Both analytical and numerical works show that magnetic reconnection must occur in hot accretion flows. This process will effectively heat and accelerate electrons. In this paper, we use the numerical hybrid simulation of magnetic reconnection plus the test-electron method to investigate the electron acceleration and heating due to magnetic reconnection in hot accretion flows. We consider fiducial values of density, temperature, and magnetic parameter β e (defined as the ratio of the electron pressure to the magnetic pressure) of the accretion flow as n 0 ∼ 10 6 cm −3 , T 0 e ∼ 2 × 10 9 K, and β e = 1. We find that electrons are heated to a higher temperature T e = 5 × 10 9 K, and a fraction η ∼ 8% of electrons are accelerated into a broken power-law distribution, dN(γ ) ∝ γ −p , with p ≈ 1.5 and 4 below and above ∼1 MeV, respectively. We also investigate the effect of varying β and n 0 . We find that when β e is smaller or n 0 is larger, i.e., the magnetic field is stronger, T e , η, and p all become larger.

Magnetic reconnection in the low atmosphere, e.g. chromosphere, is investigated in various physical environments. Its implications for the origination of explosive events (small-scale jets) are discussed. A 2.5-dimensional resistive magnetohydrodynamic (MHD) model in Cartesian coordinates is used. It is found that the temperature and velocity of the outflow jets as a result of magnetic reconnection are strongly dependent on the physical environments, e.g. the magnitude of the magnetic field strength and the plasma density. If the magnetic field strength is weak and the density is high, the temperature of the jets is very low (∼10 4 K) as well as its velocity (∼40 km s −1 ). However, if environments with stronger magnetic field strength (40 G) and smaller density (electron density N e = 2 × 10 10 cm −3 ) are considered, the outflow jets reach higher temperatures of up to 6 × 10 5 K and a line-of-sight velocity of up to 130 km s −1 which is comparable with the observational values of jet-like events.

Aims. We aim at investigating the formation of jet-like features in the lower solar atmosphere, e.g. chromosphere and transition region, as a result of magnetic reconnection. Methods. Magnetic reconnection as occurring at chromospheric and transition regions densities and triggered by magnetic flux emergence is studied using a 2.5D MHD code. The initial atmosphere is static and isothermal, with a temperature of 2 × 10 4 K. The initial magnetic field is uniform and vertical. Two physical environments with different magnetic field strength (25 G and 50 G) are presented. In each case, two sub-cases are discussed, where the environments have different initial mass density.Results. In the case where we have a weaker magnetic field (25 G) and higher plasma density (N e = 2 × 10 11 cm −3 ), valid for the typical quiet Sun chromosphere, a plasma jet would be observed with a temperature of 2-3 × 10 4 K and a velocity as high as 40 km s −1 . The opposite case of a medium with a lower electron density (N e = 2 × 10 10 cm −3 ), i.e. more typical for the transition region, and a stronger magnetic field of 50 G, up-flows with line-of-sight velocities as high as ∼90 km s −1 and temperatures of 6 × 10 5 K, i.e. upper transition region -low coronal temperatures, are produced. Only in the latter case, the low corona Fe ix 171 Å shows a response in the jet which is comparable to the O v increase. Conclusions. The results show that magnetic reconnection can be an efficient mechanism to drive plasma outflows in the chromosphere and transition region. The model can reproduce characteristics, such as temperature and velocity for a range of jet features like a fibril, a spicule, a hot X-ray jet or a transition region jet by changing either the magnetic field strength or the electron density, i.e. where in the atmosphere the reconnection occurs.

Observations show that electron acceleration in solar flares occurs in magnetic reconnection regions above the soft X-ray flare loops in the corona. Acceleration by a super-Dreicer electric field in a reconnecting current sheet appears to be the most direct way of producing electrons with the energy in range between 10keV and 10MeV. The results in this paper demonstrate that the longitudinal magnetic field efficiently 'locks' electrons in the reconnecting current sheet, thus allowing the acceleration by the transverse electric field. This mechanism may be useful to interpret the generation of relativistic ions in large impulsive flares.