou Zhou Zong

Journal / Conference

Journal Of Geophysical Research (Space Physics)

Acknowledgments

We acknowledge NASA THEMIS contract NAS5‐02099; J. Bonnell and F. S. Mozer for use of the EFI data; and C. W. Carlson and J. P. McFadden for the use of the ESA data; and K. H. Glassmeier, U. Auster and W. Baumjohann for the use of FGM data provided under the lead of the Technical University of Braunschweig and with financial support through the German Ministry for Economy and Technology and the German Center for Aviation and Space (DLR) under contract 50 OC 0302. Simulation results have been provided by the Community Coordinated Modeling Center at Goddard Space Flight Center through their public Runs on Request system (http://ccmc.gsfc.nasa.gov). The CCMC is a multi‐agency partnership between NASA, AFMC, AFOSR, AFRL, AFWA, NOAA, NSF, and ONR. The OpenGGCM was developed by Joachim Raeder and co‐workers at the University of New Hampshire. We are grateful to FGM, CIS team for providing the Cluster data, CDAWeb for providing the WIND data, and Canadian Space Science Data Portal for providing the calculation of FLR frequency. The authors thank M. Kivelson, and T. S. Hsu for helpful discussions. We are grateful to Cindy Russell for help with software and Judy Hohl for help with editing. This work is supported by NNSFC 41031065, 41074106, the Shandong Natural Science Foundation JQ201112.

Grants

50 OC 0302 NAS5‐02099

Bibtex

@article{doi:10.1029/2012JA017984,
author = {Shi, Q. Q. and Hartinger, M. and Angelopoulos, V. and Zong, Q.-G. and Zhou, X.-Z. and Zhou, X.-Y. and Kellerman, A. and Tian, A. M. and Weygand, J. and Fu, S. Y. and Pu, Z. Y. and Raeder, J. and Ge, Y. S. and Wang, Y. F. and Zhang, H. and Yao, Z. H.},
title = {THEMIS observations of ULF wave excitation in the nightside plasma sheet during sudden impulse events},
journal = {Journal of Geophysical Research: Space Physics},
volume = {118},
number = {1},
year = {2012},
pages = {284-298},
keywords = {shock, sudden impulse, ultra low frequency wave, vortex, plasma sheet},
doi = {10.1029/2012JA017984},
url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2012JA017984},
eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2012JA017984},
abstract = {Sudden impulses (SIs) are an important source of ultra low frequency (ULF) wave activity throughout the Earth's magnetosphere. Most SI-induced ULF wave events have been reported in the dayside magnetosphere; it is not clear when and how SIs drive ULF wave activity in the nightside plasma sheet. We examined the ULF response of the nightside plasma sheet to SIs using an ensemble of 13 SI events observed by THEMIS (Timed History of Events and Macroscale Interactions during Substorms) satellites (probes). Only three of these events resulted in ULF wave activity. The periods of the waves are found to be 3.3, 6.0, and 7.6 min. East-west magnetic and radial electric field perturbations, which typically indicate the toroidal mode, are found to be stronger and can have phase relationships consistent with standing waves. Our results suggest that the two largest-amplitude ULF responses to SIs in the nightside plasma sheet are tailward-moving vortices, which have previously been reported, and the dynamic response of cross-tail currents in the magnetotail to maintain force balance with the solar wind, which has not previously been reported as a ULF wave driver. Both mechanisms could potentially drive standing Alfvén waves (toroidal modes) observed via the field-line resonance mechanism. Furthermore, both involve frequency selection and a preference for certain driving conditions that can explain the small number of ULF wave events associated with SIs in the nightside plasma sheet.}
}