1. A. M. Obukhov, “On the question of geostrophic wind,” Izv. Akad. Nauk SSSR, Ser. Geogr. Geofiz. 13 (4), 281–306 (1949).
2. A. M. Obukhov, “On the dynamics of a stratified fluid,” Dokl. Akad. Nauk SSSR 145 (6), 1239–1242 (1962).
3. H. Ertel, “Ein neuer hydrodynamischer Wirbelsatz,”Meteorol. Z. 59, 277–281 (1942).
4. A. M. Obukhov, “Adiabatic invariants of atmospheric processes,” Meteorol. Gidrol., No. 2, 3–9 (1964).
5. B. J. Hoskins, M. E. McIntyre, and A. W. Robertson, “On the use and significance of isentropic potential vorticity maps,” Q. J. R. Meteorol. Soc. 111 (470), 877–946 (1985).