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Temporal comparison of nonthermal flare emission and magnetic-flux change rates  

Christiane Miklenic   Submitted: 2009-10-08 05:12

To understand the mechanisms that trigger solar flares, we require models describing and quantifying observable responses to the original energy release process, since the coronal energy release site itself cannot be resolved with current technical equipment. Testing the usefulness of a particular model requires the comparison of its predictions with flare observations. To test the standard flare model (CSHKP-model), we measured the magnetic-flux change rate in five flare events of different GOES classes using chromospheric/photospheric observations and compared its progression with observed nonthermal flare emission. We calculated the cumulated positive and negative magnetic flux participating in the reconnection process, as well as the total reconnection flux. Finally, we investigated the relations between the total reconnection flux, the GOES class of the events, and the linear velocity of the flare-associated CMEs. Using high-cadence Hα and TRACE 1600 Å image time-series data and MDI/SOHO magnetograms, we measured the required observables (newly brightened flare area and magnetic-field strength inside this area). RHESSI and INTEGRAL hard X-ray time profiles in nonthermal energy bands were used as observable proxies for the flare-energy release rate. We detected strong temporal correlations between the derived magnetic-flux change rate and the observed nonthermal emission of all events. The cumulated positive and negative fluxes, with flux ratios of between 0.64 and 1.35, were almost equivalent to each other. Total reconnection fluxes ranged between 1.8 x 1021 Mx for the weakest event (GOES class B9.5) and 15.5 x 1021 Mx for the most energetic one (GOES class X17.2). The amount of magnetic flux participating in the reconnection process was higher in more energetic events than in weaker ones. Flares with more reconnection flux were associated with faster CMEs.

Authors: Miklenic, C. H., Veronig A. M., and Vršnak B.
Projects: RHESSI,SoHO-MDI,TRACE

Publication Status: A&A (published)
Last Modified: 2009-10-08 07:40
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Reconnection and energy release rates in a two-ribbon flare  

Christiane Miklenic   Submitted: 2006-10-05 03:35

The aim of this study was to derive the local reconnection rate (coronal electric field) and the global reconnection rate (magnetic flux change rate), as well as the energy release rate (Poynting flux), in a two-ribbon flare from chromospheric/photospheric observations. Furthermore, we tested whether equal shares of positive and negative magnetic flux are involved in the flare process. A well-observed GOES M3.9 two-ribbon flare was analyzed. The required observables (ribbon expansion velocity, newly brightened area, and magnetic field strength at the ribbon front) were extracted from the TRACE 1600 Å and Kanzelhoehe Hα image time series, and a SOHO MDI magnetogram. Furthermore, the ratio of the converted positive vs. negative magnetic flux was determined. Both RHESSI hard X-ray 20 - 60 keV full-disk time profiles and subregion time profiles derived from a time series of RHESSI images in the same energy range, were used as independent, observable proxies for the energy release rate. The RHESSI images were also used to localize the sites where the bulk of the energy was deposited by fast electrons. We found good temporal correlations between the derived time profiles (local and global reconnection rate, Poynting flux) and observed HXR flux. The local reconnection-rate peak values ranged from 2.7 V/cm to 11.8 V/cm, whereas the positive and the negative magnetic flux covered by the flare emission were equal within 5 - 10 %. The results indicate that the local reconnection rate, the global reconnection rate, and the energy release rate in a simple two-ribbon flare can be derived from chromospheric/photospheric observations. Furthermore, it was confirmed that equal shares of positive and negative magnetic flux participated in the reconnection process.

Authors: Miklenic, C. H., Veronig, A. M., Vrsnak, B., and Hanslmeier, A.
Projects: RHESSI,SoHO-MDI,TRACE

Publication Status: A&A (accepted)
Last Modified: 2006-10-18 03:54
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Temporal comparison of nonthermal flare emission and magnetic-flux change rates
Reconnection and energy release rates in a two-ribbon flare

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