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We have monitored the massive binary star $\eta$ Carinae with the CTIO/SMARTS1.5~m telescope and CHIRON spectrograph from the previous apastron passage ofthe system through the recent 2014.6 periastron passage. Our monitoring hasresulted in a large, homogeneous data set with an unprecedented time-sampling,spectral resolving power, and signal-to-noise. This allowed us to investigatetemporal variability previously unexplored in the system and discover akinematic structure in the P Cygni absorption troughs of neutral helium windlines. The features observed occurred prior to the periastron passage and areseen as we look through the trailing arm of the wind-wind collision shock cone.We show that the bulk of the variability is repeatable across the last fiveperiastron passages, and that the absorption occurs in the inner 230 AU of thesystem. In addition, we found an additional, high-velocity absorption componentsuper-imposed on the P Cygni absorption troughs that has been previouslyun-observed in these lines, but which bears resemblance to the observations ofthe He~I $\lambda$10830 \AA\ feature across previous cycles. Through acomparison of the current smoothed particle hydrodynamical simulations, we showthat the observed variations are likely caused by instabilities in thewind-wind collision region in our line-of-sight, coupled with stochasticvariability related to clumping in the winds.

To $v_\infty$ and beyond! The He I absorption variability across the 2014.6 periastron passage of $\eta$ Carinae