Open AccessStatistical analysis of the relationship between earthward flow bursts in the magnetotail and low‐latitude Pi2 pulsations
Author(s) -
Kim K.H.,
Takahashi K.,
Ohtani S.,
Sung S.K.
Publication year - 2007
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2007ja012521
Subject(s) - low latitude , physics , latitude , plasma sheet , astrophysics , flow (mathematics) , geophysics , magnetic field , magnetosphere , mechanics , astronomy , quantum mechanics
Several case studies have suggested that low‐latitude Pi2 pulsations are triggered or driven by earthward flow bursts in the magnetotail. Until now, no statistical study has investigated the causality between the flow bursts and Pi2 pulsations, so the overall significance of flow bursts to Pi2 excitation remains unclear. In this study we statistically examine the relationship between earthward flow bursts and low‐latitude Pi2 pulsations. We address the following two questions: (1) Does every flow burst trigger a low‐latitude Pi2 pulsation? (2) Does every low‐latitude Pi2 pulsation have a corresponding flow burst? We use magnetic field and ion plasma measurements made by Geotail and Pi2 measurements made at Kakioka from January 1995 to July 2001. Regarding the first question, we identified 849 Geotail flow burst events in the near‐Earth magnetotail and found that ∼90% of them occurred in the region characterized by ∣ B x ∣ < 10 nT, and ∼75% occurred in the region characterized by ∣ B x ∣ < 5 nT (i.e., at locations very close to the midplane of the plasma sheet). We found that 31 Pi2 events occurred within the 10‐min interval after the peak velocity of a flow burst; that is, only ∼4% of the flow burst events produced a low‐latitude Pi2. Regarding the second question, we identified 556 Pi2 events at Kakioka at times when Geotail was in the near‐Earth magnetotail, and of these, 31 were the subset of the 849 flow bursts identified above. This gives a seemingly low (∼6%) association of flow burst with Pi2. However, we find that the association rate jumped to ∼26% when Geotail was in the region of ∣ B x ∣ < 5 nT, implying that there is a great chance of detecting a flow burst at the time of a ground Pi2 if plasma measurements are made very close to the midplane of the plasma sheet. We conclude that only a small fraction of plasma sheet flow bursts generate Pi2 pulsations, while each Pi2 likely has an associated flow burst somewhere in the near‐Earth magnetotail.