  Between the base of the solar corona and the Alfven critical point, the
solar-wind density decreases by approximately five orders of magnitude, but the
temperature varies by a factor of only a few. In this paper, I show that such
quasi-isothermal evolution out to the Alfven critical point is a generic
property of outflows powered by reflection-driven Alfven-wave (AW) turbulence,
in which outward-propagating AWs partially reflect, and counter-propagating AWs
interact to produce a cascade of fluctuation energy to small scales, which
leads to turbulent heating. Approximating the sub-Alfvenic region as
isothermal, I first present a simplified calculation of the mass outflow rate,
asymptotic wind speed, and coronal temperature that neglects conductive losses
and the wave pressure force. I then develop a more detailed model of the
transition region, corona, and solar wind that accounts for the heat flux from
the coronal base into the transition region and momentum deposition by AWs. I
solve analytically for this heat flux by balancing, within the transition
region, conductive heating against internal-energy losses from radiation, pdV
work, and advection. The density at the coronal base is determined by locally
balancing turbulent heating and radiative cooling. I solve the equations of the
model analytically in two different parameter regimes. Analytic and numerical
solutions to the model equations agree with a number of observations.
