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Pi2 pulsations observed around the dawn terminator
Author(s) -
Imajo S.,
Yoshikawa A.,
Uozumi T.,
Ohtani S.,
Nakamizo A.,
Marshall R.,
Shevtsov B. M.,
Akulichev V. A.,
Sukhbaatar U.,
Liedloff A.,
Yumoto K.
Publication year - 2015
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2013ja019691
Subject(s) - physics , amplitude , terminator (solar) , substorm , dusk , equator , latitude , geophysics , azimuth , zonal and meridional , ionosphere , polarization (electrochemistry) , phase (matter) , geology , f region , geodesy , atmospheric sciences , magnetosphere , magnetic field , optics , astronomy , chemistry , quantum mechanics
We examined Pi2 pulsations observed simultaneously at low‐latitude stations ( L = 1.15 − 2.33) around the dawn terminator. Those Pi2 pulsations observed in the sunlit region were polarized in the azimuthal ( D , positive eastward) direction. We found that the D component oscillations in the dark and sunlit regions were in antiphase, whereas the H component oscillated in phase. A statistical analysis indicates that these D component phase reversals occurred about 0.5 h sunward of the dawn terminator at 100 km in altitude, corresponding to the highly conducting E layer. The azimuthal polarization and D component phase reversals related to the dawn terminator cannot be explained by the existing models of low‐latitude Pi2s (e.g., cavity resonance or substorm current wedge oscillations). Similar D component phase reversals were also found on the dusk side although the amplitude of the D component is smaller than that of the H component. We suggest that the meridional ionospheric current in the sunlit region adjacent to the dawn terminator drives the D component oscillations in antiphase with those D oscillations produced by the oscillatory field‐aligned current (FAC) on the postmidnight side. The meridional current is expected to form a part of a current system that extends from the postmidnight FAC to the equatorial Cowling current. The D component oscillations in the Northern and Southern Hemispheres are also in antiphase, indicating that the current system is symmetric with respect to the equator.

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