Response to Comment on “Tail Reconnection Triggering Substorm Onset”

Vassilis Angelopoulos,Tai Phan,Davin Larson,Christopher T Russell,Larry Kepko,Harald Frey,Charles W Carlson,Uli Auster,Karl-Heinz Glassmeier,James P Mcfadden,I Jonathan Rae,David G Sibeck,Ian R Mann,Stephen B Mende,Andrei Runov,Xu-Zhi Zhou,Eric Donovan

doi:10.1126/science.1168045

Abstract

Lui challenges our conclusion that magnetic reconnection triggered the onset of a magnetospheric substorm. However, Lui incorrectly uses the auroral electrojet index instead of ground auroral and magnetic field pulsation signatures to determine substorm onset; single velocity and magnetic field components instead of full vectors and particle distributions to identify reconnection onset; and preliminary auroral electrojet–low index (AL) instead of ground magnometer, auroral, and magnetotail data to claim pre-existing activity.

Highlights

Angelopoulos et al (Research Articles, 15 August 2008, p. 931) reported that magnetic reconnection in Earth’s magnetotail triggered the onset of a magnetospheric substorm
If one attributes the appearance of tailward flows at P1 as reconnection onset, it occurred after substorm disturbances close to the Earth. This time sequence is consistent with the near-Earth current disruption (CD) activated before tail reconnection further downstream, suggesting substorm onset triggered by CD and not tail reconnection
The red dashed lines mark the onset of substorm activity at the satellite. (E to G) The magnetic field elevation angle at P1, P3, and P4 satellites around event onset time. (H and I) The temporal variations of the Z

Summary

Introduction

Angelopoulos et al (Research Articles, 15 August 2008, p. 931) reported that magnetic reconnection in Earth’s magnetotail triggered the onset of a magnetospheric substorm. Because only convective plasma flows, that is, flows perpendicular to the magnetic field, are relevant to magnetic reconnection and transport of magnetic flux to cause current disruption/dipolarization in the near-Earth region, only the convective flow components are examined here. If one attributes the appearance of tailward flows at P1 as reconnection onset, it occurred after substorm disturbances close to the Earth.

Results

Conclusion