part_of part of part of has part has part has_part adjacent to atmospheric boundary layer planetary surface troposphere atmospheric layer low atmospheric level A part of the troposphere which extends from the Earth's surface to 2 km (0 - 6500 ft) height. To be revised when we have information about the real definition. The definitions given by WMO cloud atlas are entered as comment, as these are not the defining features of the levels but the result of whatever it is that defines the levels (I assume temperature, density, etc. but have not yet found clear information about this). The german wikipedia page notes layers that coincide with the extent of the low étage, however, I have not yet seen further mention of them elsewhere and am thus hesitant about adding them. low étage middle atmospheric level