Statistical analysis of the sources of the cross‐polar potential for southward IMF, based on particle precipitation characteristics

Abstract

[1] There are several proposed physical processes which may contribute to the cross-polar potential and thus drive ionospheric convection around the polar caps. It is generally believed that magnetic reconnection is the dominant process, however dynamos such as viscous interaction and impulsive penetration are other possible contributors. A comprehensive statistical study has been conducted using data from the DMSP F13 satellite for passages along the northern hemisphere dawn-dusk meridian, with focus on typical two-cell convection patterns during times of steady southward IMF conditions. The results show that the lowlatitude dynamo (viscous interaction or reconnection in the LLBL) on average accounts for only 1 -2 kV of the total potential drop, values lower than those previously predicted. At rare occasions this dynamo can be a significant source of energy, however, contributing to more than 20 kV of the cross-polar potential. Citation: Sundberg, K. Å . T., L. G. Blomberg, and J. A. Cumnock (2008), Statistical analysis of the sources of the cross-polar potential for southward IMF, based on particle precipitation characteristics, Geophys. Res. Lett., 35, L08103,

Response of the ionospheric convection reversal boundary at high latitudes to changes in the interplanetary magnetic field

“…The radius of the polar cap boundary increases as the z component of the IMF become more negative [ Holzworth and Meng , ], and the plasma flow is stronger for southward IMF than northward IMF [ Heppner , ]. It has also been shown that the largest potential difference is found across the open field line region of the polar cap [ Mozer , ; Sundberg et al ., ]. Thus, while both drivers that are described by Dungey and by Axford and Hines operate simultaneously, magnetic reconnection in Dungey's model is thought to be the dominant process.…”

Properties of the boundary layer potential for northward interplanetary magnetic field

“…The method is validated by a statistical analysis showing a clear dependence between F BL and the viscous parameters in the solar wind (velocity, density and pressure), whereas the dependence on the interplanetary electric field is insignificant. The data show significantly larger boundary layer potentials compared to a previous study for southward IMF conditions [Sundberg et al, 2008], on average contributing approximately 10 kV (30-35%) to the total potential generated by the solar wind interaction. The results thus indicate that the IMF direction is a vital factor in the formation of the boundary layer.…”

“…In a comprehensive statistical study by Sundberg et al [2008] treating 2-cell convection patterns during steady southward IMF, the low-latitude dynamo was shown to be less important than previous predictions and estimates, contributing merely 1 -2 kV to the total potential drop in the average case. For close to half of the events in that data set the low-latitude dynamo contributed less than 1 kV to the total potential drop.…”

Plasma and convection reversal boundary motions in the high‐latitude ionosphere

“…The average potential difference along the CRB is about 2.5 kV for each 2 h local time segment. Considering the contribution from both the dusk and dawn sides, we find the approximately 5 kV potential difference to be consistent with the expected contribution from viscous‐like interaction, which is less than 20% of the expected average total potential (~50 kV) across the magnetosphere [ Mozer , ; Sundberg et al ., ]. In the northern hemisphere, from both F13 and F15, the average potential difference between 16 and 20 h MLT is about 5 kV.…”

“…This transpolar potential has been studied for several years to investigate the contribution of merging/reconnection and viscous‐like interaction. The potential associated with a viscous‐like interaction varies from 3 to 30 kV being estimated as about 10 to 20% of the total potential across the magnetopause from both observations and numerical models [ Axford , ; Mozer , ; Boyle et al ., ; Sonnerup et al ., ; Sundberg et al ., ; Drake et al ., ; Lockwood et al ., 2009]. Thus, while both processes that are described by Dungey and by Axford and Hines operate simultaneously, magnetic merging and reconnection is thought to be dominant in most cases.…”