Transport of thermal‐energy ionospheric oxygen (O⁺) ions between the ionosphere and the plasma sheet and ring current at quiet times preceding magnetic storms

Abstract

[1] 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 < À100 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.

Circulation of Heavy Ions and Their Dynamical Effects in the Magnetosphere: Recent Observations and Models

“…The acceleration of ionospheric ions and their transport into the plasma sheet and ring current have been investigated by particle tracing calculations for a number of years (Green and Horwitz 1986;Sauvaud and Delcourt 1987;Delcourt et al 1989Delcourt et al , 1990Cladis and Francis 1992;Peroomian 1994;Peroomian andAshour-Abdalla 1995, 1996;Moore and Delcourt 1995;Ebihara et al 2006;Yau et al 2012). More recently, Peroomian et al (2006Peroomian et al ( , 2007Peroomian et al ( , 2011aPeroomian et al ( , 2011b have investigated the access and energization of ionospheric ions to the magnetotail during geomagnetic storms by using LSK particle tracing simulation using time-dependent electric and magnetic fields of individual storm events.…”

The Earth: Plasma Sources, Losses, and Transport Processes

“…Together, these capabilities enable a cradle-tograve inquiry into the transport of low energy plasma (O + in particular) from the ionosphere into the magnetosphere and near the equatorial plane as well as its energization (e.g., Kistler et al , 2010bLiao et al 2012. Such observations motivate recent particle trajectory modeling studies (Yau et al 2012) and are also the subject of multiple global magnetospheric simulations (Lotko 2007;Glocer et al 2009aGlocer et al , 2009bBrambles et al 2011;Yu and Ridley 2013). In the following, we review our current knowledge of ion transport and acceleration based on past and recent measurements.…”

Energization of O+ ions in the Earth's inner magnetosphere and the effects on ring current buildup: A review of previous observations and possible mechanisms

“…A simulation study by Yau et al . [] showed that polar wind and other low‐energy O + ions may reach the plasma sheet under geomagnetically quiet conditions when IMF sometimes varies rapidly in polarity. They concluded that such quiet time O + outflow can provide a low but nonnegligible O + flux between the ionosphere and the plasma sheet and ring current prior to the onset of a magnetic storm.…”