  We present a novel analytic framework to model the steady-state structure of
multiphase galactic winds comprised of a hot, volume-filling component and a
cold, clumpy component. We first derive general expressions for the structure
of the hot phase for arbitrary mass, momentum, and energy sources terms. Next,
informed by recent simulations, we parameterize the cloud-wind mass transfer
rates, which are set by the competition between turbulent mixing and radiative
cooling. This enables us to cast the cloud-wind interaction as a source term
for the hot phase and thereby simultaneously solve for the evolution of both
phases fully accounting for their bidirectional influence. With this model, we
explore the nature of galactic winds over a broad range of conditions. We find
that: (i) with realistic parameter choices, we naturally produce a hot,
low-density wind that transports energy while entraining a significant flux of
cold clouds, (ii) mixing dominates the cold cloud acceleration and decelerates
the hot wind, (iii) during mixing thermalization of relative kinetic energy
provides significant heating, (iv) systems with low hot-phase mass loading
factors and/or star formation rates can sustain higher initial cold phase mass
loading factors, but the clouds are quickly shredded, and (v) systems with
large hot-phase mass loading factors and/or star formation rates cannot sustain
large initial cold-phase mass loading factors, but the clouds tend to grow with
radius. Our results highlight the necessity of accounting for the multiphase
structure of galactic winds, both physically and observationally, and have
important implications for feedback in galactic systems.
