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

Abstract

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 (V SW ) 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. (2011Erkaev et al. ( , 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 B z 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 (M A ) and magnetic local time (MLT) on the speed ratio V /V SW . 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 M A .

3D hybrid simulations of the interaction of a magnetic cloud with a bow shock

“…Spacecraft observations in the Earth's magnetosheath have provided evidence of such accelerated flows exceeding the solar wind speed near the flank magnetopause [e.g., Chen et al , ; Rosenqvist et al , ; Lavraud et al , , ; Harris et al , , and references therein]. In particular, Lavraud et al [] highlight that the position of the region of enhanced velocities is related to the orientation of the upstream magnetic field.…”

Slow mode structure in the nightside magnetosheath related to IMF draping

“…The topic of accelerated magnetosheath plasma by the draped magnetic field lines around the magnetosphere has recently received increased attention. This is due to advances made by global magnetohydrodynamic (MHD) modeling [Lavraud and Borovsky, 2008;Lavraud et al, 2007Lavraud et al, , 2013, semianalytic treatments, [Farrugia et al, 1995;Erkaev et al, 2011Erkaev et al, , 2012, as well as isolated but compelling observations [Rosenqvist et al, 2007;Lavraud et al, 2007;Harris et al, 2013]. These observations complement older observations returned by diverse spacecraft close to the magnetopause [Howe and Binsack, 1972;Chen et al, 1993;Petrinec and Russell, 1997].…”

Properties of the Equatorial Magnetotail Flanks ∼50–200 RE Downtail

“…The magnetosheath M , always larger than 1, is distributed uniformly within the range M ∈[1,4]. Supersonic plasma flows in the magnetosheath (in the already shocked plasma) can be explained by plasma acceleration by the Ampere force of draped and curved magnetic field lines in the nightside magnetosheath (e.g., Chen et al, ; Erkaev et al, ; Harris et al, ; Lavraud et al, , and references therein). The plasma sheet M , always less than 1, is distributed within the range M ∈[10 −2 ,1].…”

“…Therefore, plasma appears to be basically demagnetized (even in the magnetosheath side where the plasma temperature is low). draped and curved magnetic field lines in the nightside magnetosheath (e.g., Chen et al, 1993;Erkaev et al, 2011;Harris et al, 2013;Lavraud et al, 2007, and references therein). The plasma sheet M, always less than 1, is distributed within the range M ∈ [10 −2 , 1].…”