Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm13d2108s&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM13D-2108
Physics
[2740] Magnetospheric Physics / Magnetospheric Configuration And Dynamics, [2744] Magnetospheric Physics / Magnetotail, [2790] Magnetospheric Physics / Substorms
Scientific paper
In the near-Earth magnetotail, the neutral sheet (NSh) is bounded by closed stretched field line regions, which we call Disruption Zones (DZs). There, the magnetic field lines have both outward curvature and an outward gradient, away from the deep minimum in the NSh near about 8 - 12 RE. As a result, there is eastward ion drift and current in the DZs, in contrast to the westward ion drift and current in the NSh. This eastward current interrupts the normal westward plasmasheet current from the dawn to dusk LLBL regions, and is the current disruption that causes the Substorm Current Wedge. A double solenoidal current system develops in which eastward current in the DZs closes to westward current in the NSh. This system supplies more closed magnetic flux to the inner DZs and exerts more magnetic pressure on the NSh, causing it to thin further and move earthward. The DZ eastward ion drifts and currents are strongest where the curvature and the outward gradient of the magnetic field are most intense, namely at the earthward end of the NSh. As a result, that is where reconnection occurs near substorm onset. This location is not the usual near-Earth neutral line (NENL), but is a very near-Earth neutral line (VNENL) in the ~ X = 7 - 11 RE range. Once the reconnection occurs between two antiparallel magnetic field lines in the thin earthward part of the NSh, the tailward line of the reconnection pair becomes the "plasmoid". It has a very distinct shape, namely that of a bottle. The bottle has a long neck which is simply the thinned NSh extending from about 7 to 20 RE. Beyond that is the body of the bottle. When reconnection occurs at the VNENL, sealing the neck of the bottle, the NSh plasma in the neck moves tailward at ~ 200 - 300 km/s and spills into the body of the bottle. In the meantime, the next closed field line moves in to replace the previously reconnected line, plasma from the DZs refills the NSh, and the reconnection continues at the VNENL. When the plasma from the neck of this second closed plasmoid bottle spills into the body, the plasmoid body appears to move tailward because this second closed field has its tailward end further downtail than the first. This scenario is consistent with the measurements that show such VNENL reconnection and with the traditional "plasmoid" location in the body of the bottle. However, there are important differences. First, there is not a NENL near 20 RE but a VNENL significantly earthward of this. Secondly,the shape of the plasmoid is similar to a bottle with a long thin neck. This scenario provides a unifying synthesis of many seemingly conflicting interpretations of substorm particle and magnetic field measurements.
Bryant C. R.
McWilliams Kathryn A.
Sofko George J.
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