Seasonal and solar cycle variations in the ionospheric convection reversal boundary location inferred from monthly SuperDARN data sets

Abstract

Abstract. Multi-year (1995Multi-year ( -2013 velocity data collected by the Super Dual Auroral Network (SuperDARN) HF radars are considered to investigate seasonal and solar cycle variations of the convection reversal boundary (CRB) location for interplanetary magnetic field (IMF) B z < 0. By considering monthly data sets we show that the CRB is at higher latitudes in summer between 1995 and 2007. The poleward shifts are on the order of 2-5 • . After 2007, the seasonal effect weakens, and the highest latitudes for the CRB start to occur during the winter time. We show that the CRB latitudes decrease with an increase of the IMF transverse component at a rate of (1-2 • )/2 nT. Because of this effect, on average, the CRB latitudes are lower during high solar activity periods with stronger IMFs. We also confirm the effect of the CRB dawn-dusk shifts related to the IMF changes in the IMF B y sign.

Calibration and assessment of Swarm ion drift measurements using a comparison with a statistical convection model

“…8c agree well with the average location of the CRB found in Koustov and Fiori (2016). Blue and red curves in Fig.…”

“…All data in this figure are for periods of IMF B z < 0 ▸ events), and for periods where IMF B y > 0 (red points, 13 events). We also show here the statistically averaged CRB location inferred from SuperDARN data by Koustov and Fiori (2016). Both plots show that for periods of IMF B y < 0, the duskside CRB is shifted to more equatorward latitudes and the dawnside CRB is shifted to more poleward latitudes.…”

“…Although this is not likely to alter flow intensity in the most equatorward region of the statistical convection model, it could prevent convection foci from shifting to more equatorward locations, thereby forcing the CRB to slightly more poleward locations. Bristow and Spaleta (2013), Chen et al (2015), and Koustov and Fiori (2016) all report an asymmetry in the dawn/dusk location of the CRB. We attempted to test this asymmetry by considering Swarm measurements for periods with IMF B z < 0.…”

“…The convection reversal boundary (CRB) is a characteristic boundary separating anti-sunward cross-polar flow and sunward-directed return flow at auroral latitudes (Ridley and Clauer 1996;Chen et al 2015;Koustov and Fiori 2016). The CRB is of particular interest because it is located near the ionospheric projection of the open/ closed magnetic field line boundary (Sotirelis et al 2005;Hubert et al 2010), i.e., in the region where magnetic field lines poleward of the boundary are connected to the magnetotail lobes or the solar wind while magnetic field lines equatorward of the boundary are closed.…”

“…Due to its extensive coverage, and capability for continuous monitoring, the SuperDARN radar network is well suited for CRB mapping (e.g., Bristow and Spaleta 2013;Koustov and Fiori 2016). However, echoes are often missed in specific regions due to changing signal propagation conditions (e.g., Danskin et al 2002).…”