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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 31, issue 10
Ann. Geophys., 31, 1877–1889, 2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 31, 1877–1889, 2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 31 Oct 2013

Regular paper | 31 Oct 2013

Anti-sunward high-speed jets in the subsolar magnetosheath

F. Plaschke2,1, H. Hietala3,4, and V. Angelopoulos1 F. Plaschke et al.
  • 1Institute of Geophysics and Planetary Physics, and Department of Earth and Space Sciences, University of California Los Angeles, Los Angeles, CA, USA
  • 2Space Research Institute, Austrian Academy of Sciences, 8042 Graz, Austria
  • 3Space and Atmospheric Physics Group, The Blackett Laboratory, Imperial College, London, SW7 2AZ, UK
  • 4Department of Physics, University of Helsinki, Helsinki, Finland

Abstract. Using 2008–2011 data from the five Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft in Earth's subsolar magnetosheath, we study high-speed jets identified as intervals when the anti-sunward component of the dynamic pressure in the subsolar magnetosheath exceeds half of its upstream solar wind value. Based on our comprehensive data set of 2859 high-speed jets, we obtain the following statistical results on jet properties and favorable conditions: high-speed jets occur predominantly downstream of the quasi-parallel bow shock, i.e., when interplanetary magnetic field cone angles are low. Apart from that, jet occurrence is only very weakly dependent (if at all) on other upstream conditions or solar wind variability. Typical durations and recurrence times of high-speed jets are on the order of tens of seconds and a few minutes, respectively. Relative to the ambient magnetosheath, high-speed jets exhibit higher speed, density and magnetic field intensity, but lower and more isotropic temperatures. They are almost always super-Alfvénic, often even super-magnetosonic, and typically feature 6.5 times as much dynamic pressure and twice as much total pressure in anti-sunward direction as the surrounding plasma does. Consequently, they are likely to have significant effects on the magnetosphere and ionosphere if they impinge on the magnetopause.

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