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We present the results of a high spectral resolution study of thecircumstellar (CS) gas around the intermediate mass, pre-main sequence star UXOri. The results are based on a set of 10 echelle spectra, monitoring the staron time scales of months, days and hours. A large number of transientblueshifted and redshifted absorption features are detected in the Balmer andin many metallic lines. A multigaussian fit is applied to determine for eachtransient absorption the velocity, v, dispersion velocity, Delta v, and theparameter R, which provides a measure of the absorption strength of the CS gas.The time evolution of those parameters is presented and discussed. A comparisonof intensity ratios among the transient absorptions suggests a solar-likecomposition of the CS gas. This confirms previous results and excludes a verymetal-rich environment as the cause of the transient features in UX Ori. Thefeatures can be grouped by their similar velocities into 24 groups, of which 17are redshifted and 7 blueshifted. An analysis of the velocity of the groupsallows us to identify them as signatures of the dynamical evolution of 7 clumpsof gas, of which 4 represent accretion events and 3 outflow events. Most of theevents decelerate at a rate of tenths of ms-2, while 2 events accelerate atapproximately the same rate; one event is seen experiencing both anacceleration and a deceleration phase and lasts for a period of few days. Thistime scale seems to be the typical duration of outflowing and infalling eventsin UX Ori. The dispersion velocity and the relative aborption strength of thefeatures do not show drastic changes during the lifetime of the events, whichsuggests they are gaseous blobs preserving their geometrical and physicalidentity.Comment: 14 pages, 8 figures, corrected rotation period in section

A dynamical study of the circumstellar gas in UX Orionis