Mixing between High Velocity Clouds and the Galactic Halo
  In the Galactic halo, metal-bearing Galactic halo material mixes into high
velocity clouds (HVCs) as they hydrodynamically interact. This interaction
begins long before the clouds completely dissipate and long before they slow to
the velocity of the Galactic material. In order to make quantitative estimates
of the mixing efficiency and resulting metal enrichment of HVCs, we made
detailed 2 and 3 dimensional simulations of cloud-ISM interactions. Our
simulations track the hydrodynamics and time dependent ionization levels. They
assume that the cloud originally has a warm temperature and extremely low
metallicity while the surrounding medium has a high temperature, low density,
and substantial metallicity, but our simulations can be generalized to other
choices of initial metallicities. In our simulations, mixing between cloud and
halo gas noticeably raises the metallicity of the high velocity material. We
present plots of the mixing efficiency and metal enrichment as a function of
time.
