Quiescent Reconnection Rate Between Emerging Active Regions and Preexisting Field, with Associated Heating: NOAA AR11112

Abstract

When magnetic flux emerges from beneath the photosphere it displaces the preexisting field in the corona, and a current sheet generally forms at the boundary between the old and new magnetic domains. Reconnection in the current sheet relaxes this highly stressed configuration to a lower energy state. This scenario is most familiar, and most often studied, in flares, where the flux transfer is rapid. We present here a study of steady, quiescent flux transfer occurring at a rate three orders of magnitude below that in a large flare. In particular we quantify the reconnection rate, and related energy release, occurring as new polarity emerges to form Active Region 11112 (2010-10-16T00:S18W14) within a region of preexisting flux. A bright, low lying kernel of coronal loops above the emerging polarity, observed with AIA onboard SDO and XRT onboard Hinode, originally shows magnetic connectivity only between regions of newly emerged flux when overlaid on magnetograms from HMI. Over the course of several days, this bright kernel advances into the preexisting flux. The advancement of an easily visible boundary into the old flux regions allows measurement of the rate of reconnection between old and new magnetic domains. We compare the reconnection rate to the inferred heating of the coronal plasma. To our knowledge, this is the first measurement of steady, quiescent heating related to reconnection. We determine that the newly emerged flux reconnects at a fairly steady rate of 0.38e16 Mx/s over two days, while the radiated power varies between 2~8e25 erg/s over the same time. We find that as much as 40% of the total emerged flux at any given time may have reconnected. The total amount of transferred flux (1e21 Mx) and radiated energy (7.2e30 ergs) are comparable to that of a large M- or small X-class flare, but are stretched out over 45 hours.

22 pages, 8 figures, accepted for publication in Solar Physics

References in corpus (1)

• A Quantitative Model of Energy Release and Heating by Time-dependent, Localized Reconnection in a Flare with a Thermal Loop-top X-ray Source

Cited by in corpus (9)

• FIP Bias Evolution in a Decaying Active Region
• High-Resolution Observations of Flares in an Arch Filament System
• IRIS observations of magnetic interactions in the solar atmosphere between pre-existing and emerging magnetic fields. II. UV emission properties
• Relating magnetic reconnection to coronal heating
• Active Region Emergence & Remote Flares
• The formation and dissipation of current sheets and shocks due to compressive waves in a stratified atmosphere containing a magnetic null
• Emerging Dimming as Coronal Heating Episodes
• Measuring and modeling the rate of separator reconnection between an emerging and existing active region
• Observations of the formation of a proto-spot in a pre-existing field environment