Ion Outflow and Lobe Density

Abstract. Combined Cluster EFW and EDI measurements have shown that cold ion outflow in the magnetospheric lobes dominates the hydrogen ion outflow from the Earth's atmosphere. The ions have too low kinetic energy to be measurable with particle instruments, at least for the typical spacecraft potential of a sunlit spacecraft in the tenuous lobe plasmas outside a few RE. The measurement technique yields both density and bulk velocity, which can be combined with magnetic field measurements to estimate the centrifugal acceleration experienced by these particles. We present a quantitative estimate of the centrifugal acceleration, and the velocity change with distance which we would expect due to centrifugal acceleration. It is found that the centrifugal acceleration is on average outward with an average value of about of 5 m s−2. This is small, but acting during long transport times and over long distances the cumulative effect is significant, while still consistent with the relatively low velocities estimated using the combination of EFW and EDI data. The centrifugal acceleration should accelerate any oxygen ions in the lobes to energies observable by particle spectrometers. The data set also put constraints on the effectiveness of any other acceleration mechanisms acting in the lobes, where the total velocity increase between 5 and 19 RE geocentric distance is less than 5 km s−1.

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Dispersive Alfvén Wave Control of O + Ion Outflow and Energy Densities in the Inner Magnetosphere

Geophysical Research Letters ◽

10.1029/2019gl083808 ◽

2019 ◽

Vol 46 (15) ◽

pp. 8597-8606 ◽

Cited By ~ 1

Author(s):

A. J. Hull ◽

C. C. Chaston ◽

J. W. Bonnell ◽

J. R. Wygant ◽

C. A. Kletzing ◽

...

Keyword(s):

Alfven Wave ◽

Ion Outflow ◽

Inner Magnetosphere ◽

Dispersive Alfvén Wave ◽

Wave Control

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Auroral ion outflow: low altitude energization

Annales Geophysicae ◽

10.5194/angeo-25-1967-2007 ◽

2007 ◽

Vol 25 (9) ◽

pp. 1967-1977 ◽

Cited By ~ 26

Author(s):

K. A. Lynch ◽

J. L. Semeter ◽

M. Zettergren ◽

P. Kintner ◽

R. Arnoldy ◽

...

Keyword(s):

Electron Temperature ◽

Scale Height ◽

Electron Precipitation ◽

Sounding Rocket ◽

Time Varying ◽

Ion Outflow ◽

F Region ◽

Low Energies ◽

Moderate Energy ◽

Low Altitude

Abstract. The SIERRA nightside auroral sounding rocket made observations of the origins of ion upflow, at topside F-region altitudes (below 700 km), comparatively large topside plasma densities (above 20 000/cc), and low energies (10 eV). Upflowing ions with bulk velocities up to 2 km/s are seen in conjunction with the poleward edge of a nightside substorm arc. The upflow is limited within the poleward edge to a region (a) of northward convection, (b) where Alfvénic and Pedersen conductivities are well-matched, leading to good ionospheric transmission of Alfvénic power, and (c) of soft electron precipitation (below 100 eV). Models of the effect of the soft precipitation show strong increases in electron temperature, increasing the scale height and initiating ion upflow. Throughout the entire poleward edge, precipitation of moderate-energy (100s of eV) protons and oxygen is also observed. This ion precipitation is interpreted as reflection from a higher-altitude, time-varying field-aligned potential of upgoing transversely heated ion conics seeded by the low altitude upflow.

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