  We present the results of a high spectral resolution study of the
circumstellar (CS) gas around the intermediate mass, pre-main sequence star UX
Ori. The results are based on a set of 10 echelle spectra, monitoring the star
on time scales of months, days and hours. A large number of transient
blueshifted and redshifted absorption features are detected in the Balmer and
in many metallic lines. A multigaussian fit is applied to determine for each
transient absorption the velocity, v, dispersion velocity, Delta v, and the
parameter R, which provides a measure of the absorption strength of the CS gas.
The time evolution of those parameters is presented and discussed. A comparison
of intensity ratios among the transient absorptions suggests a solar-like
composition of the CS gas. This confirms previous results and excludes a very
metal-rich environment as the cause of the transient features in UX Ori. The
features can be grouped by their similar velocities into 24 groups, of which 17
are redshifted and 7 blueshifted. An analysis of the velocity of the groups
allows us to identify them as signatures of the dynamical evolution of 7 clumps
of gas, of which 4 represent accretion events and 3 outflow events. Most of the
events decelerate at a rate of tenths of ms-2, while 2 events accelerate at
approximately the same rate; one event is seen experiencing both an
acceleration and a deceleration phase and lasts for a period of few days. This
time scale seems to be the typical duration of outflowing and infalling events
in UX Ori. The dispersion velocity and the relative aborption strength of the
features do not show drastic changes during the lifetime of the events, which
suggests they are gaseous blobs preserving their geometrical and physical
identity.
