1 / 13

What can helicity redistribution in solar eruptions tell us about reconnection in these events?

What can helicity redistribution in solar eruptions tell us about reconnection in these events?. Image by Pevtsov & Groening 2010. by Brian Welsch, JSPS Fellow (Short-Term ), Space Sciences Lab, UC - Berkeley, Non- Expert on Reconnection.

svea
Download Presentation

What can helicity redistribution in solar eruptions tell us about reconnection in these events?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. What can helicity redistribution in solar eruptions tell us about reconnection in these events? Image by Pevtsov & Groening 2010 by Brian Welsch, JSPS Fellow (Short-Term), Space Sciences Lab, UC-Berkeley, Non-Expert on Reconnection

  2. A brief review: Magnetic helicity quantifies the linkage between magnetic flux systems. Images byM. Berger Helicityis conserved if evolution is ideal, and is approximately conserved during fast reconnection. The relativehelicity of coronal magnetic fields, which are anchored in the photosphere, is gauge invariant. True field Potential field, used as reference B Invariance arises from defining helicity with respect to a reference field.

  3. Helicity can be decomposed into linkages between and within a flux systems: “mutual” and “self”, resp. Self helicity, Hself, is twist internal to a flux system. RH is positive helicity, LH is negative helicity. Mutual helicity, Hmut, quantifies linkages between flux systems. Images byM. Berger Hmut= (γ+δ)ϕAϕB/π

  4. Hmutual has a sign given by a right-hand rule. There is a strong similarity here with magnetic configurations before and after solar eruptions. Hmut > 0 Hmut < 0 Image from Moore & Labonte1980, via Hugh Hudson’s cartoon archive In a solar eruption, underlying field becomes overlying field.

  5. Helicity conservation implies changes in Hmutual caused by reconnection produce changes in Hself, as at right.  Hence, we need to modify our pre- and post eruption cartoon! For instance: The linked circles here crudely denote Hself. Note: downward flow of helicity would limit the ability of CMEs to remove helicity (Low 2002), but could drive subsequent eruptions. Wright & Berger 1989

  6. Linton & Antiochos (2005) found that flux tubes can reconnect by “tunneling” through each other. Tunneling occurs when tubes can reach a lower energy by exchanging Hmutwith Hself. Note: perspective in (a) and (f) is face-on, but is edge-on in (b) through (e). Linton & Antiochos 2005

  7. But in situations lacking artificial symmetry, how should helicity be partitioned among reconnecting flux domains? Which partition of helicity is most likely? Hself in underlying flux Hself in overlying flux OR

  8. Back to the drawing board, to consider a better cartoon – this one with four panels! There is no real debate that “flare reconnection” occurs below an erupting ejection. If we take cartoons as evidence, then clearly the change in Hmut goes primarily into Hself in the ejection. Moore et al. 2001 x x x (Still hotly debated: (i) Does reconnection triggereruptions? (ii) Does it directly or indirectly accelerate particles that generate X-ray emssion?)

  9. But simulations also show most helicity going into the ejection! MacNeice et al. (2006): 80% of pre-eruption helicity goes into the ejection.

  10. Observations agree, too: reconnected magnetic flux from flare ribbons matches the poloidal flux in interplanetary flux ropes. Qiu & Yurchyshyn (2005) also found a strong correlation between reconnected flux and CME speed --- evidence of hoop force from reconnected flux accelerating CME? Qiu et al. 2007 Qiu et al. 2006

  11. Why should reconnection primarily occur behind an erupting CME? vA • Linton & Antiochos (2005) found tunneling to be energetically favorable for high-twist flux tubes. Is lack of tunneling evidence that pre-eruption coronal fields aren’t highly twisted? 2. Tai Phan (this meeting), citing Cowley and Owen (1989) and their own inter-planetary observations: strong shear flows inhibit reconnection. Could the CME’s Alfvén-speed motion lead to strong shear flows along the eruption’s front? 3. CMEs seem similar to “pull” reconnection. ? ? x x x

  12. The relevant slide from Tai Phan’s talk: Reconnection Onset Dependence on Velocity Shear Expectation: Reconnection suppressed if Velocity Shear DVL > VA [Cowley and Owen, 1989] Observed: Velocity shear DVL << VA In all solar wind reconnection events L N Diffusion region VL1 VL2 DVL / VA DVL = |VL1 – VL2|

  13. Summary • Reconnection redistributes helicity between mutual and self. • In CMEs, the large-scale mutual helicity changes. • It appears this goes primarily into self-helicity of the ejection. • This might constrain pre-eruptive magnetic field configurations, as well as the reconnection process in the corona.

More Related