Global Estimate of Coronal Heating due to Magnetic Reconnection based on SDO Observations

The explanation to the problem of how the solar corona is heated to the one million degrees temperature has rested on two possible mechanisms; AlfvAl’n waves traveling upwards from the photosphere that dissipate in the corona, and magnetic reconnection to release the energy stored in the magnetic field by photospheric motions. However, not enough evidence has been obtained for any of the mechanisms and a combination of both is likely to occur. In this work we consider contribution of magnetic reconnection to global coronal heating and estimate the energy flux that results from reconnection in all scales, covering down to nanoflares. The reconnection model we use is based on a quasi 3-D model that approximates the braiding of magnetic field lines produced by photospheric motion of foot-points; it is an X-point configuration with a guiding field. It also includes resistive and collisionless reconnection, depending on the local mean free path[1]. This model is applied to all length scales involved in the energy release and add them all up considering the distribution of flare sizes. In order to obtain the size distribution we use the observations of the Solar Dynamic Observatory (SDO) for 2 wavelengths in the far UV that originate in the corona, together with the corresponding magnetograms. The size distribution is determined by scanning the images at all length scales, taking the bright spots and choosing those where the magnetic field is high enough to produce reconnection. Since the resolution limit of the SDO is just above the nanoflare scales we determine the spectral index of the energy distribution and extrapolate down to these scales. First an upper limit of the energy flux is obtained by assuming all the magnetic energy in each region is released. Then, by estimating the induced electric field in the current sheet we establish a limit on the relative size of the current sheets, requiring that this energy is lower than the total magnetic energy. The energy flux estimates are in the range of 10 5 erg/scm 2 (100W/m 2 ) which is of the order needed to maintain the hot corona.