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We use autocorrelation to investigate evolution in flow fields inferred byapplying Fourier Local Correlation Tracking (FLCT) to a sequence ofhigh-resolution (0.3 \arcsec), high-cadence ($\simeq 2$ min) line-of-sightmagnetograms of NOAA active region (AR) 10930 recorded by the Narrowband FilterImager (NFI) of the Solar Optical Telescope (SOT) aboard the {\em Hinode}satellite over 12--13 December 2006. To baseline the timescales of flowevolution, we also autocorrelated the magnetograms, at several spatialbinnings, to characterize the lifetimes of active region magnetic structuresversus spatial scale. Autocorrelation of flow maps can be used to optimizetracking parameters, to understand tracking algorithms' susceptibility tonoise, and to estimate flow lifetimes. Tracking parameters varied include: timeinterval $\Delta t$ between magnetogram pairs tracked, spatial binning appliedto the magnetograms, and windowing parameter $\sigma$ used in FLCT. Flowstructures vary over a range of spatial and temporal scales (includingunresolved scales), so tracked flows represent a local average of the flow overa particular range of space and time. We define flow lifetime to be the flowdecorrelation time, $\tau$. For $\Delta t > \tau$, tracking results representthe average velocity over one or more flow lifetimes. We analyze lifetimes offlow components, divergences, and curls as functions of magnetic field strengthand spatial scale. We find a significant trend of increasing lifetimes of flowcomponents, divergences, and curls with field strength, consistent with Lorentzforces partially governing flows in the active photosphere, as well as strongtrends of increasing flow lifetime and decreasing magnitudes with increases inboth spatial scale and $\Delta t$.

Decorrelation Times of Photospheric Fields and Flows