Solar wind helium and hydrogen structure near the heliospheric current sheet: A signal of coronal streamers at 1 AU

Abstract

We have investigated solar wind flow properties associated with very low helium to hydrogen abundance ratios (A(He)) observed with Los Alamos instrumentation on IMP 6, 7, and 8 during the 1971 ‐ 1978 interval. A characteristic pattern has been discovered, consisting of correlated interplanetary field reversals, high plasma density, low and nearly identical H+ and He++ bulk velocities, low H+ and He++ kinetic temperatures and minimums in their ratio. A superposed epoch analysis of 74 well defined sector boundary crossings observed during the 1971–1978 interval provides impressive verification of the above correlation, featuring a pronounced minimum in A(He) at the sector boundary passage. Our epoch analysis provides the cleanest pattern of plasma characteristics yet found in the vicinity of the current sheet associated with sector boundaries. Because coronal streamers straddle the current sheet close to the sun, the pattern discovered is the ‘signal’ of a coronal streamer at 1 AU. Our results provide important constraints on models of helium dynamics in coronal streamers and the low speed solar wind.

Tracking Solar Active Region Outflow Plasma from Its Source to the Near-Earth Environment

“…The origin of persistent active region upflows from QSLs has been previously reported (Baker et al, 2009;van Driel-Gesztelyi et al, 2012). These upflows are thought to be due to the reconnection of comparatively dense active-region loops with surrounding lower-density loops (Bradshaw, Aulanier, and Del Zanna, 2011). Previous observations have shown the upflows to be persistent on a timescale of days where the required ongoing reconnection is driven by AR growth and dispersion.…”

“…Velocities, obtained from blueshifts, range from ≈ 3 km s −1 to ≈ 50 km s −1 and increase with temperature (Del Zanna, 2008). Non-thermal line broadening and the appearance of blue-wing asymmetries are observed to correlate with velocity (Del Zanna, 2008;Harra et al, 2008;Bryans, Young, and Doschek, 2011). This could suggest the presence of multiple upflow sites for plasma at different speeds.…”

“…The ratio of emission-line intensities from low-FIP and high-FIP ions can be used to identify coronal plasma and in particular to allow estimates of FIP bias or f FIP = A SA /A ph : the ratio of solar atmosphere to photospheric element abundance. Brooks and Warren (2011) showed that the ratio I Si X (258.375 Å) /I S X (264.223 Å) is constant to within ≈ 40 % for the log (T e /K) = 5.7 -6.2 range but deviates significantly at higher temperatures. Hence for reliable estimates of FIP bias a differential emission measure (DEM) analysis based on a range of line intensities, e.g.…”

“…Feldman et al (2009) have outlined how observations of Si X (low FIP) and S X (high FIP) lines in the EIS spectral range could be used to measure the FIP bias. This approach, which was further developed by Brooks and Warren (2011), is used in the present article.…”

Solar wind stream interfaces in corotating interaction regions: New SWICS/Ulysses results

“…It has long been known that high-speed streams originate in coronal holes [Krieger et al, 1973] and that the slow solar wind originates in the streamer belt [Gosling et al, 1981]. These two states of the solar wind were first recognized as such by Rosenbauer et al [ 1977] and are quite distinct both in their kinetic properties (density, speed, and kinetic temperature) and in their elemental and charge state composition.…”