@article{DAN_1992_324_2_a15,
     author = {L. I. Piterbarg},
     title = {Canonical variables for {Rossby} waves with closed level curves of},
     journal = {Doklady Akademii Nauk},
     pages = {316--320},
     publisher = {mathdoc},
     volume = {324},
     number = {2},
     year = {1992},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1992_324_2_a15/}
}