Dual HF radar study of the subauroral polarization stream

Abstract

Abstract. The dual HF radars comprising the Tasman International Geophysical Environment Radar (TIGER) system often observe localized high-velocity F-region plasma flows (≥1500 m/s) in the midnight sector (20:00–02:00 MLT) at magnetic latitudes as low as Λ=60° S. The flow channels exhibit large variability in the latitudinal extent and electric field strength, and are similar to the subauroral polarization stream or SAPS, a plasma convection feature thought to be related to the polarization electric field due to the charge separation during substorm and storm development. In this study, the 2-D plasma drift velocity within the channel is derived for each of the two TIGER radars from the maximum velocities measured in all 16 radar beams within the latitudinally narrow channel, and the time variation of the subauroral electric field is examined near substorm onset. It is demonstrated that the flow channel often does not have a clear onset, rather it manifests differently in different phases of its evolution and can persist for at least two substorm cycles. During the growth phase the electric fields within the flow channel are difficult to distinguish from those of the background auroral convection but they start to increase near substorm onset and peak during the recovery phase, in contrast to what has been reported previously for auroral convection which peaks just before the substorm onset and falls sharply at the substorm onset. The response times to substorm onset range from −5 to +40 min and show some dependence on the substorm location with longer delays observed for substorms eastward of the radars' viewing area. The propagation velocity of the high-velocity region is also investigated by comparing the observations from the two closely-spaced TIGER radars. The observations are consistent with the notion that the polarization electric field is established with the energetic ions drifting westward and equatorward from the initial substorm injection. The ion injection front can precede that of the electrons and hence substorm onset resulting in a negative response time of a few minutes.

Subauroral polarization streams: observations with the Hokkaido and King Salmon SuperDARN radars and modeling

“…This feature was first reported on the basis of indirect Millstone Hill observations by Foster et al (2005). Makarevich and Dyson (2007) showed that SAPS flows can exist in a dormant state for a long time, for at least two substorm cycles, and they can be intensified by the substorm processes, in agreement with Anderson et al (1993).…”

“…Koustov (sasha.koustov@usask.ca) at high magnetic latitudes of >65 • (Greenwald et al, 1995). Several recent publications have demonstrated that some of the SuperDARN radars can also be useful for studies of subauroral polarization streams (SAPS), which are fast flows at or equatorward of equatorial edge of the auroral oval (Parkinson et al, 2003(Parkinson et al, , 2005Koustov et al, 2006;Makarevich and Dyson, 2007). SAPS events have been identified and investigated for relatively low-disturbed magnetic conditions.…”

Observations of field-aligned ionospheric irregularities during quiet and disturbed conditions with EKB radar: first results

“…The only difference is the existence of the polarization stream (FCP2) before SLE onset that could be associated with enhanced auroral activity before SLE. A similar event was presented in Makarevich and Dyson (2007).…”

“…In five maps, the three separated flow channels are visible: two with V D > 0 (red symbols) and one with V D < 0 (blue symbols). Based on results of previous investigations (e.g., Makarevich andDyson 2007, Zou et al 2009 and references therein), we suppose that a western high-latitude flow channel of positive V D (FCP1) may be associated with eastward auroral jet , a flow channel of negative V D ( FCN), located to the east of FCP1 , is related to westward jet, and a low-latitude flow channel of positive V D (FCP2) is caused by the polarization stream.…”

IMF-By dependence of transient ionospheric flow perturbation associated with sudden impulses: SuperDARN observations

“…The beam-swinging technique (Makarevich and Dyson 2008) is applied for each bin to deduce a twodimensional flow vector. This method has originally been used by Ruohoniemi and Greenwald (1996) (see Figure 1 in their paper) to statistically deduce the average high-latitude convection map from SuperDARN LOSV observations.…”