Magnetic Reconnection Events in Weakly Collisional Regimes$*$

The known modes leading to macroscopic reconnection in weakly collisional plasmas, are: one related to the drift tearing mode [1] and another with the opposite phase velocity, in the ion diamagnetic velocity direction, requiring a high energy particle population [2]. Observation of islands, that suddenly appear at finite amplitude during a trigger event (like a sawtooth crash) led to the concept of metastable resistive tearing modes. But the observation of islands growing from very small amplitude without any trigger event [3] leads instead to considering the modes mentioned above requiring the prior excitation of other linearly unstable modes: a) for the drift-tearing mode, the micro-reconnecting mode, which is driven unstable by the electron temperature gradient [4]. b) for modes with the opposite phase velocity [5], pressure gradient driven macroscopic modes that have a similar phase velocity.\\[4pt] [1] B. Coppi, \textit{Phys. Fluids} {\bf8}, 2273(1965) [2] B. Coppi, \textit{Bull. Am. Phys. Soc}. {\bf45} (2000) 366. [3] P. Buratti \textit{et al}., 34h EPS Conf. on Pl. Phys. (July 2007) ECA {\bf31F} O-4.018 (2007) [4] B. Coppi, ``Collective phenomena...'' Publ. \textit{Word Scientific}, p. 59 (2007) [5] P. Buratti et al., 35th EPS Conf. Pl. Phys., (June 2008) ECA {\bf32D}, P-1.069 (2008)