Ozone profiles obtained by near-daily ozonesonde observations during campaigns at several sites in the North Atlantic are used to construct time-height cross sections of ozone concentration through the troposphere. Strong day-to-day ozone variability on the scale of synoptic meteorological disturbances is found both in the spring and in the summer throughout much of the troposphere. Layers of high ozone concentration (~100 ppb) are frequently seen in the middle and upper troposphere and are invariably associated with transport characteristics that strongly support a stratospheric source for these layers. Regions of low ozone (<40 ppb) are seen in the middle and upper troposphere associated with higher relative humidity. The connection of these events with low surface mixing ratios suggests that convective processes mix air low in ozone up through the troposphere. Vertical layering of ozone mixing ratio, which is seen at all of the observing locations, is a result of differing sources of air in the different layers. ¿ American Geophysical Union 1996