Ubiquity of quasi-horizontal layers in the troposphere

Fine laminar structures in the atmosphere have been described previously(1-9), but their characterization has been limited. The modern global coverage of aircraft flights offers an opportunity to provide such a characterization, and examine the ubiquity of such structures, in space and time. Research aircraft measuring vertical profiles of atmospheric chemical constituents frequently discern quasi-horizontal atmospheric layers with mean thicknesses of the order of 1 km and mean altitudes between 5 and 7 km (refs 10-12). These layers can be characterized and categorized by various combinations of ozone, water vapour, carbon monoxide and methane deviations from background profiles. Five commercial aircraft have been recently equipped to measure water vapour and ozone concentrations, and automatically collect vertical profile information on landing and take-off (refs 13-15). Here we synthesize measurements from both research and commercial flights and demonstrate the ubiquity in space and time of four layer types (as categorized by their chemical signatures). Up to one-fifth of the lowest 12 km of the atmosphere is occupied by such layers. We suggest that this universality reflects basic characteristics of the atmosphere hitherto unexplored, with potential implications for present understanding of a wide variety of dynamic and chemical atmospheric processes.