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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 35, issue 3
Ann. Geophys., 35, 443–451, 2017
https://doi.org/10.5194/angeo-35-443-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 35, 443–451, 2017
https://doi.org/10.5194/angeo-35-443-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 17 Mar 2017

Regular paper | 17 Mar 2017

THEMIS satellite observations of hot flow anomalies at Earth's bow shock

Christina Chu1, Hui Zhang1, David Sibeck2, Antonius Otto1, QiuGang Zong3, Nick Omidi4, James P. McFadden5, Dennis Fruehauff6, and Vassilis Angelopoulos7 Christina Chu et al.
  • 1Geophysical Institute, University of Alaska Fairbanks, 903 Koyukuk Dr, Fairbanks, AK 99775, USA
  • 2NASA Goddard Spaceflight Center, Greenbelt, Maryland, USA
  • 3Institute of Space Physics and Applied Technology, Peking University, Beijing, China
  • 4Solana Scientifica, San Diego, California, USA
  • 5Space Sciences Laboratory, University of California Berkeley, Berkeley, California, USA
  • 6Institute of Geophysics and Extraterrestrial Physics, Technische Universität Braunschweig, Braunschweig, Germany
  • 7Department of Earth, Planetary, and Space Sciences, University of California Los Angeles, Los Angeles, California, USA

Abstract. Hot flow anomalies (HFAs) at Earth's bow shock were identified in Time History of Events and Macroscale Interactions During Substorms (THEMIS) satellite data from 2007 to 2009. The events were classified as young or mature and also as regular or spontaneous hot flow anomalies (SHFAs). The dataset has 17 young SHFAs, 49 mature SHFAs, 15 young HFAs, and 55 mature HFAs. They span a wide range of magnetic local times (MLTs) from approximately 7 to 16.5 MLT. The largest ratio of solar wind to HFA core density occurred near dusk and at larger distances from the bow shock. In this study, HFAs and SHFAs were observed up to 6.3 RE and 6.1 RE (Earth radii), respectively, upstream from the model bow shock. HFA–SHFA occurrence decreases with distance upstream from the bow shock. HFAs of the highest event core ion temperatures were not seen at the flanks. The ratio of HFA ion temperature increase to HFA electron temperature increase is highest around 12 MLT and slightly duskward. For SHFAs, (TihfaTisw)/(TehfaTesw) generally increased with distance from the bow shock. Both mature and young HFAs are more prevalent when there is an approximately radial interplanetary magnetic field. HFAs occur most preferentially for solar wind speeds from 550 to 600 km s−1. The correlation coefficient between the HFA increase in thermal energy density from solar wind values and the decrease in kinetic energy density from solar wind values is 0.62. SHFAs and HFAs do not show major differences in this study.

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Hot flow anomalies (HFAs) at Earth's bow shock were identified in Time History of Events and Macroscale Interactions During Substorms (THEMIS) satellite data from 2007 to 2009. The events were classified as young or mature and regular or spontaneous hot flow anomalies (SHFAs). HFA–SHFA occurrence decreases with distance upstream from the bow shock. HFAs are more prevalent for radial interplanetary magnetic fields and solar wind speeds from 550 to 600 kms−1.
Hot flow anomalies (HFAs) at Earth's bow shock were identified in Time History of Events and...
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