Article révisé par les pairs
Résumé : The mean temperatures of the layers 50-25 mb and 25-10 mb for the two months January and February 1958 are investigated with the aid of zonal harmonic analysis, emphasis being laid on a warming (R) which occurs during the 3rd decade of January. This warming has an important zonal component (§ 3), even over the northern hemisphere as a whole (§ 2); besides it is connected with definite features in the evolution of the first two harmonics (§ 4).