摘要
A vertical current sheet is a crucial element in many flare/coronal mass ejection （CME） models. For the first time, Liu et al. reported a vertical current sheet directly imaged during the flare rising phase with the EUV Imaging Telescope （EIT） onboard the Solar and Heliospheric Observatory （SOHO）. As a follow-up study, here we present the comprehensive analysis and detailed physical interpretation of the observation. The current sheet formed due to the gradual rise of a transequatorial loop system. As the loop legs approached each other, plasma flew at - 6 km s^-1 into a local area where a cusp-shaped flare loop subsequently formed and the current sheet was seen as a bright, collimated structure of global length （_〉 0.25 RQ） and macroscopic width （（5-10）× 10^3 km）, extending from 50 Mm above the flaring loop to the border of the EIT field of view （FOV）. The reconnection rate in terms of the Alfven Mach number is estimated to be only 0.005-0.009, albeit a halo CME was accelerated from - 400 km s- 1 to - 1300 km s- 1 within the coronagraph FOV. Drifting pulsating structures at metric frequencies were recorded during the impulsive phase, implying tearing of the current sheet in the high corona. A radio Type III burst occurred when the current sheet was clearly seen in EUV, indicative of accelerated electrons beam- ing upward from the upper tip of the current sheet. A cusp-shaped dimming region was observed to be located above the post-flare arcade during the decay phase in EIT; both the arcade and the dimming expanded with time. With the Coronal Diagnostic Spectrometer （CDS） aboard SOHO, a clear signature of chromospheric evaporation was seen during the decay phase, i.e., the cusp-shaped dimming region was associ- ated with plasma upflows detected with EUV hot emission lines, while the post-flare loop was associated with downflows detected with cold lines. This event provides a comprehensive view of the reconnection geometry and dynamics in the solar corona.
A vertical current sheet is a crucial element in many flare/coronal mass ejection （CME） models. For the first time, Liu et al. reported a vertical current sheet directly imaged during the flare rising phase with the EUV Imaging Telescope （EIT） onboard the Solar and Heliospheric Observatory （SOHO）. As a follow-up study, here we present the comprehensive analysis and detailed physical interpretation of the observation. The current sheet formed due to the gradual rise of a transequatorial loop system. As the loop legs approached each other, plasma flew at - 6 km s^-1 into a local area where a cusp-shaped flare loop subsequently formed and the current sheet was seen as a bright, collimated structure of global length （_〉 0.25 RQ） and macroscopic width （（5-10）× 10^3 km）, extending from 50 Mm above the flaring loop to the border of the EIT field of view （FOV）. The reconnection rate in terms of the Alfven Mach number is estimated to be only 0.005-0.009, albeit a halo CME was accelerated from - 400 km s- 1 to - 1300 km s- 1 within the coronagraph FOV. Drifting pulsating structures at metric frequencies were recorded during the impulsive phase, implying tearing of the current sheet in the high corona. A radio Type III burst occurred when the current sheet was clearly seen in EUV, indicative of accelerated electrons beam- ing upward from the upper tip of the current sheet. A cusp-shaped dimming region was observed to be located above the post-flare arcade during the decay phase in EIT; both the arcade and the dimming expanded with time. With the Coronal Diagnostic Spectrometer （CDS） aboard SOHO, a clear signature of chromospheric evaporation was seen during the decay phase, i.e., the cusp-shaped dimming region was associ- ated with plasma upflows detected with EUV hot emission lines, while the post-flare loop was associated with downflows detected with cold lines. This event provides a comprehensive view of the reconnection geometry and dynamics in the solar corona.
基金
supported by NASA grants NNX08-AJ23G and NNX08-AQ90G.supported by NASA grants NNX08AP88G and NNX09AG10G
NSF grant ATM-0849453.supported by NSF grant AST-0908344
