A statistical study of the reconnection rate in solar flares
K.Nagashima and T.Yokoyama
Magnetic reconnection is now generally believed to play a key role in energy
release process in solar flares.The physics of reconnection, however, is not
established completely. Therefore we study the reconnection rate statistically
to put some restrictions on the reconnection model. This reconnection rate is
an important value as the index of the energy release rate and is defined as
the inflow velocity normalized by Alfven velocity.
Using YOHKOH/SXT partial-frame images, SOHO/MDI magnetograms, and GOES X-ray
flux data, we get the spatial scale, tempposter scale and the magnetic field of
each flare. We survey flares which occurred in the year of 2000 and select 482
flares whose GOES class is above C6.0. After excluding limb events due to
uncertainty of photospheric magnetgrams at the limb, there remain 84 flares
with all required data. We assume that the inflow velocity is approximated to
the size of each flare devided by the lifetime of it. From these data we find
the reconnection rate is of the order of 10^-2 under the assumption that the
coronal field is about one-tenth of the photospheric one.
Using color temperature and emission measure calculated from GOES X-ray data and
the pressure balance across the shock, we also estimate the reconnection rate.
By this method, the value is 10^-4 - 10^-3.
Correspondence
Kaori Nagashima, Kyoto University
presentation
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