Open AccessLongitudinal structure of low‐latitude Pi2 pulsations and its dependence on aurora
Author(s) -
Takahashi Kazue,
Liou Kan
Publication year - 2004
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 - 10.1029/2004ja010580
Subject(s) - substorm , physics , amplitude , geophysics , polar , polarization (electrochemistry) , local time , latitude , astrophysics , magnetic field , magnetosphere , astronomy , optics , chemistry , statistics , mathematics , quantum mechanics
The relationship between the spatial and temporal properties of auroral power and low‐latitude magnetic Pi2 pulsations is statistically studied using auroral images obtained with the Ultraviolet Imager on the Polar spacecraft and magnetic fields measured at the Kakioka Observatory ( L = 1.3). We select auroral intensification events from spatially integrated auroral power at time steps of ∼180 s and for each event determine various properties of associated Pi2 pulsations in a 300‐s time window. Since our auroral events are simply defined to be a power increase of 30% or greater, some events are well‐defined substorm expansion phase onsets reaching 50 GW, but some are weak events reaching only ∼1 GW. Nevertheless, the Pi2 pulsations show very similar local time patterns of amplitude and polarization regardless of the magnitude of the increase in auroral power. This implies that a single mechanism excites Pi2‐band oscillations over a wide range of auroral activity. A likely source of the low‐latitude pulsations is a plasmaspheric cavity mode, and our local time patterns of Pi2 parameters show features consistent with theoretical models of the cavity mode excited by longitudinally localized disturbances.