Abstract:
Using multi-wavelength observations of Solar and Heliospheric Observatory (SoHO)/Michelson Doppler Imager (MDI), Transition Region and Coronal Explorer (TRACE, 171 Å), and Hα from Culgoora Solar Observatory at Narrabri, Australia, we present a unique observational signature of a propagating supersonic plasma blob before an
M6.2-class solar flare in active region 10808 on 9 September 2005. The blob was observed between 05:27 UT and 05:32 UT with almost a constant shape for the first 2 – 3 min, and thereafter it quickly vanished in the corona. The observed lower-bound speed of the blob is estimated as ≈215 km s⁻¹ in its dynamical phase. The evidence of the blob with almost
similar shape and velocity concurrent in Hα and TRACE 171 Å images supports its formation by a multi-temperature plasma. The energy release by a recurrent three-dimensional reconnection process via the separator dome below the magnetic null point, between the emerging flux and pre-existing field lines in the lower solar atmosphere, is found to be the driver of a radial velocity pulse outwards that accelerates this plasma blob in the solar atmosphere. In support of identification of the possible driver of the observed eruption, we solve the two-dimensional ideal magnetohydrodynamic equations numerically to simulate the observed supersonic plasma blob. The numerical modelling closely match the observed velocity, evolution of multi-temperature plasma, and quick vanishing of the blob found in the observations. Under typical coronal conditions, such blobs may also carry an energy flux of 7.0×10⁶ erg cm⁻² s⁻¹ to balance the coronal losses above active regions.
