Ion Energy Steps Observed by Cluster Multi-point Mission in the Polar Cusp: Similarity and Differences

Details Ion Energy Steps Observed by Cluster Multi-point Mission in the Polar Cusp: Similarity and Differences Ion Energy Steps Observed by Cluster Multi-point Mission in the Polar Cusp: Similarity and Differences

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm54a..07e&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SM54A-07

Other

2443 Midlatitude Ionosphere, 2451 Particle Acceleration, 2706 Cusp, 2723 Magnetic Reconnection (7526, 7835)

Scientific paper

The polar cusps are two regions of the magnetosphere where the influence of the interplanetary magnetic field (IMF) is particularly strong. When the IMF is southward the plasma enters the cusp around the subsolar point or near the equatorward boundary of the cusp and on the other hand when the IMF is northward, the plasma enters through the lobes or the poleward boundary of the cusp. Subsequently the ions precipitating in the cusp are dispersed poleward when the IMF is southward and equatorward when the IMF is northward. This dispersion is caused by the motion of field lines driven by the magnetic tension away from the reconnection point. If reconnection is continuous and operates at constant rate, the ion dispersion is smooth and continuous. On the other hand if the reconnection rate varies, we expect interruption in the dispersion forming energy steps or staircase. Similarly, multiple entries near the magnetopause could also produce steps at low or mid-altitude when a spacecraft is crossing subsequently the field lines originating from these multiple sources. On 23 September 2004 the 4 Cluster spacecraft were crossing the mid-altitude polar cusp within 2-16 minute from each other. The first two spacecraft, separated by about 1min 20s observed a typical IMF southward ion dispersion, where the energy of the ions decreases as latitude increases. The dispersion was not smooth but presented discontinuities that were the same on the two spacecraft. Finally this poleward dispersion changed to an equatorward dispersion, as detected by the last spacecraft, after the abrupt turning of the IMF northward. These results will be discussed in term of temporal or patchy reconnection and we will show that the cusp dispersion takes a few minutes to change direction.

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