ABSTRACT We analyze 37 RXTE observations of the type 2 Seyfert galaxy Mrk348 obtainedduring a period of 14 months. We confirm the spectral variability previous reportedby Smith et al., in the sense that the column density decreases by a factor of ∼3 asthe count rate increases. Column density variations could possibly originate either dueto the random drift of clouds within the absorption screen, or due to photoionizationprocesses. Our modeling of the observed variations implies that the first scenario ismore likely. These clouds should lie in a distance of >2 light years from the source,having a diameter of a few light days and a density of > 10 7 cm −3 , hence probablyresiding outside the Broad Line Region.Key words:galaxies:active-quasars:general-X-rays:general 1 INTRODUCTIONMonitoring observations are a powerful tool in the study ofthe nuclear environment of type 2 Seyfert galaxies. Althoughthe presence of X-ray flux variability in Seyfert-2 galaxies iswell established (eg Georgantopoulos & Papadakis 2001 andreferences therein), our understanding of their spectral vari-ations remains limited. Nevertheless, monitoring of the X-ray spectra of a few bright Seyfert-2 galaxies have revealedsome intriguing results. For example, Warwick et al. (1988)first reported variations of the column density in ESO 103-G35. Using EXOSAT data, they found a decrease in thecolumn density by a factor of ∼ 1.7 in a period of 90 days.Warwick et al. (1993) found column density variations inNGC 7582 by a factor of ∼ 3 over an interval of about 4years, using Ginga data. They attributed these variationsto motions of clouds near the central source. Investigationof the spectrum of NGC 7582 based on ASCA data by Xueet al. (1998) confirmed the existence of significant columndensity variations (by a factor of ∼ 2) over a timescale of2 years. Variability analysis of column density variations inlarge samples of Seyfert-2 galaxies has been performed byMalizia et al. (1997) and Risaliti, Elvis & Nicastro (2002)using mainly literature data. They find variation of the col-umn density in time scales of a few months up to severalyears.Systematic monitoring observations only became feasi-ble with the RXTE mission. In particular, Georgantopouloset al. (1999), Georgantopoulos & Papadakis (2001), Smith,Georgantopoulos & Warwick (2001) present monitoring ob-servations of several Seyfert-2 galaxies (Mrk3, ESO 103-G35,IC 5063, NGC 4507, NGC 7172 and Mrk 348) spanning timeperiods from about seven days to seven months. They foundstatistically significant spectral variations in all cases. Insome objects the variations appear to be caused by intrinsicpower-law slope changes whereas in others column densityvariations dominate.In this paper we present an analysis of 37 RXTE ob-servations of the Seyfert 2 galaxy Mrk348. Previously Smithet al. (2001) have reported the results from 12 RXTE ob-servations covering a period of six months. Here we use anexpanded sample of 37 RXTE monitoring observations ofMrk 348 (including the 12 reported by Smith et al. 2001),spanning a time interval of 14 months, to investigate furtherthe nature of the X-ray spectral variability exhibited by thissource. More specifically, we investigate whether photoion-ization of the absorbing screen or alternatively motion of