Relationship between wave-like auroral arcs and Pi2 disturbances in plasma sheet prior to substorm onset

Earth, Planets and Space

Table 1 Ten substorm dipolarization events in the plasma sheet that have accompanying wave-like arc brightening structure (WLABS) in the ionosphere

Event (yyyy/mm/dd)	Initial brightening of the WLABS (UT)	Onset of auroral expansion (UT)	M ₁	Number of period	Velocity of WLABS (km/s)	Phase velocity of Pi2 δB _y disturbance (km/s)	M ₂
2008/02/02	0739:03	0741:06	187	2	−3	−38	205
2008/02/18	0913:18	0916:36	225	2	−1.6	−44	172
2008/02/26	0401:03	0404:30	185	2	2	45	172
2008/02/26	0449:00	0455:18	112	1	1.7	75	106
2008/03/05	0604:33	0607:33	134	1	2.6	68	114
2008/03/11	0533:15	0535:51	177	2	1.3	40	198
2008/03/23	0546:06	0549:39	199	2	0.93	36	214
2008/03/23	0557:09	0557:57	186	2	1.2	43	181
2009/03/19	0651:39	0654:54	177	2	−1.6	−42	185
2009/03/23	0603:51	0606:36	191	2	1.82	46	167

M ₁ and M ₂ are the recursive mean values of azimuthal mode number calculated in accordance with the wavelength defined by the WLABS and the Pi2 δB _y disturbance, respectively. And n is the number of wavelength that the Pi2 δB _y disturbance has propagated between Th D and Th E spacecraft
Positive (negative) moving velocity of wave-like arc brightening structure indicates westward (eastward) movement. Positive (negative) phase velocity of Pi2 δB _y disturbance means westward propagation from Th D to Th E (eastward from Th E to Th D)