Atmospheric lump structures were observed at Rome during two nights in the summer of 1994 by a triaxial Doppler sodar operating in monostatic mode. They appeared on sodar facsimile records at height ranges between 300 and 800 m for several hours each night. The vertical velocities within the lump structures ranged around ¿2 m/sec. Their occurrence was found to increase as the nights progressed. A Raman lidar, which was also simultaneously operated, provided high-resolution water vapor profiles. The sodar-derived wind profiles confirmed the presence of sea breeze during both nights while the water vapor mixing ratio showed steep gradients at the height of lump structures. The analysis of the two data sets provided evidence that the lumps had originated, in an otherwise neutral atmosphere, from small-scale temperature fluctuations generated in isolated regions due to thermodynamical processes of water vapor by way of condensation and re-evaporation. ¿ American Geophysical Union 1995.