  Previous hydrodynamical (HD) and magnetohydrodynamical (MHD) numerical
simulations of hot accretion flows have shown that the mass accretion rate
decreases with decreasing radius. Two models have been proposed to explain this
result. In the ADIOS model, the inward decrease of accretion rate is because of
the loss of gas in the outflow. In the CDAF model, the gas is assumed to be
locked in convective eddies, which results in the inward decrease of the
accretion rate. We investigate the nature of inward decrease of accretion rate
using HD and MHD simulations. We calculate various properties of inflow and
outflow, including the mass flux, radial and rotational velocities,
temperature, and the Bernoulli parameter ($Be$). Systematic and significant
differences between inflow and outflow are found. These results suggest that
the inflow and outflow are not dominated by convective turbulence, but are
systematic inward and outward motion. We have also analyzed the convective
stability of MHD accretion flow and found that they are convectively stable.
These results indicate that the ADIOS scenario is favored. The different
properties of inflow and outflow also suggest that the mechanisms of producing
outflow in HD and MHD flows are buoyancy and centrifugal force associated with
the magnetic field, respectively. The latter mechanism is similar to the
Blandford & Payne mechanism. We also study the effect of initial conditions in
the simulations. We find that the value of $Be$ is mainly determined by the
value of $Be$ of the initial condition. We discuss some possible observational
applications of our outflow model. These observations include the Fermi bubble
observed in the Galaxy center, and winds widely observed in AGNs and black hole
X-ray binaries.
