*Kiyohumi Yumoto[1]
,Teiji Uozumi [1],Rui Yamaguchi [1]
Hideaki Kawano [1],K. Liou [2],C.-I. Meng [2]
the CPMN group
Faculty of Science, Kyushu University[1]
Applied Physics Laboratory, Johns Hopkins University[2]
At least 5 % of 119 multiple-onset Pi 2 events at the CPMN
stations in the midnight sector of 2230-2330 LT, are found to
occur without magnetic bays (and/or with bays of amplitude smaller
than 0.4 nT at Guam) during magnetic quiet times of Kp`1. We
further made a comparative study between the Pi 2 events and
aurora ultraviolet images obtained by the Polar satellite in
the midnight sector. It is found that the Pi 2s without/with
magnetic bays occurs `10-40 s later than the start of N2 LBH-band
auroral sudden brightenings. The one-to-one correspondence of
the Pi 2 pulsations to the auroral brightenings is better than
that to the magnetic bays. These results indicate that Pi 2
magnetic pulsations may be excited by an instability just as
a manifestation of the couplings between the near-Earth magnetotail
and the polar ionosphere, and may have a role of trigger/switch
of magnetospheric substorms. In the present paper, we will discuss
on the time delay (`10-40 s) of Pi 2 onset to the auroral brightening
in detail.