HF radar polar patch and its relation with the cusp during B_Y‐dominated IMF: Simultaneous observations at two altitudes

Abstract

Recent studies have shown that the motion of the cusp can be deduced from the energetic neutral atom signals detected in the magnetosphere by the Low Energy Neutral Atom (LENA) imager on the IMAGE spacecraft. We use this approach to understand the characteristics of the formation of a polar patch seen in the dayside ionosphere. During a period of the 28 March 2001 LENA cusp signal event, the SuperDARN radars at Syowa East, Syowa South, and Kerguelen Island identified large‐scale features of a polar patch. A region of high backscatter power observed by the radars separates into two parts around 77°, and its high‐latitude part moves in the poleward and duskward direction. The separation latitude is about 5° higher than the equatorward boundary of the cusp, which is deduced from the LENA cusp signal. We interpret these observations, including features obtained with other SuperDARN radars in the northern hemisphere, as being due to the IMF BY‐controlled zonal jet flow that occurred during a period of increase in ∣BY/BZ∣, without requiring the change in BY polarity that has been often invoked in previous studies. The sharp equatorward boundary of the radar signatures of the polar patch would be an interface between the preexisting flow generally in the antisunward direction and the enhanced zonal flow. The flow enhancement appears to be a fundamental process that forms the large‐scale polar patch at latitudes several degrees higher than the cusp.

New evidence of dayside plasma transportation over the polar cap to the prevailing dawn sector in the polar upper atmosphere for solar‐maximum winter

“…Polar cap patches are large regions of enhanced F region plasma density with scale sizes on the order of 100-1000 km and plasma densities ranging from about 2 to 10 times the background density [e.g., Pedersen et al, 1998]. The patches can be observed through a variety of techniques including ionosondes [e.g., Sato and Rourke, 1964;Dandekar and Bullett, 1999], optical equipments [e.g., Moen et al, 2007;Hosokawa et al, 2010], coherent radar [e.g., Taguchi et al, 2009;Thomas et al, 2013], satellite, and incoherent scatter radar [e.g., Moen et al, 2006;Zhang et al, 2013aZhang et al, , 2015. Numerous processes have been proposed to explain the detachment of daytime dense plasma from a continuous TOI as discrete patches, such as the IMF-controlled reorientation of a cusp inflow region [Milan et al, 2002], convection jets [Rodger et al, 1994], in situ plasma depletion under an intense electric field [Valladares et al, 1994], polar cap expansion and contraction [Anderson et al, 1988], expansion of the polar cap convection pattern by pulsed reconnection [Lockwood and Carlson, 1992;Carlson et al, 2004Carlson et al, , 2006, reconnection pulses associated with IMF B y leading to plasma density gradients [Lockwood et al, 2005;Zhang et al, 2011Zhang et al, , 2013a, and patches being chopped on closed field lines by upward field-aligned currents .…”

Two azimuthally separated regions of cusp ion injection observed via energetic neutral atoms

“…In other words, the right direction of the FOV relative to the cusp injection region might be a controlling factor in the ENA detection. The importance of this factor has been pointed out by Murata et al [2007] and Taguchi et al [2009a]. Taguchi et al [2009a] have shown that when pointing in the general direction of the cusp the FOV of the LENA imager can miss the cusp signal when IMF B Z becomes strongly negative.…”

“…The importance of this factor has been pointed out by Murata et al [2007] and Taguchi et al [2009a]. Taguchi et al [2009a] have shown that when pointing in the general direction of the cusp the FOV of the LENA imager can miss the cusp signal when IMF B Z becomes strongly negative. A similar possibility should be considered for a positive B Z case, which is dealt with in this paper.…”

“…In this study, we identify the characteristics of the ion injection in the daytime sector for positive B Y during northward IMF by using a remote sensing approach with energetic neutral atoms detected by the low‐energy neutral atom (LENA) imager [ Moore et al , 2000, 2001] on the IMAGE spacecraft. The LENA imager is capable of detecting not only energetic neutral atom (ENA) emissions produced by ion injection into the cusp through a charge exchange with the Earth's hydrogen exosphere [ Taguchi et al , 2004a, 2004b, 2005, 2006, 2009a, 2009b; Murata et al , 2007; Suzuki et al , 2008] but also ENA emissions from the magnetosheath flow near the subsolar magnetopause [ Collier et al , 2001a, 2001b, 2005; Moore et al , 2003; Fok et al , 2003; Taguchi et al , 2004a; Hosokawa et al , 2008]. It has been shown that magnetosheath imaging can be done in soft X‐rays [ Collier et al , 2010].…”

Steep plasma depletion in dayside polar cap during a CME‐driven magnetic storm

“…For a similar poleward‐propagating feature, Taguchi et al . [, ] suggested that it is important that the TOI is deformed by fast azimuthal flow having less dense plasma and that the interface between the deformed TOI and the fast azimuthal flow moves poleward.…”