Resonant interaction between two planetary waves as a precursor for stratospheric warmings?

Kurzfassung

Stratospheric warmings are attributed to an enhanced planetary wave activity, occuring nearly each winter - at least in the northern hemisphere - with different strengths. The generation of stratospheric warmings is not totally understood. One of the most promising explanations is the interaction of planetary waves: in many cases, the amplitude of the quasi-stationary planetary wave 1 builds up, until it transmits its momentum and energy to the background wind field. The role of wave 2 is usually considered to be less important. Based on ERA-40 and DYANA temperature data (January-February 1990), we found evidence that a resonant wave-wave interaction between a travelling and a stationary wave 2 was responsible for a minor stratospheric warming in February 1990. The interaction being observed during four weeks can eventually be used as an indication for an upcoming stratospheric warming.