Predictability of stratospheric sudden warmings as inferred from ensemble forecast data: Intercomparison of 2001/02 and 2003/04 winters

The predictability of a minor warming and the subsequent major warming in the winter of 2003/04 is examined in comparison with that of the major warming without preceding minor warmings in December 2001 by the use of operational ensemble 1-month forecast data produced by the Japan Meteorological Agency. In the case of the major warming in December 2001 caused by amplified zonal wavenumber 1 planetary waves, the predictable period based on zonal mean temperatures in the polar stratosphere is estimated to be at least 16 days, while the warmings in the winter of 2003/04 are predictable at most 9 days in advance. Such relatively reduced predictability for the latter warmings is considered due to the rather complicated time evolution of the warming episodes with a significant contribution of smaller-scale planetary waves during the period prior to the warmings.