Open AccessTransport of thermal‐energy ionospheric oxygen (O + ) ions between the ionosphere and the plasma sheet and ring current at quiet times preceding magnetic storms
Author(s) -
Yau Andrew W.,
Howarth Andrew,
Peterson W. K.,
Abe Takumi
Publication year - 2012
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 - 10.1029/2012ja017803
Subject(s) - ionosphere , ring current , plasma sheet , geomagnetic storm , physics , population , ion , atmospheric sciences , geophysics , atomic physics , magnetosphere , solar wind , plasma , nuclear physics , demography , quantum mechanics , sociology
The presence of energetic O + ions in the ring current at the onset of a magnetic storm prompts the question of the possible role of “in‐transit” ionospheric O + ions between the ionosphere and the plasma sheet and ring current in the quiet periods immediately preceding the main phase of a magnetic storm. Thermal‐energy O + ions are often observed in the quiet time high‐altitude (>7000 km) polar ionosphere on Akebono, at temperatures of ∼0.2–0.3 eV and flow velocities of a few km/s. In this paper, we use single‐particle trajectory simulation to study the transport of these ions in the periods preceding a number of large magnetic storms (Dst < −100 nT). Our simulation shows that due to centrifugal ion acceleration at higher altitudes (above ∼3 R E altitude), about 10–20% of polar wind and other low‐energy O + ions reaches the plasma sheet during such periods; the actual percentage is a factor of ∼3 larger in the dusk sector on average compared with the dawn sector and dependent on the IMF and the O + ion temperature. This provides a low but non‐negligible flux of O + ions between the ionosphere and the plasma sheet and ring current, which is believed to constitute a significant “in‐transit” oxygen ion population over a period of a few (∼4) hours preceding a magnetic storm. Such a population could explain the presence of energetic O + ions at the onset of the main phase of the storm, when the heavy ions could potentially modify the evolution of the ring current.