  We present six new and two previously published high-resolution spectra of
the quasar HS 1603+3820 (z_em = 2.542) taken over an interval of 4.2 years (1.2
years in the quasar rest frame). The observations were made with the
High-Dispersion Spectrograph on the Subaru telescope and Medium-Resolution
Spectrograph on the Hobby-Eberly Telescope. The purpose was to study the narrow
absorption lines (NALs). We use time variability as well as coverage fraction
analysis to separate intrinsic absorption lines, which are physically related
to the quasar, from intervening absorption lines. By fitting models to the line
profiles, we derive the parameters of the respective absorbers as a function of
time. Only the mini-BAL system at z_abs ~ 2.43 (v_off ~ 9,500 km/s) shows both
partial coverage and time variability, although two NAL systems possibly show
evidence of partial coverage. We find that all the troughs of the mini-BAL
system vary in concert and its total equivalent width variations resemble those
of the coverage fraction. However, no other correlations are seen between the
variations of different model parameters. Thus, the observed variations cannot
be reproduced by a simple change of ionization state nor by motion of a
homogeneous parcel of gas across the cylinder of sight. We propose that the
observed variations are a result of rapid continuum fluctuations, coupled with
coverage fraction fluctuations caused by a clumpy screen of variable optical
depth located between the continuum source and the mini-BAL gas. An alternative
explanation is that the observed partial coverage signature is the result of
scattering of continuum photons around the absorber, thus the equivalent width
of the mini-BAL can vary as the intensity of the scattered continuum changes.
