Helicity of Magnetic Clouds and Their Associated Active Regions

Abstract

A b s t r a c t .Magnetic clouds are associated with many Coronal Mass Ejections. Many CMEs involve active regions. In this work we focus on the relationship between twelve magnetic clouds and their associated active regions. We use a cylindrically symmetric constant-a force-free model to derive field line twist, total current, and total magnetic flux from in situ observations of magnetic clouds. We compare these properties with those of the associated solar active regions, which we infer from solar vector magnetograms.Our comparison of fluxes and currents reveals: (1) the total (unsigned) flux ratios $MC/$AR tend to be of order unity; (2) the total flux ratios tend to be orders of magnitude larger than the total (unsigned) current ratios IMC/IAR', and (3) there is a statistically significant proportionality between them. Our key findings in comparing total twists aL, where L is the axial dimension of the system, are: (1) the values of (OIL)MC a r e typically an order of magnitude greater than those of (OL)AR', and (2) there is no systematic sign or amplitude relationship between them. These findings compel us to believe that magnetic clouds associated with active region eruptions are formed by magnetic reconnection between these regions and their larger-scale surroundings, rather than pre-existing structures in the corona or chromosphere.132

On the Evolution of Coronal Mass Ejections in the Interplanetary Medium

“…The thickness of the CME was modeled using the results of Tappin (2006), where 2a ¼ 0:03 AU at R ¼ 20 R and 2a ¼ 0:2 AU at R ¼ 5 AU. The thickness was assumed to increase at a constant rate, so that at 1 AU 2a ¼ 9:2 ; 10 6 km (0.06 AU ), which is similar to measurements of magnetic cloud thickness by various workers (e.g., Leamon et al 2004;Lynch et al 2005). Finally, we set ¼ 1:2 in accordance with Chen (1996).…”

The Role of Magnetic Helicity in Coronal Mass Ejections

“…Helicity is the only topological measure that is expected to be conserved during the formation of the filament channel, during the eruption and subsequent reconnection, and during the propagation of the CME to Earth. Therefore, accurate measurement and modeling of magnetic helicity are essential if we are to understand the coupling between the photosphere, corona, and heliosphere (e.g., Bieber & Rust 1995;Leamon et al 2004;Lynch et al 2004). …”

Cyclic Reversal of Magnetic Cloud Poloidal Field

“…After comparing magnetic flux and helicity in active regions and in MCs, Leamon et al (2004) concluded that MCs from active regions are formed by magnetic reconnection between these regions and their large scale surroundings, rather than simple eruptions of preexisting structures in the corona or chromosphere. Qiu et al (2007) found that the magnetic flux swept up by flare ribbons agrees with the poloidal flux in MC fluxropes and the magnetic flux in CME dimming regions agrees with the toroidal flux in MC fluxropes.…”