English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The aim of the paper is to study how auroral potential structures\udclose at high altitude. We analyse all electric field data\udcollected by Polar on auroral field lines in 1996–2001 by integrating\udthe electric field along the spacecraft orbit to obtain the plasma\udpotential, from which we identify potential minima by an automatic\udmethod. From these we estimate the associated effective mapped-down\udelectric field Ei, defined as the depth of the potential minimum\uddivided by its half-width in the ionosphere. Notice that although we\uduse the ionosphere as a reference altitude, the field Ei does not\udactually exist in the ionosphere but is just a convenient\udcomputational quantity. We obtain the statistical distribution of\udEi as a function of altitude, magnetic local time (MLT), Kp index\udand the footpoint solar illumination condition. Surprisingly, we find\udtwo classes of electric field structures. The first class consists of\udthe low-altitude potential structures that are presumably associated with\udinverted-V regions and discrete auroral arcs and their set of\udassociated phenomena. We show that the first class exists only below\ud~3RE radial distance, and it occurs in all nightside MLT\udsectors (RE=Earth radius). The second class exists only above\udradial distance R=4RE and almost only in the midnight MLT sector,\udwith a preference for high Kp values. Interestingly, in the middle\udaltitudes (R=3–4RE) the number of potential minima is small,\udsuggesting that the low and high altitude classes are not simple\udfield-aligned extensions of each other. This is also underlined by\udthe fact that statistically the high altitude structures seem to be\udsubstorm-related, while the low altitude structures seem to correspond\udto stable auroral arcs. The new finding of the existence of the two\udclasses is important for theories of auroral acceleration, since it\udsupports a closed potential structure model for stable arcs, while\udduring substorms, different superposed processes take place that\udare associated with the disconnected high-altitude electric field structures. \udKey words. Magnetospheric physics (electric fields; auroral\udphenomena) – Space plasma physics (electrostatic structures

The occurrence frequency of auroral potential structures and electric fields as a function of altitude using Polar/EFI data