Articles | Volume 31, issue 10
Ann. Geophys., 31, 1779–1789, 2013
Ann. Geophys., 31, 1779–1789, 2013

Regular paper 22 Oct 2013

Regular paper | 22 Oct 2013

Observational aspects of IMF draping-related magnetosheath accelerations for northward IMF

B. Harris1, C. J. Farrugia1, N. V. Erkaev2,3, and R. B. Torbert1 B. Harris et al.
  • 1Space Science Center and Department of Physics, University of New Hampshire, NH, USA
  • 2Institute for Computational Modeling, Russian Academy of Sciences, Krasnoyarsk, Russia
  • 3Siberian Federal University, Krasnoyarsk, Russia

Abstract. Acceleration of magnetosheath plasma resulting from the draping of the interplanetary magnetic field (IMF) around the magnetosphere can give rise to flow speeds that exceed that of the solar wind (VSW) by up to ~60%. Three case event studies out of 34 identified events are described. We then present a statistical study of draping-related accelerations in the magnetosheath. Further, we compare the results with the recent theory of Erkaev et al. (2011, 2012). We present a methodology to help distinguish draping-related accelerations from those caused by magnetic reconnection. To rule out magnetopause reconnection at low latitudes, we focus mainly on the positive Bz phase during the passage of interplanetary coronal mass ejections (ICMEs), as tabulated in Richardson and Cane (2010) for 1997–2009, and adding other events from 2010. To avoid effects of high-latitude reconnection poleward of the cusp, we also consider spacecraft observations made at low magnetic latitudes. We study the effect of upstream Alfvén Mach number (MA) and magnetic local time (MLT) on the speed ratio V/VSW. The comparison with theory is good. Namely, (i) flow speed ratios above unity occur behind the dawn–dusk terminator, (ii) those below unity occur on the dayside magnetosheath, and (iii) there is a good general agreement in the dependence of the V ratio on MA.