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We report on the first high frequency VLBI observations of the nearby broadabsorption line quasar (BALQSO), Mrk 231. Three epochs of observations wereachieved at 15 GHz and 22 GHz, two of these included 43 GHz observations aswell. The nuclear radio source is resolved as a compact double. The corecomponent experienced a strong flare in which the flux density at 22 GHzincreased by $> 150%$ (45 mJy) in three months. Theoretical models of the flareimply that the emission is likely enhanced by very strong Doppler boosting of ahighly relativistic ejecta with a kinetic energy flux, $Q \sim 3 \times 10^{43}\mathrm{ergs/sec}$. Combining our data with two previous epochs of 15 GHz data,shows marginal evidence for the slow advance of the secondary component(located $\approx 0.97$ pc from the core) over a 9.4 year span. We estimatethat the long term time averaged kinetic energy flux of the secondary at$\bar{Q}\approx 10^{42}\mathrm{ergs/sec}$. Low frequency VLBA observationsindicate that the secondary is seen through a shroud of free-free absorbing gaswith an emission measure of $\approx 10^{8} \mathrm{cm}^{-6}\mathrm{pc}$. Thesteep spectrum secondary component appears to be a compact radio lobe that isassociated with a working surface between the ram-pressure confined jet, and adense medium that is likely to be the source of the free-free absorption. Theproperties of the dense gas are consistent with the temperatures, displacementfrom the nucleus and the column density of total hydrogen commonly associatedwith the BAL wind.

VLBA Observations of Sub-Parsec Structure in Mrk 231: Interaction between a Relativistic Jet and a BAL Wind