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THEMIS observations of a Hot Flow Anomaly on 4 July 2007

THEMIS observations of a Hot Flow Anomaly on 4 July 2007. Jonathan Eastwood On the shoulders of giants… THEMIS SWT at UC Berkeley, 7 August 2007. Introduction – what are Hot Flow Anomalies?. Discovered in the mid 1980s

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THEMIS observations of a Hot Flow Anomaly on 4 July 2007

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  1. THEMIS observations of a Hot Flow Anomaly on 4 July 2007 Jonathan Eastwood On the shoulders of giants… THEMIS SWT at UC Berkeley, 7 August 2007

  2. Introduction – what are Hot Flow Anomalies? • Discovered in the mid 1980s • Hot (Ti = 106 -107 K), highly deflected plasma flow near the Earth’s bow shock [Schwartz et al., 1985; Thomsen et al., 1986] • Reduced magnetic field in the middle, with pile-up regions on the outside • Associated with the passage of interplanetary current sheets • They create gross distortions of the magnetopause on minute timescales, and associated ionospheric signatures. • Occur several times a day • Otherwise unremarkable solar wind can produce dynamic changes in the magnetosphere, because of the fundamentally non-linear nature of the bow shock

  3. The basic picture • Particles are reflected at the bow shock. They are channeled back into the upstream region along the current sheet. [Burgess et al., 1989, Thomas et al., 1991] • Hot plasma blows a cavity in the solar wind. Can drive shocks along edge, especially on sunward edge [Lucek et al., 2004] • The solar wind electric field has to point into the current sheet on at least one side Thomsen et al., 1993 • Questions: • Ion heating: particle scattering across the central discontinuity or electromagnetic ion beam instabilities? • Ions: multiple populations or single population? • Electrons ‘Maxwellian’ [Schwartz et al., 2000] – how are the electrons heated?

  4. Simulations [Omidi and Sibeck, JGR 2007] 2.5D Global Hybrid simulation

  5. Impact on the magnetosphere • Create a 5 Re displacement of the magnetopause during its passage [Sibeck et al., 1998] • Pressure pulses on the magnetopause create ground signatures [Southwood and Kivelson, 1990] • Magnetic Impulse Events [Kataoka et al., 2001, 2002, 2003] • Traveling Convection Vortices [Murr and Hughes, 2003]

  6. Themis configuration A D E C B C Green D Orange

  7. Ions solar wind (left) HFA (right) Black line = to Sun Backstreaming foreshock ions Solar wind HFA population Remnant solar wind Black line = to Sun

  8. Electrons solar wind (left) HFA (right) Solar wind (can see v) Hotter

  9. Where does Themis map to? • Event at 10:26UT • Themis at 15 MLT (afternoon, dayside) • Themis ground based observatories roughly map to the dawn flank of the magnetosphere (eastern observatories sunward)

  10. Ground based observations • GBAY - Eastern flank of the Themis ground based array • Sees magnetic impulse event (?) at 10:37 • The HFA pressure perturbation acts over the whole magnetopause • Timing is roughly consistent

  11. Propagation of pressure pulse down flanks? • THEMIS GBO Magnetometer data • Top to bottom = East to West (decreasing longitude) • As the pressure pulse associated with the HFA propagates down the tail it moves from East to West across the THEMIS magnetometer chain Petersburg AK

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