The subauroral ionosphere lays just equatorward of the auroral boundary. It maps along magnetic field lines into the inner magnetosphere, which includes the ring current (RC), innermost part of the outer radiation belt (RB), and plasmasphere adjacent to the electron plasma sheet (PS) boundary. For brevity, we call this ionosphere-magnetosphere region the subauroral geospace. The quiet time convection in the subauroral geospace is virtually featureless. During (sub)storms, latitudinally narrow jets of subauroral westward convection, subauroral ion drifts (SAID), emerge in the pre-midnight sector, while broad westward flows, subauroral polarization streams (SAPS), appear in the duskside. Just after the substorm onset, SAPS are highly structured and termed SAPSWS (wave structures). SAPSWS co-locate with RB and RC particle precipitation, radar clutter, and UHF/GPS scintillations. Though the development of SAID/SAPS and related space weather effects have been under investigation for decades, the understanding of the underlying physics, especially rapidly developing intense features near substorm onsets, is still lacking.

It is generally implied that poleward electric fields Es driving SAID and SAPS develop due to similar, if not the same, mechanisms, known as voltage and current generators. The former places SAID/SAPS between the inner boundaries of ≥1-keV ion and electron convection defined by the E×B and gradient-curvature drifts. The latter explores closure of the Region 2 field-aligned currents (FACs) through a low-conductive ionosphere, resulting in locally enhanced poleward electric field. The generator concept is based on the test (single) particle approach and has come to be called the SAID/SAPS paradigm. However, recent studies show that the paradigm is in serious error. One of the most striking discrepancies is that the paradigm predicts the timescale of a few hours, while substorm subauroral events appear in ~10 min or less.

The fast timescale and SAID’s MLT sector are characteristic of the propagation of substorm injections (hot plasma jets). Therefore, we develop a concept of the SAID channel as an integral part of a turbulent plasmaspheric boundary layer (TPBL). TPBL forms in the evening sector where the plasmasphere short-circuits reconnection-injected plasma jets. However, we still know little about the underlying mechanism of SAPS, particularly SAPS wave structures (SAPSWS), except that nonlinear plasma effects are critical. Transient SAPS enhancements also appear at times well separated from substorm onsets and correlate with auroral streamers, the footprint of mesoscale plasma jets in the magnetotail. These observations hint at a common process underlying the SAPS/SAPSWS generation and the over-arching problem of transport of reconnection-created jets toward the Earth. The required level of understanding of basic plasma processes that control the spatiotemporal development of the perturbed subauroral geospace can only be achieved using a multidisciplinary effort utilizing experimental, theoretical, and numerical investigations.

 

References

Basu S, et al: Journal of Geophysical Research 113: A00A06, doi:10.1029/2008JA013076, 2008

Makarevich R, et al: A. Kellerman, Journal of Geophysical Research 116: A11311, 2011

Mishin E, Puhl-Quinn P, Santolik O: Geophysical Research Letters 37: L07106, doi:10.1029/2010GL042929, 2010

Mishin E, Albert J, Santolik O: Geophysical Research Letters 38: L21101, doi:10.1029/2011GL049613, 2011

Mishin E: Journal of Geophysical Research 118: 5782, doi:10.1002/jgra.50548, 2013

 

Keywords:

Space weather; Subauroral geospace; SAPS/SAID; Plasmaspheric boundary layer; Substorm injection; Ring current injection; Radiation belt boundary;

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