LOCALIZED TEARING MODES IN THE MAGNETOTAIL DRIVEN BY CURVATURE EFFECTS

The stability of collisionless tearing modes is examined in the presen ce of curvature drift resonances and the trapped particle effects. A k inetic description for both electrons and ions is employed to investig ate the stability of a two-dimensional equilibrium model. The main fea tures of the study are to treat the ion dynamics properly by incorpora ting effects associated with particle trajectories in the tail fields and to include the linear coupling of trapped particle modes. Generali zed dispersion relations are derived in several parameter regimes by c onsidering two important sublayers of the reconnecting region. For a t ypical choice of parameters appropriate to the current sheet region, w e demonstrate that localized tearing modes driven by ion curvature dri ft resonance effects are excited in the current sheet region with grow th time of the order of a few seconds. Also, we examine nonlocal chara cteristics of tearing modes driven by curvature effects and show that modes growing in a fraction of a second arise when mode widths are lar ger than the current sheet width. Further, we show that trapped partic le effects, in an interesting frequency regime, significantly enhance the growth rate of the tearing mode. The relevance of this theory for substorm onset phase and other features of the substorms is briefly di scussed.