Authors: Faisal Sayed (Department of Physics, The University of Texas at Austin, Austin, TX 78712, USA), Anna Tenerani (Department of Physics, The University of Texas at Austin, Austin, TX 78712, USA), Richard Fitzpatrick (Department of Physics, The University of Texas at Austin, Austin, TX 78712, USA)

Magnetic reconnection can develop spontaneously through the tearing instability and is frequently invoked to explain eruptive phenomena in both laboratory and astrophysical plasmas, including disruptions in fusion devices, solar flares, periodic density structures at helmet streamer tips, and flux transfer events at Earth’s dayside magnetopause. In several of these environments, the presence of gravity, magnetic field curvature or other forms of acceleration often result in situations of a heavy-over-light plasma in an effective gravitational field across an embedded current sheet. In this work, we investigate the linear stability of a slab current sheet to reconnecting modes in the presence of a density gradient and constant gravitational acceleration. We demonstrate that gravity and plasma stratification significantly alter the properties of the tearing instability under both favorable and unfavorable stratification conditions. Favorable stratification stabilizes the system and suppresses reconnection, whereas unfavorable stratification substantially enhances the tearing mode. Moreover, we find that the classical constant-psi regime effectively does not exist, even for weak unfavorable stratification, for S>>1. Instead, the instability gradually evolves into the gravity-driven reconnecting G-mode, characterized by a growth rate proportional to S^(-1/3). Consequently, unfavorable stratification supports only fast reconnecting modes.