EISCAT observations of plasma patches at sub-auroral cusp latitudes

Abstract

Abstract.A sequence of 3 patches of high-density (10 12 m −3 ) cold plasma on a horizontal scale-size of 300-700 km was observed near magnetic noon by the EISCAT VHF radar above Svalbard on 17 December 2001. The patches followed a trajectory towards the cusp inflow region. The combination of radar and all-sky observations demonstrates that the patches must have been segmented equatorward of the cusp/cleft auroral display, and hence their properties had not yet been influenced by cusp particle showers and electrodynamics on open flux tubes. The last patch in the sequence was intersected by radio tomography observations, and was found to be located adjacent to a broader region of the same high electron density further south. The patches occurred under moderately active conditions (Kp=3) and the total electron content (TEC) of the high-density plasma was 45 TEC units. The train of patches appeared as a segmentation of the tongue of ionization. The sequence of patches occurred in association with a sequence of flow bursts in the dusk cell return flow. It is proposed that reconnection driven pulsed convection is able to create sub-auroral patches in the region where high density mid-latitude plasma is diverted poleward toward the cusp. It is the downward Birkeland current sheet located at the equatorward boundary of the flow disturbance that represents the actual cutting mechanism.

On the symmetry of ionospheric polar cap patch exits around magnetic midnight

“…Several mechanisms have been proposed to explain how cusp reconnection dynamics can explain segmentation of the tongue of ionization into patches and most of them are related to the dynamics of transient reconnection and includes polar cap boundary motions, current sheets, and flow channels [cf. Anderson et al, 1988;Lockwood and Carlson, 1992;Rodger et al, 1994;Milan et al, 2002;Rodger et al, 1994;Sojka et al, 1993;Valladares et al, 1994;Pitout and Blelly, 2003;Pitout et al, 2004;Carlson et al, 2004;Lockwood et al, 2005;Moen et al, 2006;Carlson et al, 2004, and references therein]. Lockwood and Carlson [1992] provided a model for patch formation in the cusp inflow region by pulsed reconnection which could explain the cigar-shaped patch forms.…”

Comparison of temporal fluctuations in the total electron content estimates from EISCAT and GPS along the same line of sight

“…4a). The ionisation enhancement might have originated from plasma patches transported over the line of sight (Foster et al, 2005;Moen et al, 2006). Such a pattern can be observed as well through the electron density integrated along the path (i.e.…”

Global Ionospheric Processes

“…We also spent significant effort pursuing a longer-term study of N-S aligned arcs observed connecting directly to the cusp, which are associated with strong precipitation and huge ion drifts, and appear to result from transient bursts of reconnection. Several new papers on patch occurrence as observed in the Norwegian sector were produced and published in FY07 by our colleagues at the University of Oslo under an EOARD grant sponsored by our task, which also provides logistical support for our research and monitoring instruments in Norway and Svalbard Moen et al, 2007;Moen et al, 2006]. Through this collaboration we also produced significant new results on the formation of polar cap patches, especially new observations of patch formation and physical constraints on motion relative to various boundaries that are not currently included in models [c.f., Lockwood et al, 2005a,b].…”