Intermittent release of transients in the slow solar wind: 2. In situ evidence

Abstract

[1] In paper 1, we showed that the Heliospheric Imager (HI) instruments on the pair of NASA STEREO spacecraft can be used to image the streamer belt and, in particular, the variability of the slow solar wind which originates near helmet streamers. The observation of intense intermittent transient outflow by HI implies that the corresponding in situ observations of the slow solar wind and corotating interaction regions (CIRs) should contain many signatures of transients. In the present paper, we compare the HI observations with in situ measurements from the STEREO and ACE spacecraft. Analysis of the solar wind ion, magnetic field, and suprathermal electron flux measurements from the STEREO spacecraft reveals the presence of both closed and partially disconnected interplanetary magnetic field lines permeating the slow solar wind. We predict that one of the transients embedded within the second CIR (CIR-D in paper 1) should impact the near-Earth ACE spacecraft. ACE measurements confirm the presence of a transient at the time of CIR passage; the transient signature includes helical magnetic fields and bidirectional suprathermal electrons. On the same day, a strahl electron dropout is observed at STEREO-B, correlated with the passage of a high-plasma beta structure. Unlike ACE, STEREO-B observes the transient a few hours ahead of the CIR. STEREO-A, STEREO-B, and ACE spacecraft observe very different slow solar wind properties ahead of and during the CIR analyzed in this paper, which we associate with the intermittent release of transients.

Observational Tracking of the 2D Structure of Coronal Mass Ejections Between the Sun and 1 AU

“…This increased the number of sample points dramatically and therefore lowered the standard error parameter defined by Rouillard et al (2010a). However even though this uncertainty was significantly lower, the realistic uncertainty is limited by the physical assumptions.…”

“…To minimise this uncertainty, observations to at least 30-40° elongations are desirable. More details on the fitting procedure can be found in Rouillard et al (2010a) and Williams et al (2009), however these authors investigate the FP method and further details on the HM method are discussed by Lugaz et al (2010).…”

“…The events in this paper were chosen on the basis of those identified by the SSW project and not by investigating an ideal case study for remote to in situ tracking (e.g. Mostl et al 2009;Mostl et al 2010;Davis et al 2011;Rouillard et al 2009a;Rouillard et al 2009b;Rouillard et al 2010a;Rouillard et al 2010b). For the four events investigated, they either did not travel towards a spacecraft (Feb 2008) May) the CME (see Figure 2b).…”

“…Savani et al (2009) displayed a different technique than the manual selection by creating an automatic tracking procedure for the density feature found in the J-map. Although this method lowers the uncertainty by reducing the standard error of the residuals, as defined by Rouillard et al (2010a) and Williams et al (2009), in practice, the uncertainty is limited by the physical assumptions used to create the formulae. This uncertainty in the true direction of propagation and velocity is more clearly visible when the results from the point-P, FP and HM methods are compared (Lugaz 2010;Wood et al 2010).…”

A review of recent studies on coronal dynamics: Streamers, coronal mass ejections, and their interactions

“…This is also important to our understanding of the streamer instability and the slow wind origin. A study on in-situ blobs has been presented by Rouillard et al [160], however, no elemental and charge state analyses were conducted. In addition, by finding in-situ counterpart of coronal structures, it is possible to settle the debate on the physical nature of the bright ray behind a CME.…”