Abstract　 　　 

　Numerical simulations have shown that the mass accretion rate of hot accretion flow decreases inward. This result has been confirmed by observations. Two models have been proposed to explain this result. In the adiabatic inflow–outflow solution (ADIOS), this is because of the loss of gas in the outflow. In the alternative convection-dominated accretion flow model, it is thought that the flow is convectively unstable and gas is locked in convective eddies. We investigate the nature of the inward decrease of the accretion rate using HD and MHD numerical simulations. We calculate various properties of the inflow and outflow such as temperature and rotational velocity. Systematic and significant differences are found. These results suggest that the inflow and outflow are not simply convective turbulence; instead, systematic inward and outward motion (i.e., real outflow) must exist. We have also analyzed the convective stability of MHD accretion flows and found that they are stable. These results favor the ADIOS scenario. We suggest that the mechanisms of producing outflow is the centrifugal force associated with the angular momentum transport mediated by the magnetic field. As an example of application, we show that the outflow can well explain the formation of the Fermi bubble discovered in the Galactic center.