Solar eruptive flare is one of the most violent eruptive events in the solar system. The accompanied coronal mass ejection (CME) which carries enormous mass and energy can affect the heliosphere environment significantly, including human's advanced technological system. Magnetic reconnection plays a crucial role in the eruptions of solar flares. It converts the magnetic energy stored in the magnetic fields into thermal and kinetic energies of massive plasma, even allows for particle acceleration, which can be important for the space weather. CME-flare current sheet (CS) is the main place for magnetic reconnection. As the CS is stretched by the elevation of CME, many macro instabilities can happen in the CS. Tearing mode instability plays a key role for fast reconnection. With the limitation of the current observational resolution, it is hard to study the fine structures in the CS by observations directly. Fortunately, numerical simulation can provide an accessible way to study the details in magnetic reconnection. In this work, we performed 2D numerical simulations for the two-ribbon flare in the gravitationally stratified solar atmosphere with the Lundquist number $S=10^6$ using ATHENA code. We found that the tearing mode instability leads to the turbulence inside the reconnecting current sheet (CS) and brings in an extra dissipation that enhances the reconnection rate in an apparent way. Different from the case in \citet{shen2011} which is gravity absent, our result finds when the kinetic energy of the upward moving plasmoid is totally converted into its gravitational energy, this plasmoid will move downward and also the PX-point below will fall together to the flare loop. Almost meanwhile an ordinary X-point upgrades to the new PX-point. This results in the descending of the PX-point height and a sudden ascending. The energy spectrum in the CS shows the power-law distribution and the dynamics of plasmoids governs the associated spectral index. We noticed that the energy dissipation occurs at a scale $l_{ko}$ of 100-200~km, and the associated CS thickness ranges from 1500 to 2500~km, which follows the Taylor scale $l_T=l_{ko}S^{1/6}$. The termination shock (TS) appears in the turbulent region above flare loops, which is an important contributor to heating flare loops. Substantial magnetic energy is converted into both kinetic and thermal energies via TS, and the cumulative heating rate is greater than the rate of the kinetic energy transfer. In addition, we first find that the turbulence is somehow amplified by TS, of which the amplitude is related to the local geometry of the TS. Generally, the more asymmetric and irregular the TS is, the bigger the enhancement factor of turbulence is.
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